Quoting Carl Denk <cdenk@windstream.net>:

>> The Dremel won't work either -- the router bit gets clogged with bits of
>> PVC very, VERY quickly and just plain stops cutting. I suspect my PCB
>> router bit isn't geared up for uPVC, or the Dremel is moving too fast
>> and melting the plastic (not surprising).
>>
> Wrong bit, one I suggested has about 1.5" cutting length, the flutes
> (grooves) are sharpened, and the spiral ejects chips. Try lower speed,
> maybe using 1/4" electric drill. Speed will melt plastic, and make a mess=
..


Will have to disagree with this.  Cutting at almost any speed will =20
generate enough heat to melt the plastic, as the bit lingers in the =20
just-cut area.  The way to not melt the plastic is to move out of the =20
area just cut as quickly as possible, so that means faster feed rate.  =20
And that means faster spindle speed.  Yes, that also means greater =20
side load on the spindle bearings, so the way to compensate for that =20
is to take shallower cuts... ie: cut a few mm deep very quickly, then =20
go around the same path again, but another few mm deep, etc.  This is =20
fairly standard milling procedure.

If you can make a wooden (or other) template for the spindle =20
guard-ring to ride on, so it follows the circle, this will make the =20
whole process MUCH easier.  And keep it cool with WD-40 also.

FWIW, you may want to cut the circle a bit smaller, then file or use a =20
sanding drum to open it up slowly to the perfect shape/size.

Or if all that fails, just send it to me and I'll CNC-mill it for you.

Cheers,
-Neil.




--=20
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