z axis zeroing

[Mark Henry]

I need help with zeroing out the z axis. Everytime I zero out the z axis it goes down to the zero plate reads .121 then goes up then back down- like it should but when it goes back up it reads 1.00 inches even though it only about .375 inches off of the board. Can anyone tell me why this happens and how to fix it? I can't carve anything untill I get this issue resolved.

[jerry_stanek]

It sounds like you have the wrong unit values set on the z

[Mark Henry]

Jerry,
Being new to CNC I'm not sure what you mean by unit values. How do I change them?

[myxpykalix]

in the shopbot control software type in VU
or go over to (V)alues/(U)nits

you should see a column that says "Z unit values" and numbers in a column. Mine says
2291.831 but i cannot say those are correct for you.

[Mark Henry]

Jack, my z value reads as follows 2979.3805. Do I need to change it?

[rb99]

Jack, my z value reads as follows 2979.3805. Do I need to change it?

Can you post the motor type and the # of teeth on your pinion? This information is required to set the value.

[Mark Henry]

the motor is model a7328-9412ktg vexta stepping motor. crazy question - how do you count the teeth on the pinion when I can't see it clearly?

[rb99]

the motor is model a7328-9412ktg vexta stepping motor. crazy question - how do you count the teeth on the pinion when I can't see it clearly?

I have used a mirror...and a flashlight...and a pointer. They are usually 18, 20 or 25 teeth.

[myxpykalix]

http://catalog.orientalmotor.com/keyword/?&plpver=11&key=all&keycateg=100&SchType=1&keyword=a7328-94I2ktg&refer=http://www.orientalmotor.com

I can't find a motor on their website with those numbers. Make sure it is a oriental motor and double check your numbers.:confused:

[rb99]

Take a picture?

[tlempicke]

If I am to write a program that will be used on different machines where one pulse will move the head in a given direction but an unknown distance I would use something like the Vu command in shopbot.

To fix your problem and clarify your thinking on the subject try this.

Move the Z to a point about two inches above the table. Zero the Z axis. give the command mz-1 (move Z to minus one inch) and enter it.
Measure the amount of movement.

Say, for instance, the Z moves a total of 1.25 inches. That is about 25% too much. Reduce the value of Vu by 25% and re-try.
After half a dozen trials you will be able to correlate the number of units change in Vu with thousandths of an inch.

A final check with a dial indicator will allow you to get the machine within .001 or .002 on a repeatable basis.

To get the C2 routine to work properly you must have the correct thickness for the Z zero plate set into it. In my case the routine was factory set to .125 or 1/8 of an inch. My plate is actually 3MM (from the factory) and when I measured it with a micrometer is was about .122. That crappy little .003 will drive you bonkers when you try to set up tabs or leave an onionskin on the bottom of your work.

Bye the Bye - I have seen any number of cases where dealers send out 3MM bits for 1/8 inch size and vice versa. When you have parts that need to fit closely this can cause a little hair pulling too!

[Mark Henry]

Ok I'm at a total loss now guys, Tom tried your way and I got it to work but the values are only good up to one inch. For instance when I key to move the z axis up to 2 inches it actually goes to 1.001, when I tell it to to go to 3 inches it is actually at 1.710. Now I discovered that my x and y axis is doing the same thing. When I zero out the z axis it returns to what it says is one inch but is actually .264.
I guess it would be to easy to hit a reset button to get everything back on line. Any help would be greatly appreciated so I can get back to carving Christmas presents.

P.S. what causes this to happen so I can make sure it doesn't happen again.

Mark