[sansbury]

I've been studying industrial CNC controls and one thing I've seen that's pretty much universal on big iron is a spindle load meter. I'm curious whether something of the sort might be useful on my X2 as I don't recall ever seeing one and a search of the forum here didn't reveal much of anything.

I'm assuming that the straightforward way to implement something like this would be to measure the current drawn by the motor using an ammeter. I'm not looking for an ultra-precise measurement, more like "No Sweat," "Getting Up There," and "Maxed Out."

What I'm envisioning is to calibrate things based on the difference between current draw with no load (i.e. cutting air) and with the spindle loaded to the point just before RPM starts to fall. You could then look at where you are on the gap between the two to get a sense of how much headroom you have.

Assuming this would give an accurate indication of % spindle capacity, I also don't know whether it would be useful in the sense that general rigidity is often the limiting factor long before spindle torque is. Even then I'd be curious whether there's enough consistency between torque and rigidity limits--i.e. maybe 50% of spindle torque is where you're going to start running into rigidity problems when milling, while you can push a twist drill very close to 100% and be fine.

Has anyone ever tested current draw and RPM on their mill to see if there's any useful information to be gained here?

[TXFred]

Is the mini-mill motor controller a Pulse Width Modulation system? (PWM)

If so, then the motor isn't getting a steady current or voltage. So you'd have to add some sort of smoothing circuit or else your needle would be bouncing all over the place.

I think it's a good idea, though, especially if it can be connected to an input to trip an emergency stop should the spindle stall.

Cheers,
Fred

[SCzEngrgGroup]

Is the mini-mill motor controller a Pulse Width Modulation system? (PWM)

If so, then the motor isn't getting a steady current or voltage. So you'd have to add some sort of smoothing circuit or else your needle would be bouncing all over the place.

I think it's a good idea, though, especially if it can be connected to an input to trip an emergency stop should the spindle stall.

Cheers,
Fred

A simple analog ammeter (not digital) will work just fine. The meter is slow enough it will filter out the PWM pulses mechanically. Load is a function of current, so current alone will tell you how hard the motor is working. The nominal over-current trip is set to about 5A, so treat that as 100%.

Regards,
Ray L.

[whitehedr]

On my X2 system the PWM signal from Mach goes
to the G540 which converts it to a 0 10vdc signal
that signal then goes to the motor control circuit for the
X2.

If you install an ammeter in series with one of
the motor wires you will get the indication you are looking for.
Make a mark on the meter face at the "cutting air"
current and make another mark on the meter face
for the fully loaded condition. Viola, spindle load
meter.

RWW

[Vogavt]

On my X2 system the PWM signal from Mach goes to the G540 which converts it to a 0 10vdc signal that signal then goes to the motor control circuit for the X2.

If you install an ammeter in series with one of the motor wires you will get the indication you are looking for.
RWW

I want to put an ammeter inline on the 0-10v side coming from the Gecko-540 to the KBLC-19PM-Mod board and also put one inline between the KBLC and the spindle motor.

Can anyone tell me what range I should be expecting for amps or milliamps or each?

[SCzEngrgGroup]

Why would you want to put an ammeter on the 0-10V line? That would provide completely useless information. That is a voltage signal, with the voltage giving an indication of requested motor speed. The current on that signal will be very low, and nearly constant. The actual motor current will give you an indication of motor load.

Regards,
Ray L.

[Vogavt]

Well that's what I thought too but I wasn't certain that as the load increased there wouldn't be an increase in voltage on the front side of things to compensate.
My bad. I was thinking there are no stupid questions.
Maybe this will of benefit for others too.


Sent from my DROID RAZR using Tapatalk 2

[SCzEngrgGroup]

Well that's what I thought too but I wasn't certain that as the load increased there wouldn't be an increase in voltage on the front side of things to compensate.
My bad. I was thinking there are no stupid questions.
Maybe this will of benefit for others too.


Sent from my DROID RAZR using Tapatalk 2

It's not a closed-loop system, so the input is totally unaware of what the output is doing. It is the job of the motor driver to do all it can to hold the speed commanded by the 0-10V signal, regardless of load, but there is no feedback unless you add a spindle speed sensor, and program the Mach3 spindle PID.

Regards,
Ray L.

[Vogavt]

Can anyone tell me what range I should be expecting for amps or milliamps or each?

Follow-up to the question for the draw on the spindle only. I'd like to get an ammeter but I see there's different ranges available soI'm holding off on the purchase.
Can I tell myself with my clamp-on multitester? Not sure if it matters that it's DC and not an AC driven spindle motor. Ignorant on the meter.

[doorknob]

I haven't done this (my X2 is currently in pieces on my bench), but my guess is that you should be able to see a variation in the AC current draw (even though the spindle operates on DC, the DC is sourced from the AC line, and so the load on the DC motor should be reflected in the AC current). You should be able to verify that with your clamp-on AC meter.

[Vogavt]

On my X2 system the PWM signal from Mach goes to the G540 which converts it to a 0 10vdc signal that signal then goes to the motor control circuit for the X2.

If you install an ammeter in series with one of the motor wires you will get the indication you are looking for.
Make a mark on the meter face at the "cutting air" current and make another mark on the meter face for the fully loaded condition.
Viola, spindle load meter.

RWW

So what range of meter did "you" use?

My deducing has come up with 15A ammeter since from looking at the KBLC pdf floating around says (at least in my setup) to use a 15A fuse on the KBLC-19PM-Mod since my motor is 2.25 Hp.
I don't expect to run full out all the time.