# heres how to get 0.0001" precision on your ancient hobby lathe



## spaceman_spiff

Criticism of what I describe here is WELCOME!!! Please, lets dissect this, tear it apart, and make it better. 

The good news is: I think I am getting control of diameters, +/- 0.0001" (tenths), on my ancient, worn out Atlas 10F lathe.

I also learned something very important about manual lathes today. That alone is almost more important than being able to cut within tenths. 

Heres how I did it, and that special thing I learned:

Notice how the handwheels are graduated in 0.001", and the space between two graduations is about 1/32"? WAY too small to control tenths, accurately anyway. Yes, you can approximate. But seems kind of strange to me that a lathe would have handwheels that coarse. Im sure when even this low grade Atlas lathe was brand new it could cut in tenths reliably. Hmm. Actually..come to think of it the Hardinge HLV-H extreme precision lathe I used at work long ago was also in 0.001". So how the heck is anyone supposed to work in 0.0001"?

Even a DRO or dial indicators wouldn't really help, because you'd still be stuck trying to turn that handwheel just that TEEENY amount! 

Well, thats where the compound tool post comes in. It will let you magnify its handwheel by MORE than you would ever want!! Yes, you can turn the handwheel 100 ticks and it will only move the cutter forward by .001" if you want!! So essentially you have made it so that each handwheel graduations of 0.001" actually means 10 MILLIONTHS of an inch! Now tenths become cake! 

The idea behind this is to just rotate the compound tool post so its a very slight angle instead of parallel to the spindle axis. To be clear, "parallel" to the spindle axis would mean that turning its handwheel would move it towards or away from the spindle.

Now think about that, if its only moving towards or away from the spindle, its not moving the tool towards or away from the work at all, is it? 

So if you put it at a very slight angle, it WILL move the tool towards or away from the work. Turns out that at around 84 degrees, for every 100 thou of its handwheel, it moves towards the work by only 10 THOU! Now each tick is 0.0001"! Tada! And if you want you could theoretically reduce that angle even further and probably multiply it by ten times again!
*
REALITY CHECK*

-You are still limited by the accuracy of the threads, ways, etc.. You cannot precisely move the tool by 10 atoms just because you have the slide at an angle. But where that limit of accuracy is is now something you can move on to dealing with, instead of trying to turn a handwheel by some teeny amount.

-The angle readings on the compound tool post are not very fine. You should get the angle to approximately where you want and then do some test cuts to confirm the new tool post handwheel versus actual increase in cut distance, and then do some arithmetic and calculate how many thou you need to turn the handwheel to get what you want. If you dont have a tenths micrometer, now you have an excuse to buy one!!

-You will likely need to rotate your toolpost so the tool is again perpendicular (or whatever you need it to be) to the work, since you are rotating the tool post. 

*RESULTS!!!

*So...does this work or not? The answer appears to be YES!

I spent the last couple hours experimenting to see if I could really make reliable cuts in one shot based solely on the handwheel. 

Material: 303 stainless
RPM: about 800
Cutter: carbide TPG322 in a very rigid insert holder and tool post
Lube: none
Diameter of workpiece: about 1/2"
Workholding: 4 jaw chuck. Stickout about 2".
Feed: automatic, about 5 thou per rev
Machine: Atlas 10F from 1944

Cutting notes:

All done in three passes. First two were easily seen. The last pass was BARELY visible taking place..I'm not sure if it was doing anything or not. I have very good vision up close and could just barely see the "line" moving by getting up real close. And to be clear, I made NO adjustments to the handwheels between passes. I just turned the motor off, used the carriage handwheel to move the tool back to the beginning of the cut, and then powered it up and repeated the cut. 

I made many test cuts. Some of them came out right, some did not. A few came out about 1 thou off!! But I think I have it figured out now.

The final two cuts I made came out within about 0.0001" of where I intended. I think what was happening with the cuts that didn't work out was that I was not taking deep enough cuts. And I also screwed up the math a few times since my calculator was dying and I couldn't read it. I would get your notepad and calculator handy and keep a log of what you do so you can figure out how deep you need to cut and what RPM/stickout you need to do, etc..

*FINAL CUT #1:*

Target radial reduction: 0.0117"
Actual radial reduction: 0.01175"

*FINAL CUT #2*

Target radial reduction: 0.0107"
Actual radial reduction: 0.0108"

(the pic shows the incremental change in diameter)

Please join in the fun and report your results!!! You will need an accurate tenths micrometer to play along. The one I'm using was $30 from horrible freight!


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## chips&more

Good job! Just wonder how much hair you have left to fall out! Holding a 0.0001” on any manual lathe is hair losing experience. More like a job for the OD grinder. If I need to achieve a critical dimension on the lathe (I don’t have DRO) I set-up a 0.0001” or better dial indicator and do some praying…Good Luck, Dave.


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## spaceman_spiff

chips&more said:


> Good job! Just wonder how much hair you have left to fall out! Holding a 0.0001” on any manual lathe is hair losing experience. More like a job for the OD grinder. If I need to achieve a critical dimension on the lathe (I don’t have DRO) I set-up a 0.0001” or better dial indicator and do some praying…Good Luck, Dave.



thanks!!

this isnt exactly the end of the battle though..Ill believe that I can really hold tenths once I've made done alot more cuts in a lot more stickouts and diameters..but for now I think it was a small victory

I doubt Id ever need to literally hold 0.0001", but if I can reliably hit +/- 0.0003" I think that would be very useful


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## Mark_f

I find this fascinating. I worked many years in an environment that required .0002" tolerances. This is hard to do at home because those kind of tolerances usually require a temperature controlled environment and the tolerance is only guaranteed at that specific temperature. Now that being said, I occasional try to cut some things at a .0002" tolerance at home and the size WILL change with temperature changes, but in the home environment I don't see it as a big problem. BUT in all those years I never thought of trying to make the light finish cuts the way you describe and In my mind it is a great idea! I finish a part to that close a size with a second cut file, hand held and the part spinning in the chuck. This seems to work good if you are good with a file. And yes there is a safety issue using a file on a running lathe. YOU HAVE TO BE CAREFUL AND DON'T STAND IN FRONT OF THE FILE!

  But I love your idea and am going to try that on my next close tolerance need. This seems it would be useful on a close tolerance bore. ( can't get my file in there)

Mark Frazier


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## spaceman_spiff

mark_f said:


> I find this fascinating. I worked many years in an environment that required .0002" tolerances. This is hard to do at home because those kind of tolerances usually require a temperature controlled environment and the tolerance is only guaranteed at that specific temperature. Now that being said, I occasional try to cut some things at a .0002" tolerance at home and the size WILL change with temperature changes, but in the home environment I don't see it as a big problem. BUT in all those years I never thought of trying to make the light finish cuts the way you describe and In my mind it is a great idea! I finish a part to that close a size with a second cut file, hand held and the part spinning in the chuck. This seems to work good if you are good with a file. And yes there is a safety issue using a file on a running lathe. YOU HAVE TO BE CAREFUL AND DON'T STAND IN FRONT OF THE FILE!
> 
> But I love your idea and am going to try that on my next close tolerance need. This seems it would be useful on a close tolerance bore. ( can't get my file in there)
> 
> Mark Frazier



Well since I've posted i've made about a dozen more cuts and have an excel spreadsheet open trying to calculate the error.

Its going to take alot more experimenting before I feel I have a solid grip on whats going on. Sometimes the cut is way off, like 1 to 2 thou! And I'm not sure why. My compound slide gib looks pretty bad. I think this sort of operation also calls for measuring how much the slide angle varies throughout the slides travel. In other words, just because 100 thou handwheel moves the tool 1 thou into the part at the beginning of slide travel does not mean it does so everywhere else in the slide travel. 

I think the idea here, is to make it so everything you do is relative to ONE moment in time..one setup, one temperature, etc...to compensate for everything for that instant you make the cut. I dont think holding tenths on this lathe is going to be possible otherwise.

So maybe one way this becomes productive is to know EXACTLY what the handwheel-to-cut constant is for say 20 thou travel of the compound slide, and keep that in reserve for your very final cut, also throwing in there the 1st, 2nd, 3rd, and even 4th finishing passes as optional stopping points as you measure between each.

For me, this isnt actually about "hitting the bullseye" on the first try, fun as that is, its more about being able to get within a very tight tolerance without scrapping the part, and in a reasonable amount of time. For me, reasonable is something like 10 minutes for a given diameter, since I wont be doing production with this and will most likely be making spindles that need very tight tolerance fits into bearings and gears. 

So if I can reliably (i.e. ALWAYS) hit +/- 0.0002" without scrapping the part, thats a win, even if it takes 10 minutes per diameter. 

