Z axis zeroing and drifting deeper problems

[bbobmc]

I am a new user. I have a 2005ish prt. I am the 2nd owner I am just starting it up. I have udated the firmware to the latest availble for this machine. I input the values for each axis so it moves are the correct scale.

I have 2 problems with my Z axis. I don't know if they are related. First problem is Zeroing Fail. I looked through the forum and I do not see any other posts that match my symptoms.
- I load and run the zzeroing file.
- After starting I get a dialog box that says "LIMIT SWITCH HIT". I am not doing this at the edge of the table, and I don't have any inputs for the limit switches activated. Is this normal?
- I click on RESUME in the limit switch dialog box
- The z axis lowers until it hits the plate. It stops and a dialog box that says "ZEROING FAILED" comes up. Input #1 makes when the tools hits the zeroing plate.
- The zeroing rotine will not continue from here. It does not lift up and do the 2nd slow speed touch off.

The second problem I have is that the Z axis goes deeper everytime it lifts and lowers back down. I manually zero the Z axis when it is touching the top of the work piece. The bit is tight in the collet.

Anyone have any ideas. Thanks in advance for your help

Bob

[steve_g]

Alpha or standard? If alpha the multiplier numbers may be wrong… this would cause it to work progressively deeper.
http://www.talkshopbot.com/forum/showthread.php?17659-Z-gets-progressively-deeper&highlight=multiplier
SG

[bbobmc]

It is a PRT Alpha. Thanks for the link. My multipliers were all set to 5. I tried setting them to 1 based on the info in the string in the link you sent. That didn't work.

I was able to fix the zeroing problem. My limit switches were set to normally closed, but they are normally open switches. After I changed the setting for that the zeroing works. When cutting a file the z still keeps plunging deeper every time it lifts and lowers.

[steve_g]

Bob…
My only experience is with an Alpha from the same era… on my machine, the x and y multipliers are 4 while the z is set to 1.
Since it’s an alpha, I doubt it’s loosing steps. Rethink what you are calling a tight collet.
SG

[bbobmc]

Steve,

I think I got it with your last suggestion. I had to put in 4 for everything except the b multiplier which was 1. I ran the shopbot logo with no problems. Thanks so much for your help

Bob

[steve_g]

Bob…
I’m glad we got you up and running!

I am however curious about your axis nomenclature… Normally you have X & Y for your horizontal movement and Z for the vertical movement. A is generally a second Z axis and B is a rotary indexer. Is your Z axis hooked up to the B channel?
SG

[bbobmc]

So, I am new to this thing and I don't know what I am doing yet. There were variables in for the A and B multiples so I thought they must matter. Thanks for telling me what they were. I don't believe the z is hooked up like you asked. When I tried running 4, 4, 1 for xyz it didn't run right. 444 worked. Thanks again for the help.

Bob