# Two collar test - how close is close enough?



## skelso (Jan 21, 2015)

I posted this in the gunsmithing forum but haven't gotten any replies so I thought I would ask here as well...

I've finally gotten everything together and done the 2 collar test. I was able to get within .002 - .003 over 6" (unsupported end larger) before I ran out of adjustment on the lathe feet. Actually, screwing the rear tailstock foot all the way down raised that corner a little over an inch but did not change the difference in the collars.

I will say I am not convinced it's a bed twist issue. The surface finish on the unsupported end is a lot rougher than the headstock end. This indicates some flex, somewhere, to me. (I did have to take 3 spring passes to get to a point where the tool traversed the length but did not cut).

The lathe is a Romi/Doall 13x20 w/ BXA QCTP, 1/2" HSS tooling. 

The test bar was a length of 2" aluminum. 

I've done some gun work in the past but it was always on someone else's machine which I assumed was properly leveled, etc but I never ran a test bar so I couldn't say for sure. Which leads me to my question, how close is close enough?

In thinking back to the gun work I have done in the past, it has always been short sections (threading a muzzle, turning a shoulder for a gas block, etc. For that type work, I can't imaging that .003 over 6" will matter much. Contouring a barrel might be noticable but I doubt I'll be doing much of that given the 20" bed length. 

I would like some input from those of you with much more experience. Thoughts and suggestions welcome.

Thanks!


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## Holescreek (Jan 21, 2015)

Since you did the test you obviously have a concern and should see it through.  Assuming you've already leveled the lathe properly before you did the test, have you also indicated the tailstock to determine if there it a height difference between the headstock and the tailstock and that there is no offset?


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## skelso (Jan 21, 2015)

Holescreek said:


> Since you did the test you obviously have a concern and should see it through.  Assuming you've already leveled the lathe properly before you did the test, have you also indicated the tailstock to determine if there it a height difference between the headstock and the tailstock and that there is no offset?



Holescreek, thanks for the reply. 

I did the test because it is a new to me lathe I shipped cross country and installed in my shop (first I have owned). I leveled the lathe with a Starrett 98 before I started. The first cut revealed .003 difference. Not being positive which way to adjust, I put more tension on the back tailstock end foot. The second cut revealed no change so I applied more tension to the same foot. I repeated this until I had that foot cranked all the way down (over an inch of travel). The difference got down between .002 and .003. I tried taking all the tension off the foot and it still showed .003.

To answer your question about tailstock, no. However I am not following you in why it would matter at this point. I only used the tailstock to support the work while relieving between the collars. When I took the actual cuts on the collars, the tailstock end of the piece was not supported.

This is the first time I have setup a lathe. The method I used was described in the owner's manual of the lathe and the same as some youtube videos I watched. If I did it incorrectly, or there is a better way, I am all ears.

I guess a better way to state my question is "What is a realistic goal in terms of difference between collars?". I don't want to beat myself up trying to get to 0 if it is unrealistic. However, if that is what I need to shoot for, I will try shimming the machine, etc to see if I can get there.


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## Holescreek (Jan 21, 2015)

> To answer your question about tailstock, no. However I am not following you in why it would matter at this point. I only used the tailstock to support the work while relieving between the collars. When I took the actual cuts on the collars, the tailstock end of the piece was not supported.



My mistake, I thought you'd done something else. I read what you wrote then rearranged it in my head.

Can you set up an indicator with a magnet (or in your tool holder) resting on the carriage so that  you can set zero the indicator on the collar closest to the head then move the carriage to have the indicator touch the other collar?  If you do this on the top you might get a better understanding of what's happening.   If you leveled the bed front-back and end-end I doubt there is any twist. However if the indicator reads differently on the top from one collar to the other it could be simple bed wear and the cutter is either dropping close to the head (typical) or further out.


