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Ian B
05-21-2008, 09:54 AM
I'd like to machine up various coloured knobs for the controls on a tractor. Preferably bright colours. What plastic is suitable for this? It needs to be machineable / threadable, hard enough but shatterproof and available in 35mm or so round bar stock. Resistance to diesel would be nice - the stuff seems to get everywhere!

Thanks,

Ian

Duffy
05-21-2008, 10:13 AM
High Density Polyethylene, (HDPE,) might work. It machines easily and comes in white, black, blue, orange, red, and green, (that I know of.) It is unaffected by most solvents. Where to get it? Try a plastics supplier. Around here, someone is packaging slab offcuts in 3 lb bags, which is handy for little jobs like slippery feet on heavy machines. These dont move on a concrete floor, but CAN be moved with a bit of effort. I assume round stock would be available.

mechanicalmagic
05-21-2008, 11:03 AM
Ultra High Molecular Weight (UHMW) polyethylene comes in many colors.

ebay (US) has Yellow, Pink, Blue and Orange available now from one seller, might make up a box with your preference of colors.
Search "UHMW"

It machines just fine, is resistant to many fluids, should be good for your application.

Evan
05-21-2008, 11:21 AM
That isn't a very demanding application except for one thing. They need to be UV resistant. For that the best is a UV stabilized HDPE product. Check with a marine chandler or outfitter for a source.

macona
05-21-2008, 03:22 PM
delrin would work. You can get drops off ebay in different colors.

bruto
05-21-2008, 04:00 PM
I just saw a posting on PM from someone who uses old billiard/pool/snooker balls for this. Apparently they machine nicely, and at least some are solid color all the way through. The person in question is from the UK, where I guess old snooker balls turn up more frequently than here in the states, but I wonder if old bowling balls would work.

Weston Bye
05-21-2008, 05:02 PM
Try pen turning supplier:

http://www.pennstateind.com/store/pen-blanks.html

diameter might be a problem, but the variety is good.

The Doctor
05-21-2008, 08:30 PM
bruto, old bowling balls are not a good choice. I had to machine a " groove about `1 " deep in a bowling ball for a friend. The inside is some sort of black stuff mixed with cork. It cuts dirtier than cast iron and is extremely abrasive.1 pass to full depth would put a very noticeable radius on a HSS tool, had to sharpen every pass. A grinding wheel is only slightly less abrasive. Also, the material does not tend to produce a nice finish, even in the 5 seconds the bit stays sharp.


Ed

doctor demo
05-21-2008, 10:49 PM
bruto, old bowling balls are not a good choice.
Ed
I was not going to stick my nose in a thread about plastic , but I just can't help myself.
WHY WOULD ANYBODY IN THEIR RIGHT MIND USE BOWLING BALLS FOR TRACTOR KNOBS?:eek: .

STEVE

Ian B
05-22-2008, 12:52 AM
Thnaks all,

Great replies as usual.

Evan, the tractor will be spending most of its time under covers or indoors when not in use, so UV resistance shouldn't be a problem (the driver is less UV-resistant than most plastics).

Good tip on the UHMW - the guy has some interesting colours; I'll see if he can put a custom pack together.

Snooker balls; mmm...

Ian

bollie7
05-22-2008, 05:23 AM
but I just can't help myself.
WHY WOULD ANYBODY IN THEIR RIGHT MIND USE BOWLING BALLS FOR TRACTOR KNOBS?:eek: .

STEVE

I think he meant to cut a bowling ball up and turn knobs from the smaller bits.

bollie7

Evan
05-22-2008, 06:13 AM
I had to machine a " groove about `1 " deep in a bowling ball for a friend.

Now I want to know why? And how?

bruto
05-22-2008, 09:41 PM
I think he meant to cut a bowling ball up and turn knobs from the smaller bits.

bollie7
Yes, that was the idea. They would be a little ungainly otherwise.:eek:

Thanks to the Doctor for the warning. I thought some might be solid plastic.