View Full Version : speaking of rake angles ------- ?

A.K. Boomer
08-25-2009, 09:30 AM
I had to use my boring head the other day and am always perplexed at how to install the boring cutter, what do you guys do? do you just eye-ball it?
That's what I always seem to end up doing, I might have actually asked this question on here before but if I did I obviously forgot the answer.

Wonder if it would be worth it to map out the relief and cutting angle and then mill a flat on the cutter for the set screws?

Am I missing something easy and obvious about this entire thing. ?

08-25-2009, 10:28 AM
What I do doesn't have any authority behind it, but it seems rational and works for me. I try to set the cutter edge exactly parallel with the slide and this is my rationale. I assume that the tool holder is in the center of the head and the flat of the tool is on the center of the shank. At this point it will contact the edge of the hole exactly tangent which will make it a neutral cutter, neither a negative or positive rake. If the tool were angled "backwards", it would present as a negative rake which I don't want. If angled "forwards" it would give me a usually desirable positive rake but runs the chance of losing the clearance behind the cutting edge and not cutting at all. It's kind of the inside out version of a lathe tool slightly below or above center.

08-25-2009, 12:32 PM
they actualy make boring bars with flats on them. I could never understand why the shank is round other then it feeds into a hole.

How about a level to set the bar? Like the one on your combination square http://www.saintytools.com/img/Combination-square-20-2021-middle.jpg
Assumeing you previously leveled your lathe that is. (How about a TDI if your lathe is not level? just crank the carrage back and forth to check angle)

Or just slap a ruler on there and visualy see if it looks straight..

Also remember that when you are inside, above center acts the same as 'below' center outside. (In that the peice will deflect the cutter out of the way to prevent hogging, but can roll up over it in extream cases)

Below center will *cause* hogging, just like above center can cause hogging outside.