# Boring problem



## mickri (Apr 1, 2017)

Hi,
I needed to increase the diameter of the shaft hole in a handwheel from 0.645 to 0.750.   I mounted the handwheel in a 3 jaw chuck and I set up my boring bar on the compound.  I brought the tip of the boring bar so that it just kissed the inside of the hole and set the dial to zero.  I had taken out the backlash when I did this.  All seems fine and I start by making a 0.002 cut.  Next cut is 0.003.  All goes well.  So I start making 0.005 cuts.  I am measuring the diameter after each cut.  When I get the diameter to 0.700 I make 4 cuts of 0.005 without taking a measurement.  I take a measurement and my diameter is 0.775.   This is 0.025 too big.   I was expecting the diameter to be 0.720.
My procedure on each cut was to 1) make the cut 2) back the boring well past zero 3) bring the boring bar out of the hole 4) advance the boring bar back to zero taking out all backlash and then bring boring bar back towards the work in the increments described above.  I was basically counting backwards on the dial.  The dial readings were 98,95,90,85,80,75,70,65,60,55.50,45,40,35, and lastly 30.
The only thing that I can think of is some how the cross slide moved.
Any ideas on what I did wrong?


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## mzayd3 (Apr 1, 2017)

You didn't take into account that you were only taking off of the radius. X2 for the diameter.


Sent from my iPhone using Tapatalk


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## mickri (Apr 1, 2017)

Thanks.  Boy do I feel stupid.


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## darkzero (Apr 1, 2017)

Dials aren't always accurate. On my import lathe I've noticed some inaccuracies. My cross slide dial reads .100" per revolution. It's pretty accurate until it gets to half a revolution, at .050" it's actually off by .002" but when I come back to 0 on the full revolution it's accurate to .100" again.

No big deal as I have a DRO but before I had a DRO I just adjusted for it. When roughing it didn't matter, then when I got closer to my final diameter, I would remeasure, zero the dial, then go on to final size. It's good practice to do this anyway.

Lathes come both ways, direct dials (diameter reading) & indirect dials (radius reading). My lathe has a indirect dial, feeding in .010" on the dial will move the cutter/cross slide .010" & remove .020" off the diameter. Direct dials is of course the opposite. Feeding .010" on the dial will move the cutter  .005" & remove .010" off the diameter. I actually prefer the indirect dials.

Get to know your lathe & what type of dials you have but I think you have learned that already. Setup a dial indicator on your tool post, zero your dial & feed in or out comparing with the distance traveled showing on the dial indicator. Make a note of your readings & going forward you'll know how your dial behaves. Might as well check the other dials while you're at it.


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## markba633csi (Apr 1, 2017)

But wait. It should have measured .740 , after the 4 cuts.  I think what happened, looking at your setup, is you grabbed the wrong crank handle by mistake maybe at
some point.  Easy to do. 
Yes/no? 
Mark S.


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## mickri (Apr 2, 2017)

Did not grab the wrong handle because I had to hold my light over the dial to be able to read the dial.  Old eyes what can I say.  But I could have  brushed my hand against the cross slide handle while moving the compound dial handle.  Like Mark said I should have still been OK   I think that I may have taken a bad measurement because my last cut was on the 30 mark which was a total diameter increase of 0.070 times 2 = 0.140.  Live and learn.  This was not a critical part.  Just a hand wheel for my mill/drill.  I will put a shim in and all will be good.
What I learned from this is that I have to 1) really think about what I am doing, and 2) be very careful when taking measurements to be sure that the measurements are accurate.


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## mikey (Apr 2, 2017)

Hey Mick, I have some questions if you don't mind.
1. What kind of boring bar is that? I can't tell. Is it a 3/8 steel bar with a HSS cutter held sideways with a set screw or is it an inserted carbide bar? If using a HSS cutter then the geometry makes a difference, especially the relief angles and the nose radius. 
2. The boring bar holder is one of those universal types that hold bars of different diameters. They are not very rigid and also have a relatively narrow base so accuracy may be affected.
3. Does your bar cut predictably? That is, if you take two 0.005" deep cuts, is the increase in ID the same? You said you took 4 cuts and measured each time until you got to 0.700". If the ID increases by 0.010" for each of those cuts then you can rely on the depth of cut for that bar. If not, then you can't.
4. If the bar was cutting predictably then taking 4 cuts at 0.005" should have brought you from 0.700" to 0.740" ID. I am not sure how you got 0.775" ID unless you dialed in a cut that was not what you thought it was. 

