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OK… Here is the semi-final result. All the V-Wheels were changed out with all new assemblies. That area is now working much better. The original wheels were really sloppy in the v-grove.
As others have stated, I’ve found It appears to be a issue with the Acme screw afterall. The pulley up top moves around because the bearing has a lot of slop and is being loaded eccentrically by the pulley and belt in one direction, but more importantly after inspecting the Acme screw the top stem is bent a bit. That’s when I noticed when I removed the pulley and washer that the top stem that the pulley rides on the washer right on top of the bearing which has a lot of give then held down with the nut still makes for a loose system. The bearing has a lot less tightness than I thought it should, however all three I’ve gotten were that loose. I can tell you that the pulley was tight to the bearing assembly.
Others stated they heard a clicking. It’s from the bearing I removed. It must be bad inside as I can feel the roughness.
The stepper motor and belt put a one sided load on that bearing assembly. It may be what others were describing as a pulley wobble or clicking sound. It was in fact the top stem of the Acme screw and a bad bearing.
So I’m going to get support to send me a new Acme screw, bearing, washer, nut, pulley and the delrin block.
Did the replacement parts remedy the issue? I just assembled my z axis 2 days ago and I find I have the same exact problems, sloppy bearing and when I tighten down the stepper and belt it torques the acme rod and causes it to wobble … this is a brand new machine kind of disappointed after spending $1600
apologies for the grammar and typos im posting from my phone…
Post update, I found that if i move the washer from underneath the z axis pulley to the acme screw before passing it through the bearing it helped about 80% I then loosened the pulley cranked down on the nylon nut to cinch the pulley to the shaft of the lead screw, loctite and tightened the pulley set screws I then had a return of the wobble so i then added an additional washer to the top of the pulley it didn’t have a large enough diameter center hole to go under the pulley or i would have done that instead, re installed the nylon nut an Eureka the rod is turning true even after pulling the belt tension with the stepper motor , i think the bearing has a bit too much play in it and by sandwiching the rod and pulley with washers it shims most of it out i can still manually wobble the lead screw by hand , i think a more precision bearing would work better in this case maybe something with cylindrical internal bearings like a wheel bearing… and tighter tolerances.
The full replacement parts solved most of the problem. The V-Wheels were a primary issue as the bottom of the V in each were irregular and sloppy in the track no matter where the eccentric nut was set.
As I reported to the company the Z-Axis bearing is a failure waiting to happen. Like what you found there is an over abundant amount of play when the Acme screw is attached. With the current design, the bearing is very sloppy and is not restrained. It needs to have a caged idler above or to the sides to stop the eccentric load of the stepper motor and belt pulling hard in one direction only. The tolerance is too loose on the bearing supplied, I already had one bearing go bad because one side is seeing way too much physical load instead of the load being distributed. Bearings do a great job of carrying up and down load when the load is equalized and within the load spec. However, the Z-Axis bearing is meant to spin and turn freely, not carry a hard one sided eccentric load like the current design has it do. There will be more failures if the Acme screw, bearing, and pulley above is not caged and restrained.
The Acme screw is another area that has issues. I strongly believe the spec’d strength of the material before the Acme screw goes through the second phase of manufacturing to cut the threads is causing the Acme screw to loose some of the original tensile strength. Why else would many be coming out of the process already deformed or bent. The number of bent Acme screws I’ve been hearing about here on the forum is unusual. Something is wrong. I ended up with two defective ones, one with a bend in the overall length, and one bent at the very top where the pulley attaches. The third and final replacement was not bent.
Right now my machine is performing as expected, however I’m keeping an eye on the Z axis for any unusual activity. I hope the company addresses the bearing and Acme screw issues. That bearing needs to be replaced with one that has less give and is restrained better at the top to eliminate the eccentric loading that “will” lead to bearing failures…
U might try moving a washer to the top of the lead screw it seems to help with evening out the tenstion on the beating I think a thicker metal
Sleeve with set screws would help
It even more I wonder if re- hardening the top of the lead screw would add more rigidity to it…
Okay, so hopefully your issue was resolved. I just set up my new xcarve and noticed the same wobble. However, I realized and this may be wrong but the ACME threads were too tight against the bearing and the last thread was causing it wobble. This seems like a design flaw as the end should have been machined flat to meet the bearing. anyhow, loosened it up and now its running just fine with no wobble.