First job is to get things dialed in to where I'm not getting these WAY OFF errors every now and then. So I'm going to try and cut only very close to the chuck and with larger diameters to reduce deflection issues as much as possible.


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## f350ca

I swing the compound as you describe when I'm using a tool post grinder. The one thou graduations on the cross feed are pretty heavy cuts for the grinder. When trying to take the light final cuts you might have some luck using a HSS bit ground as a shear tool, they're great for shaving those really light passes.

Greg


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## Karl_T

I'll just share some of my tips for accurate work on the lathe...

First I installed a quality DRO with the best scale possible on X. It easily reads your position to 0.0002 and its right, lets you see any irregularities or backlash issues. Most important step IMHO.

Second thing is be aware your lathe is made of CHEESE. Cutting forces make it move or deflect. You got to play this consistent for accurate work.

A very rigid machine makes this far easier - the CHEESE moves less. I use a Monarch 10EE for most work. (But years ago I learned to make great parts on a LeBlond built in 1910).

For fine work you can't beat a sharp cutting tool. In most cases a sharpened and honed HSS is best. A sharp tool makes the CHEESE deflect less.

Next be aware that the CHEESE deflects different with different cutting conditions and can get real funky with too light of cuts. Make your last two cuts the same. Just a for example here, but say to ruffed to 0.010 over. Remove 5 thous as first finish pass. DOUBLE CHECK your measurements  then go for broke.

If your final cut has any length to it, its going to be larger farther from the spindle. (Remember the CHEESE?)  In this case, and if you need the super accuracy; leave at least 2 tenths for file and polish work everywhere. You can't beat a quality fine cut file and stones or emery cloth to get it JUST RIGHT.

Last and most important, PRACTICE make perfect. You won't learn to make quality parts reading about it.

My two cents

karl


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## SG51Buss

f350ca said:


> ...When trying to take the light final cuts you might have some luck using a HSS bit ground as a shear tool, they're great for shaving those really light passes...



Ditto.  When I need to do sub-mill accuracy, I'll switch over to a razer-sharp, finely honed, tiny tip radius HSS bit.  Examined under a 10x eye loupe.  AND, my carriage transverse feed rate is down to 0.002".  AND, for 1/2" steels, I'll have the spindle down to around 400-300 rpms.

I usually have my compound at 30°, so it acts as a direct-read dial.  So, if it's fed-in by 0.001", that'll be the change in diameter, the cut will be 0.0005".

Chasing 0.0001" accuracy is fun.  Have you checked the finish cut for taper?


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## chuckorlando

I try to watch the .0001 decimal but My end goal is usally to hit the .001 the tenth just tells me when to stop. That being said, when I do want to get it just right, I file or emery cloth. To many variables to try to do it with the cutter. Every tool, compound angle, material, every little change will change whats moving and flexing and ringing. 

Just as an experiment, take a cut with the power feed and grab the tool post handle and pull it down and push it up. I bet you can note the depth change instantly. Even if it only moved .0001 thats your whole allowable tolerance.

If you want to hold tenths, you have to think like a tool & die maker and less like a machinist. IMO a t&d maker will lap it in, file it in, make it just right. If the tolerance is +/- .010 they work to .0001 no matter the time. Where a machinist will differentiate between the what needs perfection and what needs to hit a thou.

Broad spectrum statement that does not apply to all. Thats my opinion on the two.

Take spring cuts as well


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## Shadowdog500

I believe that Thatlazachinist discusses this in one of his videos. He points out that it does work up to a point, but once you hit the accuracy of the machine increasing the compound angle more than that will buy you little.

I just looked for the video, but the topic was imbedded in the video as a several minute side note, so it was not easy to find.  

[UPDATE]. Found it.  Start at around 7:00.  http://youtu.be/WqTliEGrhL4


I'm also curious about how you did the post cut measurements.  I am just a hobby machinist,  but I found that fine measurments take a feel. I also found when taking a fine measurment with an expectation of what it should be, I would tend to home in on the number I thought it should be while looking at the scale and subcounciously convince myself that it felt perfect. I did this without even knowing I did it. After reading that this happens to myself (and others)  I never look at the scale while taking a measurment anymore.  While taking the measurment, I look away from the scale, and adjust the micromoter until it feels right, then I look at the scale to see the result.     When I first switched to this method, I found that I really didn't have a feel at all, and had to practice on things of a known dimension until I could measure them accurately. I still practice on items of a known dimention from time to check myself time since I don't do this type of stuff everyday.

 Chris


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## george wilson

Setting the compound at an angle has long been standard operating procedure for working to very fine tolerances. The thing IS,a cut surface will really be too rough to really,truly be accurate to a .0001". You need to grind the surface to truly get the surface smooth enough to be at that tolerance. Otherwise,as soon as the turned surface gets the microscopic "fuzz" worn down,it will no longer be at that accurate a diameter.

So,the answer is,set the compound to an angle and use a toolpost grinder to achieve this close a tolerance.

However,then the problem of how good your spindle bearings are raises its head. You have to have a high quality lathe with high grade bearings to have the piece truly round to that tolerance. When I had an Atlas lathe,my grinding came out looking like the wild grain pattern on plywood. The spindle bearings,and the rigidity of the lathe just were not up to the task.

When I got my first Jet lathe,a 10" x 24",the difference was night and day. And,that was still a low cost lathe. My current lathe,a Hardinge HLVH has high grade spindle bearings accurate to 50 millionths,and a very thick,heavy bed. This lathe can actually work to that tolerance.

I had fun experimenting with tolerances too,when starting out. Keep experimenting,and you will increase your knowledge and figure out new ways to do things.


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## hermetic

A 1" long x 1" diameter mild steel bar will expand or contract by .0001" with every 10 degree change in temeprature. You are only holding these claimed tolerances at a fixed temperature, unfortunately we do not live in a fixed temperature environment. That is why engineers work to a tolerance. It is impossible to claim accuracy to 0001" when the actual size varies more than that depending on the surrounding air temperature. It is ok to do it just for fun of course, but don't fool yourself into thinking it will be the same size on a frosty morning. (Thanks to John Stevenson for the above figures)
Phil


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## spaceman_spiff

Great info guys!

I tried to reduce variability even further by doing my tests cuts on the same location on the compound, to try and eliminate error from the compounds ways and screw, I did this by:

1- making the first cut using the carriage handwheel.

2- measuring the result of #1

3- making the second cut using the compound handwheel

4- measuring the result of #3 and computing the "handwheel to feed" ratio at that range on the compound

5- moving the compound back to where it was before #3

6- repeating #1 through #3 and comparing this #3 to the previous #3

and I still saw variability around 0.0005".

These cuts are back to back, same workpiece, same cutter, same temperature, same location on the ways, etc..

I think there is at least one more "dumb" thing hiding somewhere thats costing me 3 tenths.

So I'm going to throw the following at it and see if it helps:

1- try a very sharp HSS bit as suggested
2- clean and shield the main lathe ways in case small amounts of crud are getting under them and shifting the whole carriage
3- figure out a way to move the tool in without the compound slide..perhaps a micrometer or something
4- ditch the 4 jaw and use the ER chuck thats coming in the mail

And yes its true, the only thing holding the compound slide against its screw is the cutting force. You can push it forward at any time and modify the cut tremendously. I wonder if somehow sliding the tool forward in its tool post using a micrometer would work better, while keeping the gibs locked down so the compound can't even move.  HMMMMM..

I measure the cut without looking at the display on the mic, mostly because I have to focus on getting the anvils centered. Then I use the same number of clicks on the thimble. Then I rotate the workpiece half a turn or so and repeat. It seems like I regularly get zero variability in the mic measurement this way.


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## John Hasler

spaceman_spiff said:


> Great info guys!
> 
> I tried to reduce variability even further by doing my tests cuts on the same location on the compound, to try and eliminate error from the compounds ways and screw, I did this by:
> 
> 1- making the first cut using the carriage handwheel.
> 
> 2- measuring the result of #1
> 
> 3- making the second cut using the compound handwheel
> 
> 4- measuring the result of #3 and computing the "handwheel to feed" ratio at that range on the compound
> 
> 5- moving the compound back to where it was before #3
> 
> 6- repeating #1 through #3 and comparing this #3 to the previous #3
> 
> and I still saw variability around 0.0005".
> 
> These cuts are back to back, same workpiece, same cutter, same temperature, same location on the ways, etc..
> 
> I think there is at least one more "dumb" thing hiding somewhere thats costing me 3 tenths.
> 
> So I'm going to throw the following at it and see if it helps:
> 
> 1- try a very sharp HSS bit as suggested
> 2- clean and shield the main lathe ways in case small amounts of crud are getting under them and shifting the whole carriage
> 3- figure out a way to move the tool in without the compound slide..perhaps a micrometer or something
> 4- ditch the 4 jaw and use the ER chuck thats coming in the mail
> 
> And yes its true, the only thing holding the compound slide against its screw is the cutting force. You can push it forward at any time and modify the cut tremendously. I wonder if somehow sliding the tool forward in its tool post using a micrometer would work better, while keeping the gibs locked down so the compound can't even move.  HMMMMM..
> 
> I measure the cut without looking at the display on the mic, mostly because I have to focus on getting the anvils centered. Then I use the same number of clicks on the thimble. Then I rotate the workpiece half a turn or so and repeat. It seems like I regularly get zero variability in the mic measurement this way.



