I decided to drill a hole in some .40" Evergreen Styrene with one of my Forstner drill bits. The closest I had to a 5/16" dia. was a 3/8". Nothing special about my bits as opposed to the Freud Precision Shear versions, which are designed to cut a super-smooth hole.
Photo (1) - Here's my setup...my drill press, a 3/8" Forstner drill bit, a smooth pine backing board, a sheet of Evergreen .40" Styrene and I didn't adjust the speed, which probably was a bit too fast:
Note that the flat cutting surface of the bit did not grab the sheet at all, but got hot enough because of my unadjusted too-fast speed to melt a curl that stuck to the bit. Also note the split wafer that the bit leaves after the hole is cut through the sheet.
Photo (2) - Close-up of the hole immediately after being cut with no dressing or any debris removal:
Photo (3) - Close-up of the hole after about a minute of sanding with a bit of 400 grit sandpaper (dry) to remove the tiny ridge on the hole's edge on the bottom:
It's not as nice as a hole bored with an end-mill, but with a lower speed I'm pretty sure it would be smoother. Still...not too bad and easy as pie to drill and clean up.
Cheerio!
Bob Gilmore
