Suppliers for different polymers?

[bpoulin]

I'm looking for someplace online to buy different polymers, I have a small CNC router, and would like to make some prototype machine parts for a laser engraver I have. But I have no idea where to find a good hard plastic that would hold it's threads if tapped and had screws tightened into it. I know 15 years ago my dad worked in a machine shop that had this very hard white plastic polymer that they used for first runs of prototypes to check the fit, but they have long since gone out of business. Anyone have any idea where I could find something like this?

[judleroy]

Acetal Sheet, Rod & Shapes Category | Acetal Rod, Acetal Shapes and Acetal Delrin Rod. | U.S. Plastic Corp.

[bpoulin]

Thank you for the link.

Does anyone have experience cutting/milling HDPE, or UHMW? Mainly will it hold threads well, or will it strip out with little force? The Delrin looks nice, I've seen it used on stuff before, but it's pricey for what I'm trying to do.

[Geof]

UHMW and HDPE can be milled okay but they are not strong enough for threads to carry much load, especially with smaller diameters such as 1/4" or less.

[bpoulin]

They don't need to hold a lot of load, just enough to clamp 2 pieces over an aprox` 2" diameter tube. The part will be cut out to fit around the tube, but just a hair shy of perfect fit, so the screws can clamp the piece on tight. I was planning on something like 4-40 screws, but I'm up for suggestions, the material will be 1" thick.

[Geof]

Tapping small diameter fine threads in UHMW is almost pointless. If the tap has been used previously on metal it is pointless because the plastic distorts around the (slightly dull) cutting edge and the thread does not cut correctly.

For applications similar to what you describe I have simply used either wood screws or metal tapping screws in a pilot hole slightly larger than the root diameter of the thread on the screw. The strength is comparable to, or maybe slightly better than, the same screw in plywood.

[rowbare]

As mentioned Delrin is a lot better if you are going thread it. UHMW just doesn't cut well enough for small taps.

Corian also machines well though I don't know how well it holds a thread. You might be able to get offcuts from a kitchen counter place or find some fairly cheap on eBay.

bob

[lcifers]

These work great if the plastic will not hold threads. I think McMaster Carr has them also.

SI Inserts for Plastic from PennEngineering

[lcifers]

Here they are.

McMaster-Carr