You might want to try combining these techniques with a shear tool.  It is supposed to provide a very good finish while consistently removing 1 or 2 thousandths accurately (I've never tried one myself).  

http://www.gadgetbuilder.com/VerticalShearBit.html


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## spaceman_spiff

hermetic said:


> A 1" long x 1" diameter mild steel bar will expand or contract by .0001" with every 10 degree change in temeprature.



F or C? If its F, the expansion ratio is actually 0.0000645in/in/F, if its C, its 0.000120in/in/C. (Thanks to Machinery's Handbook for the above figures)



> You are only holding these claimed tolerances at a fixed temperature, unfortunately we do not live in a fixed temperature environment.



Ring gauge standards accurate to millionths of an inch are specified at a certain temperature. The machining process is not less accurate because its result are a certain value at a certain temperature. 



> That is why engineers work to a tolerance.



No its not. Tolerances exist for economical reasons, not because of thermal expansion. Thermal expansion increases the need for tighter tolerances, it doesn't reduce it. Tolerances are not a design spec, they are a manufacturing spec to reach the design spec.



> It is impossible to claim accuracy to 0001" when the actual size varies more than that depending on the surrounding air temperature.



Hrm... master gages, interference fits, ball bearing diameters, precision 123 blocks, etc..etc..all have specifications equal or tighter than 1 tenth. The machining can be that accurate. Thermal expansion is irrelevant. Nobody is claiming they are machining something and that it suddenly becomes immune to thermal expansion. 



> It is ok to do it just for fun of course, but don't fool yourself into thinking it will be the same size on a frosty morning. (Thanks to John Stevenson for the above figures)
> Phil



So higher precision work is only okay for fun? Is that really your argument? Think about that...


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## spaceman_spiff

SG51Buss said:


> Have you checked the finish cut for taper?



The test cuts I've been making are only about 1/2" long, I measure in the middle. The ways definitely have significant wear and there probably is a problematic taper that needs to be dealt with beyond the range I'm doing these tests in, but I'm trying to solve one problem at a time and just focus on cut accuracy at a very limited carriage travel. I figure if I can get repeatability and accuracy with 2 or maybe 3 tenths, then I'll call it a day and move on to the zillion other inaccuracies this worn out hunk of iron has.


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## spaceman_spiff

f350ca said:


> I swing the compound as you describe when I'm using a tool post grinder. The one thou graduations on the cross feed are pretty heavy cuts for the grinder. When trying to take the light final cuts you might have some luck using a HSS bit ground as a shear tool, they're great for shaving those really light passes.
> 
> Greg



Something I dont understand about the grinders is, they are still subject to all the inaccuracies of the ways and slop in the screws and backlashes, so the only improvement to accuracy they would provide is by virtue of the lighter but more consistent cut forces right?


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## Bill Gruby

No, the accuracy in grinding comes from the finish. The smoother you can get the part the closer it will be. Ground finishes with the right set up will get you  much closer.

 "Billy G"


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## george wilson

Exactly what I said about ground finishes,Bill. Turned finishes are just not smooth enough to base really small tolerances on.


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## spaceman_spiff

Bill Gruby said:


> No, the accuracy in grinding comes from the finish. The smoother you can get the part the closer it will be. Ground finishes with the right set up will get you  much closer.
> 
> "Billy G"



Could you explain this further? I have never been able to get a grip on grinders and why they do a better job as far as accuracy, without the machine they are attached to also being better.

For instance, lets say the finish using the turning tool are relatively rough, but consistent. Then as long as the increase in cut is made relative to the measured finish/diameter combo, the quality of the finish falls out and isn't part of the result anymore. 

Another way to look at it is this, I'm seeing errors in the range of 0.0005" to 0.001". The finish is much smoother than that, even just eyeballing it. A 1000 microinch finish is what you get with a saw or flame cut apparently. So as long as the finish remains consistent, I dont see how improving it would increase accuracy.


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## spaceman_spiff

okay heres the latest

I changed the material to 6061-T6 aluminum. More stickout to the cut but more material in the jaws and thicker overall. Not really attempting to do anything particular by making these changes, just experimenting. 

 The rest of the setup is the same, although I did loosen the gibs a bit on the compound so its now free to jiggle a bit back and forth.

I did my first cut to establish the handwheel to feed relationship, which turned out to be 0.0001065" feed per handwheel thou. 

The rest of the cut "targets" were based on that.

I did 4 passes per cut, and at the end lightly placed a very fine file on the workpiece with almost no force for about 4 seconds, just to remove any serious flakes or burrs.

*target**result**error*0.00630.00620.00020.00710.00680.00030.00520.00500.00020.01010.00950.00060.00480.00440.0004

Hmm. At least all the errors are positive. I suppose I should try just increasing the feed by an extra 3 tenths and see what happens.


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## jtwade

Used to have to turn some bearing journals to tenths tolerances in a shop I worked at. The way I was taught to do it was fairly simple, rough size to within .005 of finished diameter. Then set up tool post grinder with the compound set at about 84 degrees. At that angle, one thousand on the dial, moved in darn close to one tenth. Forget my trig, but 84 degrees was close enough to get the part close enough:roflmao:. Never tried to get that close with a cutting bit, but see how the math works.


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## spaceman_spiff

update


targetresulterrornotes0.00630.00620.00020.00710.00680.00030.00520.00500.00020.01010.00950.00060.00480.00440.00040.00490.00515-0.00025added 3 tenths0.00490.004650.00025added 2 tenths

Well maybe I've gotten as good as it can get then. The micrometer itself is only accurate to a tenth. And now I've made the error bipolar and its also where I said I wanted it to be so the question now is, can I reproduce that at will and on what materials and locations on the bed?

If we look at this as a practical thing, if you can just INCREASE the cut a 3 tenths at a time, then you can measure and repeat until you are where you want. 

So from that perspective, now I need a test. 

Perhaps making a spindle block with two bearings, a spindle, and a block with bores, and see what kind of runout I get? Or what would be a realistic test?


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## benmychree

spaceman_spiff said:


