[Woodslut420]

I'm working on a 1980s Thermwood CNC router, and recently replaced the linear bearings that guide the Z-axis. The spindle is a big 130lb, 16hp monster. We are running Mach 3, with a Warp 9 USB smoothstepper.

I don't know if this is standard practice, but when a limit switch is triggered, the stepper motors lose power. When the stepper motors lose power, the weight of the spindle pulls the whole assembly towards the table. I guess before it was just the friction of the bad bearings holding it up.

I have been looking into counterweight systems, probably pneumatic, but first I would like to make sure that the Z-axis stepper motor NEVER loses power. Obviously I don't want it receiving signals to move in the event of a crash, but I don't think it should go completely slack.

I would love help with how to configure this in Mach 3. Does this have anything to do with signals being in Active Low or Active High? Could i solve my problem by configuring the system with a Charge Pump and having the Charge pump stay on during e-stop?

Is my issue the stepper motors? Would newer motors have brakes capable of holding the spindle up without power?

Thanks in advance!

-Nic

[Jim Dawson]

It is common to use a brake on the Z axis. https://www.omc-stepperonline.com/stepper-motor-brake/ This will most likely require replacement of the motor because you will need a dual shaft motor. A pneumatic spring might be my first choice.

I found out the hard way that on the Thermwood it is important to stop the Z at the up limit else it will screw the nut right off of the screw and the bearings will fall out. Mine didn't fall because I had the older V ways on mine, and just snugged them up enough so the Z wouldn't fall.

You could just open the step signal to the Z drive on E stop or Z limit, but not disable the drive. Not the best solution but it would work.

[CitizenOfDreams]

I have been looking into counterweight systems, probably pneumatic, but first I would like to make sure that the Z-axis stepper motor NEVER loses power.

What happens if the whole machine loses AC power? Your spindle would still nosedive. You definitely need either a brake or a spring/counterweight. Or both, considering the weight of the beast.

Keeping the Z driver enabled all the time is possible, although it would not be in Mach3 settings. You have to physically disconnect the ENABLE signal from the driver and jumper it so it would always be on.

[CitizenOfDreams]

You could just open the step signal to the Z drive on E stop or Z limit, but not disable the drive. Not the best solution but it would work.

Correct me if I'm wrong, but I think Mach3 stops sending all step/dir signals on E-stop. So interrupting the step signal may not be necessary.

[Jim Dawson]

Correct me if I'm wrong, but I think Mach3 stops sending all step/dir signals on E-stop. So interrupting the step signal may not be necessary.

Yup, you are correct. Or at least that should be correct.

[ZASto]

You can also set Mach3 to disable drives in EStop condition so you may be or may not be wrong. It's just a different point of view.
So, as first aid, I would think 'bout gas spring(s) as a counterweight for a spindle.

[Woodslut420]

Thank you so much for your replies, I'm feeling pretty over my head with this repair work.

I found out the hard way that on the Thermwood it is important to stop the Z at the up limit else it will screw the nut right off of the screw and the bearings will fall out. Mine didn't fall because I had the older V ways on mine, and just snugged them up enough so the Z wouldn't fall.

You could just open the step signal to the Z drive on E stop or Z limit, but not disable the drive. Not the best solution but it would work.

Haha, thankfully our Z is captured, and I definitely still intend to use the limit switch.
A new stepper with brake is a totally reasonable idea. Definitely in the medium term plans.

What happens if the whole machine loses AC power? Your spindle would still nosedive. You definitely need either a brake or a spring/counterweight. Or both, considering the weight of the beast.

Keeping the Z driver enabled all the time is possible, although it would not be in Mach3 settings. You have to physically disconnect the ENABLE signal from the driver and jumper it so it would always be on.

Absolutely, there are already coil springs, but they are only strong enough to keep the spindle when they're fully extended. My feeling is that I could never be confident enough in a perfect counterweight, so if e-stop were triggered in the middle of a cut I suspect the bit would fall to SOME extent, possibly ruining a workpiece.

I would like a good counterbalance AND the guarantee that while the machine is on the Z stepper is powered.

You can also set Mach3 to disable drives in EStop condition so you may be or may not be wrong. It's just a different point of view.
So, as first aid, I would think 'bout gas spring(s) as a counterweight for a spindle.

Ok, so it sounds like there are two solutions to the e-stop behavior, one achieved by removing the Enable signal from the stepper driver and jumper, and one solution WITHIN Mach 3? Maybe I'm just looking in the wrong place but I wasn't able to find the correct Mach 3 panel to modify E-stop behavior.