Larry Green wrote:


I need to drill a 1 3/4 inch hole in ABS plastic. I presently have
great luck doing this with smaller holes, up to an inch or so, using a
step drill bit. I've searched around the web, and the largest dia step
drill bit I can find is 1 3/8 inch - does anyone know of one that goes
up to 1 3/4 inch?



I have had good luck so far cutting plastics with 'wood' spade bits. I
recently needed a few 1.5" holes in some 3/4" thick nylon/polyethylene
blocks and only have a tiny Unimat DB200 lathe/mill. I had to go up in
steps as the Uni just didn't have the 'balls' to cut the 1.5" hole right
off. I was concerned about the bits 'wandering' as the point was not
cutting but with a rigid set up (using the Uni as a lathe) the holes
came out true and with an almost glass like finish. The size was bang on
to within a thou too!

I am fairly sure spade bits are available at 1.75" and they might be
worth a try (at least they don't cost much to experiment with).


A forstner or sawtooth style bit would give you a better finish and
size, I find they work very well in polyethylene and nylon.

Lee valley have them in 1-3/4 for $15.40cnd

http://www.leevalley.com/wood/page.a...at=1,180,42240