Setting absolute position

[EricSchimel]

After running my bit into my spoilboard today (totally my fault) I want to setup a low Z limit so that if I try to drive the bit into the spoilboard again I'll get a warning. I already have this setup for X and Y... Here's what I did:

I C3'd, and zero'd Z to the table. I parked X Y and Z at 0 and ran the UZ command to reset my table base coordinates to that location.

Everything is good now, I can't jog outside my XY and Z limits, and if I try to run a file that calls for sending the bit past -.02 on the Z I get a warning.

Here's the question:

I have a fixed zero plate that I use to zero my table. Every time I surface my spoil board I adjust this plate to be flush with my board so it's easy for me to zero my Z...

I have a little routine that I wrote that drives over to the zero plate and zeros itself. Is there a way that I can have this script set the table base coordinates for Z to zero. The only way I currently see that I can do this is to do all three axes at once....

The goal here is to set my Z absolute 0 coordinates every time I zero with my fixed Z plate...

Does that make sense?

[Gary Campbell]

Eric...
Yes, that is done using the same line that sets the user Z height. The "VA" command. The Z is set in the third position VA,,,.120 (plate thickness) the table Z is the eighth position.

More info in the Programming Handbook. VA positions are as follows: (count the commas) VA,x,y,z,a,b,table x, table y, table z, table a, table b

[EricSchimel]

Ah brilliant! I knew that had to be in there somewhere.

Thinking ahead here, can I do math on these values? As in, this plate is flush with the spoilboard so right now the C2 routine doesn't work, I took that routine and hard coded the plate thickness to be 0 in it so it could work... Would it be cleaner to do something like this:

VA , , , , , , ,0-&MY_ZZEROTHICKNESS, , , ,

(Not sure if can do math like this)

Thanks a bunch Gary!

[Gary Campbell]

Eric...
You can do what you wish, and yes the math can be done, but I would look at your math line posted above. The plate is always higher than the surface your are zeroing to so you should add them, or more simply, just enter the thickness of the plate.

I have never had an off table zzero block be at the spoilboard surface as it (the spoilboard) moves too much. It doesn't matter if it is higher or lower, its just a number relative to the spoilboard. Just like the zzero plate. Its an eighth thick so you set the z to 1/8 when it touches. same goes for an off table device. if its a half lower you set the z to -.5 when it touches.

[curtiss]

After hitting the C3 keys instead of the C2 keys on several occasions... I decided to place a small piece of red tape on the number 2 on the keyboard.

that seemed to solve that problem. C3 is a real bummer when you do not want it....

[EricSchimel]

Gary do do you know a way to view the current "absolute" position of the tool? I swore I found that somewhere and now I can't seem to find it...

[srwtlc]

Not Gary, but UV will show you the base coordinate offset.

[EricSchimel]

Ah I knew I had seen that before! Thank You!

That works great for X & Y, but for some reason no matter where I put my Z axis, that UV readout always shows 0....

[Gary Campbell]

Eric...
The Z may not be set unless you have a prox (limit) switch on the Z axis. The "0" position for the Z axis is just below the prox in the Z's highest position. Without a limit switch there is no good or accurate way to set a table based Z position

[EricSchimel]

I have a prox switch on the top of my Z axis which I never use (it's actually toggled off in settings), I always zero off of my fixed zero plate (it's flush with my table) can't I set my table base 0 Z to that plate?

[Gary Campbell]

Eric...
Of course you can if you wish, but to what end? This would be same to the X axis as setting table based zero to its furthest extent. If/when you understand the system the logical location for the Z zero is at its highest extent with all motion negative. Here is an article I wrote explaining this in 2010: http://www.shopbotblog.com/2010/01/the-daylight-method/

Here are a couple slides that might help you to understand:
The first shows the Z table or absolute coordinates at its highest extent, just below the prox switch.
The second shows the Table coordinates before the tool is (user) zeroed to the table
The third shows user coordinates at the top of material. Or before user Z zero to top of material

[Gary Campbell]

Eric...
If you wanted to use the table base coords for the Z and take advantage of the limits, you could do the following:
Use the ATC version of the "XYZ Zero" instead of the normal XY Zero run by "C3"
Modify the Z Zero to store the tool length (daylight value) when it sets the Z zero to your fixed plate
Store the Material offset when/if you use the ZZero plate to top of material

After Z Zero is run add a table limits line after Z Zero that sets upper limit at the tool length abs value (-5.75 * -1) from above and a lower limit of -.030 for example.
VL, , , , ,&daylight*-1,-0.030, ,1

This gives you the ability to never hit the upper limit nor plunge more than .030 into the spoilboard without getting a softlim error.

Another advantage is that you can restore the Z heights without rezero of the Z

[srwtlc]

The latest software versions 3.8.XX now have the usage of a Z axis prox built in to the standard Z zeroing file (C2) and homing routine (C3) . Zeroing the Z will set the TB coord for the Z and save the offset value to your my_variables file. Running C3 to home the machine will ask if you want to reset the Z to the last saved tool offset. You just need to run tool setup and check off that you have a Z prox switch and also enable it in the inputs (VN). You can set this up in older versions as well.