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## JR49 (Jan 22, 2015)

skelso said:


> I posted this in the gunsmithing forum but haven't gotten any replies so I thought I would ask here as well...
> 
> "I was able to get within .002 - .003 over 6" (unsupported end larger) before I ran out of adjustment on the lathe feet. Actually, screwing the rear tailstock foot all the way down raised that corner a little over an inch but did not change the difference in the collars."
> 
> Skelso,  I'm pretty sure that If as you said "the tailstock end of the test bar was BIGGER than the headstock end", then you're adjusting the wrong foot. You need to put the REAR tailstock foot back down to where it was, and raise the FRONT tailstock foot up a little bit and then test again. I'm a beginner myself but I think .003" in 6" is a lot. If I'm wrong about this, hopefully on of the "pros" will correct me. Good luck, JR49


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## Tony Wells (Jan 22, 2015)

If the right hand disc is larger, I would he hesitant to assume twist just yet. Being the bar is aluminum, there will be some pushoff which will present as taper. You didn't give specifics on the tool, but it should be needle sharp and dead on center. And spring passes are a good idea.


Running an indicator on both the top of the discs and he front can be revealing. If, while reading the front, where the tool makes contact, if there is true misalignment in the machine, both will indicate at zero. Any other reading would mean there is something going on with the tool or the bar itself moving, being pushed away from the cutting edge, for example Some, but not all lathes have adjustment for headstock alignment. Could also mean bed wear. Properly evaluating a machine is not so simple at times.

After optimizing during this test, then check the tailstock, remembering that it could be off in horizontal or vertical alignment.


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## skelso (Jan 22, 2015)

> Running an indicator on both the top of the discs and he front can be revealing. If, while reading the front, where the tool makes contact, if there is true misalignment in the machine, both will indicate at zero.



Tony,

I'm going to set up an indicator tonight to check what Holescreek suggested. I'll do the check you suggested at the same time. Just want to make sure I understand... I believe you are saying to setup an indicator on front and another on top to make sure their is no out of round, or wobble? 

Would you do this by hand or at speed?

If at speed, are you meaning I should indicate while tool is in contact to check deflection?


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## skelso (Jan 22, 2015)

Holescreek said:


> Can you set up an indicator with a magnet (or in your tool holder) resting on the carriage so that  you can set zero the indicator on the collar closest to the head then move the carriage to have the indicator touch the other collar?



*Set this up this afternoon with a .0005 indicator. The needle chattered a bit as I moved along the length of the stock but never more than the thickness of the needle.*



Tony Wells said:


> If the right hand disc is larger, I would he hesitant to assume twist just yet. Being the bar is aluminum, there will be some pushoff which will present as taper. You didn't give specifics on the tool, but it should be needle sharp and dead on center. And spring passes are a good idea.
> 
> 
> Running an indicator on both the top of the discs and he front can be revealing. If, while reading the front, where the tool makes contact, if there is true misalignment in the machine, both will indicate at zero. Any other reading would mean there is either twist in the bed, or possibly headstock misalignment.



*Tony, after rereading your reply several times and thinking about it I now assume you meant to set an indicator up on the front of the stock and move it down the length as I did on top in Holescreek's test. Is that correct? If so, I set that up too and found no change across the collar closest the headstock but .001 - .0015 difference between that collar and the unsupported collar.*



Tony Wells said:


> You didn't give specifics on the tool, but it should be needle sharp and dead on center. And spring passes are a good idea.



*I didn't reply to this portion of your reply this morning because I wanted to have the tool in hand so I could be as specific as possible. I was incorrect, the tool is not 1/2" X 1/2", it is 3/8" X 1/2". It is one that I ground years ago in the gunshop (with the help of a tool and die maker friend who is now deceased or I would ask him for help). Prior to starting this test I honed it on a diamond stone until razor sharp (or so says the 1-1/2" gash in my hand where I bumped it by accident loosening the compound's bolts...) I tried to take some pictures but they didn't come out too well... 

*End edge angle is 75 degrees
Side edge angle is 8 degrees
Back rake is 8 degrees
Side rake is 8 degrees 
No end radius


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## Holescreek (Jan 22, 2015)

If I understand correctly you got no difference running the indicator across the top from collar to collar but you are measuring .003" difference in the collar diameters.  To me, it indicates bed wear because the indicator followed the dip the carriage dropped into when it made the cut.  I've seen worse, I inherited a lathe that had .025" wear as received, it took a lot of scraping to fit that one.


