I have a Bulkman3D CNC with linear rails and ball screws using Nema 23 motors. I have not used it for a while and tried to re-commision it after clearing a bit of rooom.
I noticed the left hand Y Axis was skipping occasionally and, after few tests, decided this must be down to it being out of square.
My question is what is the best way of squaring this up.
It has end plates which connect to the profiles and hold them together and then intermittent profile along the length on the bed. I currently have the Gantry removed after a general clean up, have applied some grease to the bearings and wanted to discuss possibilities before re-attaching the gantry ( in case any suggests it should be removed first). Is there a simple solution for this or am i over thinking as usual ?
Any help appreciated. Any questions will be answered to the best of my ability.
Did you check to see if the couplers are snug? I would also take a tape measure and Measure across opposite corners of the Y axis extrusion to see if the measurements are the same. That is back left to front right and visa versa. If they are way off, then you may be out of square. That’s where I’d begin.
Hi and thanks for the reply, I am fairly sure it is out of square, by aroung 7 - 8mm i think.My question was more to do with the best way to square considering the way it is assembled. if it is “twisted” (it was the left hand rail that was skipping) what is the best way to re-align and tighten so it doesnt move again, and i am i better doing it while the gantry is in place or do a preliminary without it then again afterwards. Its pretty hefty bit of kit when assembled and i feel moving it again once the preliminary is done ( no gantry) would be detrimental to the process ?
Well on my openbuilds rig, I measured from the front edge of the X axis wheel plates to the front edges of the Y axis endplates Iusing a machinist 6" rule divided into 64ths. I found that easier than using a digital caliper. The right was farther back than the left yielding a longer measurement. I undid the coupler at the right lead screw so I could even it up and then retightened the coupler screw. I used some aluminum foil as a shim too on one of the upright parts and the x axis. So in this case squaring it up was pretty easy. The only real play is in the connecting corners. Mine is 1000mm x 750 mm at the moment.
It looks like you don’t have a flat bed; that will make it hard to get coherent motion.
For mine, I started building my table with a thick piece of MDF as a fairly stable planar reference, built the table to the MDF as a reference, and then attached the router to the flat table face to hold it square and flat.
This thing is very heavy, it sits quite sturdy on the surface (or has so far).
I reassembled today and set it up as best i could, i know it is still about 5mm out when then gantry is fully forward but as the limit switch is on the side that is slightly out i moved the switch forward so it never gets to skew as bad as before. i have cut some holes in the Ply bed thats sits on top of the frame, and it didnt skip at all so i have my fingers crossed. i dont really do anything that needs precision and will re-visit if i find a need to.
Are both y axis beams the same length? If so, you need to get the twist out of the frame. As mentioned measure diagonally across the frame both directions. If you do not build it square, it will never cut square. Also, once it is built square, jog the gantry up to the front of the frame until both sides touch the front. I do this regularly with my machine to re square the gantry to the frame y axis beams. But this only works if the frame is built square.
Before chasing square, I’d first separate “binding” from “lost steps.” With the gantry off, each Y side should move smoothly by hand over the full travel with the motors disabled. If the left side has any tight spots, check rail alignment, ball screw alignment, coupler/grub screws, bearing blocks, and whether the screw is slightly preloading the carriage.
For squaring, I’d loosely assemble the frame, measure diagonals corner-to-corner, and adjust until they match, then tighten gradually while rechecking. After that, refit the gantry with the Y carriages/plates slightly loose, jog it gently to let things settle, then tighten in stages. Also check that both Y motors are moving the same distance and one isn’t losing torque due to wiring, driver current, acceleration too high, or a sticky connector after sitting unused.
I am lucky enough to have got a big oak desk for cheap when I first got my machine. I put crazy wheels on the legs so I can move it around, I then extended the top so it’s 5’ x 5’ and 1 1/2" thick. So there’s that.
Corner by corner squaring is the most accurate way to know that it is square. If the machine is going to stay in the same place for a long time I would mount it with some aluminum angle to its platform. But make sure the platform is ‘flat’ first.
I would also dis-assemble the linear bearings and clean the raceways, balls, and wipers. The rails as well. It’s worth the time knowing that that is not the source of resistance. The ball screws as well, But patients is the pain there. I dis-assembled my ball screws and cleaned them and it took only four hours each…Yay!
That and cleaning your end bearings will give you the confidence that the only thing that can ‘make’ the machine skip a ‘beat’ has to be electronic. EMI from a power cord that touches a stepper wire, or a loose connection. Chasing EMI is like chasing lightening…
