Z issues

[Stagecraft]

I'm having problems when using my Z zero plate...it is working in that the z routine will run, the cutter will come down, make contact, but then it seems to put just a little much force on the bit before lifting up.
I'll then find that the part file I cut may be too deep by as much as 1/8 inch.
This doesn't happen when I take the time to manually set the Z zero to the material but obviously this is a bit too slow a process at times.
I did see another thread ( http://www.talkshopbot.com/forum/showthread.php?t=13250 ) where the Z Plate input was changed to input 2 and that solved the problem. I'd like to give it a shot but I'm kinda' lost at just how to do it...anybody out there that could help? Thanks - Boyd
PS, the machine is a 2004 PRT upgraded to Alpha and uses only one cable with no alligator clip, its well grounded and the red input light does come on when making contact.

[adrianm]

Are you sure the thickness of the plate is set correctly? If that's out then the offset added during the routine will give you that problem.

[Gary Campbell]

Boyd...
Are you using a router or spindle?

In most cases, if the input 1 light works when the plate contacts the bit, that input circuit is OK. Swapping to IP 2 wouldnt give any difference.

Should you decide to change to IP 2, there would be modifications made to the input wiring and you would have to modify the ZZero file. You may want to contact tech support for help diagnosing the problem before making these changes.

Sometimes coated bits cause this. Also, sand your zzero plate to ensure good contact

[Stagecraft]

Gary, Adrian, thanks for the replies.
I'm using a Columbo 5hp spindle and I seldom use coated bits.
I'm not certain that the Z routine plate thickness is correctly set, I can put a set of calipers on the plate to check it, but how do I go about confirming or altering the command line in the program?
This problem may have been present for a long time but up until now this machine has been used primarily for ripping sheet goods, so dead-on depth accuracy wasn't an issue. - Boyd

[jerry_stanek]

Look under tools in the shopbot software for set up go through the set up and you will be able to put the thickness in.

[Stagecraft]

Thanks Jerry!

[curtiss]

Say your plate measures .137

The instant the bit touches the plate the z reading on the your screen should reset to .137

This should be confirmed on when the second touch is made.

If you watch your screen you may find the problem.

[Stagecraft]

Thanks Curtis, I did go through setup and found that the Z plate settings were off. They were set to a plate thickness of .136" when in fact the plate measures .122"
When running the Z zero routine, the cutter makes contact and the screen shows .122"
Although the settings were off, they weren't off enough to explain the results that I was getting (sometimes cutting .125" too deep).
I've already run tests on the Z with a dial gauge just to confirm that my value settings were correct and it seems to be moving within accepted tolerances...still stumped. - Boyd

[Gary Campbell]

Boyd....
Check the backlash on the Z pinion (and its condition) and make sure that the grub screws are both tight. (wrench bending tight)

[curtiss]

....Although the settings were off, they weren't off enough to explain the results that I was getting (sometimes cutting .125" too deep).

Does the z data on the screen show that the z is cutting to the proper depth during the operation of the file ?

If the data is showing correctly, and it is still cutting too deep, something is slipping or a ratio could be off,

Is the bit still tight, and zeroed to the surface after the cut or has it moved ?

[Stagecraft]

Curtis, sorry so late to reply, a busy couple of days around here!
When cutting, the screen is displaying the correct depth pass. I've double checked my values and they are what they should be.
As mentioned earlier, when I set the Z manually by running the bit down to just touch the material surface, the job will cut perfectly. Its only when I set the Z via the plate that I have issues, I'm starting to think that Gary may be onto something with the backlash suggestion.
I had been pondering upgrading to the gear reduction motors anyways...maybe nows' the time to bite the bullet and order them. - Boyd