trident downward z motion sounds like a grumpy walrus

[swh41]

Hi. I just built my first Trident, LDO Rev D. It is working, but somewhat rapid downward z motion (as when homing or z-tilt) sounds like a grumpy walrus. The cause is vibration of the rear lead screw. I can silence it by damping the vibration with a finger near the top of the lead screw. I don't know the exact physics of the vibration/chattering, but sure it is my fault. I failed to notice that LDO's recommended printer config did not did not default to the correct TR8x4, wondered why my prints were short, and when I finally realized the problem, in my excitement to try out the fix I failed to remember I had to edit each individual extruder config. So that next first homing went... badly and probably tweaked the lead screw and/or the POM nut.

The printer seemed to work well enough to print most of the remaining parts with it but it doesn't sound right and I'm wondering if the problem is affecting the z offset a bit.

I removed and inspected the POM nut and saw a bit of thread wear. But didn't notice obvious cracking. The lead screw seems ok, but haven't pulled the motor out to lay on a surface.

Things I've thought of:

• Replace the POM nut if I can find the same one for sale, and see if that matters.
• Try to straighten the lead screw (might do more harm than good?)
• Lubricant?
• Replace the motor assembly.
• Craft a damper to lightly hold the top of the lead screw

But before I do that, thought I'd check to see if it's obvious to the experts what the next thing is to do.

 

[the23rdwarrior]

Do you have stealthChop active on Z ?

 

[swh41]

I'm stunned. I did not have it on, don't hardly know what it is, but since you asked, I tried setting all z stealthchop_threshold to 999999 and the first home briefly made the sound but all subsequent moves are now quiet! All of the downward z motions that used to make a noise are quiet!

So the klipper docs suggest preferring "spreadCycle", but evidently spreadCycle is inducing vibration and triggering a resonance it my printer?

For completeness sake, since my first post, I had removed and inspected the rear stepper, put it on the edge of a quartz flat surface to look for bends (did not find any). Did notice a small chip in one of the threads near the top (~7 threads down), and wondered if this is enough to put the screw out of balance enough to matter. But that's the closest I got to finding anything wrong. Upon reassembly I inverted the POM nut with the long end facing down, in case that would do something, which I briefly thought had worked, but once the chamber was up to 40C, the sound was back with a vengeance.

It never would have occurred to me that the stepper config might need to change.

Thank you!

 

[the23rdwarrior]

It's not recommended to have stealthChop activated on a/b motors but it's fine on z.

Have fun!