Height Mapping?

I noticed in Jonathan's build thread that he and JazzCNC mentioned height mapping which seems to be mapping the height of the machine bed. Can anyone give more info on this? Can it be done with Mach3, and how?

Thanks!

In most cases it's easiest to just skim the bed using the machine, but since my bed is aluminium I want to make sure it's as close to 'flat' as possible so that I can remove the minimum amount of material when I skim it. If what you're probing is aluminium, then since it's a conductor you can just put a metal bar in the spindle with a wire connected to it then connect the other wire to what you're probing (i.e. the bed in this case). Connect those to one of the inputs on your breakout board, configure it as the probe input in mach3 and away you go...A quick Google search will find you the probing code.

Ahh I get how it works now, but how would one take that data input and implement it in order to compensate for the bed? Sorry, I did try a Google search but only found mention that it is possible.

Not much help for me since the top surface of my bed is HDPE but still interesting. I just spent this afternoon adjusting mine - got it within 0.3mm now.

I needed a variant of height mapping for milling SMD pcbs (even skimming the bed ain't good enough, because when you clamp the pcb board it distorts...meaning your board ain't level anymore).

I spent eons trying to get a working solution for Mach3. This one seems to be firmly in the category "the codes out there, but I've never done it" .......which roughly translates into....."spend yonks trying to find something that'll work" - I really wished I'd not tried! It's all very well getting your machine to probe height, but it's another thing entirely integrating the probed height data with your G-code file.

In the end, I just ponied up & bought CNC-USB ...which does all this without any effort whatsoever........ CNC USB Controller - "Warp" - measuring and cutting warped toolpath - YouTube

Of course the CNC-usb method only work on materials that conduct (copper, metal etc) Not sure how you'd takle hdpe (place some foil ontop of it....and probe that?)