Z axis getting off square while printing

I’ve been running the Low Rider all day yesterday and most of this morning. And I either just noticed the problem or something happened. I’m still learning some of the CNC stuff so just let me know if it is a simple user error. For starts here are the specs of my machine.

Mini Rambo board with the basic firmware

5’x10’ table with DWP611 Dewalt router

I use ESTCAM for writing my G Code and Repetier Host ran from my laptop hooked up USB to the board to run the program.

The problem I’m having is that I’m trying to cut out a part from 1/2" thick blonde wood and my Z axis is getting off. I just had to Emergency stop the Low Rider by pulling all the power because it was about to crash itself. I was running a program with a 1/4" bit set to

z+ = 1.5mm

a(z+) = 90

f(xy) = 20

f(z) = 1.5

s = 24000

The program had ran for approximately 10 minuets then I noticed that the Z axis was extremely off(about 3/4") when I heard the router having problems cutting because it was plunging to deep. I leveled the z axis by hand before I started.

Any advice is greatly appreciated and just ask if I left out an important pieces of info.

Looks like you have a lot of weight on the side that isn’t lifting? The bar and hoses and stuff. That concentrates the load instead of a more even distribution, and because it is a long bar it is acting as a long breaker bar and possibly tweaking the angle binding the screw. See if you can easily turn the lead screw with your fingers.


Either move the bar or slow down your Z moves, both rapid and plunge. You are wired in series on the Z correct?

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The only weight I have added to the Z axis carriage is the 3d printed pen holder. I don’t have a vacuum hose hooked up to it I think your looking at the protective cover for the stepper motor wire. And the system I’m using to keep my wires out of the way is attached to the XY plate not the Z plate.

Yeah they are wired in series with the wiring harness I ordered from you. What speed would you recommend for the z axis?

Can you easily move the coupler with your finger all the way up and down?

I was half wrong, but what I tried to clarify above is the lead screw is very sensitive to it angle. If the side plate is kicked in or out at all the screw will be very difficult to turn.

I would keep it under 10mm/s for sure.

It is really odd for one side to be off when wired in series. Usually if one gets jammed up the current does not flow to the other so check your coupler as well it might be loose.

Okay. Both couplers are easy to move with my fingers. I’ll try slowing down the Z moves and see what happens with that.

If one coil is intermittent, then the steppers can “jump” across the gap when not experiencing any load, but skip as soon as there is resistance. This happened to me the other day. The side with more resistance will skip, while the other side is jumping the gap. At least, that’s what I think happened.

You can inspect all the motor connections, and you can also disconnect the Z motors from the mini-rambo (with power off, please) and check the resistance across either coil with a multimeter. They both should be pretty small (10-20 Ohms, IIRC).

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I had to work this weekend so didn’t get a chance to mess with anything yet. Though I ran the LowRider up in the air off anything just to see what it would do. It still dropped but I was able to hear a odd back feed?(a sort of weird buzzing) sound from the Z motor giving me issues. I’m seriously thinking about taking my wire management system off and taking apart that side of the machine and replacing that Z motor. Any input is welcome. I’m currently in the process of putting my MPCNC back together because I took its Mini Rambo board for the LowRider and replaced it with a full-sized Rambo just trying to get a second opinion before I go through a lot of hassle.

Hard to say without being there. Steppers can make noise, not always.

So an update I have taken all the weight off the machine and I am now just using it with me holding the wires so they don’t get tangled and I have changed my z stepper motors. The Low Rider is still dropping down twice as much as it is suppose to on the one z axis? Any off the wall idea is appreciated.

Is either side dropping the exact right amount? Does the bad one drop the exact same distance every time?

Your issue isn’t normal and does not line up with anything that I have heard of. The above questions are looking for other issues but good measurements here will tell us a lot, and the larger the distance the better. For example don’t test with 1mm, test with 50mm or more.



G92 X0 Y0 Z0

G1 Z50 F240

G1 Z0 F240

Did you source both Z screws from the same vendor? Any chance one is a 2x and the other 4x? How about the steppers? One 1.8° and the other 0.9°?

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Not completely sure of the cause of the problem but after going everything with a fine tooth comb I had to tighten a couple screws and it is running great now. Fingers crossed it stays that way.

Wood Gnomes

Though on a side note. Anyone ever break a set screw inside the coupler? I my overzealous to make sure everything was tight I cracked the hex head on the set screw so I can no longer remove it but is completely secure on the motor. I just foresee if I ever have to change the motor or screw I’m going to have to just by a new stepper and coupler.

I’m having a very similar problem right now too. My one Z axis is skipping and the other rises just fine, so its off kilter and ends up too low when trying to travel. messed up a couple cuts by not paying attention. I managed to make a real nice cut last night by just making it one long slow full depth cut.

I’m going to replace a motor and adjust my wires and hopefully that fixes it. i have them wired in series.


How much of an angle would mess it up? Its a little off but only a degree-ish. The screw is still pretty darn easy to turn by hand, almost falls under its own weight but not quite unless I’m pushing down a lil.