Frustrating to miss a bore, especially when it counts. I switched to inserted tip carbide bars for this very reason - I needed predictability.


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## mickri (Apr 2, 2017)

The boring bar is a 3/8 bar.  The cutter is HSS and is held in place by a set screw.  This setup came with my lathe.




The more I think about what I did I can see errors that I made.  My first big error was not realizing that my cuts were twice as deep as I thought because of the radius verses diameter.  My second big error was inaccurate measurements.  I just took some more measurements.  If I was really careful the measurement is 0.775.  But if I wasn't careful I got measurements that ranged from 0.751 to 0.789.  When I was taking measurements after each cut I thought that I was getting consistent measurements but I realize now that I was anticipating certain measurements and I got what I was looking for rather then taking careful measurements to see what was actually happening.  Because of the small cuts the chips were a fine grit.  It was hard to get the grit out of the bore when taking measurements.  I think that a dirty bore also affected my measurements.  In the future I will come up with something to clean the grit out of the bore.
I have also discovered that I now have some play in the cross slide.  I thought that I had gotten this adjusted properly after I had cleaned the lath.  So I will revisit adjusting the gibs.
I am learning as I go here.  Nothing that I want to make in the near future will have critical dimensions.
Thanks for all the help.

Chuck


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## 4GSR (Apr 2, 2017)

Blame it on the CD player....

I've done the exact thing mis-reading the mike by one turn, which is =0.025"

Ken


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## mikey (Apr 2, 2017)

Chuck, this is how we all learn so don't be too hard on yourself. Boring is the most difficult and confusing "basic" operation there is on a lathe. Let me make a few suggestions:

1. Reduce your overhang to a minimum. In your first pic, the bar is sticking out way more than it needs to be for the thickness of the material and this can lead to a lot of deflection of the boring bar. Stick the bar out only enough to get the job done. 
2. If you are using a telescoping gage to measure your bores, buy a ring gauge to check your technique. Knowing what the ring should measure, it allows you to verify your technique. Boring is as much about measurement as it is about cutting. On the other hand, if you're measuring the bore with a dial caliper then you are not going to get consistent readings, at least not enough to bore accurately with.
3. Buy or make a better boring bar holder. The length of the holder should be at least 3-4 times the diameter of the bar and it needs to be solidly anchored. If you have a QCTP, consider a holder that looks like the Aloris 4D; it is a vastly better holder than what you have and better than those that lock a bar down with set screws. 
4. Use a bigger bar if you can. The bars like you used need a lot more room to work because you have a tool bit sticking out of the side. This limits the diameter of the bar, which leads to greater deflection. Brazed carbide or HSS/cobalt boring bars are smaller in size so you can use a bigger, stiffer shank on them. Inserted tip bars are also compact. The best option are inserted tip carbide bars that are very stiff for their diameters; they also cut very predictably.

Lots more to say about boring but I just wanted to give you some food for thought. Hang in there, it gets better.


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## mickri (Apr 2, 2017)

Since this is a non-critical part I built up the bore with JB Weld today and will give it another try in a couple of days.
Mikey thanks for all of the suggestions.  I will take the boring bar out of it's holder and see if it can be held by my tool post.  If the tool post will hold the boring bar I will post a picture of my setup to see what you guys think.
Thanks
Chuck


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## Rockytime (Apr 2, 2017)

FWIW, I often make a go-no-go gauge before I bore.


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## mickri (Apr 4, 2017)

Success!  I did my do over today and I have a nice tight but not too tight fit.  I want to thank everyone for their suggestions and advice.  I particularly want to thank Mikey for the time he spent responding to my emails.  His advice was invaluable.  Thanks Mikey.


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## mikey (Apr 4, 2017)

Yup, you're welcome!


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## Charles Spencer (Apr 4, 2017)

Rockytime said:


> FWIW, I often make a go-no-go gauge before I bore.



Hey, that's a great idea for precision work.


