"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

And my choice would be a Forstner bit. I make holes in HDPE a few dozen
times a year. Twist drills won't do. Spade bits make for rough holes.
Forstners - fed at slow rpm and an adequately fast feed rate to prevent
softening of the work - make for a smooth hole in one cut.


I took your suggestion and used a Freud carbide tipped forstner bit. 1.5" diameter holes,
32 mm deep, 40+ in all. If I pecked right the currlies flew off, if I pecked wrong, I had
to stop the mill and pick the wad off.

What would you consider slow? I was doing about 900 rpm, feed tended to be agressive in
order to get chips that would break off when I retracted.

Hole finish was way better than that spade drill.

That was fun.


Wes