MPCNC Nema 23 Z axis

Hey!

Some weeks ago I bought an ready to mill MPCNC and started rebuilding anything the seller did, because it was awful. After that I was milling some wood and 1mm aluminium, with good results, except Z measurements. After checking many wholes where not as deep as they should and when milling my vacuum table I recognized, that everytime he was lifting Z the height changed randomly. Sometimes he was 3mm higher than before, sometimes, 2mm deeper. I thought it would be the frame and rechecked - everything was fine. When “levelling” the flute was at the same height in every corner.

Then I increased the driver voltage. At about 1.2V I got great results. After a few days I had to mill aluminium and thats why I´m writing this post: I saw, that the Z axis wasn´t able to handle the Z holding torque and the motor was getting very very hot. I got big step losses and sometimes he liftet the spindle and was stottering.

After having this problem I was thinking about solutions for that problem. I´m a 3d printer builder since some years and had some nema 23 laying around. and want to change the nema 17.

Some in this forum were milling aluminium already with the nema 17 but I cant understand how. I think the nema 23 could be the solution, but are there already finished designs, especially for the Z motor?

Have a nice day!

William

Good morning (4:25am in Arizona),

I just finished the process of adapting Ryan’s NEMA 17 printed parts to NEMA 23 for my Lowrider 2.

If no one has already adapted the MPCNC Z mount to NEMA 23 I will be glad to look at the project. I plan to start working on my own MPCNC in the near future anyway. I intend to use NEMA 23s on a 25.4mm (1") frame.

What spindle/router are you using and what board? The nema 17 should have no problem holding the spindle up in me experience

Hey Bryan,

Holding is not the problem. But when milling aluminium the part is pressing the flute up and thats what the nema17 can´t handle. Im using the Makita RT0700 with MPCNC Arduino Nano Shield and DRV8825 drivers.

Good Morning Tom (2:12pm in Germany now),

I printed the adapter for Z (thingiverse thing:3229607) and the mounts for X and Y (thingiverse thing:2146802). Will test Z today and Y/X on monday.

99 % of the time it is Z axsis movement speed set to fast in the g-code or firmware or both

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The other 99% of the time the Z skips steps because the Z lead screw is binding, usually because the lead screw nut retaining screws are too tight. They should be left somewhat loose to allow for proper self-alignment.

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Hey Tim,

Speed is at 200mm/min.

Hey Blaine,

I´ll try that, but never heard about that.

Thanks!

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even in firmware G00 commands can be faster they are normally set in firmware not the G-code and the lead screw binding can not help either :grinning:

Also, do you know the holding torque of the motors? Not all 17s are equal, and since you bought them from a guy instead of a retailer, could just be a weak stepper.

Hey Tim,

Yes, I set the maximum in firmware AND gcode, so 200 should be fix.

Hey Tony,

They seem to be the standard nema17 from stepperonline with 46Ncm.

The point is: I´m only getting this problem with circular pockets (dont know the right vocabular for this word) and combined holes. The outline seem to work well with aluminium. So maybe the problem is there too, but less then.

It is definitely possible to mill aluminum with nema 17s.

This is an extreme example, with perfect cam and a few mods, but still clearly nema 17 motors.

Hey Jeff,

Wow, thats impressive. But actually I´ve never seen his Z motor.

Apart from the double bearings and 10mm belt, which important upgrades did he do?

Maybe my flute is just rubbish.

Ok, I checked out his other videos - everything nema17
BUT: He is using an metric leadscrew instead of TR8. So you have much less torque on your Z motor, because of the much steeper thread.

And maybe the last post in this thread: I think I got the wrong aluminium…

EN AW-1050A is way to bad for milling.

Sorry for wasting your time and thanks for all your tips!

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People sometimes use a 1 start T8 leadscrew, because they accidentally order it, or they have a large router. If your problem is drag in the nut, that don’t make a difference, but it will have 4x, the lifting force for the same torque. But you also need to go 4x slower. A conservative max speed for a 4 start leadscrew is 10mm/s. For a 1 start, 2.5 mm/s is moving the motor st the same speed. You can probably go a little faster, because you have more lifting force. Just something to consider.

Your original issue, where you bumped the voltage up to 1.2V, sounds like something else is wrong. And you shouldn’t have to go that high to get reliable Z.

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Hey Jeff,

After changing to better aluminium I was able to mill it. But after a few minutes the motor is randomly turning the other way. So if he went 1mm down he is going 1mm up (without showing in the software). Thats very strange.

Can you post some photos of your Z-axis assembly? That might help with the diagnosis.