> Criticism of what I describe here is WELCOME!!! Please, lets dissect this, tear it apart, and make it better.
> 
> The good news is: I think I am getting control of diameters, +/- 0.0001" (tenths), on my ancient, worn out Atlas 10F lathe.
> 
> I also learned something very important about manual lathes today. That alone is almost more important than being able to cut within tenths.
> 
> Heres how I did it, and that special thing I learned:
> 
> Notice how the handwheels are graduated in 0.001", and the space between two graduations is about 1/32"? WAY too small to control tenths, accurately anyway. Yes, you can approximate. But seems kind of strange to me that a lathe would have handwheels that coarse. Im sure when even this low grade Atlas lathe was brand new it could cut in tenths reliably. Hmm. Actually..come to think of it the Hardinge HLV-H extreme precision lathe I used at work long ago was also in 0.001". So how the heck is anyone supposed to work in 0.0001"?
> 
> Even a DRO or dial indicators wouldn't really help, because you'd still be stuck trying to turn that handwheel just that TEEENY amount!
> 
> Well, thats where the compound tool post comes in. It will let you magnify its handwheel by MORE than you would ever want!! Yes, you can turn the handwheel 100 ticks and it will only move the cutter forward by .001" if you want!! So essentially you have made it so that each handwheel graduations of 0.001" actually means 10 MILLIONTHS of an inch! Now tenths become cake!
> 
> The idea behind this is to just rotate the compound tool post so its a very slight angle instead of parallel to the spindle axis. To be clear, "parallel" to the spindle axis would mean that turning its handwheel would move it towards or away from the spindle.
> 
> Now think about that, if its only moving towards or away from the spindle, its not moving the tool towards or away from the work at all, is it?
> 
> So if you put it at a very slight angle, it WILL move the tool towards or away from the work. Turns out that at around 84 degrees, for every 100 thou of its handwheel, it moves towards the work by only 10 THOU! Now each tick is 0.0001"! Tada! And if you want you could theoretically reduce that angle even further and probably multiply it by ten times again!
> *
> REALITY CHECK*
> 
> -You are still limited by the accuracy of the threads, ways, etc.. You cannot precisely move the tool by 10 atoms just because you have the slide at an angle. But where that limit of accuracy is is now something you can move on to dealing with, instead of trying to turn a handwheel by some teeny amount.
> 
> -The angle readings on the compound tool post are not very fine. You should get the angle to approximately where you want and then do some test cuts to confirm the new tool post handwheel versus actual increase in cut distance, and then do some arithmetic and calculate how many thou you need to turn the handwheel to get what you want. If you dont have a tenths micrometer, now you have an excuse to buy one!!
> 
> -You will likely need to rotate your toolpost so the tool is again perpendicular (or whatever you need it to be) to the work, since you are rotating the tool post.
> 
> *RESULTS!!!
> 
> *So...does this work or not? The answer appears to be YES!
> 
> I spent the last couple hours experimenting to see if I could really make reliable cuts in one shot based solely on the handwheel.
> 
> Material: 303 stainless
> RPM: about 800
> Cutter: carbide TPG322 in a very rigid insert holder and tool post
> Lube: none
> Diameter of workpiece: about 1/2"
> Workholding: 4 jaw chuck. Stickout about 2".
> Feed: automatic, about 5 thou per rev
> Machine: Atlas 10F from 1944
> 
> Cutting notes:
> 
> All done in three passes. First two were easily seen. The last pass was BARELY visible taking place..I'm not sure if it was doing anything or not. I have very good vision up close and could just barely see the "line" moving by getting up real close. And to be clear, I made NO adjustments to the handwheels between passes. I just turned the motor off, used the carriage handwheel to move the tool back to the beginning of the cut, and then powered it up and repeated the cut.
> 
> I made many test cuts. Some of them came out right, some did not. A few came out about 1 thou off!! But I think I have it figured out now.
> 
> The final two cuts I made came out within about 0.0001" of where I intended. I think what was happening with the cuts that didn't work out was that I was not taking deep enough cuts. And I also screwed up the math a few times since my calculator was dying and I couldn't read it. I would get your notepad and calculator handy and keep a log of what you do so you can figure out how deep you need to cut and what RPM/stickout you need to do, etc..
> 
> *FINAL CUT #1:*
> 
> Target radial reduction: 0.0117"
> Actual radial reduction: 0.01175"
> 
> *FINAL CUT #2*
> 
> Target radial reduction: 0.0107"
> Actual radial reduction: 0.0108"
> 
> (the pic shows the incremental change in diameter)
> 
> Please join in the fun and report your results!!! You will need an accurate tenths micrometer to play along. The one I'm using was $30 from horrible freight!



Pretty much a big waste of time, especially on a notably imprecise machine, ways, geometry, and unmentioned, spindle bearings.  Cutting tools are a large part of the accuracy equation as well; we do not need to have such complication in the (machine's) ability to measure, all that is necessary is an accurate finish cut, leaving a very small amount of stock to (lightly) file and subsequent polishing with abrasive cloth.  It may be another matter with ultra precision machines, but turning and grinding is the real answer for more complicated precision parts that turning alone is not likely to give.


----------



## SG51Buss

That 'shear' tool article was fascinating, and so counterintuitive that I had to re-read it 3 times before it sunk in.  Gotta try that someday, including the 'notched' parting blade.

 Thanx...

On the thermal expansion issue, I've always wondered if hi-quality micrometers expand uniformly with shop temperatures, yielding the same measurements on same-temperature workpieces, or if the bows are designed to mitigate that expansion, including the 'warmth' of the operator's palm.

It's interesting that your 0.0002" - 0.0003" errors are consistent.  I wonder if that's caused by the rounded edge of the carbide insert.  When I first started using insert tooling, I  also experienced a similar reduction in depth-of-cut to bit-advance ratio.

Oh, wait.  That consistent error may also be caused by not being at a precise 84.26° compound angle.  Look at the error to target-feed ratios.  For example, in your second test, to get the 0.0071" target, the compound was advanced 0.071"?  The 0.0003" error over that 0.071" travel is about a 0.24° angle...


----------



## John Hasler

SG51Buss said:


> That 'shear' tool article was fascinating, and so counterintuitive that I had to re-read it 3 times before it sunk in.  Gotta try that someday, including the 'notched' parting blade.
> 
> Thanx...
> 
> On the thermal expansion issue, I've always wondered if hi-quality micrometers expand uniformly with shop temperatures, yielding the same measurements on same-temperature workpieces, or if the bows are designed to mitigate that expansion, including the 'warmth' of the operator's palm.



As far as I know they are made of invar 

http://en.wikipedia.org/wiki/Invar

to minimize thermal effects.


----------



## dsh1001

First of all, congratulations on figuring out that trick. That is something a person would normally learn at the elbow of a master machinist and you came up with it yourself. Nice

Grinders definitely create a very fine finish. I don't beleive that, in itself, gives a ground finish any better dimensional accuracy though. Think of the finish as a peaks and valley on the surface of the part. Whether you are talking about a lathe finish of 125 microinches (pretty darn rough) or a ground finish of 10 microinches (pretty darn nice finish) you are still doing your measuring on the peaks of that finish. The very fine tolerances come from the very fine cutting tools (grit of the grinding wheel), the wide contact with the part for even pressure dispersal, the rapidly rotating cutting tools (which makes the grinding wheel essentially one wide tool instead of thousands of tiny tools)  and the very fine advance of the grinding wheel usually in the range of ten millionths to a hundred millionths (.000010 to .000100). 

Just my two cents,
David H.


----------



## Andre

I think MrPete222 showed this in one of his videos. Nonetheless it is a great trick! I'd play along but my lathe doesn't have dials :lmao:


----------



## george wilson

Ground finishes that are done properly definitely leave smoother finishes than turned finishes. That is why all manner of parts that need to be accurate are ground. The valves and valve stems on your car are ground,for 1 simple example. They need to fit accurately into their holes without the "peaks and valleys" that turned parts have,becoming soon worn off,resulting in undersize valve shafts that leak oil.

If you look around at
what things are turned and what are ground,or even precision lapped,you will begin to understand why ground surfaces are used. The surfaces of ball bearing races are ground. Even the outside surfaces are ground. This to again,prevent the "peaks" of a rougher surface from wearing off,leaving the bearing loose in its mounting.  Really precision things like gage blocks are first precision ground down to very close limits. Then,to make their surfaces even smoother,and more long lasting of tolerances,they are lapped until they actually stick together,so flat and smooth are their surfaces.

So,grinding not only makes the surface smoother,it makes a longer lasting surface that will remain at that diameter.

One final,but very important reason for grinding is that many,if not most real precision surfaces have been made longer lasting by hardening them. This applies to all kinds of moving and sliding parts as well as gages. They have to be ground since they are hardened.

By the way: If you look at a precision grinding machine while the wheel is grinding a surface,you will notice that the grinding is done at the leading edge of the wheel,not over the entire surface. Plunge grinding operations ,like crankshaft journal grinding,do involve the whole surface of the wheel. Most grinding operations do not involve the surface of the whole width of the wheel. The wheel has to be dressed very often in cases where the whole wheel is used,as on crankshafts,where there's no room to move the wheel sideways. Possibly for every grind. I don't do automotive work.

You really do not need an experienced master to tell you these things. You can look at mechanisms and see for yourselves what is ground and what is not. However,you must always enter into these investigations with an open mind,and not with your mind already made up. Open mind is needed to really learn.


----------



## Bill Gruby

dsh1001 said:


> First of all, congratulations on figuring out that trick. That is something a person would normally learn at the elbow of a master machinist and you came up with it yourself. Nice
> 
> Grinders definitely create a very fine finish. I don't beleive that, in itself, gives a ground finish any better dimensional accuracy though. Think of the finish as a peaks and valley on the surface of the part. Whether you are talking about a lathe finish of 125 microinches (pretty darn rough) or a ground finish of 10 microinches (pretty darn nice finish) you are still doing your measuring on the peaks of that finish. The very fine tolerances come from the very fine cutting tools (grit of the grinding wheel), the wide contact with the part for even pressure dispersal, the rapidly rotating cutting tools (which makes the grinding wheel essentially one wide tool instead of thousands of tiny tools)  and the very fine advance of the grinding wheel usually in the range of ten millionths to a hundred millionths (.000010 to .000100).
> 
> Just my two cents,
> David H.




 The peaks and valleys are not as pronounced on the Grind Finish, hence the super accuracy. I do not grind for a living. I use it on rare occasions in the hobby. My use of it and the results I get are what I stand by.

 "Billy G"


----------



## chuckorlando

Your not grinding on the surface of the wheel. Just the leading edge.As you advance the part and that edge is used up the portion just behind the leading edge becomes the new edge so to speak. If you wer grinding on the whole flat it would take seconds before the wheel was no longer touching as you burnt off the "cutting surface". 

