[Dubliner]

A search gave me hundreds of CNC related solutions, but can you cut .25 in HDPE with 100w cutter?

[zax15uk]

I would say 'yes', but it may take several passes and the results may not be acceptable. HDPE does not cut well and you can expect a lot of melting at the edge.

ABS is a better option, and yes 1/4" won't be a problem.

Zax.

[Tweakie]

From my experience HDPE machines beautifully with CNC but when it comes to laser cutting, that's another story.
HDPE melts rather than cuts and I needed a lot of air assist to remove the melt, then the final cut looked a bit like it had been cut with a plasma torch. I chalked this up as a failure and decided HDPE and lasers are not good friends.
Be interested to hear others results with this material.

Tweakie.

[Dubliner]

Thats what I was afraid of, unfortunately this is a small part similar to a gasket and .125 in wide in some places, so Tweakie, can you share, bits feeds & speeds and hold down for a 3in x 3in "gasket" with 40% of it being .125 inch wide in .25 material? I suppose I should be asking this over on the CNC side :-)

[Tweakie]

Obviously you must not get it hot so adjust feeds and speeds accordingly but any 2 flute endmill would be OK. Most of the time I use a single flute carbide, designed I think for wood.
My preferred hold down method for most wood and plastics is double sided sticky tape onto a sacrificial MDF base.
You can really get a beautiful surface finish on HDPE with possibly some whiskers on the edges but don't be tempted to sand it.

Tweakie.

[zax15uk]

That's my technique too... carpet tape onto sacrificial MDF and a SHARP 2-flute endmill. Keep the feedrate down and cut in 1 pass.

The other option is to leave a couple of tabs (bridges) to hold it in place and then either manually cut or machine them away later.

Zax.

[Tweakie]

Dubliner,

This little chap was milled from HDPE - note the slight furriness around the edges where it was cut out.

(the prancing moose was a joke for my F1 Ferrari supporter buddy who just happens to own a Volvo).

Tweakie.