lathe cutting bits

Wayne · 2004-07-28T00:31:53+00:00

I'm so very confused.I have 3/8" shank holders with HSS inserts. I have 1/32 and 1/64radius inserts.I was testing the cutting straightness of the lathe with a1" steel bar over 5". The results I got were 2 thou biggerat the headstock than at the free end.I then had a professional in to look at my issue. He said thebit I was using wouldn't give me proper results. I was using the 1/32,and he said it needed to be at the biggest 1/64. He ground aHSS blank with a knife edge. Then he tested using 1" aluminum.He then aligned the headstock, which he said wasn't that far off.(On a previous visit he straightened/levelled the bed).When he got done it was straight within a few thou over 4" or so.After he left I tried my test again using the 1/64 bit. With thesteel bar it was still bigger at the headstock, but only by .001.Using the aluminum bar it was off by .0005.On both bars after cutting toward the headstock, I left the bitwhere it was, and reversed the feed toward the tailstock.More material was cut off. When I measured them, it was only offa few thou.I don't know how it could be larger at the headstock, and thencome out straight on the 2nd cut. And what good are indexable insertsif they don't cut straight?Once again I'm so confused.Wayne

Jul 28, 2004 23 Replies

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Gunner 22 years ago

Even my stiff as an anvil Hardinge HLV-H will, depending on the material and diameter, take a spring pass.

A good way to check, is to make your cut normally, right to left, then reverse your feed and go back to the right without changing the cutting depth. You will be surprised on how much and how close to the headstock it will shave off on the return.

Gunner

"At the core of liberalism is the spoiled child - miserable, as all spoiled children are, unsatisfied, demanding, ill-disciplined, despotic and useless. Liberalism is a philosphy of sniveling brats." -- P.J. O'Rourke

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Tim Williams 22 years ago

Reminds me of Dave Gingery giving boring advice: Advance the cutter say .025" and take a pass. You might take off .017 the first, and (some more, etc....) and left with a thou or half a thou shy of the actual tool position after a few passes.

I still don't know how he managed to build all those machines with that 4" long 1/4" boring bar.

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

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Ace 22 years ago

As your experience "grows", you'll find .002 inch on the dia. is more in the realm of grinding.

With lathe work, more consistent results are obtained with a heavier cut. Suggest you use .010 on dia. as a finishing pass.

Why? You are putting more of a force on the whole setup, which takes up the slack in bearings, etc.

It also puts the actual "point" of the cutting tool below the surface of the material as opposed to just skating across the existing surface.

Spring passes are fine when necessary, but in most cases should try to avoid as a common operation.

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