Prusa's White Lies
Tired of fighting these two white lies Prusa tells customers:
- Prusa bearings are pre-lubricated.
- Belt tension is shown on the LCD status screen.
Arrgh.
RE: Prusa's White Lies
At least PLA is recyclable.
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Prusa's White Lies
The MK3S I just assembled had bearings that appeared to be completely dry, the first MK3 I assembled had the bearings soaked in Chi-Lube. Had to clean them before I lubed them. I lubed the new printer with Speed-X. Not sure if it's any better than the Finish Line PTFE grease I used on the first one though.
I wasn't able to determine exactly what the heck the belt status number meant from reading online, mine reads X 283, Y 282 but I just keep tightening until I just couldn't get the belt to skip if I held the pulley shaft with pliers and pushed on the table or extruder. My numbers are supposedly too high but I'm not going to tighten any more unless it starts shifting layers on me.
Do you folks have any idea how the Einsy arrives at the belt tension numbers?
RE: Prusa's White Lies
basically measures motor current
RE: Prusa's White Lies
basically measures motor current
So if that's the case then a bound up axis with a loose belt could show the same reading as a loose axis with a tight belt? I guess the takeaway is that you need to ensure each axis slides freely on it's own, the steppers aren't rubbing anywhere, and the belt has enough tension not to skip teeth.
Belt Tensioners? Was: Prusa's White Lies
I believe there are belt tensioning tools. Kind of like a pliers with a gauge for belts. Has anyone tried one?
Also, I use food grade synthetic lube
I am the inveterate tinkerer. I can tink up most anything.
RE: Prusa's White Lies
I believe there are belt tensioning tools. Kind of like a pliers with a gauge for belts. Has anyone tried one?
Also, I use food grade synthetic lube
Here is a home made one for the XCarve:
I am the inveterate tinkerer. I can tink up most anything.
RE: Prusa's White Lies
thingiverse belt tension tool
RE: Prusa's White Lies
I made a simple balance beam with weight that tugs up on the lowest belt with ~8 ounces or 250 gram force... deflection goal measured at 15/64" plus or minus. The math provides about 8 pounds belt tension for the 15" X belt span. The 12" Y belt span requires a bit less deflection. I arrived at 8 pounds belt tension from the Gates spec of 2 lbf minimum and 25 lbf maximum (6 mm belt). Motors have a radial load max around 11 lbf at 1/2 inch.
A fish scale or trigger pull gauge work equally well to pull on the belts.
ps: I have run with 30 lbf, down to loose. I can perceive little difference between 5 lbf and 30 lbf (except belt stretch at 30 lbf requires recalibrating X & Y).
RE: Prusa's White Lies
thingiverse belt tension tool
Thanks David.
I am the inveterate tinkerer. I can tink up most anything.
RE: Prusa's White Lies
Keep in mind that Thingiverse tension tool is a relative measure, and not calibrated to anything like lbf.
RE: Prusa's White Lies
You forgot one
#3. The Raspberry Pi Zero W is a great way to add Octoprint
RE: Prusa's White Lies
I didn't hear about the need to add more bearing lube until recently - I assembled mine in March. I guess I'm going to need to grease up the rods and hope that is sufficient?
RE: Prusa's White Lies
I didn't hear about the need to add more bearing lube until recently - I assembled mine in March. I guess I'm going to need to grease up the rods and hope that is sufficient?
The grease seals work both directions: keeping grease in and out. For quickest effect, best to apply machine oil to the rods and let that work through the seals. Grease can eventually work inside due to wear and lack of precise rod alignment, but may take longer to do any good. A Misumi engineer recommended normal car engine oil as an emergency lubricant: essentially anything you have available is better than running on the anti-rust oils the bearings ship with.
RE: Prusa's White Lies
Having built my (squeeky) MK3/S, I am about ready to lube the bearings.
Are there any guidelines on the easiest way to remove the bearings without doing a complete disassembly?
I kind of hate to mess with it... It is printing beautifully.
RE: Prusa's White Lies
No easy way - full disassembly is easiest. Just get grease or oil on the rods and keep them lubed until you get time to do it right. My original bearings lasted almost 3 months. At that point I replaced them with Misumi bearings which lasted almost twice as long, but I set them on the original also worn out rods, a mistake because I thought I could get away with turning the races to unused areas of the rods.
RE: Prusa's White Lies
I've just run the life expectancy numbers of typical LMU bearings on a 3D printer like ours ... I am NOT impressed. One manufacturer states life expectancy of their linear bushings as 50 kilometers. On a Prusa MK3 printing a 210 mm square box at 35 mm/s, that's only 198 hours. lmao. What a bunch of Whoop Arse.
Printing smaller things extends those hours a bit, but not by a large margin since there is a minimum speed the printer obeys... so to be gracious, I'll say bearings have exceeded their base spec at at 250 hours. If I am very generous with loading factors (50 Newton / 11 lbf bed load) , we might get 4x the base value: 1,000 hours.
Not surprisingly, that 1000 hour estimate is about what I am experiencing on Y before the bed starts doing odd things and I have to add rubber bands to hold things together and order new bearings.
RE: Prusa's White Lies
I've just run the life expectancy numbers of typical LMU bearings on a 3D printer like ours ... I am NOT impressed. One manufacturer states life expectancy of their linear bushings as 50 kilometers. On a Prusa MK3 printing a 210 mm square box at 35 mm/s, that's only 198 hours. lmao. What a bunch of Whoop Arse.
Printing smaller things extends those hours a bit, but not by a large margin since there is a minimum speed the printer obeys... so to be gracious, I'll say bearings have exceeded their base spec at at 250 hours. If I am very generous with loading factors (50 Newton / 11 lbf bed load) , we might get 4x the base value: 1,000 hours.
Not surprisingly, that 1000 hour estimate is about what I am experiencing on Y before the bed starts doing odd things and I have to add rubber bands to hold things together and order new bearings.
Sheesh. Thanks for reaffirming my decision to ditch the PR bearings and use vesconite ones on X/Y. At least those don't also take your rods with them when they wear out...
RE: Prusa's White Lies
Sheesh. Thanks for reaffirming my decision to ditch the PR bearings and use vesconite ones on X/Y. At least those don't also take your rods with them when they wear out...
Don't you want the rods & bearings paired, or at least from the same manufacturer? In other words: You'd want to replace both rods & bearings at the same time, no? (Mine are fine, just reading ahead.)
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Prusa's White Lies
Sheesh. Thanks for reaffirming my decision to ditch the PR bearings and use vesconite ones on X/Y. At least those don't also take your rods with them when they wear out...
Don't you want the rods & bearings paired, or at least from the same manufacturer? In other words: You'd want to replace both rods & bearings at the same time, no? (Mine are fine, just reading ahead.)
Vesconite are plastic bushings specifically machined to the Prusa stock rods. No need to replace 'em, and they're dirt cheap compared to igus or misumi. IIRC doing X/Y with the $3 offering would have cost $18.
https://www.vesconite.com/3d-printer-promo/
I have a thread on my experience with them here: