Thought I’d share my method for doing a cut-out toolpath and avoiding cutting into the tape and wasteboard.
I have a piece of tape on my wasteboard next to where I normally cut projects. When setting the Z height for a toolpath that will cut completely through my material or doing a rough cut-out that I want to be sure I’ve left a little more than an onion skin, I zero off the tape using a post-it. Then I use the thickness I programmed into my toolpath to raise the tool off the bed from there using the jog screen, then re-zero.
This lets me design a project without knowing the exact thickness of my material down to 100’s of inches. So, for example, I was designing a finger jointed box, I knew my material would be around 1/2" so I programmed my cut-out toolpath with 0.51 thickness. When I picked out my material, it was 0.48" (after planing a slight bow out of it). Before I run my toolpath, I zero off the tape, then use the jog in CM to raise the bit 12.95mm and re-zero… Shapeoko don’t care, it’ll happily cut air for a pass.
I use a similar method and just set my wasteboard to -cutDepth. I use gcode to do this by sending G10L20P1Z-12.85
If I’m cutting aluminum or something I always make sure to start my paths above the stock, though.
I’m using aspire, it won’t let me choose both top and bottom of the stock for the same project. If I’m doing a project with toolpaths that don’t include cutting all the way through the stock, wouldn’t I have to have all my v-carve and pockets referenced off the bottom of the stock? That sounds confusing.
They reference off the bottom, but if you’ve described the stock properly to aspire, it’ll just work - it’ll do the math that pretty much says “to the bottom of the material, add the thickness of the material (that you tell it), and that’s the top of the stock where you should vcarve”. All the “zero” does is tell the software where to reference from, and your input of material thickness is just telling it how much to offset from that point. It’s the same thing, the difference is where the math happens and who is doing the thinking and work. I’ll trust the machine far more often than my error prone brain to get that one right every time.
The top of the material is not necessarily where I’ve told Aspire that it is… as in my above example, my material ended up being 0.03" lower than I told it during design. My v-carve, pocket, or 2.5D cut wouldn’t work properly. The machine would go to the supposed top of the material, but would just be cutting air. Okay for a pocket if you want to specify how much material to leave, but if you are looking to hit a certain depth, it’ll be too shallow. By referencing the top of the material I can zero my bits off the top of the material for most of the cuts, and then zero off the wasteboard when I need to cut all the way through.
My method is for designing project where you have a rough idea of the size of your material, but need to set the maximum thickness that it will be and go from there without having to redo the design. Currently doing 4 boxes in oak. Even though the boards are all “about” the same thickness, having all gone through the planer at the same time, they actually vary from about 0.47-0.485" thick. I could use the same design with no changes on boards that are down to 0.4" because the surface carvings are at most 0.2" deep.
That is a good option, just not the best for me. I can prepare solid stock with my planer and sander much better and faster than doing a surfacing pass, even if it’s not perfectly within 1/100". If I’m working with plywood, a surfacing pass is not an option at all, and neither is the planer. With plywood, the only good choice is to plan for thicker than you’re material will be, then zero off the wasteboard for the cut out toolpath.
The way I have used it in Carbide Motion, was to zero out my cutter on the waste board (set z to zero)… then jog my cutter up exactly .75 inches ( or what ever height I told the software was my stock thickness)… and then zero the z axis again ( set z to zero again).
This way if my stock was only actually .71 inches… the cutter will cut .04 inches in the air… rather than cut .04 inches into my table.
I believe that carbide motion will not let you enter a -.75
Inch z value into the software (when the cutter was on the wastebaord) That’s why I had to jog the z axis up .75 inches and set z to zero. If you then were to then lower the cutter back down to the wasteboard… the z value would read -.75 inches…
I use double-sided foam tape from 3M on all my project pieces, which raises the piece about 2-3mm off the surface of the wasteboard. Then when I zero the z-axis I use a thin sheet of paper between the piece and the bit. When I feel a slight bit of resistance I know I’m good within a fraction of a millimeter. Then I set my cut for stock thickness + 1mm and it cuts it out clean. Rarely is the wasteboard touched. The foam tape isn’t cheap, but it works amazingly well. I haven’t had to use clamps or any other means to hold the piece to the surface. I’ve only had one piece in over 100 dislodge from the surface, and that was due to user error. I was cutting some parts from 7-ply birch plywood and forgot to place tabs in the outline. Bad mistake. The piece came loose, pinched the bit, and the project tore loose.
But, again, the tape is really effective, gives a bit of clearance, and probably only costs a couple dimes per project…