I believe Mr Wilson's point was not that they would not mic the same off the machine. But rather, the sharper taller peaks from the lathe would wear very fast (provided something is wearing on it) thus leaving you .0001 or what have you, under the desired size.





dsh1001 said:


> First of all, congratulations on figuring out that trick. That is something a person would normally learn at the elbow of a master machinist and you came up with it yourself. Nice
> 
> Grinders definitely create a very fine finish. I don't beleive that, in itself, gives a ground finish any better dimensional accuracy though. Think of the finish as a peaks and valley on the surface of the part. Whether you are talking about a lathe finish of 125 microinches (pretty darn rough) or a ground finish of 10 microinches (pretty darn nice finish) you are still doing your measuring on the peaks of that finish. The very fine tolerances come from the very fine cutting tools (grit of the grinding wheel), the wide contact with the part for even pressure dispersal, the rapidly rotating cutting tools (which makes the grinding wheel essentially one wide tool instead of thousands of tiny tools)  and the very fine advance of the grinding wheel usually in the range of ten millionths to a hundred millionths (.000010 to .000100).
> 
> Just my two cents,
> David H.


----------



## Micke S

A tool post grinder in combination with a hi resolution DRO, or the trick presented in OP, will make great surface finish to the correct diameter. Turning is as said above not good enough for creating a silk lean surface.


----------



## george wilson

That was 1 point I made,Chuck: peaks will soon wear off,or become compressed if going through a hole in a ball bearing,etc.. Soon the turned part will be undersized. Several other reasons also for grinding,though.

Cars shipped by railroad to distant dealers had to have their wheel bearings replaced upon arrival. This was because of the slight but constant jarring of the tracks. Even though the cars had precision ground bearings in their wheels,even that was not good enough. The very minute "peaks and valleys" of the grinding wore enough to cause the wheel bearings to soon become shot.

The solution to this problem was "super finishing",which I think Chrysler invented( It's been a while since I read about super finishing). They started doing this to several of the different parts in cars,such as pistons. It greatly improved the number of miles you could drive before needing a complete overhaul.

I read an old Mechanics Illustrated magazine from the 30's long ago. The title of the article was "How you can get 50,000 miles out of your car". These days that is nothing. It is due to better finishes on parts,better alloys,better lubricants,and other things that we get so many more miles out of cars today. Super finishing is one of the most important factors.


----------



## f350ca

spaceman_spiff said:


> Could you explain this further? I have never been able to get a grip on grinders and why they do a better job as far as accuracy, without the machine they are attached to also being better.
> 
> For instance, lets say the finish using the turning tool are relatively rough, but consistent. Then as long as the increase in cut is made relative to the measured finish/diameter combo, the quality of the finish falls out and isn't part of the result anymore.
> 
> Another way to look at it is this, I'm seeing errors in the range of 0.0005" to 0.001". The finish is much smoother than that, even just eyeballing it. A 1000 microinch finish is what you get with a saw or flame cut apparently. So as long as the finish remains consistent, I dont see how improving it would increase accuracy.



A couple of reasons I can think of.
No matter how stiff the lathe your using is there is some flex due to the force exerted by the cutter, the light passes made with a grinder exert nearly no force, and that is diminishing as the wheel removes the metal. As the wheel advances into untouched metal there may be some side load, but the very high surface speed of the wheel quickly removes the bulk and the next section of the wheel sees less and so on, till at the end the wheel is rotating above the material and removing virtually nothing.
When using carbide insert cutters there is a considerable radius on the cutting edge. If you try and remove a very small amount of metal say .001 or less your no longer cutting the metal but rather burnishing it as the cut is smaller than the radius. 

Greg


----------



## george wilson

As a note: My first lathe was a Sears Atlas 12". It was guaranteed to turn to .001" accuracy ONE INCH from the chuck!! If you're getting 1/2" of accuracy,you aren't too bad off!!


----------



## Shadowdog500

John Hasler said:


> You might want to try combining these techniques with a shear tool.  It is supposed to provide a very good finish while consistently removing 1 or 2 thousandths accurately (I've never tried one myself).
> 
> http://www.gadgetbuilder.com/VerticalShearBit.html



Thanks for the link, I'm going to try this.  Shame the first  link to the paper he got the idea from is gone, I would have liked to read that one too.

Chris


----------



## MozamPete

spaceman_spiff said:


> Well, thats where the compound tool post comes in. It will let you magnify its handwheel by MORE than you would ever want!! Yes, you can turn the handwheel 100 ticks and it will only move the cutter forward by .001" if you want!!



I use a similar trick on my old lathe. The hand wheel measures on the lathe are all imperial but I tend to work in metric. So I set the compound to 23.2 degrees and then a thou on the hand wheel gives 0.01mm of movement in the diameter. Saves having to do any inch to mm conversions - I measure using a metric micrometer, figure out what I need to take off (say 0.1mm), then just dial up 100 time that in thou on the compound (10 thou on the compound in this case).


----------



## hman

I just found this thread, and read the whole fascinating thing.  Thanks to ALL of you for your expertise!  I've heard about the technique previously, but having all the details gone over and hashed out has definitely ben of value.

Just one point that I don't recall being mentioned ... maybe I missed it, or maybe it's so obvious it didn't need to be mentioned.  But I'd rather it be redundant than unmentioned:

Be sure the cross slide is locked during the cut.

Thanks again!


----------



## 12bolts

spaceman_spiff said:


> ......The one I'm using was $30 from horrible freight!......



Does the paperwork with your mic say it is accurate to tenths or has a resolution of tenths?
And have you checked your mic on some standards that are accurate to better than tenths?

Cheers Phil


----------



## John Hasler

12bolts said:


> Does the paperwork with your mic say it is accurate to tenths or has a resolution of tenths?
> And have you checked your mic on some standards that are accurate to better than tenths?
> 
> Cheers Phil



I think that for his purposes repeatabiliy to a tenth suffices.  He's not making shafts that must fit bushing made in another shop.


----------



## spaceman_spiff

12bolts said:


> Does the paperwork with your mic say it is accurate to tenths or has a resolution of tenths?
> And have you checked your mic on some standards that are accurate to better than tenths?
> 
> Cheers Phil



All my measurements for these tests are relative so checking it against an absolute standard wouldn't mean anything, only when I actually try to hit a specific diameter will the mic accuracy come into play. At that point, it will almost certainly be a spindle surface meant to fit inside a bearing race, so I will use the bearing race itself as the "standard" and shoot for a relative change for that. Never knowing the actual diameter of anything lol


----------



## spaceman_spiff

John Hasler said:


> I think that for his purposes repeatabiliy to a tenth suffices.  He's not making shafts that must fit bushing made in another shop.



You are correct sah...I will most likely be fitting bearings to a shaft so I will make relative measurements to the bearing


----------



## spaceman_spiff

hman said:


> I just found this thread, and read the whole fascinating thing.  Thanks to ALL of you for your expertise!  I've heard about the technique previously, but having all the details gone over and hashed out has definitely ben of value.
> 
> Just one point that I don't recall being mentioned ... maybe I missed it, or maybe it's so obvious it didn't need to be mentioned.  But I'd rather it be redundant than unmentioned:
> 
> Be sure the cross slide is locked during the cut.
> 
> Thanks again!



I have been avoiding locking the cross slide because it moves the tool post slightly when doing so and adds another variable. However it may be worth looking into if the amount it moves is repeatable.


----------



## spaceman_spiff

f350ca said:


> A couple of reasons I can think of.
> No matter how stiff the lathe your using is there is some flex due to the force exerted by the cutter, the light passes made with a grinder exert nearly no force, and that is diminishing as the wheel removes the metal. As the wheel advances into untouched metal there may be some side load, but the very high surface speed of the wheel quickly removes the bulk and the next section of the wheel sees less and so on, till at the end the wheel is rotating above the material and removing virtually nothing.
> When using carbide insert cutters there is a considerable radius on the cutting edge. If you try and remove a very small amount of metal say .001 or less your no longer cutting the metal but rather burnishing it as the cut is smaller than the radius.
> 
> Greg



Yeah but my point is, whatever your cutting/burnishing passes do, as long as they are repeatable, then the accuracy shouldn't be any different, even if the finish is inferior.


----------



## spaceman_spiff

george wilson said:


> That was 1 point I made,Chuck: peaks will soon wear off,or become compressed if going through a hole in a ball bearing,etc.. Soon the turned part will be undersized. Several other reasons also for grinding,though.
> 
> Cars shipped by railroad to distant dealers had to have their wheel bearings replaced upon arrival. This was because of the slight but constant jarring of the tracks. Even though the cars had precision ground bearings in their wheels,even that was not good enough. The very minute "peaks and valleys" of the grinding wore enough to cause the wheel bearings to soon become shot.
> 
> The solution to this problem was "super finishing",which I think Chrysler invented( It's been a while since I read about super finishing). They started doing this to several of the different parts in cars,such as pistons. It greatly improved the number of miles you could drive before needing a complete overhaul.
> 
> I read an old Mechanics Illustrated magazine from the 30's long ago. The title of the article was "How you can get 50,000 miles out of your car". These days that is nothing. It is due to better finishes on parts,better alloys,better lubricants,and other things that we get so many more miles out of cars today. Super finishing is one of the most important factors.



