Machining uhmwpe plastic

[mickri]

I am going to be making new rudder bearings for a friend's Santa Cruz 27 sailboat. The recommended material is uhmwpe. It comes in tubes and we might get lucky finding a tube with the correct OD and ID. I am not going to hold my breath on that. Anybody have any experience machining this stuff. I have a Craftsman 12 x 36 and use HSS tooling.

 

[Aukai]

Not sure if you've see this one or not.

Machining Ultra-High Molecular Weight Polyethylene (UHMWPE): A Plastics Guide

Source: Plastics Today Ultra-high molecular weight polyethylene (UHMWPE) is part of the umbrella of polyethylene thermoplastics. Other peers include

aipprecision.com

 

[mickri]

Haven't seen that. Interesting reading. I think their applications are way more high tech than the bearings for a sailboat rudder. I wonder how it machines using HSS. I will find out.

 

[Aukai]

Tooling needs to be sharp, and a recommended coolant is what I think I've seen.

 

[mickri]

Found this which gives clearance and rake angles and speeds and feeds. Recommends HSS tooling for turning at 600 to 1000 rpm. chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.plasticsintl.com/media/wysiwyg/Fabricating_and_Machining_UHMWPE.pdf

Finding some conflict about how easy it is to machine.

 

[MrWhoopee]

I machined quite a bit of it. Just slightly better than machining rubber. Use sharp tools, the "chips" will be ribbons. It is not dimensionally stable and is nearly impossible to get a decent finish. Tends to melt. Don't expect to hold a close tolerance. Great abrasion resistance.

I thought they used Delrin for wet bearings.

 

[Provincial]

I machined quite a bit of it. Just slightly better than machining rubber. Use sharp tools, the "chips" will be ribbons. It is not dimensionally stable and is nearly impossible to get a decent finish. Tends to melt. Don't expect to hold a close tolerance. Great abrasion resistance.

This is my experience, too. For the application the OP mentions, a fine finish is probably not an issue. Loctite on the OD of the bushings at installation would be a good idea.

I wonder if "burnishing" by pushing a heated tool through an almost-to-size bore would produce a smooth finish and precise bore diameter?

 

[Karl_T]

If you have a shop vac, set it up near the tool. Suck all the strings out before they make a HUGE fuzz ball.

On a lathe, I used HUGE relief and rake angles, almost a thick knife

 

[mickri]

The above link I posted doesn't work. Here is the same info. http://www.plasticsmag.com/ta.asp?aid=3862

Making Santa Cruz sailboats was not high tech. These boats were made 40 to 45 years ago. These guys were into fiberglass and were true pros at hand laid up fiberglass. I doubt that they used any specially machined parts. Talking with my friend it sounds like the existing bearings are 2" OD 1.5" ID. Would not be surprised if they used off the self tubing that they cut to length. Going to inspect everything next Saturday.

 

[jbobb1]

Not sure if there are different grades of this polyethylene, but I have been machining a lot of this: https://www.mcmaster.com/8701K47/
I've been making bushings for reciprocating pumps I've been rebuilding for a customer using very sharp cemented carbide.