Where is zero Z again? I'm a dope.....

[johnm]

Folks -

Okay - I just KNOW I'm doing something dumb.... Lately I've been having trouble establishing zero Z. This means that either all my cuts perform flawlessly, inches above the material, or SB technology does its level best to jam the router all the way to the collet through the table.

I've been doing everything in PW1 - setting Z for the machine bed and going on my merry way. The cuts look like they occur properly in 3d, stepped cuts, etc... I've ran the 0Z routine in SB, at machine bed height and that worked fine. Now I also have set 0Z from the top of the material - I suspect that this is where I'm getting in trouble.

If I set 0Z on the machine at the top of the mat'l and have 0Z in PW set at the machine bed, that would have the actual position of the cutter tip too deep by the thickness of the material. This could account for the BIG noise the router made and the stains in my underoos when this somehow occured.

It seems like OZ should alwys be the machine bed, but I've discovered a blind spot that keeps screwing me up. As a newbie to 'Bots and PW, it seems like there are too many places where the same information is used, and that mislocations of reference points is a vulnerable area. But at least I didn't crash a probe into what was it, Mars, because I didn't convert meters to feet... Where and when would you specify the different locations of 0Z, and for that matter, the corner or center of the workpiece as XY0Z.

I'd appreciate any sage wisdom for an easier method of operation for preserving my router and my shorts.

John

[jsfrost]

John,

I too have lost shorts in the early learning stage; eventually it will happen to me again.

Depending on the task and your preferences, you could chose to have zero anywhere, although most choices would make little sense. The important thing is to decide where you will zero when you start your PW design, and consistantly input your toolpaths depths relative to that reference. And obviously, use the same reference to Z0.

Jim

[paco]

Hi John!

One thing that might help to clear thoses two different ways to "zero" the Z axis in CAM is to actually look at the output file (before running it on the machine)....

In PW 1 & 2 (and all ArtCAM products I believe), when one zero at the top of the material blank, the Z values of the output file will be negative...

---
Cut in a single pass...
---

MS,1.7,1.5
JZ,1.000000
J2,0.000000,0.000000
J3,0.413540,2.465460,0.525
M3,0.413540,2.465460,-0.500000 <---The plunge
CG, ,0.454893,2.055344,1.971323,-0.008370,T,-1
CG, ,2.922237,0.521435,1.963832,0.407533,T,-1
CG, ,4.408585,2.221017,-0.504439,1.940875,T,-1
CG, ,3.371307,4.226475,-1.990787,0.241293,T,-1
CG, ,1.726111,4.344321,-0.953278,-1.765442,T,-1
CG, ,0.413540,2.465460,0.692344,-1.881582,T,-1
J3,0.413540,2.465460,0.525
J3,0.000000,0.000000,1.000000
JZ,1.000000
J2,0.000000,0.000000

---

...when one zero at the machine bed, the Z values will be positive...

---
Cut in two pass...
---

MS,1.7,1.5
JZ,1.000000
J2,0.000000,0.000000
J3,0.413540,2.465460,0.525
M3,0.413540,2.465460,0.250000 <---1st plunge
CG, ,0.454893,2.055344,1.971323,-0.008370,T,-1
CG, ,2.922237,0.521435,1.963832,0.407533,T,-1
CG, ,4.408585,2.221017,-0.504439,1.940875,T,-1
CG, ,3.371307,4.226475,-1.990787,0.241293,T,-1
CG, ,1.726111,4.344321,-0.953278,-1.765442,T,-1
CG, ,0.413540,2.465460,0.692344,-1.881582,T,-1
M3,0.413540,2.465460,0.000000 <---2nd plunge
CG, ,0.454893,2.055344,1.971323,-0.008370,T,-1
CG, ,2.922237,0.521435,1.963832,0.407533,T,-1
CG, ,4.408585,2.221017,-0.504439,1.940875,T,-1
CG, ,3.371307,4.226475,-1.990787,0.241293,T,-1
CG, ,1.726111,4.344321,-0.953278,-1.765442,T,-1
CG, ,0.413540,2.465460,0.692344,-1.881582,T,-1
J3,0.413540,2.465460,0.525
J3,0.000000,0.000000,1.000000
JZ,1.000000
J2,0.000000,0.000000

---

You'll sometime encounter this variation that some users zero the Z axis at the machine bed BUT STILL USE THE TOP OF THE MATERIAL BLANK AS THE REFERENCE...

Zeroing at the top of the material blank is I think a "standard" among CNC... but still, both can be used; one just have to understand the concept and actually know...

[beacon14]

"If I set 0Z on the machine at the top of the mat'l and have 0Z in PW set at the machine bed, that would have the actual position of the cutter tip too deep by the thickness of the material."

Actually, this situation will result in the cutter being higher than you expect by the thickness of the material. Telling the machine to make a full depth pass at z=0 will result in the tool just skimming the top of the material

The best method is to choose a system that works for you and stick with it. Most CNC users seem to work off the top of the material, some from the table surface, but very few go back and forth from one to the other.

[paco]

About the "variation" I've refered about; maybe I should have detailed... since I think it's interesting to know... I use it everyday...

My rule is when I work with machining strategies that involve depth accuracy and surface machining, I will zero the Z at the top of the material.

For toolpaths that are cutout (profiling) I usually zero at the surface of the spoilboard then add the material thickness then zero; this is all done in a subroutine I've wrote/modified (it prompt me for blank thickness)... the idea is that I avoid gouging in the spoilbaoard as much as possible and this late way is quite accurate since I don't have to mesure accuratly the materiel blank precisely...

As David, I would encourage to stick with one the way; from the top of material OR from the bottom but avoid going back and forth with this...

[mikejohn]

John
Quite a lot of good stuff was posted here (http://www.talkshopbot.com/forum/cgi-bin/discus/show.cgi?tpc=29&post=20997#POST20997), covering most of this problem.
................Mike