Milling UHMW

[SpecialtyTool]

Im about to mill some UHMW. Any advice would be appreciated. Milling a couple bosses 1.25 tall. Using a 1" 2 flute HSS end mill for most of the operation.

[Chris Rizzo]

I can't stand UHMW. Sooo greasy. Make sure your holding it very well. If you leave it in a vice overnight, the part will be compressed a bunch in the morning (like .02-.03!). Hope you've got loose tolerances cause this stuff can move. Also pulling alot of material off one side (like it sounds like you might be doing?) is a recipe for major major warpage unless you have a big heavy block. Otherwise not much to it, just soft. Turning is a real headache with chip control. If your doing any kind of production run, I'd recommend spec'ing virgin material. Alot of the recycled stuff can really make you chase your tail batch to batch.

 

oh, your original question . Probably ramp contour around the boss with a finish pass at bottom. Tool is good, although I'm partial to 3 fluters

 

hth

[#Rekd™]

Single flute router type cutters work well on this stuff.

[headhunter]

I agree with Chris. It's not terrible to cut, but will move/warp on you if your taking a lot of stock off. I've used HSS and carbide on it. Both do fine as long as they're good and sharp. Had to mill some 1/4" thick sheet down to 1/8" and put a bunch of grooves in it. If I didn't take the thickness down in equal amounts on both sides, it would bow up like a taco and would tend to shrink a little.

[Goldorak]

just put the part in hot water for about 2 minutes then let it cool before final machining , don't ask me why but it works like a stress relived , our plastic supplier give us this trick a couple years ago

[jeff]

I can't stand this material.

Although it's easy to cut,.it's very unstable.

Your tooling better be razor sharp, or else you will have a hell of a time trying to deburr this stuff by hand....an Exacto-knife works ok to "peel" the burr off.

If you have any tolerance to hold, rough it out within .05" or so, and let the part sit overnight on the bench,because it WILL move on you.

 

Edit:

Just saw Goldorak's trick, I haven't tried that yet, but it's worth a shot.

[SpecialtyTool]

Its a pretty good size part. 3-1/2" x 5-1/4" x 24". I mainly need advice on depth of cut and feeds and speeds.If its as hard to hold as you say can I take full depth and width. What kind of feed rates am I looking at?

[jeff]

You can run as fast as your machine can go, BUT it all depends on how good you're holding onto the part, because it will want to squirt out of the vise.

It's very easy to cut.

It's like Delrin, in that regard, but like nylon in the way that it doesn't like to break a chip,just not as "hard" as nylon.

For a starting point, run it at the same speeds as you would run a 6061-T6 aluminum part, then go up from there.

[SpecialtyTool]

You can run as fast as your machine can go, BUT it all depends on how good you're holding onto the part, because it will want to squirt out of the vise.

It's very easy to cut.

It's like Delrin, in that regard, but like nylon in the way that it doesn't like to break a chip,just not as "hard" as nylon.

For a starting point, run it at the same speeds as you would run a 6061-T6 aluminum part, then go up from there.

 

Im going to be holding on to over an inch of the thickness in two vises.

[BenK]

just put the part in hot water for about 2 minutes then let it cool before final machining

 

Plastic has a memory all you need to do is give it a little heat and you can return it back to its original shape in a lot of cases. I used to work for a plastic company before going to school.

[jeff]

Im going to be holding on to over an inch of the thickness in two vises.

 

Make sure that the area that you are holding on to, is square and flat, because it could still squirt out of the vise, it's all in the cut, and how much force your'e putting on the part.

Don't let this scare you, 1" is still pretty good holding stock, but it's still UHMW