proper material 2

[edstimator]

I need a bearing/wiper material to use on a slow motion sliding polished chrome rod think linear motion. short throw Like three inches. I would like the material to be castable at low temps and slide free of friction within reason. Fairly stiff as it would have a max 50 pound load on each bearing.
Any suggestions?

 

[patprimmer]

From the somewhat inadequate info supplied, my best guess is polyurethane. There are many grades to choose from. The supplier should be able to advise.

I am presuming you are using the word castable in an appropriate manner and you have correctly rejected other possibilities for method of manufacture.

Regards
Pat
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[edstimator]

Yeah, you're not dealing with a rocket scientist here. I just build stuff in my garage and right now I need a table to move in x y z motion so I'm trying to cast my own plastic bushings because the linear motion crap that is off the shelf is priced like gold and I'm working with a silver budget here. I'm trying to cast the bearing into a mould so I can try different size shafts without having to buy new sets of bearings each time. Prollly doesn't make much sense but it's kind of like sex, you don't have to be good at it to enjoy doing it.

 

[patprimmer]

Non castable materials like nylon (Nylatron) or HDPE or acetal (Delrin) or PTFE (Teflon) would probably make a better seal/bearing but they need to be machined or moulded. You are probably stuck with PU, maybe PU with a slip additive like Teflon powder. Powdered grapgite worked into the surface helps somewhat if black discolouration is acceptable.

Regards
Pat
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[edstimator]

discoloration isn't an issue as all of this is on the underside of a sliding table. Delrin seems like the obvious choice but I was hoping for a more economical solution. sounds like the pu with teflon or graphite may suit the bill. I have tried impregnated bronze but there is a stickiness initialy that causes sort of a jerking motion that is unacceptable. I need a smoother start from the rest position.

 

[patprimmer]

Plastics won't be so good from a static friction point of view as they tend to mould to the opposite surface on a micro scale. Generally the harder and smoother both surfaces the lower the stiction. Once again I think this is where graphite is good.

Regards
Pat
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[edstimator]

actually you may have pushed me onto a path that I have kicked around and that is to use rollers on the shaft. I was going to fabricate the bed with rollers by welding a jig for the roller bearings to ride in proper position on the shaft but I have some castable plastic in the garage and I may give that a try to make the frame of the trolly that holds those bearings in place.
I could cast directly into a clay mould. I know! Which plastic right?
I don't know but I think it's a smooth on product.
I'm going to think about doing it like that. I have been looking for a project for that plastic for a while now.
Thanks for your help. It really was helpful and actually learned a couple new terms to research.

 

[MikeHalloran]

Off the wall:
{
If you support the guide rods in ball bearings and drive them with a chain or belt so that they are always slowly rotating, the stick/slip problem should be greatly reduced, regardless of bushing material.
... at the expense of some added complexity, I admit.
}

If you have access to a lathe, you can buy Delrin rounds and machine your own bushings to whatever spec you need. PU is indeed castable, but I think you will be disappointed at the amount of graphite, or oil, or grease, that's required to keep it slippery.




Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

Yes, plastic bushings are not real expensive to buy, either. Nor are oilite bronze. You can cast babbit if you are so inclined to do so, and the assembly dictates a cast-in-place installation.

Oak also makes a decent bearing material (relative to no bearing at all) and was used for centuries as such. Lignum Vitae is better, but a little more difficult to come across at your local lumber yard. The guy behind the counter will most likely have no idea what you're talking about.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[edstimator]

The problem is that the parts cost 17.00 bucks and the shipping is 25.00
Just sayin......cost is relavant and if your dinkin in the garage with other expensive tools that crap can add up. Sides, I kinda get a kick out of poorgoying parts and tools which is a good thing because I have had less than stellar results on occasion.

 

[edstimator]

I'm a newb here to this site but happy to converse with free thinking men. All of the advice given has been apreciated and thought upon.Some of the advice was very good but it was all very generous and I thank you. Not closing the thread, just sayin......