Tool change without losing zero (reliably)

Does anyone have a foolproof method of changing bits without accidentally shifting your x/y zero? I have about an 80% success rate, just looking to improve. Currently I just change the bit being as gentle as possible, but obviously not gentle enough sometimes. What’s everyone else do?

I’ve seen people use shaft collars to set the height and then they just pop in the new bits after a pause in the G code. Something I want to practice with myself.

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@Stairguy If your v wheels, threaded rods/ACME lock nuts and anti backlash nuts are all properly installed as described in the installation instructions, you can send the command $1=255 to the Longmill controller in the console window. This will engage the stepper motors and prevent any movement.

Many users use this in vertical Longmill mounts to stop the weight of the X gantry from slowly moving down when the Longmill is idle. You can search this command in the forum search and you will see lots of posts about this.

I would check to make sure everything is properly tightened first.

Are you using both wrenches to tighten your bits in the collar?

Most definitely two wrenches, I never trust the thin hollow shaft with a hole in it to take torque. $1=255 sounds like the perfect solution I’m looking for, never thought of that. Does it need to be disabled somehow before running the next file?

That command just leaves the motors engaged or powered…the gcode will then make the steppers move the axis. That’s probably a simplistic explanation, but that’s what I have read.

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I just change the bit and then use the touch plate to reset Z zero. Works like a charm for me.

That’s my typical approach, but every once in a while I get a little too rough with the wrenches, or don’t realize I’m leaning into it and the whole gantry moves a little. Most of the time I’m just paranoid and think it moved. The few times it has caught me off guard has me looking for a method with a higher success rate though. So far $1=255 looks like it is going to be my solution, unless someone chimes in with something different.

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