Okay, guys, here's an update. One thing I also noticed with this material is that it seems quite heavy for its size, which is 6" square (for $11 on eBay).
Based on gustafson's and bosleyjr's notes, I set fire to this stuff once again. Steady blue flame, no smoke, no smell at all!
Then I went out in the garage and put a flat edge of the piece against the belt sander. No 'sawdust' at all, just a mess hanging off the exit side (see photo). Next I drilled a #36 hole and ran a 6-32 tap in. The stuff drilled okay, long continuous chip coming out (see photo), but the tap squeaked as it went in and very little material was actually removed (the small bits in the photo).
You know, at this point I really don't care much what material I use for my project; I just was told that Delrin is a pleasure to work with. To prove the design I first used a piece of 1/2" plywood. The for the first 'real thing' I graduated to phenolic material (the brown stuff made from cloth and whatever), which worked really well, actually. But based on the recommendation, I turned to Delrin, which I now think I got gypped on. Here's what I'm making:
The piece in question is that brown block, phenolic in this case. It's 1.3" square with a 30mm hole in the center. A saw slot allows this to clamp that metal part, an audio transducer, and hold it to the 1/8" backplate. I drill the 30mm hole with a Forstner wood bit, which is why I'm looking for a good material to fabricate from. I know, I know, I should be using aluminum, or at least milling that 30mm hole, but I'm not a machinist. So I need to be able to make these in small quantities using my band saw, drill press and belt sander.
If there's a better material, I'll use it. The phenolic works, but it's rather brittle and I'm afraid to torque down much on those 6-32 screws holding it to the backplate. Something with a bit more 'give' might be good, and I don't want to tax the cutting edge on my 30mm wood bit of course.
Thanks for all your help!