boring bar cuts better on the way out

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!
 
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.
 
A google books search May find you a PDF of Machine shop Practice Vol. 1 & 2. Mark
 
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.
 
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?
Click to expand...
 
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.
 
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.
Click to expand...
 
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