[craigjh]

Hi all,

I purchased some sheet material of what I thought was HDPE (or PE) off EBAY (from a local shop re-fit). Turns out it's not what I thought it was, but I'm not sure what it is!!! Was advetised as perspex, I had asked was it like "chopping board" type material and the response was yes. Anyway I have it now so would like to know what I've got!

I intially suspected it may be fibre-glass, but have nil experience with fibre-glass other than knowing it's hazedous to cut.

It drills quite easy and I even tapped a thread through it. Is it FG? Or just hard plastic? Maybe it is perspex. but I thought perspex was more brittle. One sheet of aprox 1200x1500x20mm is almost a 2 man lift. Heavy stuff. I have 4 sheets of that size and 3 of a thinner (aprox 12mm) size. The thinner sheets are quite bowed, which I also didn't think FG would do?

I've attached some photos hoping one of you could help me out. I'm sure it'll be easy for someone.!.

-Craig.

[kevin swan]

Looks like uhmw

[janders57]

This site might help you identify it:
Plastics Identification Guide - Modern Plastics

[judleroy]

Looks more like polypropylene to me. It's hard to tell when your not holding it in your hand. The smell it gives off when cut or burned is how I usually can tell what I'm working with.
Judleroy

[craigjh]

Thanks Kevin, Janders, & Judleroy.

I'll do some further research given the information you have provided.

I'll search for some examples of Polypropylene to compare. I have used Polyethylene (white chopping boards) in my build, but this stuff is a lot harder than that.

I'm hoping to be able to machine it, but want to understand what it is first for obvious reasons.

Janders - that's a handy data sheet, thankyou. I'll have to arc-up my blowtorch (with caution.....). (flame2).

[rowbare]

Check this post on HSM: The Home Shop Machinist & Machinist's Workshop Magazine's BBS - View Single Post - What is this odd plastic?

bob

[craigjh]

Cheers Bob. I used yours & janders identification guides togethor and both lead me down the path to Polyurethane. Further researched reveals a lot of different classes/hardnesses etc. After further experimentation, I'm reasonable confident to cautiously try to cnc some letters/numbers out of this stuff I have. I'll just need to slow my router speed down a lot I think.

Cheers for the help everyone.

[janders57]

Craig,

Just curious, how did this material work out for you?


Jon

[craigjh]

G'day Jon,

after following your flow chart, and the one that Bob posted, I'm reasonably confident that it is a Polyurethane. I haven't CNC'd anything with it yet due to my router running at 30,000 rpm. I plan to get a speed controller for it soon www.SuperPID.com - Super-PID Closed-loop Router Speed Controller to allow me to experiment with some other materials, including this Poly.

I had no particular purpose when buying this stuff, just saw an opportunity and bought it (only $40 for 7 pretty large sheets). I now need to create something impressive to justify the purchase.......! Why do I do that.....!?!

Cheers.

[janders57]

I now need to create something impressive to justify the purchase.......! Why do I do that.....!?!

LOL, well if you ever figure that out, let me know. I do it all the time! I've got far more potential projects sitting around here than I'll ever have time to complete.

Jon

[rusel]

Hi
It looks like good stuff to play with and sound like you have enough to play with. Keep us updated.
The bowing can come from a small temperature difference on the faces making one side expanded and the other contract and then it might stay like it till it is force back.
Let us know how the speed control works out

Russell

[Dougal]

It doesn't look or your description sound like polyurethane (PU). PU is noticably rubbery even in the hardest grades and very flexible in a sheet like that. PU is also really ugly to drill.

I'd be thinking polypropylene. It's quite easy to distinguish between polyethylene (PE, HDPE, UHMWPE etc) and PU as PU burns instead of melting.

[craigjh]

Hi Dougal,

thanks for your input. Being no expert on plastics, I used the identification charts the guys have posted in this thread. The attached one that Bob provided proved easiest to follow for me. It steered me towards PU due to 1-sinks in water, 2-continues to burn once lit, 3-no drip, 4-definate yellow flame.

Upon your doubts, I've googled some more and agree that PU seems to be mainly softer than what I have here. I've re-visited the chart and I'm now heading in the other direction, towards possibly an Epoxy?

Also now looked further into Polypropylene (PP) after yourself and Judleroy think this is possibly what it is. I'd initially ruled it out due to a small sample sinking in water, but maybe the chart isn't entirely acurate in that respect. Other website info on PP seems to line up, other than it appears PP should float.

My head is hurting again......... how about I throw a mask on and just cut it!

[Shane.S]

Hi, looking at your photo's the way the material has chipped and cracked and also the swarf of the drill bit indicates that the material is arcylic. Cutting at 30,000rpm will be fine so long as swarf is removed from the cut.