Grind a 1/4" HSS bit to 1/32" width for about 1/4" of length to
form a parting/grooving tool. A bit of relief front-to-back and
top-to-bottom doesn't hurt, but very little is required. Once
it's made well, stay away from the grinder thereafter. You can dress
it up when it needs it with a few strokes of a diamond hone. I have a
couple of such bits I've been using for a decade, will admit that I've
also broken a few, It only takes about 10 minutes to grind a new
one.

You'll find a lot of other uses for that bit as well. With the
skinny part that short, it's no problem to skin a slot to wider width
if the cutting corner is sharp. This is one place where you don't
want a radiused edge. Such a tool won't deflect in acetyl or even
reasonably free-machining metal. I've recently used such a tool on
303 stainless. Just a couple of days ago I was making cylindrical
bushings of steel, OD of .205", ID of .165 or so. I drilled
barstock for ID, machined to OD for half an inch, parted off bushing
of various lengths in the region of .015 to .030 with such a tool.
The experiment was a flop but the machining went OK....

I've made many narrow slots in acetyl, most a lot deeper than 3/32"
when making high-voltage high-frequency pi-wound coil bobbins. For
deeper cuts (some .750 deep, .032 wide) I used a cutter made by
silver-brazing material from a broken HSS slitting saw to a 1/4"
square of mild steel and grinding to shape. No relief on the sides of
that tool but it runs straight and true.




On 1 Aug 2004 00:23:31 GMT, "Walter Harley"
wrote:

I have a Sherline! Finally broke down and got myself a lathe. Now I am
trying to learn to use it.

I want to turn a rectangular-profile slot approximately 1/32" wide, into an
acetal (moderately hard plastic) shaft with an OD of 1/2". The slot wants
to be maybe 3/32" deep; that is, OD of the inside of the slot is 5/16". (In
case this description is unclear, imagine making a grommet.)

What kind of tool should I use to do this? Should I use a parting tool?
Should I try to grind something more or less like a parting tool?

My concern with doing it with a parting tool is that, although it might work
for this particular problem, I think I'm limited to cutting a slot exactly
the width of the parting tool. It would be nice to learn how to make slots
of various widths, including fairly skinny ones.

Thanks in advance!