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## Tony Wells (Jan 22, 2015)

If the indicator follows the cut surface(s) with little or no deviation, then you can probably rule out tool pushoff. The tool path would be the same as the indicator path. From the front that is. If the diameter difference is twice what the indicator reads, then the problem likely is simply tool pushoff.

From the top, ideally there would be no deviation either, provided the measured diameters were the same. 

You are looking at 2 planes this way, one likely due to headstock misalignment or way twist, the other due to wear in the elevation of the ways.

BTW, these tests are done with spindle stopped.


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## skelso (Jan 22, 2015)

Tony Wells said:


> BTW, these tests are done with spindle stopped.



LOL! I think my brain was still asleep when I read your reply this morning... I couldn't, for the life of me, follow what you were telling me. I reread it later in the morning and understood it fine.


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## skelso (Jan 23, 2015)

Thank you all for the help! The answers Holescreek and Tony gave led me to some tests that reassured me the main was not badly worn. The answer JR 49 gave led me to try adjusting the front foot. I gave it a half dozen cranks and took another cut. When I measured that y ime, t he unsupported end was smaller so I knew I had gone too far and adjusted back the other way.

My micrometer is accurate to .001 but has .0005 marks. I now have the difference down to less than .0005 over 6"


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## JR49 (Jan 23, 2015)

Skelso,  Thanks for saying that my answer helped. As a total beginner, this is the first time I have been able to answer a machining question. I would like to thank all the "pros" on this forum, because, the little bit of machining know-how I have learned, was ALL from this great forum. Thanks to all, and happy New Year, JR49


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## rick9345 (Jan 26, 2015)

I never do test collars/diametrs with unsupported ends.
for true readings must be done between centers(not a chuck and a center)
center tailstock to spindle first


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## gaston (Feb 4, 2015)

To answer the question I shoot for a difference of 0. 
usually the test bar unsupported will show the alignment of the headstock. the larger end at the tailstock end indicates the headstock 'aimed" away from the operator. If you try to "fix" a missalignment with jack screws, you are only jacking the lathe around unless it is bolted down at the center point on both ends them you can address a twisted bed. 
usully lathe missalignment is at the head or tail stocks and not to hard to fix, unless its badly worn.
this is my personal findings with my Voest (my big lathe) and my clausing 1236vs (small lathe) your milage may vary


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## randyc (Feb 6, 2015)

rick9345 said:


> I never do test collars/diametrs with unsupported ends.
> for true readings must be done between centers(not a chuck and a center)
> center tailstock to spindle first



I would think that you're penalizing yourself unnecessarily by adding yet another variable to be considered.  Is the error due to headstock misalignment ?  Bed wear ?  Tailstock alignment ?  Any combination or all ?  It's admirable if one can deal with all of that but I'll stick with a simpler model - no tailstock center - to minimize the number of problems I need to think about.

After obtaining satisfactory results, the two-collar test bar can be _carefully bored for centers_ and then used for tailstock alignment.


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## rick9345 (Feb 7, 2015)

randyc said:


> I would think that you're penalizing yourself unnecessarily by adding yet another variable to be considered.  Is the error due to headstock misalignment ?  Bed wear ?  Tailstock alignment ?  Any combination or all ?  It's admirable if one can deal with all of that but I'll stick with a simpler model - no tailstock center - to minimize the number of problems I need to think about.
> 
> After obtaining satisfactory results, the two-collar test bar can be _carefully bored for centers_ and then used for tailstock alignment.


  I was answering for the bed leveling/twist.
I  use a hardendened/ground bar DTI both at chuck and out 6 in , then run DTI horizantally both side and top to check headstock. I have had success algining tailstock with DTI mounted on/at chuck. The ground bar(mine is 2 in) can be extended out 12 in and with DTI on  bar outer end one can visually watch twist as feet are adjusted. Finialized with 2 collar test.

