Z Setting Question - Microswitch

For a microswitch used for Z axis, would this be a normally open or a normally closed switch?

If normally open, could I just put a terminal onto one of the screws which holds the hotend and connect this to the Duet, and the other Duet lead goes to a metal plate of fixed thickness which can be put out on the bed just to home.

Then when the head goes down, the nozzle will contact the metal plate, complete the circuit and give us a reference point for Z. Of course this would need a clean head, with no plastic residue.

I do this with my CNC mill and it works perfectly with Mach 3.

Can I do this with the Ormerod?

Rob.

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robbycar
.... could I just put a terminal onto one of the screws which holds the hotend and connect this to the Duet, and the other Duet lead goes to a metal plate of fixed thickness which can be put out on the bed just to home.

Then when the head goes down, the nozzle will contact the metal plate, complete the circuit and give us a reference point for Z. Of course this would need a clean head, with no plastic residue....
Rob.

Yes this should be possible and work similar to your CNC, on my printer " a clean head, with no plastic residue" is rarely the case.

My similar thoughts, just for homing is to have the wire go to a sprung loaded 'contact pin' that are used for PCB probing. This would be clipped onto the hot end close to the nozzle. This has the advantage of a spring to absorb 'over travel' and also removes the plastic residue issue.

I hadn't thought about the switch sense NO or NC, just thought of the NO mode, so look forward to hearing what this is.

Should be better than my piece of paper setting up I still use.....

---

Ormerod #007 (shaken but not stirred!)

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robbycar
For a microswitch used for Z axis, would this be a normally open or a normally closed switch?...

normally closed

micro switch for Z homing:
[forums.reprap.org]

Erik

Bugger!

With Mach 3 you can software select the pins sensing either high or low.

Perhaps this may be possible in the firmware?

Rob.

Edited 3 time(s). Last edit at 05/20/2014 04:41AM by robbycar.

You can certainly change it in the firmware. There is no gcode setting and I don't think there is a simple define for it but it would be a simple fix nonetheless. The big challenge is setting up a build environment to compile and build it...

Another option would be building an inverter using a transistor and a couple of resistors.