How to square an XL Core XY Gantry
I am replacing the motor mounts and core XY plastic parts with new PCCF parts. With the belts off I was checking the gantry, and it's not square to the front. Per the belt tensioning instructions it's important that the gantry be square with the front.
Prior to disassembling everything I was able to force the gantry square with the belts, however this seems wrong to me because your essentially putting a bind on the linear bearing block by forcing it crooked with the belts.
I've contacted support and they said they'd get back with me.
I'm curious if anyone else has removed the belts and checked this, and if it was crooked, how did they fix it.
I'm a mechanical engineer and have designed many machines using pairs of linear rails, and understand a few different ways to align 2 sets of rails, however in this case I'm not sure what the alignment is based off of. I'm hoping they'll provide some assembly instructions, as I assume they have some, since the gantry comes preassembled.
Any input would be appreciated as well
See the video below explaining the issue
Best Answer by Brian:
I'm happy to report that after disassembling the gantry and replacing the plastic parts with the PCCF ones I printed, the gantry is perfectly square on both sides now and touches evenly on both sides when moved all the way forward. I can only assume either the original parts were out of tolerance somehow, or it was tweaked during the original assembly at Prusa.
RE: How to square an XL Core XY Gantry
Suggest you measure the length of the top rails for starters.
You need a benchmark before you start to investigate.
What is the plus minus tolerance of rail lengths, a question maybe for the Prusa engineers.
But is this GAP really important, have you tried printing a say 80 mm cube? and measured.
RE: How to square an XL Core XY Gantry
Suggest you measure the length of the top rails for starters.
You need a benchmark before you start to investigate.
What is the plus minus tolerance of rail lengths, a question maybe for the Prusa engineers.
But is this GAP really important, have you tried printing a say 80 mm cube? and measured.
I have measured the length of stickout of the rails from the extrusions and it's nearly identical, within .05 mm. The engineers were smart in the fact that the length of the rails is not important because there is a clearance in the extrusion end caps for the rail. I.E. the length of the rails will not affect where the front stops are.
Unfortunately I did not print a calibration cube because I wasn't aware this issue existed until I already disassembled the printer. Prior to taking it apart I had no apparent issue with the printer other than VFA's along the x and y axis.
As far as if the gap matters, I think it does because in the belt tensioning instructions it wants you to ensure that the gantry sits flush against the front stops. I'm my case this is only possible if I force it against the stops with the belt on the right side. This leads to unequal belt tension (which I did experience) and also forcing the linear bearing to be in a slight bind due to the belt forcing it crooked.
Currently I'll wait for customer services response, but I'm wondering if there might be some play in the gantry mounts that might allow me to move the right side forward. But this is all a guessing game unless I know what I need to align the gantry to. I'm hoping they'll provide some sort of assembly instructions.
RE: How to square an XL Core XY Gantry
I'm happy to report that after disassembling the gantry and replacing the plastic parts with the PCCF ones I printed, the gantry is perfectly square on both sides now and touches evenly on both sides when moved all the way forward. I can only assume either the original parts were out of tolerance somehow, or it was tweaked during the original assembly at Prusa.
RE: How to square an XL Core XY Gantry
Maybe too soon to ask but did squaring it up fix any printing issues at all, or was it just a conveniently timed find?
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RE: How to square an XL Core XY Gantry
Maybe too soon to ask but did squaring it up fix any printing issues at all, or was it just a conveniently timed find?
I haven't finished putting it back together yet. I should be able to do some test prints tomorrow.
RE: How to square an XL Core XY Gantry
After replacing all of the PETG parts with PCCF, installing the new o-rings rings, and swapping the smooth pulleys for toothed pulleys on the x axis, I can confirm that there is no noticable difference in the print quality.
Apparently the slightly skewed gantry wasn't causing any immediate issues, likely because I was pulling it square with the belts. Probably long term it will help with wear on the bearings because it's not being pulled slightly crooked. Also, now, my belt tension is perfectly even on both sides, where before it had to be about 10 hz higher on the right side in order to pull the gantry square with the front.
As a disclaimer my VFA's were not bad to begun with. I mainly did this upgrade because I wanted to replace the motor mounts with PCCF, so I went ahead and upgraded the o-rings and the pulleys at the same time as it didn't make sense to me to run the toothed portion of the belt over the smooth pulley.
As a final note, I will say that the printer sounds different now. It must be that the PCCF motor mounts resonate different than the PETG ones did.