Adjusting Grbl / Lightburn for solenoid based drag knife

I’m fitting a drag knife to my laser cutter - removing the laser head and putting a knife there instead, actuated with a solenoid for the Z.

It kind of works already with no changes from how I use lightburn for the laser, since I set lightburn to 100% power in line mode - that causes the PWM to be 100% duty cycle, which means the solenoid keeps the knife down.

However, I wonder if I can get slightly better results by configuring either GRBL (on the Ortur board), or configuring lightburn - if the X and Y are held steady for just a moment while the Z (AKA PWM) changes. In other words, when PWM changes, I want no other movement for a few milliseconds.

I tried setting $32 to off (e.g., laser mode off), but then the solenoid stays down all the time even during Moves. I didn’t figure out why yet.

I’d expect there’s something I can do related to “spindle spin up time” but my search-foo across the web didn’t figure it out yet.

Any tips for me for my hack?

Sure, but I don’t have one, nor the space :grinning_face_with_smiling_eyes: This hack might be quick and easy! My other idea is to (ab)use the 3d printer frame for it. The laser frame really is just a (not high torque, but probably enough for thin vinyl and paper cutting) X Y movement system… (and similar for the 3d printer, that’s a generic XYZ system that just happens to have a hotend on; but the bed size is 1/4 the size…)

I can fit a new control board / new grbl if needed, but I realised maybe the current control board is good enough.

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