First, industry standard or not, the guy probably refers to mills with a T-slotted metal surface.
Mostly not intended for sheet material.
It is called a SPOIL-board for something ... A cheap board that can be spoiled.
I know of major players that advice Zwork-zero = top of material.
He shortcuts material thickness but you probably have to account for that any way.
The angles in the PC stand all relate to thickness for example.
Second, he doesn't zero on the spoil-board, he zeros just above that.
Further he uses tape to fool everything so he would not touch the surface at all.
But if you look closely in the video, the MDF surface is still marked slightly.
G0 Z0 ...
G1 Z0 Fxxx will not always end precisely at Z=0.00000, that may even relate to plunge FEED.
All depends on the repetition accuracy of your CNC setup.
If step-loss occurs then we can't speak of any accuracy of repetition.
Servos hunt and closed-loop or hybrids actuators have a rotary indexer with some degree of accuracy.
Common cutters pull down when cutting material, reversed angled will push up.
There will always be some degree of axial play and it may even be spring loaded.
Anything under stress will give a little, your portal, your linear guides, ...
Bottom line: It will never be exactly zero.
While cutting fully trough we need to account for all that play, for example with a spoil-board.
When spoiled to some degree it can be replaced cheaply.
MDF is then cheap but not extremely dimensionally stable and not stable over time (Moisture)
To ensure a flat surface you need to process that when attached to your setup.
In other words, you need to face mill the entire spoil-board to make it as flat as possible in regards with your X&Y axis.
Remark that in the vicinity of clamping bolts it is compressed, between them it buckles, this can't be repeated twice.
Solid core board (Trespa), HDPE or PP is then a better solution.
Lastly, I think that the Math behind TABs is: While cutting (< Zstart) and the thickness is above Zfinal.
Below you will see that the single toolpath does not cut at Z=zero.
On the other hand, 'b' & 'c' are clearly drawn below the top surface (Dashed red).
I don't understand the lower level for the path at the right in
Screenshot from 2024-03-30 12-46-29.png
- From the G-Code output:
- Safety level Z50
- Zsave = 8
- Single toolpath: Zcut = Z3.1 (Not retracting at TABs as it is already more than 2 above zero)
- Double toolpath: Zcut1 = Z1.55 retracting to Z2 at TABs ; Zcut2 = Z0 retracting to Z2 at TABs
For a single pass it seems to be:
-(zStartDepth+zCuttingDepth)
For more passes:
-(zStartDepth + (zCuttingDepth - zStartDepth) / zPasses * pass)
If you replace
Zpasses and
pass by 1 in the second it is not the same as the first ...
Regards,
CVH