DIY linear bearings (no PLA)

uGen Wrote:
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> That is interesting to hear. I knew that UHMWPE
> doesn't absorb air humidity like PA does, but did
> not have any information about other fluids. Any
> reason why I should not use PTFE (besides
> obviously not working better than the unlubricated
> bearing)?
> One of my goals was to have a completely wet
> lubrication-free printer for maintenance's and
> portability's sake and PTFE dry lube was sort of a
> borderline consideration in case performance is
> not as expected.

I'm not sure I follow, but what you have should be good enough. You can also try carbon powder as a lubricant but it is even more messy.
I recommend running dry if you don't want to use mineral spirit/hydrocarbon lubes. Why do you backlash from a wet lubricant?

Yeah, carbon indeed is also used as a lubricant...and will look terrible on the pretty white UHMWPE

It's mainly because I am a lazy slob I try to optimize my RepRap. If I can make my own bearings with the added benefit of not having to spend time and money to lubricate the bearings properly, I would be more than happy to do so. Besides, after building a heat insulating chamber, I would expect that wet lubricants will have to be replaced more often if I don't go the high-temperature lubricant route (which might add logistical complexity).

At this point, the bearings aren't the problem anymore. The slider rod is... Decent quality shafting is $3/ft... And linear bearings only cost $0.75 in bulk. The fact that UHMW is cheaper is a good DIY thing, but to scale up someone needs to cut/shape/mold/ build a carrier for / etc... the price could be as low as 40.25 and most importantly, the noise would be lower. However, if it was a good long term solution, I think you'd see it more often in 2D printers, which all use brass bushing on steel shafting. the tolerances are probably more accurate and the cost probably lower for the brass, along with longer lifespan.

Yeah, the shaft indeed troubles me. Not because of the price, but rather because it is still one of the parts that we cannot easily and consistently make. I am doing all this research and experiments in DIY linear bearings partly because I am interested in the original idea of RepRap.
That said, I am using slightly more expensive (~5€/400mm) Cf53 steel shafts for my printer. The V2A shafts I tested my bearings on do not really compare to how smooth the UHMWPE run on the linear guides.

Actually, an old Epson printer I took apart some days ago had plastic bushings in it. You might be right about the lower price as the plastic bushings I found are pricy for an injection-molded small part. However, the comparison of service life depends on the environment. There are accounts of nylon nuts for leadscrews lasting much longer than brass or bronze ones for the same application. Probably this is because they were used in abrasive environments. Plastic tends to embed wear inducing debris and thus removing it from the system rather than grind over it again and again like metal nuts, so brass bushings might last longer, but only in the right conditions.

A couple of points:
-why not make the bearing housing from metal, heat the shaft, and sandwich press a piece of flat plastic bearing material against the shaft?
-many plastics will deform at raised temperatures in the above setup. Prolly UHMPE would. Lowers cost greatly and allows easy replacement of the liner.
-the above setup gives you some of the construction advantages of poured Babbit: you can achieve alignment in the molten state, you get a strong metal shell for attachments, etc.
-why not try solid teflon?
-my comments based on the work using acetal pressed under heat to create zero backlash nuts for acme shafts.

--slick

UHMW is not most plastics. It can't be thermoformed. It can be thermodeformed. At least, that is my current understanding, that the theoretical actual glass transition temperature is above the charring point of this material. This is why most UHMW is sintered from powder. IT is also why "extruded" UHMW tends to look funky.

But it is also what gives it utility as a bearing. Were it to heat up, locally, at the microscopic level, plastic would melt and wick away through friction, over time you'd get a sloppy bearing.


slick Wrote:
-------------------------------------------------------
> A couple of points:
> -why not make the bearing housing from metal, heat
> the shaft, and sandwich press a piece of flat
> plastic bearing material against the shaft?
> -many plastics will deform at raised temperatures
> in the above setup. Prolly UHMPE would. Lowers
> cost greatly and allows easy replacement of the
> liner.
> -the above setup gives you some of the
> construction advantages of poured Babbit: you can
> achieve alignment in the molten state, you get a
> strong metal shell for attachments, etc.
> -why not try solid teflon?
> -my comments based on the work using acetal
> pressed under heat to create zero backlash nuts
> for acme shafts.
>
> --slick

so what happen to OILON? TBH, like simba said, once it wears out a little, the play comes in and ... i wonder for light duty apps, will teflon do its lifespan any good?

