Official Luthiers Forum!

I was curious to see what router bits other people use for machining plastic when doing pick guards and back plates. I discovered quickly that upward spirals don't always eject the cuttings and they wind up as a ball of party streamers rotating at 19k rpm. That can sometimes mark the plastic, even through the protective coating. Also when drilling 1/8" holes with Precise Bits drill for routers the same problem occurs. With an outside contour, this is not a issue as I band saw the rough shape before cutting with a down spiral. Using a down spiral for inside contours in plastic isn't something I would normally consider. In the past, I've used a 1/4" single flute straight cutter on acrylic with good results and have been thinking this might be worth a try, as the single flute can probably eject the material with less tendency to wrap around the bit. Anyone have experiences or thoughts to share? Thanks,

Bob

I sand plastic with 120grit belt then polish with a tycro cone.

Use "O" flute bits......(half moon) from a good maker.

Blessings,

Kevin

+1 on O-flute bits. Onsrud is the brand that we use. Slow your RPM. 19K is way too fast IME. Amana makes a nice bevel bit for plastic. It uses inserts.

We use downcuts for all straight cuts. This requires a light sanding on the back to get rid of the burr. You also need to cut a deeper channel in your fixture to give the chips somewhere to go.

It's been so long I can't remember what a single flute straight O-flute bit cut like on plastic.

Thanks Kevin and Sheldon for the info. I did some investigating and found single and 2 flute O bits with down, straight and up spiral configurations. My natural inclination would be to rout an interior pickup hole with an up cut. This could be an erroneous assumption as I've been routing neck and pickup cavities (in wood) with a down cut bit to keep the top edge clean with good results. Sheldon, it sounds like you're using a 2 flute down cut for interior pickup holes, is that correct? I assume you're also referring to the Amana V groove cnc bit for beveling. I've been using something I got from McMaster, but I don't like the finish it leaves.

I'm using a K2 cnc with a Porter Cable 7518 variable speed router. I'll experiment with slowing down the rpm as suggested. It goes as low as 10k, but loses it's torque down there. Presently, all my work is one off prototypes, so I don't have dedicated tooling for these projects. MDF, double stick tape and screws are my constant companions! Thanks again.

Bob

http://www.amanatool.com/ingroove/

Yes, they are a V-groove bit. 90 degree bevel. Single flute so there's lots of room to clear chips.

We use downcuts for pickguards to keep from lifting them off the vacuum fixture and because I don't want to have a burr on the top edge of a PG.