Thrust Bearing for Z-Axis

Hi there,

a few months ago I installed an axial thrust bearing on the Z-Axis of my 3d printer, which greatly improved the quality of my prints. I got the idea from the RatRig V-Core (see RatRig pillow block assembly ). Although I don’t own a RatRig Printer (my printer is a highly modified Ender 5), the pillow block from the RatRig fitted even without modification. The purpose of the bearing ist to take the load off the stepper-axle to increase precision of the print and the lifetime of the motor. If you push on the axle of a NEMA17 Stepper you can feel it move quite a bit and that is completely gone after installing such a bearing.

I was wondering, if such a bearing wouldn’t be a good thing on the MPCNC, as there is the whole weight of the Z-Axis pushing against the stepper axle (in the case I don’t miss something here). It shouldn’t be that hard to implement. On my MPCNC Primo F build I will try to modify the Z-Motor part like this. Is there a way to get the corresponding STEP-File or something like that? I’m using FreeCAD on an elderly notebook, so editing complex stl-files is not an option… Of course I will share the part I create!

To my understanding the Z-Coupler part is intended for forces going in the opposite direction (if I got it right these forces are created by the router bit).

Best regards

That seems like a good idea. The Z is under compression.

The early MPCNCs had a bearing there (the coupler was different, we were using all thread at the time). It wasn’t a thrust bearing. I’m not sure why Ryan removed it.

I would wonder if you could measure a difference with and without it. The Z accuracy is pretty good on these CNCs. I doubt you would see any difference in something like mdf (which has an upper limit in resolution/quality anyway).

There is already a bearing to support thrust loads, but it is a 608 bearing and not specifically a thrust bearing. As long as the bearing isn’t awful, it should support the load just fine.

The 608 bearings and the motor bearings have some play in them individually from how they are constructed, but opposing the 608 against the motor bearing can take up the slack.

The natural weight of the Z axis is held by a compressive load on the rod that transmits to the shaft of the motor and the motor bearing supports the load. If the router bit tries to lift the Z axis then the screw is in tension and it’s held down by the coupler gripping the screw and the bottom side od the coupler rides on the 608 bearing.

Properly assembled, you shouldnt feel any play whe pushing/pulling on the lead screw.

So I guess it’s a long way of saying that I don’t think there is a problem. A thrust bearing might also work in place of the 608, but I don’t think it would make mich difference.


I wasn’t sure if it was still in the primo.

The LR doesn’t have the 608 bearing.

But then, we use a springy coupler, too, right? So wouldn’t that flex befor any serious axial load was transmitted to the stepper?

The compressive load on the screw should transmit directly because the screw is supposed to butt against the motor shaft. And in tension only the bottom half of the coupler supports the load, so there is no tensile load on the coupler.

A slight ‘preload’ should squeeze the screw against the motor shaft to take out the play in the bearings. If the screw is not butted up against the shaft then the Z axis will be squishy.