I use maple or oak hardwood. Cheap, easily machined, plenty strong and won’t harm the cutter at all. I think them a little more grippy than my hdpe ones, too.
I used poly carbonate because i found it in the trash at work. Most materials will work. Remember that the side to side motion is what is the primary thing to prevent.
My 2 cents… Make your first set out of something cheap like plywood. You will probably get some additional ideas on refining the shape and functionality as you use them. Once you have spent some time with them and figured out what works and what doesn’t for your particular type of work, then maybe make a more permanent set.
Thanks for the reply everyone. I think I’ll use all of this but start out with plywood and work up to better materials once I get the design dialed in.