Axis not turning consistently



  • You have to tighten the nuts on the brass anti backlash nuts. I tightened mine until the screw wouldn't move or barely move when turned by hand. Then backed off the nuts by a 1/2 turn or so, letting the screw turn freely, but still minimizing play. I wouldn't use WD-40, since that stuff evaporates, 3-1 would work.

    If, after doing this, the stepper motors stall, then you have a misalignment. You'll want to go through each subassembly, loosen every bolt, then tight each end one at a time, moving that particular axis to one side as you tighten each side. You'll want to remove at least the Z axis to get to all the individual bolts there. This process is a pain in the ass, but worth if it is done right. You can test the z-axis before reinstalling it, by plugging it in, and using the stepper motor to travel the z-axis carriage.

    Hope that all makes sense! I'll see if I can do a video later today to demonstrate this.



  • @cesnyderces Let me ask a slightly different, related question. When I was putting things together I was not real happy with the bearings on the slide rails. The rails passed through, but it felt like there was "gravel" in the bearings. It just wasn't a smooth slide - jerky. Never stuck, but not smooth. At least 8 of the 12 bearings were like that to varying degrees. I didn't see anything on the bearing surfaces. Is this normal? Could I have a bad set?

    I will go back and readjust the backlash nuts as you suggest. Actually a very similar thought occurred to me overnight. I was contemplating doing something similar anyway.



  • The rails aren't as smooth as I'd prefer, but I think that's due to the chroming process used. Not as even as I'd prefer, but nothing that can really be done about that. Maybe some light sanding with 2000 grit wet/dry sandpaper, but I'd be hesitant about doing that, in case any slop occurs. Not really to worried about that. If you have any binding, then when you loosen the nuts, then things travel smoothly, then there's a misalignment. What's important, is to make sure there is as little backlash as possible, without missing any steps, and minimizing any binding. This might take several tries. Pretty sure I've had mine apart at least 4-5 times fine tuning the alignment.

    Mind you, I'm not an expert, but, I do now have a smooth traveling setup, and dead nuts accuracy. Still have to buy a mm based dial indicator, but with the slide calipers, it's working very well. Still learning how to get Fusion 360 gcode xport to work nicely with GRBL.


  • Active Member

    @Willie said in Axis not turning consistently:

    @cesnyderces Let me ask a slightly different, related question. When I was putting things together I was not real happy with the bearings on the slide rails. The rails passed through, but it felt like there was "gravel" in the bearings. It just wasn't a smooth slide - jerky. Never stuck, but not smooth. At least 8 of the 12 bearings were like that to varying degrees. I didn't see anything on the bearing surfaces. Is this normal? Could I have a bad set?

    I will go back and readjust the backlash nuts as you suggest. Actually a very similar thought occurred to me overnight. I was contemplating doing something similar anyway.

    I soaked my bearing in cleaner, then used WD40, to clean the cleaner, then added a drop of oil.



  • @mrmister

    That actually is probably a good idea, there's probably dust, dirt or manufacturing debris in there. Just have to be careful not to lose any of the bearings, course. I am concerned though, that petro chemical based products might break down the rubber material that houses the bearings. Not too worried mind you, as the bearing themselves are fairly cheap. Might be a concern for some though.


  • Active Member

    @cesnyderces

    I removed the bearings from the wheels. There are 3 pieces to the bearings.

    2 bearings
    1 Spacer between the bearings



  • I'd have to take a closer look at mine, mine looks like there are at least 10 mini bearing on three sides. Wonder if yours is different?



  • Well, I think I've got it going. Z-axis and X-axis were fairly simple. Loosened up the backlash nut a little and loosened and retightened various screws so things could line up a little better.

    Y-axis was a pain in the arse. First, it had the worst of the 6 slide rods. There were some ridges on that rod I was wondering if I was going to cut a finger on! Then there apparently was a slight bearing misalignment across the table for one of the rods. Giving one of the bearings room to move just slightly out got things moving reasonably smoothly. But the real problem was a misalignment between the screw and the stepper. Everything would move just fine till I'd couple the screw to the stepper. Then everything would bind up. Final solution was to move the stepper about a mm lower. Once I did that the stage moved much better.

    Now the funs done. I'll have to figure out how to actually use it!

    Thanks for the help. Your ideas got me going in the right directions.



  • If you move the gantry to one side, then tight then screws down, gently at first, then move the gantry to the other side, tighten it down gently, repeat, until things are locked in place, it should move smoothly beyond that point. That goes for all axis's too. If it's binding at any point, then it's still misaligned. Trust me when I say that when you think it's good, it's got a LOT of room for improvement. lol.



  • Just as a final comment, things are working very well at this point. A little bit of tweeking as suggested above helped.

    But the biggest improvement was sparingly lubricating the lead screws. I had a can of spray silicon lubricant intended for the bearings and chain on my garage door. The can says the lube forms a dry lubricant layer that "doesn't attract dirt". I sprayed a bit of the lubricant into a plastic cup and used a Q-tip soaked in the liquid to apply the lube sparingly to the screws. That made a huge difference. After application turning the screws by hand was noticeably easier. And the chatter the anti-backlash nuts were making completely disappeared. All the axis run smooth as can be now.


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