Yeah but we're talking about cut accuracy not lifetime accuracy of the surface. If whatever inferior surface thats created by using turning tools is repeatable, why would it be any less accurate than a superior finish surface?


----------



## spaceman_spiff

Micke S said:


> A tool post grinder in combination with a hi resolution DRO, or the trick presented in OP, will make great surface finish to the correct diameter. Turning is as said above not good enough for creating a silk lean surface.



I think the idea of a superior finish versus an accurate diameter are being mixed up. One does not necessarily come along with the other. A tool post grinder will not correct pitch error in the tool post screw or the tool post ways not being straight.


----------



## spaceman_spiff

benmychree said:


> Pretty much a big waste of time, especially on a notably imprecise machine, ways, geometry, and unmentioned, spindle bearings.  Cutting tools are a large part of the accuracy equation as well; we do not need to have such complication in the (machine's) ability to measure, all that is necessary is an accurate finish cut, leaving a very small amount of stock to (lightly) file and subsequent polishing with abrasive cloth.  It may be another matter with ultra precision machines, but turning and grinding is the real answer for more complicated precision parts that turning alone is not likely to give.




Using the compound to increase resolution is a very old and standard procedure. Filing is not an accurate machining process.


----------



## spaceman_spiff

SG51Buss said:


> It's interesting that your 0.0002" - 0.0003" errors are consistent.  I wonder if that's caused by the rounded edge of the carbide insert.  When I first started using insert tooling, I  also experienced a similar reduction in depth-of-cut to bit-advance ratio.
> 
> Oh, wait.  That consistent error may also be caused by not being at a precise 84.26° compound angle.  Look at the error to target-feed ratios.  For example, in your second test, to get the 0.0071" target, the compound was advanced 0.071"?  The 0.0003" error over that 0.071" travel is about a 0.24° angle...



Okay I really want to make sure I understand you here...maybe this is the answer!

I set the compound angle very imprecisely, just turned it until it was around 84 and clamped it down.

Then, I figured out the actual relationship between handwheel and tool feed by measuring it. By turning the stock true, then feeding the compound by 100 thou, cutting and then measuring the result. Which came out to about 0.0001065" feed for every 0.001" of compound handwheel. And then I did the tests based on that. 

So when I was trying to hit 0.0071", I rotated the handwheel by 0.0071 / 0.0001065 = 66.7 thou. 

But I want to make sure that explains what you are saying..it does right? 

Im actually pretty comfortable if I can maintain 3 tenths. It definitely is tantalizing to see if I can get down to 1 tenth but I have a feeling that may be impossible. 

However, when I get my ER32 chuck, I'm going to repeat these tests and do everything as close as possible to the chuck and see if that helps. It will be several inches closer to the spindle bearings than the 4 jaw chuck setup I'm doing now. I have to think there is a tenth or so to be had by the reduced runout!


----------



## Mark_f

I love this post, but I ain't steppin in this pile ). It is interesting and the opinions are so varying. One thing I KNOW, my mics have an instruction sheet ( who'd a thunk it?) . They say to handle them by the ends. It says DO NOT HOLD BY THE CENTER OF THE BOW. It says the warmth of your hands will change the accuracy. That being said , the change is slight. I was taught this very early in my training.( we worked in a temperature controlled environment). But I do not believe this is a problem to most of us as I don't know about yours, but my little shop runs a wide range of temperatures, especially this time of year. it was 40 in there today. We want to get cuts as close as possible and I do this by making a close fit. The amount of closeness usually determines whether I need a 2 pound or 4 pound mallet to put it together.

Mark Frazier





12bolts said:


> Does the paperwork with your mic say it is accurate to tenths or has a resolution of tenths?
> And have you checked your mic on some standards that are accurate to better than tenths?
> 
> Cheers Phil


----------



## 12bolts

spaceman_spiff said:


> All my measurements for these tests are relative so checking it against an absolute standard wouldn't mean anything, only when I actually try to hit a specific diameter will the mic accuracy come into play. At that point, it will almost certainly be a spindle surface meant to fit inside a bearing race, so I will use the bearing race itself as the "standard" and shoot for a relative change for that. Never knowing the actual diameter of anything lol



You have missed the point of my questions. Just because your display reads to tenths, or hundredths, does not make the tool accurate to that. Resolution is no indication of accuracy.
You cannot check the accuracy of a tool on something that is only accurate to the same level you are shooting for. A master must be better than what you are checking it with.
Repeatability is another, as well as accuracy across the range. You alluded to some unexplainable errors in your measurements.

Cheers Phil


----------



## chuckorlando

If you never get there, I'm enjoying you giving it a go. Lotta good info gets drug out in a post like this





spaceman_spiff said:


> Okay I really want to make sure I understand you here...maybe this is the answer!
> 
> I set the compound angle very imprecisely, just turned it until it was around 84 and clamped it down.
> 
> Then, I figured out the actual relationship between handwheel and tool feed by measuring it. By turning the stock true, then feeding the compound by 100 thou, cutting and then measuring the result. Which came out to about 0.0001065" feed for every 0.001" of compound handwheel. And then I did the tests based on that.
> 
> So when I was trying to hit 0.0071", I rotated the handwheel by 0.0071 / 0.0001065 = 66.7 thou.
> 
> But I want to make sure that explains what you are saying..it does right?
> 
> Im actually pretty comfortable if I can maintain 3 tenths. It definitely is tantalizing to see if I can get down to 1 tenth but I have a feeling that may be impossible.
> 
> However, when I get my ER32 chuck, I'm going to repeat these tests and do everything as close as possible to the chuck and see if that helps. It will be several inches closer to the spindle bearings than the 4 jaw chuck setup I'm doing now. I have to think there is a tenth or so to be had by the reduced runout!


----------



## george wilson

My point about a ground surface vs. a turned surface with peaks and valleys is this: You cannot use a surface with peaks and valleys for anything because the peaks will wear off readily. If the shaft is inserted into the hole in a bearing,the peaks will soon be mashed flat(we are talking about a VERY small amount of metal here). The tolerance of the shaft will change. The surface will become worn if used for any purpose other than to look at.

So,what have you really accomplished other than entertaining yourself making a piece of metal to supposedly close tolerance? 

If you grind the surface,your shaft will be smoother,and the surface will not be burnished by use as much by far as a turned surface. If the surface is hardened and ground,then you have a truly durable,useful surface that has practical use.

I have said this a number of times in previous posts. I hope you get the point.

Now that you have discovered the old trick of setting the compound to an angle,and being able to work to closer tolerances,the next thing to do is get a better lathe and a toolpost grinder. Then,use your knowledge to make something wherein you can APPLY close tolerances usefully. Perhaps a small engine,for example.

When you get to be an experienced machinist(I assume you are not since this is in the beginner's section,forgive me if I am wrong),you will discover that working to .0001" in a practical application is not as easy as it might seem.


----------



## John Hasler

spaceman_spiff said:


> All my measurements for these tests are relative so checking it against an absolute standard wouldn't mean anything, only when I actually try to hit a specific diameter will the mic accuracy come into play. At that point, it will almost certainly be a spindle surface meant to fit inside a bearing race, so I will use the bearing race itself as the "standard" and shoot for a relative change for that. Never knowing the actual diameter of anything lol



Repeated measurements on a standard (or the same spot on a piece of hardened and ground shaft of unknown diameter, for that matter) could give you a handle on the repeatability of your instrument.


----------



## spaceman_spiff

John Hasler said:


> Repeated measurements on a standard (or the same spot on a piece of hardened and ground shaft of unknown diameter, for that matter) could give you a handle on the repeatability of your instrument.



Thats what I'm doing when I'm measuring the stock after I cut and zeroing the mic on it. I really doubt the stock is changing in diameter from the pressure of mic anvil, especially with torque limiting thimble.


----------



## george wilson

You need to handle your mike with gloves if you really want to work to tenths.


----------



## spaceman_spiff

george wilson said:


> So,what have you really accomplished other than entertaining yourself making a piece of metal to supposedly close tolerance?



Achieving tenths precision on a worn 1944 Atlas lathe for the purposes of spindle creation and bearing fitting is a task that needs to be broken up into smaller pieces rather than approached simultaneously. First I need to achieve tenths in the best case scenario I can create, which will, in a few days, be cutting as close to the spindle as possible in an ER collet. Once I have achieved +/- 2 or 3 tenths at that location in steel and at a few important diameters and with 100% reliability over say a dozen attempt, then I'll try further out from the spindle with tailstock support. And then probably achieving the concentricity required to have two surfaces at tenths precision so they can fit through two bearings in a spindle head. 

