In the machine shop, often when we were drilling "grabby" metals like copper and brass and brittle plastics like plexiglass and polycarbonate, the machinist would modify the drill bit to put a zero or slight negative rake angle on the cutting surface of the drill bit - not really negative, but closer it. Standard 118-degree bits usually have a rake angle of about 25 to 30 degrees. This essentially reduces the "screw" action of the bit making it less likely to grab, pulling the material into the bit.
They would essentially put small flat or slightly negative angle on the cutting edge by touching it on the side of a grinding wheel. I know its not a good practice to use the side of a grinding wheel, but for this purpose it works pretty well. The negative rake gives the drill bit more of a scraping action rather than a cutting action which makes it less likely to grab. I don't think we ever bought drill bits that had a negative rake since they could be made by modifying standard bits so easily in the shop. I would assume they would work the same with very hard and brittle woods.
At home for plastic pen blanks (and segmented blanks) I usually go to a specialty drill bit that is sharpened to give it a 60-degree point which is much pointier than the typical 118-degree bits. This makes the bit enter the material more gradually and distributes the cutting pressure to give it a smoother, peeling type of cut which is also less "grabby". They also work good on more heat sensitive plastics as they don't cause as much heat as standard drill bits (or negative rake bits). The sharp point also really helps prevent grabbing and blowouts when the bit is exiting the blank (although this can also be handled by using a long blank and not drilling all the way through, using a saw to cut off the excess exposing the drilled hole). Sometimes we purchased 60-degree bits (I think they were even called drill bits for plastic) for drilling through thinner and softer plastics like ABS and nylon).
As to JT's question about segmented blanks, I use the 60-degree ones for drilling these. I think the more gradual entry helps when penetrating into different materials in the segment. I especially noticed less problems when drilling through brass, copper, and aluminum separators in segmented blanks. With standard bits I tore segmented blanks up when drilling far more often than when I started using the pointy bits. I really can't speak to how a negative rake drill might work through segmented blanks though.
Dave
