I have an 4x10 unit and I’m putting the spoilboard on the second crossmember, about 16.5 inches off Y zero. When laying it out in Aspire I have the overall layout of my machine and the spoilboard placed on the second crossmember. When I create a tool path for the counter bore holes will the coordinates of the holes be automagically translated via the touch plate? So the corner of my spoilboard is 0,0 and the first bore hole will be 1.85, 0.7874
Thanks
Welcome, no stupid questions!
Physical space is in ‘machine coordinates’. When you ‘Home’ your machine, where it stops is Machine 0,0,0. The machine thinks in machine coordinates and keeps track of where it’s at in machine coordinates. You can monitor these values by using the ‘Switch to Machine Coordinates’ button in Mach4. You’ll know you’re in Machine Coordinates mode and that it is unusual to work in machine coordinates mode because a wide red LED strip will flash at you as a reminder to switch back to Work Coordinates.
CAM software thinks in ‘Work Coordinates’ and the digital read out (DRO) in Mach4 will display ‘Work Coordinates’ by default, for which the 0,0,0 point is set by the operator. By pressing the Zero X/Zero Y/Zero Z buttons in Mach4 you are setting the Work Coordinate System (WCS) Zero. By using the touch plate, you are simply automating the pressing of those same buttons really. There can be more than one of these positions, and they’re logged in ‘memory slots’ referred to by G5x - like G54, G55, G56. By default you start working with G54.
So when you use the touch plate, that sets your 0,0,0 that the software is looking to work off of. Any number in the gcode is based from this point. (there are other scenarios where things move in increments and not absolutes but that’s for another discussing, your CAM software doesn’t really mess with that).
Thanks . These are just extra letters to meet the min requirements
I use my probe and I measure each crossmember and find the center. Then I can accurately place the holes for the M8 screws to keep the spoiboard and flow-through fixturing secured.
If you don’t have a probe, I attached the STL file for the AvidCNC touch off plate adapter. It was originally designed specifically for this purpose. With a good 3D printer you can realistically see about 0.002" to 0.005" accuracy. Use a roll in nut and M8 to secure it before the touch off.
I just wrote a small script to probe down first to find the surface and the back up a tad and then into the Y+ bounce to get a better reading and then Y- to find the other side. Calculate the center taking into account the tool diameter (I actually use a 8mm dowel pin). Save out the X,Y,Z as a CSV file and import them into Fusion 360.
Keep that file because over time, rerun it and see if your crossmembers are moving on you.
Over time I have actually built a model of my table. I have to re-calculate it again because I adjusted the crossmembers but on this time around I have the whole thing scripted and the CSV will be automatically generated.
CenterlineMount.stl (275.0 KB)
When building mine, I noticed that the crossmembers are ideally 400mm center to center, and measured from the front along each side to space them accordingly. I don’t like using “distance from previous” as errors accumulate, and a chunk of lumber is not a precision device.
Having said that, my plan is to create an ideal set of coordinates for the nuts, and let the machine tell me where to put them, rather than measure zillions of points. I might have to tweak a crossmember or two but I hope not 
Is there some easy way to fix the t-nuts in place in the track, so they don’t move between boltings?
I’m curious how close to ideal your crossmembers ended up, and how far they move per year…
This time I cheated! 
I cut a template out of 6.35mm steel on the laser cutter. When I flattened the template out with two clamps they allow about 359 millimeters distance between them with a shop temp of about 68 degrees.
The real point was to not just get the distance apart from each crossmember consistent but to get the ends of the crossmember parallel to each other. I think I managed pretty well. It looks like I am less than >1.1 mm difference in distance and parallel to each end.
And yes, that completely messed up the square of the machine! 
Oh, I agree! Automate, automate, automate!
But here is the real power of having this data in your CAD program, besides cutting accurate mounting holes for your spoilboard;
The biggest reason I have an accurate representation of my CNC in Fusion is for cutting and printing fixtures and jigs. Huge time saver. Make the machine make me more accurate. The less my human hands are mess’n around in there the better my product is.
I should probably make my F360 machine simulation available to everyone on this forum but I have too many pokers in the fire! Maybe I should set up a GoFundMe for them and when they reach a funded stage then work on them 
Another hint: if your design includes dog holes, do a test run of the hole toolpath first to make sure that the holes you get end up being exactly the size you specified in VCarve or Fusion. There are many reasons why that might not happen, including not squaring or tramming your machine properly before cutting the spoilboard.