Traditional bushing 8x15x24mm (LM8UU)

thingiverse

Human: Traditional bushing for 8mm rods. Don't use MoS2 grease for printed bushings, it's a total failure. PTFE spray can oil works great with PETG bushings if wiped dry after saturation. I haven't tested silicon-based or lithium-based lubricants yet. I searched for graphite dry lubricant spray as my first choice but couldn't find any in my area so I chose PTFE spray can oil instead and it seems to work fine if wiped dry after saturation. My initial attempt at greasing the Y-axis used MoS2 dark grey grease, which worked perfectly with linear ball bearings. However, when I tried using MoS2 dark grey grease on printed bushings made of PLA or PETG, they didn't work at all. The bushings seemed to be working fine initially but after one day or less, they started to get stuck on the rods and the stepper motor struggled with resistance to move. No-go for MoS2 grease and printed bushings! I printed a new batch of PETG bushings and tried them with sprayed PTFE oil (tens of thousands of PTFE balls per mm², micro gap fillers). I used a threaded rod to grind the bushings to tolerance by slowly moving the bushing back and forth along the threaded rod while rotating it. Grind for a bit, then check the bushing against the bearing rod, grind some more until satisfied with the tolerance. If the bushing slides easily along the rod when dry but sticks when saturated with PTFE spray can oil, you're good to go! I ground the bushings until they slid effortlessly by gravity on the rods but stuck to the rod when saturated with PTFE oil. When satisfied with the tolerance, I saturated both the rods and the bushings with PTFE spray can oil and then thoroughly wiped them clean with toilet paper, inside and out. When wet, the bushings didn't fall by gravity on the rods; they were sucked to the rods due to viscosity, but when wiped clean, they fell easily and quickly along the rods. Lesson 1: MoS2 dark gray grease works perfectly with linear ball bearings if applied inside the bearings. The linear ball bearings run quiet and smooth with MoS2 dark gray grease (bearing quality may vary). Lesson 2: MoS2 grease is completely useless for printed bushings, neither PLA nor PETG! At least not with fine tolerances between the rod and bushing. Lesson 3: PLA might be partially dissolved by MoS2 and refined oils, I'm not sure, but it could be why the smoothness feels okay at first but not the next day. PETG is resistant to oils and greases, or so they say. Lesson 4: PTFE spray can oil works great with PETG bushings if you saturate the inside of the bushings and on the rods with PTFE oil, move them back and forth rapidly by hand for a while, and when done, wipe them completely dry inside and out. It's essential to understand that if wet by oil (or grease), the bushings stick to the rod due to viscosity and boundary layer adhesion. Wipe everything dry using fresh toilet paper after saturated with PTFE spray can oil, remount, and realign carefully, and you should end up with a quiet linear PETG bushing heatbed – I did!