View Full Version : Machining a Delrin disk

08-01-2012, 11:35 PM
I need to make a Delrin disk, 3.75" in diameter, approximately .125" thick, with a .0625" deep pocket, except the very edge of the circumference, where the pocket would stop. In the center I need a cylinder (milled into this part) approximately .3125" in diameter and .3125" in height. Was planning on buying a small disk on McMaster-Carr, probably 4" in diameter and .5 thick.

The question is, how do I hold it down to accomplish this? Any special endmill that I should be looking for? I've never machined Delrin, so I know nothing about it. I have a old Bridgeport and a rotary table.


08-02-2012, 12:22 AM
Just did some bushings today in Delrin. You'll get long stringy chaff but cuts nice with just plain HSS. In fact, I used a parting tool for the OD on a lathe. With an end mill, it should give flakes. Use double-sided tape to hold the disk to your RT.

My questions is: How are you getting a .3125" high cylinder out of .125" thick stock? :eek:

08-02-2012, 12:23 AM
Endmill: NEW sharp cutter, maybe a 3/8" or 1/2" diameter to keep the cost down. Do NOT let it rub on the plastic, generates heat and dulls the cutter. Run a bit faster than steel. Air cool. Climb mill a .010" finish cut.

Mounting: I would double back tape it down, with light toe clamp just for safety, whenever you can.

Note: Part is going to dome or potato chip, unless you take some material off the back side (and are lucky).


Peter N
08-02-2012, 03:44 AM
That's really a job for the lathe (you probably know that anyway). Any chance you could 'borrow' one for 15 minutes? That's about all it would take.

08-02-2012, 11:53 AM
Delrin (or acetal) is easy to machine. Treat it like aluminum but don't dwell anywhere. Keep it cool with air. It is a lathe job but if that isn't an option then the easiest way to hold it is by the centre. If you can make a through hole then bolt it down with a piece of sand paper under to keep it from spinning. If you can only make a blind hole then tap it and screw it down with a stud (or large set screw). If neither is allowable then glue it to an aluminum plate with crazy glue and heat it with boiling water after to release. Leave some thickness so you can finish the back side flat after doing the front.

IF this is to be used in an acid environment use acetal, not Delrin. They are NOT the same material. Delrin will break down in even vinegar or tomato soup, acetal will not.

08-02-2012, 02:16 PM
FWIW, double sided carpet tape is really good stuff. It's thinner than many of the other double sided tapes I'm familiar with and it sticks about three times as hard. One word of warning, though: if you leave it on a surface for more than a couple of hours or if you accidentally spin the part, the tape becomes a real PITA to remove from steel/cast iron. You'll want some powerful solvents to cut the adhesive.

I've used it to stick an 8" diameter acrylic disc to a lathe faceplate (and many other things, too!) and the tape normally remains on the cast iron and peels cleanly off of the plastic, even if you let sit for a long time. I always keep a roll in my portable tool box and a roll in near the lathe/mill.

08-03-2012, 11:55 AM
Thanks for the help and sugestions. I knew that some sort of tape was available for applications like this but I didn't know how you would get the part off IF I used it.

My lathe, EMCO Maximate mentor 10P, automatic cross feed is broken. In other words, it won't feed when engaged. Don't know how to fix it, so I thought I would use my BP and RT instead.


08-13-2012, 07:51 PM
I ended up using my lathe to make the part and did so in aluminum instead. Is there a way to make this using only one bit. If so, I wasn't able to figure out how.