@jay_s_uk Where homing at the top makes sure that I remain within the limits of the machine, it won't keep be from plunging into the T nuts in the spoilboard. Since there is a variety of lengths that the tools could be. I recognize that this makes sense from the machine point of view, and this is the way that the machine currently on the drawing board is going to operate, but I'd have liked to be able to use the firmware axis limits as a safety/sanity check.
@dc42 I'm not sure that it would help. The problem with swapping bits in a router is that the amount of bit sticking out from the collet is different every time I change it, and in fact the router position within the gantry has a certain amount of variability as well, so if I take the router out of the clamp to clean or service it and put it back in, even the collet is in a different position relative to the machine limits. I'm not sure that I want to spend time chasing the machine limits every time I change a bit or service the router.
I believe that in general use, it's safe to say that I am not running any jobs, certainly not creating any jobs that are pushing the envelope of the motion limits of my machine. While homing the tool to the spoilboard isn't optimal, it provided a way (or so I hoped) to use the axis limitations of the machine to give me a convenient way to do a sanity check on my CAM work.
I will get the same end results (or close enough) to homing hte machine at the top and seting axis limits to the machine motion limits if I simply allow the axis limits of the machine to plunge into the spoilboard approximately as much as the most commonly used tool length, which will (most probably) keep the router collet off of the spoilboard, and depend on reasonable CAM to keep from damaging a bit, or T nut. I can actually safely lift the Z axis well beyond its usable range. The bearings on the Z axis slide will lose contact, but they will just contact again as I lower it.
20210501_043727.jpg
Anyway, this is the first project I completed with the Duet connected to the CNC. It's carved from a piece of 3/4" pine, and houses my PanelDue 5i