Find Right stepper motor for CNC

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fentigkou32
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Joined: Wed Mar 11, 2020 8:28 am

Find Right stepper motor for CNC

Post by fentigkou32 » Wed Mar 11, 2020 9:46 am

Hi all,

It's about time I got out of the dark ages when it comes to drilling my boards and I wish to build a CNC machine. While I understand how the drill info is sent to the machine which steps motors to get to the right place I am unsure about which motor to go.

Just about in every project I have seen the large square stepper motors but I saw these:
https://www.oyostepper.com/goods-88-Nem ... Motor.html
https://www.oyostepper.com/goods-73-Nem ... Wires.html
Are these acceptable for a small light weight machine? I know that torque might be an issue which is why I would make the axis and table as light weight as possible. Could these be used?

All the best,
Robin

Bertus Kruger
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Re: Find Right stepper motor for CNC

Post by Bertus Kruger » Sun Mar 15, 2020 6:47 pm

Those will work but the small engraver machine usually use Nema 17 steppers. The are a size down from the Nema 23 you are looking at...

ShaneNZ
Posts: 3
Joined: Sat Jun 27, 2020 1:36 am

Re: Find Right stepper motor for CNC

Post by ShaneNZ » Sat Jun 27, 2020 2:40 am

It also depends on how you are going to move the axis.

Belt drive has the least mechanical advantage so usually compensated for by using a bigger stepper motor. A pulley with a diameter of 15mm will have a circumference of approx 46mm, so one rev of the stepper = ~47mm travel. Good for speed, but easier to overcome the torque of the stepper.

Acme screws and ballscrews usually run 5mm pitch, so you will have less speed, but higher torque for the same stepper. Ballscrews also have far less backlash without the need of anti-backlash setups.

I used M6 threaded rod on my first CNC (1mm pitch). That had horrible speed, but generated a massive amount of force (Nema17 2.5A steppers) So much so that it pushed an axis clean off the end of the smooth rod, taking the mounts with it, when I messed up an endstop. Lesson identified right there.
My 3D printer uses belts on the X and Y, and I can stop those with one finger, The (dual) z uses threaded rod, and it's already driven the extruder right through the glass plate (I'm clearly a slow learner)

Another consideration is what parts do you want to move. Options are fixed or moving gantry, with pros and cons for each.
And finally...the Nema number refers to the size of the faceplate. Nema17 means a 1.7in sq faceplate, 23 = 2.3in sq. What's important is the torque rating and current draw.

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