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______________________________________
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@redreprap: I found out that the vendor from whom I got my UHMW-PE also sells oil filled Nylon 6 (I suppose that either is Oilon or very similar to the Oilon you know). Unfortunately, the workshops in art school were closing for holidays and I had to quickly make my bearings without much further research and modifications in order to have anything running at all. So my printer is running with UHMW-PE now, but I might have found an interesting alternative to Oilon that I will try first because I already ordered it: Nylon filament (Taulman 618). It may not be oil filled and resistant to moisture absorption, but at least it is printable, which I think is one important factor in choice of material.
The bearing design needs a major redesign anyway and I would like to learn how to use a lathe, so I might try to turn an Oilon bearing in the near future.

I read forum posts about how to make a POM nut for ACME screws. This idea intrigued me, but like Simba said, there are some problems with the properties of UHMW-PE.
You COULD weld it, but you would need to apply 20 bar of pressure onto the interface in order for the plastic to properly fuse.

Unfortunately, pure PTFE is not really wear resistant. I guess a bearing made out of that will wear down in no time, even with light loads. PTFE with additives might behave differently, but I guess we are slowly approaching rather exotic and expensive materials if we went this route.

uGen Wrote:
-------------------------------------------------------
> That is interesting to hear. I knew that UHMWPE
> doesn't absorb air humidity like PA does, but did
> not have any information about other fluids. Any
> reason why I should not use PTFE (besides
> obviously not working better than the unlubricated
> bearing)?
> One of my goals was to have a completely wet
> lubrication-free printer for maintenance's and
> portability's sake and PTFE dry lube was sort of a
> borderline consideration in case performance is
> not as expected.

Its a personal choice i think, all plastics are useful, but UHMW is a clear winner IMO

PTFE is TOXIC when heated too high. Fluoro anything is usually more stable by more harmful to manufacture/burn.
Delrin is OK but explosive if heated in the presence of brass (read: fireworks).
UHMW is less toxic and food-grade naturally. IT also seems to have better wear resistance and lower COF than the others.

UHMW is cheaper, hands down.

I would use PTFE where machining is or hardness is needed. UHMW is somewhat squishy and totally lacks resistance against creep deformation - its probably this same property that would make it a better bearing to deal with poor tolerance.

I'm trying this UHMW thing again on smooth shaft now.

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PTFE is TOXIC when heated too high. Fluoro anything is usually more stable by more harmful to manufacture/burn.

But there is no way that a bearing on a RepRap reaches such high temperatures, so I don't have to worry about its toxicity. Even if locally, a tiny little fraction gets heated due to friction, the amount of harmful substances produced would be far below safety thresholds.

Quote
Delrin is OK but explosive if heated in the presence of brass (read: fireworks).

Where did you get that from? Never heard of this before.

UHMW-PE itself is non-toxic as it is pretty much inert. That is also one of the reasons it can be used in knee joint prostheses, but of course the manufacturer might add other substances to the pure polymer product.
Coefficient of friction really depend on the material combination of the sliding surfaces, so it is hard to generalize.

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UHMW is cheaper, hands down.

That's one of the reasons why I would like to continue using this material (if only one could print it!).

Quote
I would use PTFE where machining is or hardness is needed.

I wouldn't. PTFE creeps more than UHMW-PE, is softer and has terrible wear characteristics.
Creep seems to set in only if a certain load is applied. At least that is the case in Dyneema / Spectra lines which are made of UHMW-PE fibers. If I remember correctly, you can apply 20-30% of the maximum rated load before the rope starts to show signs of creep. Applied to our printers, I would say that we are way below this threshold, so there is pretty much nothing to worry about.

Good points. The notes on delrin explosion is far fetched, only that you can never be too careful when its your fault someone gets hurt...I got this tip from a polymer injection company.

Does anyone know what a good price point would be to ask a machinist for? I'm thinking of eventually setting up a (Read: dirt cheap, low profit) reprap house and wanna buy them in bulk. I assume somewhere between $2-$5 per bearing?

I tested nylon recently and found this to be bad - high friction. Delrin worked as well as UHMW.

Hello!
I have an idea with UHMWPE the linear bearing.
If to use UHMWPE the sticky tape (is on sale on Amazon) wrapped on a shaft, glue slice outside , and to clamp the printed halves of the casing?
I can't check it, I while have neither printer nor UHMWPE.

I apologize for google.translate..