1/8, 1/4, or 1/2 stepping??

[vonkal]

I just finished a CNC conversion on my Harbor Freight mini mill with 200 oz/in motors and Hobby CNC controller board. Everything works ok, but I am occasionally missing steps as if the motors are under powered.

Can anyone tell me which stepping configuration provides the most torque? I am currently ¼ stepping and want to know if changing to 1/8 or ½ stepping could help this problem.

[pminmo]

What is your software set at for max step rate? What kinds of accelerations? What is your power supply voltage?

[vonkal]

pminmo,

OK, here is the setup as I have it now.

Mill = Harbor Freight Mini Mill
Software = Mach3
Motors = Hobby CNC 200 oz/in
Controller Board = Hobby CNC 4AUPC Rev.2

Current Settings
1/8 stepping (have also tried ¼)
IPM = 18.866
Acceleration = .55in/sec
Volts = Set at the board at .54 v @ 3amps (I think this equates to about 30 volts at the motors)

I couldn’t find the “Max step rate” that you asked for. If there is any other info you need, please let me know. If anyone has the same setup and can let me know what worked for them, it would be greatly appreciated.

Thanks

[pminmo]

IPM is what I was getting too. Is that what you are cutting at, or rapids? I was really looking for what power supply voltage. Do you know where your missing steps, all axis, one axis, when cutting, when doing rapids?

[vonkal]

In all cases I seem to miss steps at the end of the travel on the Y, it gets very tight there.

Also, I miss steps on the Z, and that can happen almost anywhere in the travel. I am fairly sure that the only reason I am missing steps is because the load becomes too large for the motors to handle, and it’s because of the mill.

My X is the only axis that travels stop-to-stop easily by hand or with the motor.

All missed steps occur at almost any speed, but are reduced when I lower the feed rates. Changing from 1/4 to 1/8 stepping seems to make little, if any difference.

[pminmo]

Power supply voltage? The new hobbycnc pro board or old one?

[pminmo]

got any pictures of your wiring?

[vonkal]

35VDC is what the unit is rated at, and I think that’s what it’s putting out. I hope that is what you are asking for.

The board is the old one. I also have the new one, but haven’t built it yet.

I have no pictures of the wiring. Do you mean the controller? I am fairly sure that all is wired correctly, as the motors run very smoothly. I think they just need a little more umph!

[pminmo]

Since you say it misses X steps and that axis moves freely, I'm not convinced it's lack of power. One other question, what is the screw pitch of the minimill?

Also have you tried half step at lower rates?

[diecutter]

You mention that you seem to lose steps where each axis is hardest to move by hand. You may want to try backing off the dovetail gibb screws at the tight end of travel so you have a shake free, but easy travel throughout the range of each axis when moved by hand. You may also want to put a counterweight on the Z axis to counter its inertia. Adjusting my gibbs made all the difference since my Steppers are only 150 oz. in. cheapies which amplified the problem.

[vonkal]

I edited my last post that said I missed "X" steps. I meant "Y" in the first line.

I have not tried 1/2 step yet, but was thinking of trying that next, if somone like you recomended it. So now I will.

The tpi on X and Y is 20. On the Z, slightly less, but it has to compensate for the rack and pinion as well as the mass of the head itself (I doubt the torsion rig compensates well).

[vonkal]

diecutter,

Yep, I hoped that I could do just that. But I can not get my Y gibs adjusted properly. I can get a smooth fit in the middle of travel, but as it comes to either end of travel (last 1/2 inch) it binds up. If I adjust for no binding on those ends, then too much slop in middle. Bad gibs, poorly cut dovetails? I don't know. Been thinking about switching to brass gibs. Do you think that might help?

On the counter weight... just picked up a pully and cable yesterday. Can't find any lead for the weight yet, but I will. Can't wait to get rid of that torsion arm.