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? https://reprap.org/forum/read.php?1,886655,886655#msg-886655 Fri, 12 Jun 2026 04:20:24 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?1,886655,886677#msg-886677 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886677#msg-886677 Navin_R_Johnson General Sun, 24 Oct 2021 13:16:08 -0400 https://reprap.org/forum/read.php?1,886655,886671#msg-886671 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886671#msg-886671
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.

Quote
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.]]> qrp-gaijin General Sat, 23 Oct 2021 07:36:40 -0400 https://reprap.org/forum/read.php?1,886655,886670#msg-886670 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886670#msg-886670 MechaBits General Sat, 23 Oct 2021 07:33:50 -0400 https://reprap.org/forum/read.php?1,886655,886669#msg-886669 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886669#msg-886669 obelisk79 General Fri, 22 Oct 2021 23:46:30 -0400 https://reprap.org/forum/read.php?1,886655,886668#msg-886668 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886668#msg-886668
Quote
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?]]> qrp-gaijin General Fri, 22 Oct 2021 23:29:46 -0400 https://reprap.org/forum/read.php?1,886655,886667#msg-886667 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886667#msg-886667
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]]]> the_digital_dentist General Fri, 22 Oct 2021 22:40:14 -0400 https://reprap.org/forum/read.php?1,886655,886665#msg-886665 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886665#msg-886665
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.]]> ComeWhatThey General Fri, 22 Oct 2021 20:18:17 -0400 https://reprap.org/forum/read.php?1,886655,886663#msg-886663 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886663#msg-886663
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.]]> obelisk79 General Fri, 22 Oct 2021 17:26:41 -0400 https://reprap.org/forum/read.php?1,886655,886661#msg-886661 Re: How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886661#msg-886661 ComeWhatThey General Fri, 22 Oct 2021 10:27:02 -0400 https://reprap.org/forum/read.php?1,886655,886655#msg-886655 How to judge quality of printed PLA LM8UU/LM6UU bushings? https://reprap.org/forum/read.php?1,886655,886655#msg-886655 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?]]> qrp-gaijin General Fri, 22 Oct 2021 06:09:22 -0400