I agree I skipped a step. Thanks you caught it.
The important thing is to devlope a repeatable method that gets one to their desired level of accuracy.  There are many methods. Equipment at hand kinda dictates the method.


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## randyc (Feb 7, 2015)

rick9345 said:


> ....Equipment at hand kinda dictates the method...



Absolutely !


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## astjp2 (Feb 28, 2015)

I collected enough parts to actually measure my ways with a DTI, that round bar on the inverted V is cast iron that I chucked up in the mill, its a copy of the King way alignment tool.  I used a .0005 DTI, but I also have a .0001 that seemed to jump around a lot when I rolled it along the ways.  I found that a light coat of oil also stopped the chatter when using the tool.  Tim
http://www.hobby-machinist.com/attachments/front-way-jpg.72188/


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## randyc (Feb 28, 2015)

astjp2 said:


> I collected enough parts to actually measure my ways with a DTI, that round bar on the inverted V is cast iron that I chucked up in the mill, its a copy of the King way alignment tool.  I used a .0005 DTI, but I also have a .0001 that seemed to jump around a lot when I rolled it along the ways.  I found that a light coat of oil also stopped the chatter when using the tool.  Tim
> http://www.hobby-machinist.com/attachments/front-way-jpg.72188/



That is a neat tool and very ingenious.  If you're referring to Richard King (KingWay), I'm proud to claim him as an acquaintance if not as a friend.  Can you provide a link to Rich's tool, I'd very much like to see it !  

Very nice work, nice setup and a good suggestion regarding the oil coating !  I'll be interested in your future findings


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## astjp2 (Feb 28, 2015)

I did a search on here, there were several posts on ones that others have made.  Richard told me that if I wanted to make one that it was not a trade mark infringement or patent or something like that as long as I am not selling them.  I had to make 2 different sizes, the first one I made was about 1.25" in diameter, with a half inch groove, I made the one in the picture about half that size and it fit my lathe quite well.  I also bought several different clamps, 2 more starret mag base posts that were threaded where they screw into the way alignment fixture.  I have 3 or 4 different DTI's but only 1 is .0001 the rest are .0005.  My next purchase is an alignment shaft for my lathe.  I need a MT4.5 to fit the spindle so when I start scraping the head I can get the head alignment close so I am going to get it from Millers machine tools, they claim no run out and .0001 or less for straight and conconcriticy.  Tim


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## randyc (Feb 28, 2015)

Thanks, Tim.  Rich is a great guy, unsparing of his time and always willing to help/educate others as you doubtless know !  A few weeks ago, for example, he went to a seller's home to evaluate a lathe for a newbie who was considering buying it.  He'd never even met the potential buyer except on a forum !


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## dian (Mar 1, 2015)

Holescreek said:


> If I understand correctly you got no difference running the indicator across the top from collar to collar but you are measuring .003" difference in the collar diameters.  To me, it indicates bed wear because the indicator followed the dip the carriage dropped into when it made the cut.  I've seen worse, I inherited a lathe that had .025" wear as received, it took a lot of scraping to fit that one.


 
to get 0.003 difference the wear would have to be huge at 2" diameter.


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## astjp2 (Mar 1, 2015)

My non hardened Rockwell bed was worn .0087 near the head stock.  So its possible.  Tim


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## dian (Mar 1, 2015)

o.k., vertical wear 0.01": 0.01*2 + 1*2 = 1.0001. root of that is 1.000049. (pythagoras.) so radius has increased by 50 milionths for 2" stock. besides carriage will average out.

not much help to op though. maybe think about it some more and take a straight edge to the ways. or the level, i believe you have one. maybe the problem is with the jaws. they might be gripping in the back only. to check, take two round pieces of same diameter (preferably ground) or make them, with a hole in them. attach a rod on one and slip it through the other one. chuck them up with moderate force, one in back, one in front and see if one moves (probably the front one). if that how it is, get a cbn insert, make a boring bar for it and hard turn the jaws. be shure to preload them, look that up or i can elaborate.

oh, and check the jaws in the middle too, as they can be worn round.


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