How to judge quality of printed PLA LM8UU/LM6UU bushings?

In an attempt to reduce noise, and also just because I want to try it, I am replacing the LM8UU/LM6UU linear bearings in my printer with printed PLA bushings of the same size, using this model: [www.thingiverse.com] . The printer is a Printrbot-style Cartesian design (Portabee) with guide rails for the X-, Y-, and Z-axes along which the bearings or bushings slide.

I adjusted the diameter of the 3D model so that the printed bushing requires some force to be pushed into the smooth rod along which it slides, for a very tight fit. Then I spent about 15 minutes sliding the bushing up and down on the rod quickly, occasionally rotating it slightly, to wear down the interior surface of the bushing by friction and heat, until the bushing could slide smoothly over the rod.

How would you recommend evaluating whether or not the bushings are working well? In other words, what are the likely problems that will occur, and how will those problems manifest themselves in the print? For example:

1. If the bushings have too much static friction, how can that be detected? By printing small circular parts at low speed and checking the roundness of the result?

2. If the bushings become too loose over time due to becoming ground down by the guide rails, how can that be detected? I expect the overall print will become "sloppier" somehow, but are there any specific signs to watch out for that would indicate a too-loose fit of the bushings?

Edited 1 time(s). Last edit at 10/22/2021 08:11AM by qrp-gaijin.

Don't have the answer to your questions unfortunately, but also interested in using these. Going by the reports it seems like a better option than using cheap LM8UUs or knock off IGUS bushings. I have seen some people recommending that you ream the bushing to the correct size by using a drill bit of the same diameter as your rod, so I can't imagine the fit needs to be especially tight.

as long as its an open air frame this will work, but PLA will turn to putty if you end up enclosing the printer.

I designed some in FreeCAD earlier this year and printed them in PETG, I found 'sticktion' to be a problem with mine, even after applying some teflon lubricant spray. Best of luck, PLA should pose less issues in regards to sticky/friction properties. Another hack-ish kind of approach to 3d printed bushings was to print the bushing and use teflon tubing for the contact portion. I'm sure you can find some ideas on thingiverse for this.

I'd consider any of these options to be less than ideal, but will certainly work.I think the teflon tube approach would be the most forgiving in regards to mechanical tolerance since the tubes will flex to conform.

I dunno, if there were any major issues with them you'd probably hear about it from people who use them. And pretty much every first hand report I've found is positive. I think they probably have a few things going for them, firstly since they're clamped in place they don't really have an opportunity to warp, the (ideally) non-PLA part they're attached to keeps their shape for them. And secondly, the other face of the bushing is in contact with a solid steel tube, which represents a significant thermal mass. Even after several hours printing in an enclosure, I imagine that would do something to draw heat away from the bushings.

It seems like these can be a lot more forgiving than any bushing that's just a solid tube all the way through, whether it's teflon, polymer or brass. Probably because of the flex induced by the igus style flutes, which allow them to work with much less strict tolerances.

And one day you'll take the printer to a friend's house and stop for coffee or lunch on the way leaving the printer in the car in the sun and that will be the end of your printer.

Why would you use PLA for this instead of some other plastic?

PLA is completely awful for anything that you want to last, especially anything that includes sources of heat such as a hot end, bed heater, and stepper motors.

[www.youtube.com]

Edited 1 time(s). Last edit at 10/22/2021 10:45PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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obelisk79
I designed some in FreeCAD earlier this year and printed them in PETG, I found 'sticktion' to be a problem with mine, even after applying some teflon lubricant spray.

How exactly did you observe "sticktion" to be occurring? Did the "sticktion" actually impede motion during printing, causing missed steps and causing your prints to come out deformed? What sort of deformations occurred? What kind of models can be used to test for this?

yes it caused sticking, particularly when going from a non-motion state to moving. Once it was moving along the linear rod, it was fine. But it did cause issues on direction changes, trust me, when it happens, you will know. It was audible and resulted in artifacts in prints. I didn't use them for very long and it was a while ago so I can't really describe the artifacts.

Edited 1 time(s). Last edit at 10/22/2021 11:50PM by obelisk79.

If it took 15 minutes of sliding to get the tolerance you wanted, how long will it be before you get the tolerance you dont want

I've aborted this experiment after observing high static friction in some quick, unpowered trials with my Z-axis rods.

What I had failed to consider previously was the effect of slight misalignment on the amount of friction generated by the bearing.

With the printed PLA bushing, although it has a good fit with also almost no friction when sliding straight up and down along the rod's axis, in a simulated misaligned case -- where I pushed the top of the bushing to the right, and the bottom of the bushing to the left, while simultaneously trying to slide the bushing up and down the Z rod, there was a great amount of static friction detectable by hand. So a slight misalignment of the bushing with respect to the axis will suddenly cause a great deal of friction, unlike "real" LM8UU bearings. With an original LM8UU bearing (containing small ball bearings on the inside), there was no detectable difference in friction between the aligned case and the misaligned case -- real LM8UU bearings maintain low friction even if misaligned.

I did not use any lubrication on the inside of the PLA bushing. I expect that if I did, this would improve the performance.

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ComeWhatThey
Don't have the answer to your questions unfortunately, but also interested in using these.

For now, I've suspended further investigation because there are other higher-priority things I need to repair on the printer. I hope to return to this investigation sometime, and also would be interested in hearing any results of your trials.

FYI, Igus sells iglide printer filament designed specific for bearings. Might be an option if you need custom shapes or sizes.