Cutting speeds - physical basis ?

I was just wondering what the physical basis is for different materials
requiring different cutting speeds to get a good finish ? The only thing I can
think of that has units of speed and might be a possible contender os
crack-propagation speed but is this what the cutting speed actually depends on
can anyone say ?
Many thanks,
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Hi, good question but as you will have guessed not easily answered. There has been and still is considerable debate about the mechanics of machining and the determination of cutting parameters from theoretical rather than empirical methods. The two models usually discussed are the thin zone model which looks at the performance of the material in shear and the thick zone model which looks at the plastic deformation of the material. have a look here for a very basic introduction and some interesting diagrams:
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It appears to be a work in progress although it does give plenty of references to individuals who have produced papers on the subject in the last 30 years or so. Try searching for "Piispaneu or Merchant" for thin zone theory and "Palmer or Oxley" for thick zone. If you Google on Mechanics of Metal Machining you will find plenty of theories to keep you busy, unless you are cutting some new exotic material that is not yet in the charts I stick with the empirical myself.
Best regards
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As you guess, this is one of those questions which is much easier to ask than to answer.
What goes on at the cutting edge of a tool depends on a huge number of factors including the failure mode of the material being cut (brittle v ductile), the response of the material to strain (e.g. hardening), the shape and material of the tool tip, the presence and mode of action (physical and/or chemical) of any cutting fluid and the rate of heat transfer away from the cutting zone. If you want a starting point, a very good book is:
Metal Cutting Principles (2nd Ed.), M C Shaw. Oxford University Press, Oxford, 2005. ISBN 0-19-514206-3.
But it has some pretty heavy physics in it if you don't already have a physics/materials/engineering background.
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Norman Billingham
Answering that would require a full model of the cutting process; I'm far from clear such a thing exists.
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Thanks to all who replied for the pointers. I will try to find the book = Normal=20 mentioned in a library somewhere (it's =A367 at Amazon).
Thanks again,
--=20 Boo
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£5.75 for the paperback.
£5.75 for the paperback.
ISBN 0198590202
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