Any danger in changing the Z Zero routine?

[ryan_slaback]

I have a new Alpha and up till now everything has been going smoothly. Today I chucked a 13/64 bradpoint in a keyless chuck adapter I made and used it to cut about 2000 holes in 1/4" hardboard. When I used the Z zero routine everything worked swell with the exception that when the machine bottommed out on the plate it then desires to go up to 2.000 in the Z. This time there was not that much room in the spindle travel so it bottomed (topped?) out and lost position and had to be reset.

Am I at risk of problems if I modify the Z zero routine so that rather than touching and then going to 2.000 it instead only goes to a lesser Z like .750 or so? I can see this as a problem in the future as well if I ever carve anything thick.

[brian_harnett]

I have mine set to .50 I dont see any problem with changing it. I wonder why it is set so high to begin with?

[gwilson]

I have mine set to 1 inch, my question is are you zeroing out to the table top or top of your material. I zero at top on material and have had goodluck so far.

[paco]

I have mine set to VC safe Z; I can set what I need or the default work.

Nothing wrong with hacking the code Ryan; have fun! Just work on copy (backup first) and test your changes in secured conditions for the machine, the tool bit and the spindle and you.

[bcammack]

I revised my StartMove routine to add a random value to the X/Y coordinates. I have an unetched rectangle of printed circuit board about 2"x3" that I bonded to the table near the 0/0 point with contact cement. It takes the place of the Z-Zero plate that ships with the ShopBot.

Pardon the lousy formatting, this forum isn't very accomodating of that sort of thing.

***********************
STARTMOVE:

' add a random value < 2 to each axis coordinate so
' we don't poke the Z-plate in the same place every time.
' Brett C. Cammack - June 24, 2006
&my_tempoffset = ((INT((RND(1) MOD 1.000) * 1000) / 1000)*2)
' shouldn't be smaller than .1", though
IF &my_tempoffset < 0.10 THEN GOTO STARTMOVE
SML01:
' shouldn't be bigger than 2", either
IF &my_tempoffset < 2 then goto SML02
' if it is, subtract 1" from it and check again.
&my_tempoffset = &my_tempoffset - 1
GOTO SML01
SML02:
&my_ZzeroStartX = &my_ZzeroStartX + &my_tempoffset
&my_ZzeroStartY = &my_ZzeroStartY + &my_tempoffset
' Hit OK to move to your preferred starting point to start the routine.
PAUSE
IF %(3) < &zup THEN JZ, &zup
J2, &my_ZzeroStartX, &my_ZzeroStartY

RETURN

[ryan_slaback]

So I looked at what I think is the file (zzero.sbp)...

How do I change it?

[myxpykalix]

I'm a newbie so check with others to confirm this. I believe when i initially ran my setup routine it gave me a place to input the safe Z height. In shopbot control console go to Tools/Shopbot setup follow prompts and there is a section for setting the safe Z height. But check with others to confirm this.

[paco]

Ok, here how it goes in the Zzero routine;

-first it read the #90 custom cut which refer to 'my_variables.sbc'. All variables all loaded.

-then it scale according to the units used.

" &zup = &my_ZzeroSafeZ * &SCALE"

-from there you know that the Zzero routine, use '&my_ZzeroSafeZ' variable from the 'my_variables.sbc'. But inside the Zzero routine, this variable is calculated and become '&zup'.

So you need to change the value of '&my_ZzeroSafeZ' inside the 'my_variables.sbc'; that's the value after the '='. You can set it to whatever value you'd like. Like I wrote, I have set it to '&my_ZzeroSafeZ = %(28)' so it use the VC (commmand) safe Z value; so I can change it easily to whatever I want without changing the code each time.

It's not nuclear science but double check yourself and work on copy so you can revert to the original at anytime if you mess up the code.

[don62]

how accurate and consistent is the z-zero routine? i do engraving and z height accuracy to .01" is critical. to me there seems to be a variable as to z speed, when the circuit is closed and how far the z axis moves before the software tells the motors to stop. i have a prt96 with the 'old' steppers

[paco]

The slower the better (2nd plunge); if the Z speed is consistent at each zeroing, it will be very consistent... as much as you are at it though.

Notice: consistency doesn't mean accurate. I've develop a zeroing method that is as much consistent every time as I can but if I would require a VERY accurate Z height, I would double check with a fine paper gage. That's in fact how I set the Z plate thickness in the my_variables.sbc file.

My next concern (main) about Z accuracy would be hold down.

[don62]

i agree on the factor of plunge speed. my definition of accuracy is that it 'reads' the thickness of the zero plate as the actual thickness of the plate. my def of consistent is that it reads the same thickness each time.

you make a good point about the 'hold down' which particulaly applies to the zero plate - if it has 'wobble' or movement, it will distort the measurement.

appreciate the help

[bcammack]

[you make a good point about the 'hold down' which particulaly applies to the zero plate - if it has 'wobble' or movement, it will distort the measurement. ]

That's why I elected to go with a permanent z-zero plate installation by bonding a small piece of 0.0625" thick unetched printed circuit board to the tabletop with contact cement.