I have a problem with my Y-axis being a couple degrees out of square. I have managed to fix it, but after a couple of hours of machine work the problem comes back. I have changed the belts, and changed the pulley bearings and it is still the same. I have added an image to better clarify the problem.
I thought maybe i should try changing the linear bearing blocks, but it is a bit of a complicated and a costly fix and im not even sure if it will help.
The machine is a chinese co2 laser with a 900x600mm bed.
If anyone has ever encountered similar problem, or have any idea on how i can fix this permanently i would appreciate the help.
When set up both sides should move the same. So it would seem there is movement between one side and the other. Coupler loose? Maybe some pictures of the drive system.
Hi. Thanks for the reply. There is no coupler installed anywhere on the machine. What i failed to represent on the sketch is that the transmission shaft is not actually directly connected to the motor but through pulleys that serve as a reduction gear box. Here is the image of it:
I’d suggest first fixing, then creating matched alignment markers on each pair of mating components, then running until the machine goes out of square.
Examining the alignment markers may give you an indication of where the issue is coming into play.
Have you checked to make sure that the Y-axis transmission shaft is square to the Y-axis rails and that all components are on a plane?
I fix it by disconnecting both of the Y axis belts and pushing the gantry all the way to the bottom. I use a square tool to make sure the gantry is square before reconnecting the belts.
I wouldn’t know where to place markers. I have not thought about checking the squareness of the transmission shaft relative to the gantry, and i will definitely check that out.
Pulley to gear, gear to shaft, pulley to belt, etc… basically anywhere where two components meet and transmit motion. You have unaccounted motion somewhere in the chain. Just need to identify where.
I have checked that also. I have come across a video suggesting a fix for this problem by losening the pulley and rotating it a little bit on it’s shaft. It did work at first but the problem came back. I made sure to tighten it good. The belts are brand new as i said, and they have metal wires inside them for strength. The old ones had something like cotton threads or whatever.
So , with a witness mark on the shaft and pulley, you can confirm the pulley is slipping but the set screw(s) aren’t holding it in position?
Remove the pulley and look for marks on the shaft created by the set screw(s). If none, the screws aren’t hard enough, or torque is insufficient, or screw type/material is wrong. Assuming the shaft is even moderately hard (likely if is straight and surface ground.) The screws need to be hardened cup point or cone point. Chinese hardware is notoriously soft and sloppy. Good hardware is expensive…American, German, or Japanese.
If yes, and the marks are sharp and round, the screw is coming loose. Loctite the screw.
If yes, but the marks are radial/smeared around the shaft, the shaft is too soft. Possibly consider a shaft/bearing adhesive (loctite green, 609)
What i was trying to explain is that i was the one that losened the pulley and rotated it around the shaft. The pulley was tight before, there was no slipping. After i finished rotating it i tightened it again. I losened the pulley to try to correct the axis alignment.
The teeth on the two drive pulleys must be aligned to keep the two belts in alignment. If they’re not aligned, then the gantry will be cocked by the misalignment.
If the setscrews in the pulleys rest on flats in the shafts, then that should happen automagically. You can check that by looking at the belt teeth as they enter or leave the pulley: both belts should have their teeth in the same position relative to their pulleys.
To align the pulleys on round (non-flatted) shafts, position the gantry where you can properly square it, then loosen one of the pulleys. Square the gantry by letting the loose pulley turn, clamp the gantry in position so it can’t move, then wiggle the loose pulley to let it settle in the proper position. Tighten the pulley and mark its position on the shaft so you can keep an eye on it.
The shaft may have a flat on one end and not on the other, so you’d align the pulley on the non-flatted end to the other one.
I would secure the gantry on the drive side and wiggle the other side to detect any movement. You have checked the belt attach to gantry for any looseness?
It is difficult to be 100% sure if the pulleys are aligned since they have flanges on the sides to prevent the belt from sliping off, thus covering the view. Comparing them in different positions it does look like they are aligned well. I didn’t remove the pulleys from the shaft before so i am not sure if the shaft do have a flat spot. When i was rotating the left pulley around the shaft it was very tight and difficult to rotate it. It has 2 tightening screws in it and even with them unscrewed it was very tightly fitted to the shaft. I aligned them now for the 3rd time the same way i did before and will monitor it closely. If it goes bad again i will try your idea with letting the pulley align itself by losening it.
They only way i could wiggle the gantry on one side is by removing the belts on that side. With belts attached there is no wiggle room whatsoever. It seems pretty tight. The belts are not loose in any way. I have checked multiple times and have tried different degrees of tightness to see if it has any effect, but nothing changed.
That’s a bad sign: it suggests the screws have raised burrs on the shaft that are scoring the inside of the pulley.
Although it seems unlikely, perhaps one of the belts is skipping a tooth or two as the machine runs. To check that, make a mark on each belt extending onto one tooth of its drive pulley. Those marks should always be aligned, so the next time the gantry gets cocked, take a look at those marks.
The X axis rails are not square to the Y axis rails so losen up the Xrails and use a square to align the Y to the X rails,put the square on the Y now align the X to the right angle of the square do this for both X rails, its a pain in the A to do this but I had a simular problem . In the factory they just mount the parts to the holes in the chasis and eyeball the alignment and many times the holes are off so some of the holes may be slotted.