Once I can reliably do all that, I can justify trying to improve the finish quality so its longer lasting, as required. If I can get the finish needed to do without grinding or hardening, thats what I'd prefer, because its simpler, but if it proves necessary I'll deal with it when the timing makes sense.



> If you grind the surface,your shaft will be smoother,and the surface will not be burnished as much by far as a turned surface. If the surface is hardened and ground,then you have a truly durable,useful surface that has practical use.



Yes correct. But not related to the idea of achieving higher cutting precision.



> I have said this a number of times in previous posts. I hope you get the point.



And I you. 



> Now that you have discovered the old trick of setting the compound to an angle,and being able to work to closer tolerances,the next thing to do is get a better lathe and a toolpost grinder. Then,use your knowledge to make something wherein you can APPLY close tolerances usefully. Perhaps a small engine,for example.



I have quite a bit of work left to say I can reliably control diameters in tenths over a reasonable range of carriage travel. This is just the beginning. 



> When you get to be an experienced machinist(I assume you are not since this is in the beginner's section,forgive me if I am wrong),you will discover that working to .0001" in a practical application is not as easy as it might seem.



When did I say I thought it would be easy?


----------



## spaceman_spiff

12bolts said:


> You have missed the point of my questions. Just because your display reads to tenths, or hundredths, does not make the tool accurate to that. Resolution is no indication of accuracy.
> You cannot check the accuracy of a tool on something that is only accurate to the same level you are shooting for. A master must be better than what you are checking it with.
> Repeatability is another, as well as accuracy across the range. You alluded to some unexplainable errors in your measurements.
> 
> Cheers Phil



The micrometer is accurate to 0.0001".


----------



## darkzero

george wilson said:


> You need to handle your mike with gloves if you really want to work to tenths.



As well as being in a _proper_ climate controlled environment, without that making comparison measurements to the tenths is not really accurate.

There's a reason why Mitu puts covers like this on their mics.





I'm not a machinist by trade, although I have mics that have 1 tenth resolution as well the DRO scale on my lathe's X axis, I don't try to hold a tolerance to a tenth, I just use the extra resolution for reference.


----------



## chips&more

12bolts said:


> You have missed the point of my questions. Just because your display reads to tenths, or hundredths, does not make the tool accurate to that. Resolution is no indication of accuracy.
> You cannot check the accuracy of a tool on something that is only accurate to the same level you are shooting for. A master must be better than what you are checking it with.
> Repeatability is another, as well as accuracy across the range. You alluded to some unexplainable errors in your measurements.
> 
> Cheers Phil




For this application the mike only needs to have “precision”.  The mike does not need to be “accurate”.  And it’s 59 replies and counting!...Good Luck, Dave


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## spaceman_spiff

george wilson said:


> You need to handle your mike with gloves if you really want to work to tenths.



Nah. Holding the mic for 5 seconds by the plastic isnt going to change the measurement.


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## John Hasler

spaceman_spiff said:


> Thats what I'm doing when I'm measuring the stock after I cut and zeroing the mic on it. I really doubt the stock is changing in diameter from the pressure of mic anvil, especially with torque limiting thimble.



I'm suggesting that you make a seperate project of determining the repeatability of your mic.  For example, measure two different dimensions of a reference object such as a gage block alternately 100 times (writing the measurements down) and then do statistics on the results.


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## george wilson

For comparative purposes ONLY,his mike does not have to ACTUALLY be reading true diameters. He's only using it for theoretically consistent readings.He still needs to protect it from the heat of his hands. That mike does not look like it has sufficient insulation. Even if it did,if I was using it often, I'd still use gloves.  I use gloves when using my Starrett Master Machinist's Level. If I don't,it will warp ever so slightly and not give me true readings over the length of my lathe. Getting my lathe level is where I tend to go a bit overboard! Fortunately,my HLVH has  built in 3 point contact,and does not need leveling. It stays true to itself with no twisting. My 16" lathe needs leveling,though.


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## 12bolts

spaceman_spiff said:


> I think the idea here, is to make it so everything you do is relative to ONE moment in time..one setup, one temperature, etc...to compensate for everything for that instant you make the cut. I dont think holding tenths on this lathe is going to be possible otherwise.


Whilst you are making the cut the work is heating and expanding. The tool will take off more from the dia from start of cut to finish of cut. At the level of accuracy you are aiming for it would be measurable.


spaceman_spiff said:


> and I still saw variability around 0.0005". These cuts are back to back, same workpiece, same cutter, same temperature, same location on the ways, etc..


Nope not the same temperature from cut to cut. When I am aiming for press fits, close sliding fits, or just as good as I can make it. I will take the last cut after the work has cooled.


spaceman_spiff said:


> The machining can be that accurate. Thermal expansion is irrelevant. Nobody is claiming they are machining something and that it suddenly becomes immune to thermal expansion.


So is the thermal expansion irrelevant, or not?


spaceman_spiff said:


> Thats what I'm doing when I'm measuring the stock after I cut and zeroing the mic on it. I really doubt the stock is changing in diameter from the pressure of mic anvil, especially with torque limiting thimble.


Nope but the thermal expansion of your work will change due to friction.


spaceman_spiff said:


> Nah. Holding the mic for 5 seconds by the plastic isnt going to change the measurement.


If you think you can take an accurate measurement in less than 5 seconds from pick up to put down of the tool you are mistaken.

Cheers Phil


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## spaceman_spiff

12bolts said:


> Whilst you are making the cut the work is heating and expanding. The tool will take off more from the dia from start of cut to finish of cut. At the level of accuracy you are aiming for it would be measurable.



You're exaggerating the effects.

The cut I'm making, in 6061, at about 10 thou radial at 850 rpm, is around a 1/25th horsepower cut. Maybe 30 watts. The block of aluminum I had chucked up is maybe 300 grams. Specific heat of aluminum is about 0.9 J/g/K, and the cut lasts about 8 seconds. So in that time, maybe 240J goes into the cut. The majority of that heat goes into the chip. But even if 100% of it went into the workpiece, which it certainly does not, that would raise the temperature by about a whopping 1K or maybe 2F. Resulting in an expansion of maybe 0.000011" inches since the section I'm cutting is about 0.7" diameter. But really, almost all the energy goes into the chip, and the workpiece is cooled by the air moving around it. So the expansion is more like in single digit millionths of an inch.

Plus, I'm making the measurements at roughly the same time after the cuts anyways, so most of the change resulting in expansion drops out of the relative measurement anyway.



> So is the thermal expansion irrelevant, or not?



The idea that thermal expansion is not relevant in this case and also that nobody is claiming that machining makes things irrelevant to thermal expansion are not mututally exclusive or even related.



> If you think you can take an accurate measurement in less than 5 seconds from pick up to put down of the tool you are mistaken.
> 
> Cheers Phil



I dont think it, I know it. The mic is already within 10 thou of the diameter because I just zeroed it before cutting. Its slides right over the workpiece in a second and I've done it dozens of times now. 5 seconds is a little long actually.

According to Mitutoyo I could hold the BARE frame for 120 seconds with my bare hand and it would only expand by 0.00008", and they say adding the plastic insulator would significantly decrease that. 

For anyone interested in some juicy precision measurement tips, check out:

http://www.mitutoyo.com/wp-content/uploads/2013/04/E11003_2_QuickGuide.pdf


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## BillWood

Hello,

When trying for these high levels of accuracy would a dead centre from the tailstock into the loose end of the workpiece help to prevent minor deflection at the loose end of the workpiece ?

Or are you doing all of the tests very close to the supported chuck end so this doesn't matter.

Bill


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## Shadowdog500

spaceman_spiff said:


> I dont think it, I know it. The mic is already within 10 thou of the diameter because I just zeroed it before cutting. Its slides right over the workpiece in a second and I've done it dozens of times now. 5 seconds is a little long actually.
> 
> According to Mitutoyo I could hold the BARE frame for 120 seconds with my bare hand and it would only expand by 0.00008", and they say adding the plastic insulator would significantly decrease that.
> 
> For anyone interested in some juicy precision measurement tips, check out:
> 
> http://www.mitutoyo.com/wp-content/uploads/2013/04/E11003_2_QuickGuide.pdf



Thanks for the useful link for a mytutoyo micrometer!
Did you upgrade to a mitutoyo micrometer?

If not, do you have any reference material From Harbor Freight that indicates how long you can hold your $30 micrometer before you get measurable expansion?

