Setting up soft limits in UCCNC .. "Logic"

[Kitwn]

I'm a bit concerned that anyone thinks that "going past zero" is in any way relevant when you are using Mach3/UCCNC. Maybe in the days of archaic controllers that did not have any homing/work offset capability this might have mattered but not today.

The point here is that homing sets machine zero, either directly by putting home switches at the zero point, or somewhere else with an appropriate offset (at the right-hand end of travel, in the most extreme case). But that is absolutely nothing to do with where the zero point is on the work. First thing you do when you plonk the stock on the bed and clamp (assuming that you have already homed the machine) is to move the spindle to where you want (0,0) to be, and then set "work coordinate zero" to that point. Maybe x and y at the same time, maybe separately. Effectively you are doing the same thing when you set tool height - this is setting z coordinate zero, indirectly. Your gcode will, if generated by any modern CAM package, be working in terms of work coordinates. Nothing at all to do with machine coordinates. For example, recently, I have been machining work where the X zero work coordinate is at the right hand side and most of the machining is done with negative X coordinates. I told my CAM software where I wanted X=0, set the spindle to the RH edge of the stock and set work coord X to zero, and away it all went.

This machine/work coordinate confusion is a bit complicated to follow at first sight but it soon becomes second nature and you won't even think about it, but it is absolutely critical to using CAM and the machine in harmony. I sorry if I have misunderstood what was being said, but the idea that you need to set machine zero somewhere on to the bed just so that you can move to negative coordinates could be very misleading to anyone new coming to this.

Neale,
I'm not going to argue with a word of this, and I am coming at it from a wood-working gantry router perspective which is different to a mill. Like you I often reposition the work coordinate zero to suit the job but this will be a known position relative to the homed (0,0) position so that it can easily be re-acquired after an E-stop or other driver-disabling event.

The OP was confused regarding numbers to put into these values but the main points I wanted to make are the need to pull away from the switches to a specified point after hitting them, (0,0) being the obvious label to put on that point in my view, and that the area the workpiece can fit inside will often need to be smaller than the area defined by the soft limits which primarily exist to prevent crashes but also specify the limits of movement of the centre of the cutting tool. The best numbers to use then fall out from there.

Kit