Velox CNC Z axis slip

Within a few months of getting our Velox CNC, we began having issues with the z-axis slipping. The issue seems to be with the coupling hub that goes between the servo and z-axis lead screw. In particular, the lead screw slips within the coupling. I was wondering if anyone else has had this issue and if you were able to find a solution?

Just a wild guess here, but have you tried tightening the coupling?

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So much so that I broke it tonight :worried:.

Bummer. What exactly broke? Pics?

The clamping collar snapped. The picture shows its pre-snapped state. After some thought on the issue, I think the problem is that the shaft coming out of the lead screw is slightly undersized. It appears that what Velox did was machine down the end of the lead screw to a 1/4" shaft but they undersized it. I’m not sure what will fix this short of making a new lead screw. These clamping collars are not made to be over-tightened.

A new coupler shouldn’t be too hard to find at places like McMaster, Misumi, or places dedicated to selling CNC router parts.

A small amount of retaining compound on the shaft works wonders for slipping couplers. Not ideal since it becomes a fight to remove it later but when you’re dealing with undersized shafts and, in the case of your pictured coupler, non-precision couplers the options are limited. Unfortunate that it’s busted…

Thanks for the tip on retaining compound! I didn’t know this existed. New parts will be here Monday.

Keep it off the plastic bit though! And clean/degrease everything first before applying the retaining compound.

If you want it to never come out, Loctite 680 on the shaft. And I do mean never. It takes a torch to remove. But, regular blue medium strength loctite on the screw is a good idea.

If you’re particularly ambitious and have the tools for it, you could modify a compatible 6 [mm] coupler half to have the right fit for your undersized 1/4" nominal shaft end.

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