Oddity with material thickness in Easel demo

The Easel demo for Carvey is configured for a 0.125 inch thick piece of two-color HDPE (i.e., X: 6 in; Y: 6 in; Z: 0.125 in). But what ships in the Carvey is a 0.250 inch thick piece of HDPE. Okay…

The demo engraves a 0.0625 thick picture of an Easel using those material dimensions cited above. And the engraving in that 0.250 inch thick piece of HDPE was indeed about 0.0625 inches deep for me. Sweet, but what gives? The physical material was twice as thick… I note that when I put in material and claim the actual thickness of the material plus waste board, the Carvey cuts too deep.

Is there a documented rule that I’ve missed somewhere like subtract 0.125 in from your material thickness? Again, the actual Easel demo (for the Carvey at least) appears to be setup to use a material thickness 1/8th inch less than the material Inventables supplies for the demo. But the engraved depth comes out reasonably close to correct for that demo. Perhaps when Carvey homes Z it reckons it is higher above the physical Z=0 then it really thinks it is? (I suppose I could figure out how to get the gcode out Easel and see if there’s a, say, G92 post homing that asserts a Z
height which isn’t correct.)

Anyhow, enlightenment appreciated.

The demo gcode probes the Z axis and then asserts the Z position as being 0.5 inches (which is the thickness of the clamping bracket). As the material is clamped beneath the bracket and the commanded cut positions are put below Z=0, the thickness of the material should not matter: it could be a mile thick and yet engraving down to Z=-1.575 (mm) would still yield the correct depth of cut, 0.0625 inches.

So, I can see why the demo declaring the wrong material thickness is irrelevant. But still leaves me a bit mystified as to why cuts I’ve made on other materials have been too deep. Calibration would seem to not be an issue given that the HDPE demo material cut fine. And the material was not bowed. However, it is possible that the L-shaped clamp-with-probing point cocked itself at an angle? I didn’t look for that.

Anyway, I’ll consider this topic as closed as I’ve at least answered my initial question about the oddity with the declared material thickness in the demo: it’s the wrong thickness declared, but owing to the structure of the gcode it’s a difference which makes no difference.

The reason your cut depth can go deeper than the material is that you may have carved out a pocket in your waste board, for example to seat a PCB or other material and keep it properly flattened.

I don’t understand why the thickness of the material matters in Easel other than the convenient slider that allows you to specify your cut depth. In fact, there should be an auto-detect height functionality that uses the smart clamp and sets the height + possible cut depth range for you…future feature request.

When exporting Gcode from Easel, you’ll see the beginning works like this (I’ve added comments for clarity):

G90                         (distance mode (absolute))
G21                         (length unit (mm))
G28                         (return to home [hit limit switches])
G21 G38.2 Z-71 F80          (unit=mm, straight probe down until we hit smart clamp)
(once the smart clamp gets hit from previous command, the straight probe stops and we continue to next command)
G10 L20 P1 X16 Y-11 Z12.7   (set coordinate system data [location of where we are relative to smart clamp])
(note Z12.7 means 12.7mm [0.5in] from smart clamp which is the distance between top of material and smart clamp)
G54                         (select coordinate system 1)
G0 Z20                      (rapid linear motion [bring bit back up])
G0 X20 Y20                  (rapid linear motion)