On Tue, 15 Jun 2004 16:07:36 GMT, "Ed Huntress"
wrote:

wrote in message

I'm a bit puzzled by your emphasis on the importance of tool
height because skive tool cutting action is not affected by this.

I normally set the tool height so that it cuts over a narrow
region roughly in the centre of its 45 deg edge i.e. halfway down from
the top of the tool. However any part of the whole cutting edge can be
brought into play, cutting with the same cutting geometry, by simple
adjustment of the tool height. This is quite useful because, as soon
as the initial cutting edge region starts to dull, a fresh region can
be brought into play by a making a small change in tool height.

Jim





I think I had the geometry of your tool clearly in mind yesterday, but I
lost it, and I have to run now so I can't go through the mental gymnastics
again.

But, to answer your question: a skiving tool usually is a form tool, and it
can be -- and often is -- cut with no top rake and no front or side
clearance. Form tools don't cut to the side, they plunge-cut. To get front
clearance, they're run below center height, which has the additional result
of making the cutting angle negative.

They also can be given front clearance all around the form, which allows
them to be set on-center or even above-center. My experience with them comes
from two places, the primary one being a turret-lathe form-cutting
operation, and we used our tools set above-center to get effectively
positive top rake, with hand-ground front clearance.

Your tool actually sounds like something else, if I understand it correctly.
My comment about the top rake refers to the fact that these shearing cutters
I'm describing, or whatever you want to call them, typically have a lot of
positive rake and a lot of front clearance, which is the combination that
can cause a tool to grab and dig into gummy or "grabby" material, like brass
or hot-rolled mild steel. But the positive rake is intended to make a clean,
sharp slicing cut, and it's considered to be part of the tool design.

I haven't experimented much with finishing tools. I just take old designs
off the shelf and try them. I consider myself fortunate when one actually
works. d8-)

The thing that made me think of those shearing cutters when I read your
description was the idea that it was shearing chips off like a knife, which
is what the cutters that I'm familiar with actually do.

This is a place where a picture is worth 10,000 words, I think.

Ed Huntress



I'm not sure where you're located but I think perhaps we have a
language problem. In UK parlance a skiving tool is a tool used to
slice or pare a thin slice of material which is just what this tool
does. It continuously slices off a thin ribbon of swarf which exits as
a long thin spiral. There is no way that this tool could be used as a
form tool. The cutting action is not infeed - it's longitudinal
traverse towards headstock.

As I noted in the original post it's not a new concept - I'm
pretty sure it originated in the early days of lathes with carbon
steel spring tools and swan neck tools when almost any outlandish
shape was tried in efforts to improve the process.

To help visualise the device I've posted a couple of pictures in
the drop box titled "Skive Tool". The tool shown is a Mark 2 version
with the business end formed by a lump of stellite brazed to a mild
steel shank. The stellite is brazed high on the shank so that when
mounted in a tool holder set for normal centre height the cutting
action occurs near the middle of the 45 deg skiving edge. The bilious
purple colour is my colour code for a stellite tool.

The pictures show clearly the 45 deg location of the cutting
edge, the 40 deg clearance behind the cutting edge is visible but less
obvious.

Jim