Middle Assembly / Z Wobble

MPCNC question for you all… I noticed yesterday that I have some play in my middle assembly. If I grab the z at the top by the stepper and the bottom and push/pull I get wobble - or whatever the correct term is… I am thinking I should not be able to do this and not sure how I solve for it.


How long is your z axis? How long are your X and Y axes?

Is it moving exactly up and down (backlash), or like you can bend it?

These were the tube measurements:

PCs Inch Description
3 35.4 1 od x .049w 304 s.s.weld tube A269
3 29.4 1 od x .049w 304 s.s.weld tube A269
2 12.5 1 od x .049w 304 s.s.weld tube A269
4 4.5 1 od x .049w 304 s.s.weld tube A269

Not really up and down… more so back and forth pivot… maybe I can try to shoot a video show what I am talking about.

It’s cutting ok but just not sure if I should be concerned about it or not.

Cutting is kind of all that matters?

This is exactly why I say not to attach things on the z axis motor mounts. It is a torque multiplier, with a linear increase. Any force on the top translates directly to the bottom. half the length 2 times the rigidity, every single mm matters. So you shaking it is like using a breaker bar on the lug nuts of your car, instead try and move it from the very tip of your cutting bit, this is all we care about. For every half the distance to the carriage it will be two times harder to move the bit.

Plus a little extra for your x and y flex, but it should be minimal even though those are kinda long axes.

i have same problem when i cut, the bit moves left and right, my z axis is short, i have everything setup for cutting max 5cm of material, i don’t have anything atached on the z axis. The feedrate even if it’s slow or fast i have the same problem. i dont know how to fix it.


You should start your own thread, and give all the specs of your machine, gcode, how far off your cuts actually are, and the bit you are using.

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thanks for the help Ryan.