# boring bar cuts better on the way out



## ericc (Dec 6, 2014)

Hi.  I resharpened my boring bar, and something strange happens.  It does not seem to cut much when advancing it into the bore, but it does cut a lot more on the way out.  It is quite a bit more.  It just takes a sliver on the way in, but really hogs a big chip on the way out.  This still does the job.  I tightened up the saddle hold down/gib, but it still seems to cut this way.  Otherwise, the cut is fine, and the finish is good.  When I look carefully, the cutter is cutting in the middle on the way in, and pretty much all along the edge on the way out.  Does the grind need to be a little more pointed, so that the cutting is only going on in one place?


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## astjp2 (Dec 6, 2014)

Something must have changed for either the angle or radius.


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## Bill Gruby (Dec 6, 2014)

When you reground the tool you inadvertently changed something. What you changed is hard to say without seeing it. Can you get a picture to us?

 "Billy G"


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## Karl_T (Dec 6, 2014)

first guess is you no longer have radial relief. Its rubbing on the bore ID

Karl


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## Bill C. (Dec 6, 2014)

ericc said:


> Hi.  I resharpened my boring bar, and something strange happens.  It does not seem to cut much when advancing it into the bore, but it does cut a lot more on the way out.  It is quite a bit more.  It just takes a sliver on the way in, but really hogs a big chip on the way out.  This still does the job.  I tightened up the saddle hold down/gib, but it still seems to cut this way.  Otherwise, the cut is fine, and the finish is good.  When I look carefully, the cutter is cutting in the middle on the way in, and pretty much all along the edge on the way out.  Does the grind need to be a little more pointed, so that the cutting is only going on in one place?




What type of bar are you using?  If you have the type that uses 1/4" square tool-bit, check the front cutting edge to see if is rubbing below the cutting edge. That type can be sharpened using the tool support on your grinder.  I usually set them about 5 degrees so the body of the bit would be shaped before the edge.  

Now if you said the bar was cutting in both direction of travel then that is tool pressure.  To correct that is to take a very light cut on your final pass or use a bigger diameter bar.


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## Ebel440 (Dec 6, 2014)

I would think it's not cutting on entry due to a change in angle or something else.  The bar is bending on the way in and on the way out its cutting better due to the angle on the back side of the tool being sharper.  I had this happen when I dulled a boring tool on a hard piece of steel.


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## BRIAN (Dec 7, 2014)

Try setting the bar just above centre and see if this helps.

Brian.


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## silence dogood (Dec 7, 2014)

I realize that in this case something is not right.  How ever in certain cases, would it not make more sense to bore from inside to out?  Such as a blind bore, it would be less chance of a crash, I think.  So how would one grind the bit?  I'm asking because I still have a lot to learn and I'm curious. Mark


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## markknx (Dec 8, 2014)

Check the relief angle on the front side it might be to little so the edge will just rub instead of cut. compare it to the back side. Mark


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## Karl_T (Dec 8, 2014)

silence dogood said:


> I realize that in this case something is not right.  How ever in certain cases, would it not make more sense to bore from inside to out?  Such as a blind bore, it would be less chance of a crash, I think.  So how would one grind the bit?  I'm asking because I still have a lot to learn and I'm curious. Mark



the grinding would be the same. I suggest you get a book on machining. i've heard, 2nd hand, that this series is great
http://www.amazon.com/Machine-Shop-Practice-Vol-1/dp/0831111267

In general the cutting tool relief is a bit tricky. It needs to be an arc just smaller than the bore you are cutting.


If you don't have a DRO, a carriage stop is the way to go. You may have to make one. It should clamp quickly to your front way. Now you can bore right up to a hard stop. Years ago, I made one for my old LeBlond, I use a 1/2x20 all thread and made a simple dial - one full turn is 0.050"


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## timmeh (Dec 8, 2014)

Have had to do this on a fairly hefty lathe (Niles 500x1000mm B/C) using indexing carbide insert tooling, rough cut IN ok, finish cut OUT was and still is the only way on that lathe. Whatever works is what ya do!


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## ericc (Dec 8, 2014)

Thank you for the suggestions.  I suspected that it was caused flexing, since I needed to stick the tool out a little farther since I was boring a ring, and the compound was in the way.  Looking carefully at the tip of the tool, the front and rear edges are slightly different.  The boring bar is not rubbing.  It has pretty generous clearance, plus they make a funny noise when they rub, and this one does not make that noise.  I'll regrind it and give it a try.  I need to make one out of a piece of 5/8" round with the tool sticking out.  This should flex less.


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## markknx (Dec 9, 2014)

A google books search May find you a PDF of Machine shop Practice Vol. 1 & 2. Mark


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## epanzella (Dec 9, 2014)

If it cuts from the middle of the tool on the way in you won't be able to bore to a shoulder no matter how good it cuts on the way out. Everybody has this pretty well covered but I'll add the obvious in that if you changed the angle of the compound or tool holder it will affect your cutting angles.


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## Smithdoor (Dec 9, 2014)

Most time it is found in how yow sharpen the tool bit.
Please post photo of your cutter

Dave 



ericc said:


> Hi.  I resharpened my boring bar, and something strange happens.  It does not seem to cut much when advancing it into the bore, but it does cut a lot more on the way out.  It is quite a bit more.  It just takes a sliver on the way in, but really hogs a big chip on the way out.  This still does the job.  I tightened up the saddle hold down/gib, but it still seems to cut this way.  Otherwise, the cut is fine, and the finish is good.  When I look carefully, the cutter is cutting in the middle on the way in, and pretty much all along the edge on the way out.  Does the grind need to be a little more pointed, so that the cutting is only going on in one place?


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## ericc (Dec 9, 2014)

I couldn't really find a good picture browsing on the web, but I found one in an old copy of a machinist's handbook.  I figured out what the problem was.  There was insufficient clearance on the front edge of the bit.  Combined with the additional stick out required, it was causing the bit to flex inward and cut less.  Then, it cut on the backwards feed, since it had more clearance.  The slight bending caused the chip to roll off near the middle of the bit.  I will try grinding the front, and if it doesn't work, I will take a picture.

Meanwhile, I will make a larger bar for the bigger job.  Most of my work to date has been on bores 0.4" or less.  This piece was quite a bit larger.


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## Smithdoor (Dec 9, 2014)

Try 
http://www.hobby-machinist.com/vbdownloads.php?categoryid=56



ericc said:


> I couldn't really find a good picture browsing on the web, but I found one in an old copy of a machinist's handbook.  I figured out what the problem was.  There was insufficient clearance on the front edge of the bit.  Combined with the additional stick out required, it was causing the bit to flex inward and cut less.  Then, it cut on the backwards feed, since it had more clearance.  The slight bending caused the chip to roll off near the middle of the bit.  I will try grinding the front, and if it doesn't work, I will take a picture.
> 
> Meanwhile, I will make a larger bar for the bigger job.  Most of my work to date has been on bores 0.4" or less.  This piece was quite a bit larger.


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