UHMW press fit help.

[Speedy]

I recently purchased an older commercial dual barrel tumbler. nice old school made 3/4 driven shafts, bronze pillow bearings.

I pulled it apart as the driven wheels are all crumbling and shattering, expected with its age. looks like the factory might have casted/injected these.

I plan on making them myself, I require 8 and to speed the process up I figured the foundation of the bushing should be steel, I can pick up locally 3/4 ID x 1'' OD x 2L which is perfect as the stock ones were 2'' long and if I calculated this correctly it would give me .250 wall thickness to tap for grub screws to fasten to the driven shaft.

now, with the steel base I would want to make the wheels out of UHMW, can I simply make the ID 2 thou smaller and press fit onto the smooth steel bushing?
when I drill for the set screws I will drill everything at the end so the setscrew gets the UHMW and steel.

should I also use a 2 part epoxy when I press them together like JB weld?

I never worked with UHMW or similar, I am curious if they might slip on the steel bushing's while keeping the heavy tumbler barrels spinning. (yes the grub screws will stop this, but id rather no slip between the UHMW and steel bush to not stress the grub screw)

 

[petertha]

I don't have a lot of UHMW experience, but what little I did: it can be weird stuff. Sometimes it will machine just like metal & then you will get another shape & it can distort or finish somewhat unpredictably, particularly hole drilling & reaming I found. Generally it likes razor sharp tools. If there was a way to press fit the bushing & ream after, that would be a safer bet than estimating shrinkage. Failing that, trial & error.

I don't think it favors normal epoxy too much. Its kind of an inherently greasy offstandish surface to most common adhesives, almost Teflon-like natural releasing. probably better to mechanically attach if you can. I've also made some low load bushings out of nylon & it seemed to stick 9at least better) with CA type adhesive. But which nylon I cant say, there are so many flavors.

 

[Speedy]

thank you,
so I would be pressing in a steel sleeve, so I don't have to worry about distortion or re reaming, the steel sleeve slides onto the 3/4 bar drive shaft, the UHMW acts like the tread to spin the tumbler.
UHMW seems like finicky stuff!

would you recommend another material? I just pulled UHMW out of my memory.
all this has to do is support the tumbler and turn it. if there is a more suitable material I am all ears

 

[Ratshooter]

Based in my experience with UHMW, I would bore the center hole with a wood bit, such as a forstner type, THEN make the bushing to fit. Even with razor sharp tools, I've had tough luck hitting a dimension. Deep cuts seem to give better results.

Hope this helps, TC

 

[Speedy]

what if I were to scrap the UHMW idea, is there a better material that's easier to work with?
something more ideal for a press fit and taking a adhesive if needed?

 

[chrsbrbnk]

delrin would be a much better bearing material for the purpose

 

[petertha]

I just bought some Acetal (aka Delrin according to this site). I think mine is copolymer black. It seems to machine very nice but that's about all I know for now. There are other variations with various fillers. They have a quicky reference Plastics Guide.

OLM has good selection of various plastics in reasonable stick sizes. No affiliation, just a happy customer & very appreciative of their shipping terms to Canada.
http://www.onlinemetals.com/merchant.cfm?id=181&step=2&top_cat=181

 

[kf2qd]

UHMW is just a plastic. One thing to be aware of is that, in thicker sections it does outgas a bit, and thus will shrink in cross section. Holes will get bigger, and O.Ds will shrink a bit. Drill your hole slightly smaller and let sit for a few days, then finish for a tight press, and press your bushing in. Make a smooth taper to get it started. If you are worried about slipping on the bushing then knurl it before pressing it in. It is easy to work, need sharp tools.

 

[Ratshooter]

A second thought: Ever considered wood?

 

[Speedy]

Hi guys the plastic suppliers here also recommended delrin instead.
2 feet of 2.5 diameter for $60 best I could find, didn't think this stuff was that expensive.

I have considered wood but I think the plastics will hold up better, or so I hope.

 

[petertha]

OLM has shorter sticks but looks like 2" dia is largest they offer
http://www.onlinemetals.com/merchant.cfm?pid=21240&step=4&showunits=inches&id=1509&top_cat=181

Depending on what your finished shape is, maybe better to buy in sheet form?
https://www.onlinemetals.com/merchant.cfm?id=970&step=2&top_cat=181

Yes, plastic can be quite expensive depending on the type