Question about ZPlus design

I had some issues with the ZPlus tonight where it refused to move up or down and there was a lot of grinding. While troubleshooting, I came across a piece that I don’t understand. If you look at the ZPlus image here Shapeoko Z-Plus - Carbide 3D, you see the two bolts that connect the spindle plate to the mechanism that rides on the lead screw. Just above and slightly to the right of those bolts you can see a white dot. That white dot is a small cylinder about 1/4 inch in diameter and about an inch long. It screws into the plate and just seems to hang there. It is not connected to anything on its opposite end. In my case, the end of mine is chewed up as though it had gotten tangled up with the lead screw…there is a screw-pattern roughly dug into the cylinder. What is the purpose of this piece?
While were here and focused on the ZPlus, the mechanism that rides on the lead screw (it’s two blocks with a spring between them)…is that the anti-backlash nut mentioned in the ZPlus description? Is there any reason anyone would want to increase or decrease the spring pressure (if that’s actually possible)?

Could you post a photo? (or better still send it in to

I believe the part you’re asking after is the post which triggers the Z-axis homing switch.

Of course that’s what it’s for. Also, after more thought, the screwlike scratches on it aren’t from the lead screw; they’re from the pliers that were probably used when the rod was installed. That doesn’t explain the grinding and stopping of the Z, but after cleaning things out with high pressure, everything seems smooth and back to normal.

Glad to hear you’re up and running!

For maintenance, please see:

I had also asked a question about the mechanism that rides on the lead screw. Without taking it apart (which I am not inclined to do since the I need the machine right now), it appears in it simplest form to be two nuts separated by a spring. Does this part need maintenance/greasing/etc.? Is there any reason to adjust the tightness of the spring? Does this part wear out? For example an accident, let’s say the tip of the bit on your spindle was 1 mm above the stock and you did a g0 z-20. What would fail if something broke? Would the stepper go first? Or would that nut mechanism go first? With the original Z assembly, the belt would skip over the teeth.

It’s my understanding the leadscrew is self-lubricating since it’s Delrin — if that’s not the case, I’m sure @Luke will correct me.

Usually the stepper motor will skip, but we have had a couple of damaged leadnuts — if this occurs, just drop us a line at and we’ll get it sorted out.

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