boring bar cuts better on the way out

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ericc

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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?
 
Something must have changed for either the angle or radius.
 
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"
 
first guess is you no longer have radial relief. Its rubbing on the bore ID

Karl
 
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...


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

Brian.
 
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
 
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
 
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
Click to expand...

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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