spindle causing steppers to jog

[Ben L]

I Have an issue, where with the spindle only running at rpm 3500+ my steppers start to "clunk" at irregular intervals. putting my hand on the x axis stepper it feels like it moves a tiny bit.

On occasion I seem to be now gaining steps on the z axis I dont know if i'm correct but from what ive read it sounds like it might be electric noise is being produced somewhere like the spindle brushes. Ive run this machine for a few hundred hours without this issue and if I slow the spindle down to 3000 it stops completely.

So Id like to replace the brushes even just to rule that out.

EDIT I took the brushes out and they seem fine, ive ordered some new anyway, I'm absolutely perplexed. Ive been round all the connections and wiring, but cant find a fault at all.

Any and all help most welcome as always!

cheers

Ben

[Ben L]

Changed the title of the thread in the hope someone can help with this.
After taking out the brushes and replacing them its been fine for a week. but today. scrapped an expensive piece of material due to the gaining steps.

Is it noise or something else? Ive added thew riser block recently but I cant see how that would have changed anything.

Beyond frustrated with it.

[Steve]

Ben,

It does sound like an electrical noise issue. The spindle motor does not have an encoder fitted so the speed it's actually doing is set by the voltage.

When the machines are tested the drive is tuned using an external tachometer to set the top speed.

Do you have any way to check what the machine is doing?

The motor is a DC motor and if they become demagnetised they start to run over speed.

If it's running over speed you get arcing on the brushes which could cause the problem.

While you can turn the top speed down on the drive this increases the current in the motor for the speed which can cause the motor to get worse.

I would suggest you check the speed. If it's running fast turn it down using the max speed pot on the drive then check the DC voltage. If it's demagnetised too much you may need to get the motor repaired or replaced.

[Ben L]

Thanks Steve, what you've said makes complete sense. Ive just got a tachometer so i'll measure the spindle speed and adjust the pot accordingly if required with any luck that will sort it.

[Steve]

Hi If the spindle is running over speed by too much turning down the pot will will correct the RPM but as a lower voltage is creating the same top speed the current into the motor will increase.

Various things can cause demagnetization. Over current, repeated stalling, over voltage and running over speed.

If the motor is demagnetized I would advise setting the maximum speed lower than previously set. Recheck the speed at intervals to check if it is getting worse.

[Ben L]

Hi If the spindle is running over speed by too much turning down the pot will will correct the RPM but as a lower voltage is creating the same top speed the current into the motor will increase.

Various things can cause demagnetization. Over current, repeated stalling, over voltage and running over speed.

If the motor is demagnetized I would advise setting the maximum speed lower than previously set. Recheck the speed at intervals to check if it is getting worse.

Thanks Steve, Checked it just now and it was reading only 200rpm over speed, Ive trimmed it slightly down to match the 3000 rpm Mach, that said, reading what you've written should I turning the voltage up instead and setting the rpm lower within the control software, would that be a better tuning solution?

[Steve]

No turning it down is better. if the motor over speeds it sparks creating noise.

If max RPM is not too much of an issue you may be better setting it at 2800RPM

[Ben L]

No turning it down is better. if the motor over speeds it sparks creating noise.

If max RPM is not too much of an issue you may be better setting it at 2800RPM

Will do thanks for the help Steve

[Ben L]

i wanted to say i figured this out. its very basic conversion and whoever did it used a 5v out off the denstep board to power the spindle v5 board. The denstep manual says don't power anything like this off the board. so a cheap dc psu later and all is well.

Soon i'll get round to more advanced conversion. Ive bought the parts just waiting to have the time.