RE: Skewed XY-Plane (Z Rods, Heatbed)
They should have at least 2 part numbers because the cable length is different. I ordered the ones with the long cable and the pitch is correct.
[...]
In the next days I will check the C1 of a colleague. It was one of the first batch and I am quite curious...
Yes, of course the motors configurations with different cable lengths have different part numbers. I was referring to a differentiation by lead screw pitch.
If your colleague's Core One was factory-built, I think it is less likely to have this issue. My theory is that the problem arises (mainly?) with kit builds, because the kits contain motors from two different batches: Four in the pre-packed motor set (which has the motors that also go into an MK4s), and then one lead-screw motor is added separately and presumably comes from a different shelf, picked at a different time.
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit. I never get built printers from Prusa, I like the building experience 😉
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit. I never get built printers from Prusa, I like the building experience 😉
I was referring to your colleague's Core One, which you said you planned to look at next.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Well, I have a kit and it has the left screw pitch off. And I also have a prebuilt one and it has the rear screw pitch off. So it's not just the kits that suffer from the screw plague. Also it's not like these are 4 short ones and 2 long ones. Instead it's: 2 shortest, 3 +- equals, and 1 the tallest. Something like -0.25mm, 0, and +0.5mm. Unfortunately I don't have sufficiently precise tools to measure in absolute lengths. But the bad news it's NOT just TWO batches of screws.
RE: Skewed XY-Plane (Z Rods, Heatbed)
It was also a kit.
And yes, I checked it today. Same issue. The front left motor (same as with my months older Core1). Swapped the motor with a good one. At least the trapezoid nuts did not bind, they ran freely.
I also adjusted the belt tension with the new resonance method, which is extremely useful. That is a very good feature.
Next week I will deal with support when I'm back in the office.
RE: Skewed XY-Plane (Z Rods, Heatbed)
For a simple sanity check, try the test that @petulf suggested. It won't be affected by other causes of skew.
RE: Skewed XY-Plane (Z Rods, Heatbed)
For a simple sanity check, try the test that @petulf suggested. It won't be affected by other causes of skew.
Yes, that's the most direct test -- a distortion-free measurement of each screw's pitch, without the need to remove the screws from the printer (yet) and without the risk of mis-counting threads.
Just don't expect Prusa support to buy into this measurement. At least when I spoke with them a few months ago, they were apparently not aware of this forum thread, and certainly not of this measuring method.
RE: Skewed XY-Plane (Z Rods, Heatbed)
I printed a measuring tool. A U-shaped part, 224mm long and every 20mm a small nub. It fits on the rod and shows if there is a problem or not. I can post it if you like.
RE: Skewed XY-Plane (Z Rods, Heatbed)
Well, I have a kit and it has the left screw pitch off. And I also have a prebuilt one and it has the rear screw pitch off. So it's not just the kits that suffer from the screw plague. Also it's not like these are 4 short ones and 2 long ones. Instead it's: 2 shortest, 3 +- equals, and 1 the tallest. Something like -0.25mm, 0, and +0.5mm. Unfortunately I don't have sufficiently precise tools to measure in absolute lengths. But the bad news it's NOT just TWO batches of screws.
I remember discussing this with @jürgen a few weeks back in another thread. Back then Prusa support, if I remember correctly, even gave the tolerances they would expect from the motors, and they all will fit the tolerance, as such there is no bad batch. The problem is that different production runs (or even multiple suppliers) of the motors got different deviations from the tolerance and when you get parts from batches with large deviations you get the skew. Upgrade kits are probably more impacted as the new motor is nearly sure from a different batch than the mk4s motors, again if the deviations are compatible you won't notice much, if they diverge ... skew.
Aside from Prusa adding more checks when building a kit nothing we can do but ask for a replacement.
Probably another reason for Prusa to move away from the kits (buikding in house and testing for skew may be more efficient than checking all rods beforehand).
RE: Skewed XY-Plane (Z Rods, Heatbed)
Please post your tool. Great idea!
RE: Skewed XY-Plane (Z Rods, Heatbed)
Just to add another datapoint to the collection, I put a Starrett #98 level on the bed, leveled it with a few sheets of paper on one end (my bench isn't perfectly level) and ran it top to bottom. I did this left-right and front-back. The difference over travel, left to right, was 2 divisions, which is 0.010"/foot or about 170 arcseconds. Front to back it was half that. My Core One is a kit purchased during the Black Friday sale.
I'm not sure it's reasonable to expect better than that from rolled leadscrews. Ground, sure, but the price of ground screws is probably an order of magnitude more. It shouldn't have any effect on prints because the error would be distributed over a huge number of layers. It seems to be linear. The only effect would be the top to bottom parallelism of a tall print, an issue one would have to deal with even with an injection molded part.