how to free-wheel only one stepper

[PaulRowntree]

I would like to have my Z stepper freewheel while X and Y remain powered. This is to manually do a touchdown to find a zero plate. I was going to have a switch disconnect two of the leads to the motor (from the G540), but would like to know if this is a bad thing to do while the driver is running?

Is there a better way to allow one axis to freewheel? I am using Mach3.
Cheers!

[stk2008]

Hi

Why not use a piece of paper in between the tool and work piece then move the Z down in 0.001" increments till it drags on the paper then remove the paper and move the Z down another 0.002"?.

this is how I do it any way its close but not perfect.

[rowbare]

You are pretty much guaranteed to blow your drive if you disconnect the motor while under power.

This is cheap and easy: XYZ Probe modification

bob

[MasterAnubis]

With my old software I turned off the controller, then set it where the software thought the table was. Now, with Mach3, I use the stepper with a piece of paper, (a receipt is thinner) like stk2008 suggested. Then when it touches enough to rip the paper, I zero the Z.

I'm a bit paranoid when it comes to cycling power unnecessarily and try to avoid it when possible.

If you disable the axis you may get the freewheel you want. I've not tried it.

[louieatienza]

THe best way I found, is to hand tighten the collet nut just enough for a slip fit. Drop the Z down till it hits your work and the bit slides a little into the collet. Then zero it out, raise the Z, and tighten. Works pretty accurately; I can cut Mic6 with the plastic on the back side, and cut through the entire piece while leavivng the plastic almost intact!

[jsheerin]

If you disable the motor, when you turn it back on it will typically jump away from the position you had it in. So if you zero your machine and then enable the drives, that probably won't be very accurate.

[ssutton]

Bob is right, I design circuits for a living, if you disconnect the motor from the driver board/card under power you are sure to blow the driver. Some drives offer a pin in that will cause the drive to go to zero amps when the pin is activated. If your drive is so equipped, then you could go that route and toggle it thru Mach.

Scott

[Aryantes]

I highly recommend looking at the aussie tool setter that rowbare mentioned.

You will use this Z probe before every cut. It is so easy.

Make sure your Z acceleration is very high though, as I have heard some stories where the fragile tips of V engraving tools have broken as soon as they impact the touch plate.

I've never had this happen though.

[Mariss Freimanis]

The G540 will not be damaged by disconnecting the motor while the drive is powered. However, we don't recommend doing that because powered up disconnects are damaging to the connectors due to arc-erosion.

A much better way is to short-out the current set resistor on the DB-9 connector (pins 1 and 5). When this resistor is shorted, the motor current goes to zero amps and zero torque.

Mariss

[PaulRowntree]

The G540 will not be damaged by disconnecting the motor while the drive is powered. However, we don't recommend doing that because powered up disconnects are damaging to the connectors due to arc-erosion.

A much better way is to short-out the current set resistor on the DB-9 connector (pins 1 and 5). When this resistor is shorted, the motor current goes to zero amps and zero torque.

Mariss

Thank you all for your help. I know about the auto-zero codes and techniques, but it always semed like a bit of 'excess automation' considering that I was standing there anyway having just changed the tool. I use the paper method now, and was looking at something that would be more precise while not having to do so many 0.001 advances of Z. My tool moves up in the collet when tightened, so that is out. My Z motor is double shafted, and with a small knob on the exposed shaft I can easily move it with 0.001" precision, and this has a good manual feel as well.
I like Mariss's idea a lot; the G540 is very robust (it has survived in my hands this far) and if it can be made to freewheel.. great! Can the resistor be shorted out with a switch or should it be gradually shorted by puting a poteniometer in parallel with the fixed one (or even just move the resistor or pot to the machine's Z stage where I will tweak it) ?

[ger21]

Thank you all for your help. I know about the auto-zero codes and techniques, but it always seemed like a bit of 'excess automation' considering that I was standing there anyway having just changed the tool.

Every post I've seen from people that have added an auto-zero seem to say it's the best addition to their machine they've done.

I too used the paper method for about a year, and didn't it was that big of a deal. I was wrong.

It is hands down the biggest time saver and best addition you can make to a router.

And adding it is far easier than what you're attempting to do to disable your motors.

[PaulRowntree]

@ger21 : I guess that was a bit like waving a red flag in front of a bull.
Gerry, I accept the challenge, and will try the auto zero first.
Cheers!