Machining UHMW polyethylene question

dml66 said:
Everything I read prior to working with UHMW plastic is that abrasives will not produce a good finish. That said, I do have some scrap pieces, and I do have sandpaper from 180 grit to 3000 grit, it can't hurt to give it a try
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I didn't have any luck at all, grinding or sanding UHMW. It only made surface finish worse and hardly removed any material. Makes sense as that's exactly what UHMW is designed to do. If you've got a scrap piece to experiment with, do give it a shot; maybe I just wasn't using the right abrasive.
 
dml66 said:
Everything I read prior to working with UHMW plastic is that abrasives will not produce a good finish. That said, I do have some scrap pieces, and I do have sandpaper from 180 grit to 3000 grit, it can't hurt to give it a try
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Interesting to know , a nice new sharp file might work instead.

Let us know how the sanding test goes, I would presume the finish will look a little dull as it's a soft material but should be smooth and flat.

Stu
 
stupoty said:
Have you tried a manual wood plane ?

Stu
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Have not tried that only because I don't have one. That said, Black Friday is right around the corner...hmmm, maybe it's time to pick one up.

I should add, I'm not presently a woodworker, I had to give that up years ago because of moving. I do still have a few woodworking tools like a router and chop saw, maybe a rusty chisel or two,
 
dml66 said:
Have not tried that only because I don't have one. That said, Black Friday is right around the corner...hmmm, maybe it's time to pick one up.

I should add, I'm not presently a woodworker, I had to give that up years ago because of moving. I do still have a few woodworking tools like a router and chop saw, maybe a rusty chisel or two,
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I would not pick up a new plane online unless it were a veritas or lie nielsen. That being said, there are plenty of good old planes at garage sales, and ebay (you'll generally pay a little too much).

Most of the other new planes are garbage, and the other high priced are way over priced and gimmicky.
 
woodchucker said:
I would not pick up a new plane online unless it were a veritas or lie nielsen. That being said, there are plenty of good old planes at garage sales, and ebay (you'll generally pay a little too much).

Most of the other new planes are garbage, and the other high priced are way over priced and gimmicky.
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Yeah the second hand market is the place to find hand planes , I did get one of the indian clones (a block plane) which was quite good for the price.
Restoring planes is quite therapeutic also and if you find you have started a collection you should be able to list them on ebay for at least what you got them for. :)

Stu
 
For milling, use a brand new sharp single flute cutter and cut conventional at a low (1000 RPM). Like said before, the feed must be fast enough to avoid rubbing and melting the plastic.
If you use a table saw, you need a (new) blade made for plastics and feed fast enough to avoid rubbing en melting the plastic.

POM can be used also. It is harder than UHMPE/UHMW and there fore easier to cut with a good finish.

Given the size, I would do this on the CNC router so cutting conditions can be optimized.
 
The project design changed after I tested a prototype; instead of a square, parallel-sided slot, I decide on a V-block arrangement.

I made a holding jig using 1"x1" aluminum angle stock and a piece 3/4" thick white oak. The oak's edge grain is cut to 45°, the aluminum is fastened flush to the oak's beveled edge. The UHMW square stock is then fastened to aluminum angle stock. The jig lets me take the bulk of the material off with the miter saw, finish milling is done on the router table using the compression spiral bit.

Here's a picture of the hot mess:

20231122_125457.jpg

The finish is not a mirror, nor does it need to be, it's clearly better than the finish I managed with the straight bit. The piece is overlength, the lead in and tail out sections will be excised on the miter saw. The two UHMW pieces will be attached to a base so that they resemble a V-block, riding in said V-block is a very smooth stainless steel ball foot. Thanks for all the help, I learned a lot!

20231122_125637.jpg
 
If you mill (face), you should see 2 types of cutting grooves, the one when the tooth hits the stock on the front cut and when the tooth hits the stock on the back cut. Both must have the same depth. To me, it seems your cutter is not square to the table.
In the picture a very rough cut that shows both grooves.
MP_M1A_MD_Fawn_Bongo_PC_SCPN_2f.jpg
 
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