Z Zero Setup Questions

[bud_wilson]

I owned and operated a 2001 PRT BenchTop for several years and I recently purchased a 2001 PRT 96x48 . It had set in a shop for approx. 10 years without ever being used. It was purchased, setup, tested and never used. It is virtually new. When built, it was not ordered with a Z Zero plate. Before I ever re-essambled it, I ordered a new Z Zero plate from SB. Now, I am having trouble getting the Z Zero plate to work correctly.
I installed 3.4.27 SB operating software. When using the C2 command to zero the bit to the top of the material, the bit will lower to the plate, touch it, stop and give a reading of .125. It does not return to a higher position, but will touch the second time and then stop. The SB reading will then change to 1.000". It does not move either up or down from this point. At this point I manually zeroed the Z and gave it a 4" move command. It then moved 5" up.
I am wondering if because it was not manufactured with a Z Zero plate and then I installed one later could it be that this is the problem. All the motors are 3.6 and are all the same. Is the Z motor supposed to be different from the rest?. According to the Assembly Manual the Unit Values are: X & Y is 733.3860 and Z is 916.7324 and I have set them to this. Both X & Y movements are correct.
After having said all that, any help you can give would be greatly appreciated.
Bud Wilson

[gc3]

sounds like unit value for z axis is wrong

what size (tooth count) pinion is on the z?

you also need to ck the z zero plate thickness and enter that into the shopbot setup under the tools tab

[beacon14]

Use the keyboard control (SK or just K) to move the tip of the bit to the surface of the table. Escape out of Keyboard mode and type ZZ to set the current Z position to 0. Then type MZ 4 or MZ 5 and Enter, and measure how far the bit ends up above the table. If it moves the correct distance the unit values are correct.

(You say it moved 5" up when you gave it a 4" move command, but it started at Z=1 - so did it move 5" or did it move 4" and end up at Z=5, 4" above the point where it started the move?)

Rest assured it is not because the machine was not ordered with the z-zero plate. Assuming you have the plate wired to the correct input switch (you can touch the plate to the bit or any grounded surface and see which input switch light comes on), once you figure out the problem it will work just fine.