[itman496]

So I made a cnc machine out of a bunch of aluminum, steel, and v-slot rail.







But it has an issue. For some reason, despite a 54V power supply for the steppers, and triple stack nema 34 (one for X, two for Y) motor, it can't go very fast? The motors manage about 200rpm before going into unhappy vibrate mode. They are not even really being loaded, either. The machine is very low friction, and the screw drive isn't hard to turn either. Acceleration is not it, either, even when I turn it way down, it still does it. I am using CW250 5A stepper drivers (which I hope aren't the problem, but alas, I assume they are, but I'm not sure how to fix this)

The issue with this is that with the 1/2-10 acme screws, the machine has a top speed of 20IPM. Which is very slow.

Anyone know why this is a thing? The drivers are set to 8x microstepping, acceleration doesn't affect it either.. Slow or fast, it still has the issue.

[ger21]

It's a combination of 1/2-10 acme screws, cheap drives, and motors that are much too large.
This is a very common beginner mistake. Buying inexpensive, poorly matched components. In the end, they usually end up costing much more because they all get replaced.

With steppers, as rpm's increase, torque drops off. The larger the motor, and the higher the inductance, the faster the torque will fall off. Because of this, a much smaller motor can often give 5x the performance of a much larger motor in an application that requires higher rpm's.
Your 1/2-10 acme screws require 1000 rpm to achieve 100 ipm feedrates. Larger steppers can often have a maximum usable speed in the 300-400rpm range. Steppers in the 300-400 range can reach 800-1000 rpm, if they have low inductance. Small motors can be even faster, but may not be strong enough for your application.

What are the specs of the motors you have?

First thing I would do is switch to 5 start 1/2-10 acme, which will give you 5x the speed.

I'd then switch to a smaller Nema 23 motor that will be able to spin faster, and have more torque at higher speeds. The 381oz 3.5amp motors are typically very good performers with the 5 start screws.You want a motor with an inductance in the 2-2.8 range. Lower is better.

And last, a better drive than has anti resonance features for smoother running and even more speed. A Gecko G540 or Leadshine MX4660 are both 4 axis drives that should run much smoother and probably faster than what you have now.

[stargeezer]

You also appear to be using a smaller pulley on the motor driving a larger pulley on the screw. This will also give reduced screw RPM. Flip them around for a small upgrade. I can't tell what ratio you are using, but placing a bigger pulley on the stepper and a small pulley on the screw will help.

[itman496]

Ah, darn. I was hoping it wasn't a stupid mistake I made. This is what I get for trying to do it all myself haha..

I'd rather not replace the threaded rod as it was an adventure and a half making those stupid things on the lathe so.. Would a single stack nema 34 go any faster? So I don't have to re-do the motor mounts?

Another thing I was thinking was making an adapter plate with a speed up pulley on it, ie two pulleys and a ratio that increases the speed some amount. Right now its just two identical pulleys on the motor/screw.

if it means anything, (since I have a crap motor probably) the Z axis seems to also top out at a similar speed, with a different driver and a nema 23. But that might just because of a weak motor.

The leadshine driver looks really good, actually.. Might save up for that. I wish I had posted here when I was picking components, but alas. Thank you for the advice. I think I will try to 3D print/mill an adapter plate to have a ratio increase on the x and y drives of 6:1 because I assume at 150rpm these nema 34's are still very powerful.

This is the motor I am using: Stepper Motor, NEMA 34, 7.8V | MPJA.COM

Thanks again for the advice. I made the machine draw a circle earlier, I'm very pleased.

[stargeezer]

I think these are what I'm running. Stepper Motor, NEMA 23, 5.7V, Dual Shaft | MPJA.COM

[ger21]

Would a single stack nema 34 go any faster? So I don't have to re-do the motor mounts?

It depends on the ratings.
Like I said earlier, you want motors with an inductance of 2-3. Yours is 24.

[itman496]

What about this?

Stepper Motor, NEMA 34, 3V | MPJA.COM

it has an inductance of 4. How much of a speed increase would that be?

I also came up with this zaney 6:1 speed increasing pulley retrofit-bolt on thing but.. if that motor can get me to 100IPM I'll just suck it up and buy three of them..

[stargeezer]

How about - Stepping Motor, NEMA 23, 4.5V | MPJA.COM or Stepper Motor, NEMA 23, 3.6V | MPJA.COM would be my choice.

[itman496]

I should be able to mill out adapter plates to bolt those in.. Thank you.