Slight slop in the right hand z-axis

Hi, I’ve had my AO-101 for about 2 weeks now and just found that I can ‘click’ the right-hand x-axis bar mount on the z-axis, up and down by about a full mm. Obviously this could put the z-axis out of calibration way too easily. The left-hand side has no slop at all and I’m sure this is the correct state.

Any ideas what could be wrong?


There are 4 screws on the X axis bar clamp. You should be able to tighten the bar clamps. Jog the Z axis up and down afterwards to see if the movement in the Z axis is smooth and consistent.

What he is talking a out is repeatable on my machine too. Tightening the claps won’t fix this problem. What happens if you grap the z-axis on the right side you can move it up/down with little effort. The left side with the x-axis motor doesn’t do that. It moves where the right threaded rod goes through.

I received my AO-101 a few weeks ago with similar slop in the z-axis. Originally my right-hand z-axis was so bad that the left side would move and then the right side would jump about 1/4" in the direction of travel. It turns out that the 4 screws holding the right x-axis end-clamp together were totally loose and tightening those made a major improvement.

There still is a slight (approx. 1mm) amount of play on both x-axis end-clamps. Either end can be moved up/down and a slight noise can be heard as the z nuts hit the top/bottom of their cavities. I’m not sure this could be fixed by tightening, but would probably need some sort of spring washer inside to take up the slop.

I don’t know that this slight amount of slop is a problem though, since during printing, the z-axis only travels up and there’s probably a negligible amount of pressure being exerted upward by the print itself on the z-axis. This kind of slop would be a major problem with a mill since the object being milled would be exerting forces against the cutter as it plunges into the material.

My Lulzbot AO-101 is now doing this exact same thing as well. I heard a clunk when I was homing the axis today. Mine’s about a week old. I didn’t understand your post exactly but now I see the problem in my own bot and it makes perfect sense.

I noticed mine only clunks on the down stroke. This is only after about maybe 12 hours of actual printing.

To reproduce, I gained some Z, then dropped a little in increments. The right hand of the Z carriage sticks and falls every so often.

I am also concerned that the two linear rails are not parallel, and I noticed out of the box my acme screws have a TON of wobble. It’s a bit worrysome.

Keep in mind, in any mechanical system backlash (the technical term for this slop) is unavoidable. Mechanical parts like the acme z-axis screws and the z-nuts don’t fit perfectly. If they did, there would be so much friction, you’d need a much bigger motor and you’d probably melt the end-clamps. So, a tiny amount of play in the nut is good, but what you don’t necessarily want is the slop between the z-nut and the end-clamp in the z-axis.

I didn’t specify the x/y-plane because I believe the end-clamps are designed specifically so the nuts are slightly loose. This allows the nuts to move horizontally in the x/y-plane so that if the acme screws aren’t perfectly straight, and wiggle back-and-forth as the z-axis moves up and down, the x-carriage doesn’t shake violently and damage itself. Keep in mind the slides with the pillow-block bearings are the precision part of the z-movement that keeps the print-nozzle aligned in the x/y-plane.

Yeah, it’s a bit different than backlash here… but yeah… I know… It’s not needed really because during a print it’s always going in one direction so the slop like that on a 3dp doesn’t matter. The backlash (to my understanding) happens all at the change of direction point. This was more… energetic and rhythmic and happening 3 or 4 times every 10 mm.

I was also starting to have issues with it sometimes putting down a great first layer and sometimes not. I’m doing some huge prints so it suddenly matters (apparently… I’m a bit new to 3d printing). I checked the tightness on everything and it was ABS tight to me.

I started looking and poking and I think I figured out what was up on my bot though. One of the two motors in Z had spun independently about 1/2 turn or maybe 1.5 turns too much. Not sure how, but easy fix.

I ran the machine through a cross pattern calibration and it was fairly clear. I was able to carefully rotate the motor coupler while the machine was running (since I’ve watched quite a few cals now I was aware when Z fires I was ok with the risk) and thus quickly tram the machine back in. Sorta. Anyway, after doing that the clunking stopped. I did the normal cal thing and everything pretty spot on. I also wiped down the ways… er… rods? with some kimwipes and the low pitch growl stopped.

I think I’ll invest in a dial indicator and tram the machine out as part of my calibration routine.

Yeah, one of the first things I did after tightening up my right x-axis end-stop screws was to check that the height on the left/right sides of the x-axis were the same. Since there is nothing coupling the left/right z-screws to one another they could potentially become unaligned causing the slides to bind. I did this by laying a depth gauge across both x-axis rails on one side and measuring the depth to the aluminum frame and then doing the same for the other side. I also used this method to level the print bed.

My right Acme screw also has some wobble in it. I took it out, rolled it on a table, and verified it has a slight bend to it. I don’t think it’s affected any of my prints though.

The biggest things I’ve found affecting my prints are a dirty print bed (need to clean with acetone often), and the need for some active cooling. I think I may try to print a fan mount out to fix that.