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## epanzella (Apr 8, 2017)

I just can't do anything with a hand wheel dial. I keep forgetting the numbers and back lash sometimes gets me. I stuck a DTI on the back of my Xslide and a sliding stop on a 1/2" bar that I threaded into the carriage. This has been a Godsend for me in the accuracy department. You can also watch it during the cut to see if the slide moves at all. 
It's also a good idea to let the bracket protrude enough to prevent damage to the DTI if you forget to slide the stop bracket to the side and ram your Xslide into it.


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## SmokeWalker (Apr 8, 2017)

mickri said:


> Thanks.  Boy do I feel stupid.


A friend of mine who's been a toolmaker for 40+ years told me one day when I was having this problem, "The hardest thing in machining is a hole. To make a hole that's _round_, _on size_, and _where you want it _is the hardest thing." I don't beat myself up too much when I screw up a hole. Turning, sure, but holemaking? That's always dark magic.


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## jamby (Apr 8, 2017)

SmokeWalker,  I agree and it gets even worse with smaller holes.  At .750 the bar is rigid compared with a .250 hole,  which I won't try without a reamer.

Jim


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## Silverbullet (Apr 8, 2017)

LATHES we had you couldn't depend on dials, so every cut was done with an indicator set up. To this day I only use indicators for cuts.


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## NortonDommi (Apr 8, 2017)

Hello Mickri,
                      As has been stated tool deflection,(spring), is something to take into account. Also as has been said you want as little protrusion as possible on any tool.
  Here's a couple of pics of a boring job I'm doing for a friend.  These are idler wheels off his Kubota 1 3/4 ton digger. the face seal got dirt in it, the oil leaked out and subsequently the whole caboodle failed. Then the track fell off .
  I am doing a repair  by boring, shrink fitting sleeves and fitting shielded annular double row ball bearings and new pins,(axles).
  When I got within cooee of the finish size I ran the bar twice through the wheel for each cut. It always amazes me how much swarf comes off even after you think you have just touched the mark.
  So my thoughts are you did nothing wrong other than not consider tool spring, you got off lightly.
  I've just taken a few more pictures for my mate so I can post here if you are interested.
P.S.  The only reason I am using a mill rather than a lathe is because the wheel rims had already been built up and centering/leveling on a mill table was easier and I'm lazy but the same factors of tool spring hold true.
  The last pic is using a cut-off tool to skim the last 1/2 thou off a sleeve. They work great for fine finishing cuts and the thin blade allows working close to chucks and centers.

 - Barry.


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## mickri (Apr 9, 2017)

Hi Barry,
Thanks for the suggestions.  I got a lot of good advice from Mikey and changed my setup to eliminate as much deflection as possible.  One of the biggest things was to keep the bar protrusion as short as possible.  On my original set up I had the boring bar out too far and the boring bar holder was not very rigid.  On the redo  I was able to mount my boring bar in my 4 way tool post holder.  This was way more solid than using the boring bar holder that I first tried.
  This was a good learning experience.  The part was not critical.  It was just a replacement hand wheel for my mill/drill.  I still wanted to get the fit as close as possible.  My end result could have been a touch better but I am satisfied with the end result.
Mikey showed me some examples of good holders and I plan to make one in the future.
Chuck


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## NortonDommi (Apr 9, 2017)

Mickri, 
             As long as you are on track aye. Every job is a learning experience even those you've done before.
I just have to say that this site is great for finding answers to questions you would not ask in some company.
Here I feel free to admit a mistake so somebody else does not follow.
  - Cheers,
  Barry.


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## Tozguy (Apr 9, 2017)

Yesterday, turning a drill chuck arbor to fit in a boring bar holder, was aiming for .750''
I don't trust the dials on my lathe because of backlash, flex, etc.so when getting close I measure after every pass. When the dial read .775'' I thought perfect, dead on! (I only saw the 75, its that 'anticipation' that you mentioned). Wonderfull smells were coming from the kitchen, job had gone really well so far, thought I was done so parted it off. Turns out that a .775'' arbor doesn't fit a .750'' hole.

But I got it set up between centers and took the extra .025'' for a perfect fit. It was probably how it should have been done to start with.

I find it hard not to let my guard down towards the end when a job goes really well.


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