Parting tool rake?

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rake60

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Rake in a parting tool as all about chip control.
A slight front edge rake will cause the chip to curl
Sometimes that is a good thing, sometimes it isn't.

If you look a the new carbide parting inserts, like this
one from Iscar;
ArticlesTangGrip2009_2703_2.jpg

You see both frontal and side rake.
That geometry causes the chip to curl and roll inward narrowing
the chip so it has much less chance of hanging up in the groove
and breaking the tool. I doubt that kind of relief could be hand
ground at home, but it does make for a good example of why it is
made as it is.

Rick

 
Bill S said:
I'm in the process of changing the rear cutoff tool holder I had made previously from normal blade with the lathe running in reverse to upside down, and was wondering if it would be advantageous to have positive rake on the parting tool. I did some research and couldn't find anything regarding it. The holders I have used before had no rake. Any thoughts?

Bill

Once you start parting upside down you'll never do it any other way. ;D You don't say if you are running HSS or carbide. I make my own parting tools from 5/16" Crucible HSS on my surface grinder. .050" wide at the top, .035" wide at the bottom, about 5* clearance on the front of the tool and no top rake. I part a lot of 4140 and the tool mows through like butter. With the tool upside down gravity does most of the chip clearing for me so I really don't need a chip that curls out from the cut. :)
 

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