Hi all, I have a LEAD1515 with the high Z mod. Every now and then the right hand Y axis will bind. The left hand Y axis will keep moving while the right hand one makes the dreaded binding noise. I rush to hit the e-stop to stop the X gantry ends getting bent out of shape. To fix this I turn off the controller so I can turn the Y axis by hand by turning the stepper coupler. I notice that the closer I move that axis to the front of the machine the more difficult the coupler is to turn by hand. If I loosen the nuts on the two lead nuts on the right hand Y axis then the coupler turns freely. If I tighten those nuts up tight then it's very difficult to turn. I'm guessing this is related to why it's binding. Question: how tight should the lead nuts be on the gantry plate that's mounted to the Y lead screw? How can I adjust these so they're not loose, but also so they allow the Y axis to move without binding? When it binds like this I normally clean both Y screws with a cloth and lubricate then with "dry" PTFE chain lube. Does anyone have any tips on what to do to minimise binding like this? It's only happening at 3600mm/min. The X axis will move at 4200mm/min easily. I've had the Y axis moving at 4200 in the past. Would it benefit from removing the two lead nuts and replacing it with a single centred anti backlash nit like the Y axis has? How can I tell if the nut blocks are worn out? Do I need to use a shim so that when the nuts are tightened up it doesn't warp the screw (assuming that's what's happening)? Also, is there a reason that these machines don't use brass nuts? I have another home built machine that has flanged brass nuts and they work very well. Thanks.
The nut blocks should be tightened to the gantry plate tight enough to stop it moving and no more. When adjusting the nut blocks, tighten one to the plate, gently squeeze them together and tighten the second - the aim is to have each nut block touching either side of the thread, but not gripping it tightly. Check bearing seating in the end plates to make sure the leadscrew is not being pulled out of alignment. Lubricate the leadscrew with DRY ptfe or silicone spray ONLY - never use oil or grease. My machine has been in regular use for four years without any sign of the nut blocks wearing significantly. Alex.
In some installations there should be 3mm spacers under the nuts - review the assembly video of your machine to see if you forgot a step
If you included a 1mm spacer on the wheel axles between the wheel and the 6mm spacer you need to include a 1mm spacer between the 3mm spacer and the nut block to get everything to align properly. 5.5mm (1/2 wheel thickness) + 1mm shim + 6mm shim = 12.5mm to face of plate 2.5mm (screw offset from wheel CL) + 6mm (1/2 nut block thickness) + 1mm shim + 3mm shim = 12.5mm to face of plate
Thanks for the feedback everyone. I'll try these troubleshooting steps out. I have a couple of extra questions if you don't mind: When I have the nut blocks tightened up adequately would you expect it to be much more difficult to turn the stepper coupler by hand, or should it be about as easy to turn? This will give me something to aim for. How I do make sure the lead nut is square? I.e. that the hole is perfectly in line with the lead screw? I have been moving the gantry under power slowly (1000 mm/min) with the nut loose with the expectation that the nut with naturally sit square. Is this the right approach?
Should be easy to turn. The idea is to dial out radial free play and prevent whip by having two nuts - not to clamp. Your squaring approach is good enough - its not particularly sensitive to that
My nut blocks have two hexagonal recesses on one side to take the locking nut. On the other side it has two 2mm deep recesses that are exactly 9mm in diameter. The 3mm spacer is 10mm in diameter, so it's only touching the nut block 0.5mm around this recess. I suspect that me tightening the nut block into place has deformed the edge of this recess and now it's not spaced properly and this is what's causing that axis to bind. Is the nut block supposed to have a recess on the side that's flush against the plate? It seems like an odd design especially considering how the spacer sits over the hole. Here's the exact nut block I have, you can see the recess on this page: https://www.makerstore.com.au/product/8mm-acme-nut-block/ Thanks, Allistar.
That recess is (I believe) a hangover from an earlier design (the nut blocks have been used in several different machines and for several years). Some suppliers are beginning to use a nut block without that recess, but in the meantime a rectangular 3 mm spacer across the whole nut block (with holes for the screws obviously) solves that problem. Alex.
Thanks Alex. I happen to have 3mm acrylic which is nearly perfect. With 2 sheets of paper I can get the full width to 15.01mm which is good enough for me. When I pulled the nut blocks out I could see that the 3mm spaces had sunk into those recesses quite a bit. The total thickness was only 14.5mm. I'm in the process of replacing the nutblocks with new nutblocks and acrylic spacer and 'll see how it goes. It is difficult to remove and refit the nutblocks without pulling the gantry apart!
The 9mm recess was for the screw head to be recessed. Not sure if there was ever a design where this was really necessary. But yes it can cause problems. I've had to stuff a couple Mini V Wheel Precision Shim (openbuildspartstore.com) in the hole on occasion. Note: if you have the extra washer in the wheel stack, you'll need to shoot for 16mm here.
Just a note, that the recess has been there for a long time, as have the spacers. Used in all the designs, over many many machines, actuators etc without issue. The issue isn't the recess - but I would say if that happened, the screws tightening the leadnuts to the plate was overtightened quite a bit.
I don't have the extra washer in the wheel stack. The plate to plate gap on my machine is nearly exactly 43mm. What would cause me to need an extra spacer in the stack? Is this for a different size aluminium extrusion, or narrower wheels maybe? The left hand Y axis is set up the exact same way and it moves very freely when turning the coupler manually, so I don't think the other side should be any different.
