Thread: Surface finish
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Default Surface finish

On Mon, 14 Jun 2004 15:28:51 GMT, "Ed Huntress"
wrote:


Congratulations! You've just reinvented the angled knife-tool, a finishing
cutter from the 1930s. g

I'm being only slightly facetious. This is nothing like a traditional knife
tool. It doesn't really have a standard name, but you'll see it called
several things, including an "angled knife tool." It should be called a
slicing tool, or something like that.

An angled knife tool typically is ground from round stock. It has a lot of
front clearance and a lot of top rake, which you get by grinding a groove
into the top of the bar, roughly half-way through. You must hone it very
sharp. The front of the tool is ground straight across, so that, if you
presented it square to the work, it would create an impossibly wide chip.

So you don't present it square to the work. You rotate the cylindrical tool
on its axis perhaps 15 degrees counter-clockwise, as you're looking from
behind the tool, into the work. The edge is now angled to the work so it can
slice, or shear, on an angle.

Then you start a very light cut. If you have the tool height set dead
on-center, you make only a fairly narrow, very thin, knife-slice chip, right
in the center of the cutting edge. Make sure you don't set this tool even
slightly below-center. Err on the up side, if you must err at all.

It's a near-last resort for getting a good surface on soft, gummy steel. The
last resort is a file. g

Watch out, it can grab if you cut too deep. This is a problem mostly on
long, thin workpieces that can flex and climb over the cutter. In that
regard it's like cutting brass with a lot of positive rake.

Ed Huntress


Sounds pretty similar to the sort of tool I've been playing with.

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