Chris


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## SG51Buss

spaceman_spiff said:


> ...I set the compound angle very imprecisely, just turned it until it was around 84 and clamped it down.
> 
> Then, I figured out the actual relationship between handwheel and tool feed by measuring it. By turning the stock true, then feeding the compound by 100 thou, cutting and then measuring the result. Which came out to about 0.0001065" feed for every 0.001" of compound handwheel. And then I did the tests based on that.
> 
> So when I was trying to hit 0.0071", I rotated the handwheel by 0.0071 / 0.0001065 = 66.7 thou.
> 
> But I want to make sure that explains what you are saying..it does right?



Yep, sure does.  Doing the first cut and second cut with the bit under load sure sounds like apples-to-apples to me.  Doesn't have to be a precise angle since you're using feed/cut ratio.

That 0.0001065" feed per 0.001" compound travel is a 0.1065 ratio, 6.114°, or a 83.886° compound angle.
Just for reference here, a true 0.1 ratio is 5.74°, or a 84.26° compound angle.

Do you think it would be worthwhile to find what the true compound angle is, measured without any cutting loads?  And if it differs from your derived value?

Leaving the compound angle as-is, you could chuck-up and true a reference rod, zero TIR at the chuck, find the TIR a few inches out and rotate the chuck to split that in half, so that the vertical plane of the test rod is parallel to the spindle.  Then, with a dialgauge, measure the infeed value over a long compound feed.

Similar to way I setup my 8° compound angle:  http://www.hobby-machinist.com/show...-ER-32-collet-chuck-to-an-Atlas-Craftsman-618

Of course, the compound feed is the hypotenuse, and the infeed is the SIN leg...


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## spaceman_spiff

Shadowdog500 said:


> Thanks for the useful link for a mytutoyo micrometer!
> Did you upgrade to a mitutoyo micrometer?
> 
> If not, do you have any reference material From Harbor Freight that indicates how long you can hold your $30 micrometer before you get measurable expansion?
> 
> Chris



You mean besides the fact they are both made out of identical or nearly indentical materials? Multiply it by a factor of 10 and you'd still have an irrelevant expansion at the time scales we're talking about. And there is no reason it would even be a factor of 10 let alone 2.


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## higgite

John Hasler said:


> You might want to try combining these techniques with a shear tool.  It is supposed to provide a very good finish while consistently removing 1 or 2 thousandths accurately (I've never tried one myself).
> 
> http://www.gadgetbuilder.com/VerticalShearBit.html



John, and others who haven't tried it, if you're into smooth finishes with little to no extra work, you need to try a vertical shear tool. Beautiful finish on aluminum, steel and brass, even on my bench top lathe. For example, last week I made a brass snap cap with a tangential tool and wanted a nice, smooth finish on it, so I emery clothed it. Needed another one and remembered I had a shear tool in the drawer that I haven't used in a while. I did the last .002" DOC finish cut with the shear tool. Didn't need emery cloth. And the tool itself is super easy to grind.

On topic, I didn't set the compound angle to 84.26 degrees, or 5.74, depending on your reference axis. I didn't need that much precision. )

Tom


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## John Hasler

higgite said:


> John, and others who haven't tried it, if you're into smooth finishes with little to no extra work, you need to try a vertical shear tool. Beautiful finish on aluminum, steel and brass, even on my bench top lathe. For example, last week I made a brass snap cap with a tangential tool and wanted a nice, smooth finish on it, so I emery clothed it. Needed another one and remembered I had a shear tool in the drawer that I haven't used in a while. I did the last .002" DOC finish cut with the shear tool. Didn't need emery cloth. And the tool itself is super easy to grind.
> 
> Tom



Thanks.  If it ever gets above 20F in my shop again I'll try it.


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## george wilson

I won't lock it since Nelson didn't. But,I'll be glad to see this long,convoluted list of repudiations go on down the list and vanish. And this after criticisms were asked for in post #1.


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## John Hasler

george wilson said:


> I won't lock it since Nelson didn't. But,I'll be glad to see this long,convoluted list of repudiations go on down the list and vanish. And this after criticisms were asked for in post #1.



IMHO it's one of the best discussions we've had in months.  Nothing wrong with a bit of argument as long as it doesn't get personal.


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## george wilson

When a person just will not listen to sound reasons why a ground surface is called for in high precision,it gets to be a bit of a pain.

And,that last statement about the HF mike being made of the same materials as a Mitutoyo(is it really?),so it must be as good, was right off the wall. I can list a dozen reasons why the HF mike probably is not as good. But,why bother?


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## John Hasler

george wilson said:


> When a person just will not listen to sound reasons why a ground surface is called for in high precision,it gets to be a bit of a pain.
> 
> And,that last statement about the HF mike being made of the same materials as a Mitutoyo(is it really?),so it must be as good, was right off the wall. I can list a dozen reasons why the HF mike probably is not as good. But,why bother?



He didn't say it was as good.  He just said it would expand at the same rate due to both being made of invar.


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## george wilson

There's no telling what crappy grade of metal was used in a real cheap instrument. There are lots of home brewed grades of cast iron out there in Asia.


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## BRIAN

Hi all
Just so us at the small end of the shop can get something out of this intense discussion I looked at the title and went into the shop 
, turned the compound to the required angle, then then took apiece of HSS and roughly made a shear tool didn't even hone it.
Found the worst piece of hot rolled steel that I scrounged from the local blacksmith and took a cut with a carbide tool just to remove the rubbish,  ended up with the normal B--- A---- finish.

placed my new shear tool in the lathe  and took a cut of .002" WOW It started to look smoother ,another two passes and I had a acceptable  (to me) finish. 






Now if I am trying to make two parts fit together I need to take fine cuts,  so now I try the compound just one division and it takes off a very fine sliver so I now measure the size to see if I can take off a controlled amount. 
My daddy's mic that he bought just after the war. WW1 not WW2, will not measure down to these sizes. so I had to turn to my cheepo metric mic that measures down to.01mm This is a figure almost non existent in my usage.

Repeated cuts  show I can happily hold a .01mm change in diameter so the cut must be half that, Boy am I pleased.
This is going to help me when it comes to making the crank for my engine.
The argument about shop environment ETC don't mean a thing to many of our members Just trying to make chips

Just remember the title said  ( ancient hobby lathe )  and this thread is a big help to those starting out on this never ending hobby.
.Brian.


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## higgite

I think it has been a good discussion for the most part. But, what I'm taking away from it is that the theory is solid (you can't argue with math), but the application to hobby lathes is pretty iffy for frog hair precision purposes. ymmv

John, off topic for an instant... 408 yards... in 3 quarters... not too shabby. 

Tom


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## Micke S

spaceman_spiff said:


> I think the idea of a superior finish versus an accurate diameter are being mixed up. One does not necessarily come along with the other. A tool post grinder will not correct pitch error in the tool post screw or the tool post ways not being straight.



Do you really think diameter and surface finish are mixed up, and has anyone so far claimed that a tool post grinder has the capability to correct pitch errors and defective ways ? ondering:


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## chips&more

higgite said:


> I think it has been a good discussion for the most part. But, what I'm taking away from it is that the theory is solid (you can't argue with math), but the application to hobby lathes is pretty iffy for frog hair precision purposes. ymmv
> 
> John, off topic for an instant... 408 yards... in 3 quarters... not too shabby.
> 
> Tom




That’s it exactly. It looks good on paper, using the offset compound and all. But in the real world, it’s basically dream land trying to hold 0.0001” with variables like a worn out lathe, tool bit material, tool bit geometry, tool pressure, operator finesse, type of job/material, ambient conditions…to name a few. But it’s fun talking about it…Good Luck, Dave.


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## John Hasler

george wilson said:


> There's no telling what crappy grade of metal was used in a real cheap instrument. There are lots of home brewed grades of cast iron out there in Asia.



That's easily determined.  Cool the instrument to 50F, measure a 1" block, heat to 100F, measure again.   By my calculations if it's invar he'll see less than a tenth change, if steel or cast iron perhaps half a thou.

Your Mitutoyo might do much better, of course.


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## hermetic

Spaceman_spliff

"Ring gauge standards accurate to millionths of an inch are specified at a certain temperature. The machining process is not less accurate because its result are a certain value at a certain temperature" 

They most certainly are specified at a certain temperature, and unless the workpiece is at the identical same temperature, you will not know what its actuall size is, if it can indeed be said to posess an actuall size as at these levels of dimension actuall size depends more on temperature, which was my point.

I am not saying it is not possible to remove another tenth, what I am saying is what has been said above by several people, if you want to remove another tenth best let the job cool to room temp for 1/2 an hour then measure again, and you may find you do not need to.

Specifically, what jobs do you work on where you NEED to hold this level of accuracy on the finished components?
Phil


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## 12bolts

I think this thread has run its course.

Cheers Phil


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