Z-AXIS moves only 25% of what it should

I just installed a new makita spindle on my MPCNC and wanted to finally try cutting something instead of just drawing. That’s where I noticed that while X and Y movements are very precise, the Z movement is exactly one fourth of what it should. If I try moving 10cm the Z axis from the control panel it moves exactly 2.5 cm. All the other motors travel perfect distances, but the depths are all 75% off. What could it be that causes this strange problem? Is there some setting I can tweak to make the motor spin 4 times more?

I modified the DEFAULT_AXIS_STEPS_PER_UNIT from 800 to 3200 to correct the movement. This in theory should have worked but in reality it generates some strange behaviours where it doesn’t really move the right amount during a cut. It carves a pocket and then when it’s time to do the finishing pass it does it in the air…in the simulation this setup previews correctly so I’m pretty sure it is something that has to do with my Z axis issue.

What hardware and electronics are you using?

When you make such giant numbers to move the Axis your CPU can not handle higher speeds. Try g0 Z20 F100, if that works correctly you just have a speed issue.

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I created a .gcode file with only “g0 Z20 F100” inside, when I launch it I get no motion or feedback whatsoever from the machine, I’m not entirely sure what the result should be but when I launch it it’s like I did nothing.

Anyway with the DEFAULT_AXIS_STEPS_PER_UNIT set to 3200 I managed to get some test jobs done in styrofoam. Considering what you just said, probably the height issues I’m having are because it sometimes skips some fast movements due to my 3200 steps setting. At moderate speeds it all works fine for now.

I’m using the lcd dual endstop firmware, and the hardware suggested for the arduino/ramps build, I’m using cheaper clones for the arduino and the ramps, and the same drivers shown in your build instruction, plus generic chinese nema 17 motors off banggood.

I don’t know if I’m allowed to post links, it’s just to show what I’m using:

Ramps: https://www.amazon.it/gp/product/B07BSRS9WS/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Mega: https://www.amazon.it/gp/product/B071W7WP35/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Stepper Drivers: https://www.amazon.it/gp/product/B07K9ZB7M5/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Motors: https://www.banggood.com/Nema17-59Ncm-2A-1_84-lead-48mm-Stepper-Motor-For-3D-Printer-CNC-p-1252415.html

Run it from repetier’s command line.

You did not show your leadscrew.

I suggest your rapids and plunges no more than 8mm/s, if it is a regular piece of all thread.

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Right, here is the leadscrew.

What should that code do? I mean How do I know I’m having a good or bad result?


It will move the z axis up 20mm.

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Yeah, that lead screw has exactly one quarter the pitch. It’ll have to be spin four turns to get the same as one turn with the stock screw.

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Crap! I thought that T8 indicated one and only one type of screw. I can’t believe you can have 2 screws so different under the same name! So I need a T8 screw with a 8mm pitch…

It’s the X2 part you need to keep an eye on. The T8 just means it’s an 8mm diameter trapezoidal leadscrew. The X part is the thread pitch. You can get different pitches to do things like faster movement, or more torque. The higher the pitch, the farther it will go per revolution, so faster, but less torque.

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I had to educate myself on this too. Technically, the “pitch” is the distance from one thread to the next, but these lead screws have “multiple starts” which means there are multiple helixes around the screw and the nut advances multiple threads each revolution. The “lead” is the distance traveled per revolution, which is where you want 8mm. But the pitch might still be 2mm.

Looks like Ryan’s Amazon link needs fixing; this is the one I got: https://www.amazon.com/OctagonStar-L300mm-Start-Screw-Printer/dp/B01HBHUSPQ



Got myself a “4 starts” T8 off amazon and fixed the problem. Thank you all very much for the prompt support.