- October 14, 2017 at 9:25 am #45950
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, MartinOctober 14, 2017 at 9:37 am #45951
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 user thanked author for this post.October 14, 2017 at 10:22 am #45953
Yes, it’s a bummer indeed 🙁 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.
Martin.October 20, 2017 at 2:11 pm #46354
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:
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 TR8*4 or TR8*2? 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.
MartinOctober 21, 2017 at 8:30 pm #46400
Yeah, typical cut depths are measured in tenths of a mm. IIRC (please correct me if I’m wrong) TR8*2 means one revolution moves 2mm, TR8*4 one rev moves 4mm, TR8*8 one rev moves 8mm. With 1:32 stepping you have 200*32 microsteps per revolution, so with TR8*2, 3200steps per mm, TR8*4, 1600 steps per mm and TR8*8 800 steps per mm. So even with the TR8*8 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 TR8*8 will be able to move the Z four times as fast as TR8*2 will.
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