I've just gotten my CNC machine and it looks like the Duet 3 6HC is going to work well for it.
Looking at the code, it looks like CNC support is in active development which is great.

However the key missing part I've noticed is lack of spindle speed feedback.
Having the feedback means it could be displayed on screen, the CNC can dwell until it's up to speed and so on.

Looking through the code I realised that there's already tachometer support sitting in the code - there's full tach support for fans. I believe many VFD's output a similar one pulse per revolution signal as fans (mine does).

I'm wondering if the functionality for fans can be copied over to the spindle code to allow for spindle speed read out and then adding the extra functionality like dwell and adding UI elements shouldn't be too difficult.

Is this just on the todo list or is there a specific reason this wouldn't be feasible?

I'm trying to sort out my emergency stop situation and I have a possibly appealing option.
I'd like to E-Stop without killing the UI at all which means very fast debugging and getting going again.

It's recommended to kill all the power which is certainly safe, but rather inconvenient if all the software goes down.
The problem with non-power killing methods is it appears Reprap Firmware can't interrupt the currently running command, so if there's a long move it'll continue moving before stopping.

What I'm wondering is what is the behaviour of Reprap Firmware if I power the 5v rail from the SBC, and emergency stop kills 24v power?

Doing it that way should be ideal:

• Motors stop immediately
• The Pi and Reprap Firmware stay alive so no rebooting

However does Reprap Firmware detect the loss of 24v power? If the spindle isn't turned off then that might be less than ideal and require additional circuitry to handle.
And what does it do to the current job? Does it pause it/stop it or try and keep running it?

If that can be answered that would save me from wiring everything up in that configuration then finding out there's a problem with it.

I've just gotten my CNC machine and it looks like the Duet 3 6HC is going to work well for it.
Looking at the code, it looks like CNC support is in active development which is great.

However the key missing part I've noticed is lack of spindle speed feedback.
Having the feedback means it could be displayed on screen, the CNC can dwell until it's up to speed and so on.

Looking through the code I realised that there's already tachometer support sitting in the code - there's full tach support for fans. I believe many VFD's output a similar one pulse per revolution signal as fans (mine does).

I'm wondering if the functionality for fans can be copied over to the spindle code to allow for spindle speed read out and then adding the extra functionality like dwell and adding UI elements shouldn't be too difficult.

Is this just on the todo list or is there a specific reason this wouldn't be feasible?