Prusa i3-X - Z-axis motors not in sync

[bluemike807]

I've upped the voltage to the motors to 1.0V and still no joy.

The right hand motor/rod turns fine. When turning the rod manually there is little to no resistance.

However when turning the left hand motor/rod, there is significant resistance.

Detaching the rods/couplers from the motors and running them shows that they run together in sync. But once reattached to the drive rods, the left hand unit cannot turn against the resistance.

I've oiled the rods, turned up the voltage, sanded a few contact points on the acrylic frame - still nothing.

When you send commands, the 'good' side moves fine, and the bad side just grinds. Have to emergency shutdown otherwise it strains the axis.

Where do I go from here?

[Mark]

check if the left hand rod is bended or not, or the couplers, is the 5mm hole and the 8mm hole concentric?

[bluemike807]

Solution Found:

Took the rod out and visually checked it to confirm that it was straight and did not have any defects or damage.

After isolating it, it became clear the resistance was between the road and the threaded bearing. In comparison, the second Z-axis rod/bearing was smooth.

Here's how I fixed it.

I removed the Z-axis structure and secured it so the X-axis arm would be stationary and the rod move freely so as not to bend the X-axis rods.

Then I chucked the threaded Z-axis rod to a power drill, protecting the threads of the rod with a few wraps of hockey tape.

I lubed up the threaded bearing with cutting oil and ran the rod through it up and down from end to end at speed with the drill.

When I got to one end of the threaded rod, I lubed up the coupling again, and reversed the drill. Rinse and repeat.

Definitely solved the problem. The threading between rod and bearing is like butter. Turned out so well I went and did the same thing to the other side to ensure they had the same resistance.

I'd almost recommend this to anyone building the kit (I just built mine). As it will prime those important bearings for function and lubricate the threaded rods from end to end.

A QUICK EDIT

I found out afterward if you use my drill method you will need to go back and clean the entire threaded rod. Found out it was gummed up with metal debris from the bearing. I took a clean, oily rag and ran the Z-axis up and down, pressing and moving the rag along the rod as it moved. It was surprising the amount of metallic debris that was pulled out. Afterward, the whole axis moved perfectly, no hangups or slowdowns.

[Mark]

very efficient method! thanks for sharing!