Please Advice

Hello all, it’s been a while. The MPCNC is working great, but I currently need the Z-Axis motor for another proyect. I’ve a spare Nema 17 Geared Stepper Motor (Gear Ratio: 5.18:1 and Step Angle: 1.8°) that could be used for Z. The thing is that the math is killing me.

x16 microstepping with an M8 threaded rod (not a leadscrew).

(360 / 1,8) x 16 x 5,18 / 1,25 = 13260,8 steps/mm

That looks way too much, is this accurate? If so, what would be the drawback? Limit speed?

Thanks, Martin

PS: Motor specs:

The speed is going to be a bummer, without the reduction your max was 8.4mm/s (~16mm/s with 16th stepping)and that is max, strongest is less than that by far, reduce that by 5x and you max speed will be 1.68mm/s. (3.2mm/s @ 16th stepping). Not super horrible but a bummer.

Steppers are pretty cheap you should probably look into getting another without the reduction.

I believe your math is correct, try it and measure but keep it slow or the board will reset.

1 Like

Yes, it’s a bummer indeed :frowning: I didn’t test it because it will need a different mount and haven’t printed one yet.
Will do asap and give it a try.

Thanks for the quick reply.

Quick update just in case someone is considering doing this. Don’t please… It really is super slow. Using the geared motor was horrible. I could almost hear him begging for his life.

The funny thing is that after removing 4 screws, beneath the gear box there was a normal nema17 (duh for me… :P). The only difference was that the axis is geared and very small. I printed a new coupler and installed like this.

Haven’t cut anything since the motor swap, but it looks promising.


As for buying another motor, I actually want to buy a motor with an incorporated leadscrew, like the ones they sell on Robotdigg:*4-leadscrew

What’s stopping me is that I can’t decide which type. The current MPCNC is using TR8*8 right? If so, I might go that route.

But what about TR84 or TR82? They will require less torque and achieve higher resolution, but I guess that this kind of resolution is negligible for cnc.


As always, any suggestion is much appreciated.




Yeah, typical cut depths are measured in tenths of a mm. IIRC (please correct me if I’m wrong) TR82 means one revolution moves 2mm, TR84 one rev moves 4mm, TR88 one rev moves 8mm. With 1:32 stepping you have 20032 microsteps per revolution, so with TR82, 3200steps per mm, TR84, 1600 steps per mm and TR88 800 steps per mm. So even with the TR88 you have 80 steps of resolution when trying to move a tenth of a mm. Any of those has way more accuracy than you’ll actually be using, but TR88 will be able to move the Z four times as fast as TR82 will.