Centroid Community CNC Support Forum

Got a strange problem driving me nuts. Im getting random Z home errors when powering up at times and sometimes after its been running and I run the CNCM.hom file manually to test. Half the time it will go to Z home bounce off the switch and go back and set the DRO to 0.0000. Sometimes its off up to .0026 and sets the DRO to that Z position for zero. At times I can restart everything and its back to Z 0.0000 on Z home. The ABS counts are off when this happens. I disabled the other axis and ran the systest limit switch/home test several times thinking it might be Z limit switch errors but it appears to be nuts on everytime according to test results. I moved the Z limit slide dog about 1/8" think it could be a marker pulse issue. I have under .001 backlash on the Z axis which I attribute to the 8" long belt drive. I re checked the ballscrew calibration numbers and its right on using a 3d Taster on a 3" test block. Tried retuning the DMM 1.8Kw drive but it makes no difference. No quad or diff alarms when this happens, its just off . Thought it could be the machine Z axis Disc brake that mounts over the pully shaft but it took it clear off and made no difference. Y and X axis always home to 0.0000. What allows the ABS counts to be off from the commanded position without any alarms and just sets home someplace other than ZERO.

Note that the same 51 counts appear in the "Error" column.

At the point when you took the picture, if you were to have pressed emergency stop; then released emergency stop; then commanded a move to Z0 (e.g. using MDI or by pressing Tool Check), chances are good that it would have returned to zero.

This is a sign of lost command counts between the Oak unit and the DMM drives: the DMM drive is failing to execute all of the movement that was clocked out to it.

Yea. Now I'm really confused. Tried the tool check button and got. G28 set too low. My machine home at power up is set to Home switch. It homes to just off each limit switch. That means my z axis travel is all negative. Tool check won't allow negative positioning to get to the g28 -5.175 set for my tool change height. I cant figure out how to set the z home to get to tool change height on power up home. Modify the hom file ?

CNC12 will only do a Tool Check move if Z is at or below the G28 position (so that the move goes up). If you are above the G28 position, pressing the Tool Check key will just display the warning message. This is to keep inattentive users from crashing tools or probes, after they have set a significant negative G28 height.

But that is a distraction here. You are just trying to find out where Z ends up when the control tries to move it to machine zero. You could do the same thing, no questions asked, by using F3/MDI to run "G53 Z0".

To reduce the likelihood of lost command steps:
1) Solder the shield of the axis interface cable to the shell of the DB25 connector at the DMM drive
2) Increase your acceleration time (try 0.3 seconds instead of 0.1 seconds)
3) Buy better servo drives

Lol. Ok. Point noted. Shields are on shell. These are factory from dmm. Forget the errors for now. How do I set z home to be at tool change height in hom file?

Well Not sure if its right but it seems to work like I want . ( It mirrors my MiniMill)
Home File
M92/Z
G91 G20 G1 Z-5.175 F40 ( I added this )
M26/Z

And in the M6 mac file I changed the head clearance
G53 Z5.0

And of course reset all my tools.

I am not sure quite what you are trying to achieve there.

I would leave Z home at Z home. I.e.: Then, since you generally want the head to go first to carousel level (not home) when it is time to change tools, set your G30 and G28 positions both to whatever distance you need, down from home (e.g. -5.175, if that is the distance it takes to get from where M92 finds home, down to your carousel).

When it comes time to troubleshoot loss-of-position issues, it is helpful to have set machine home (with M26) at exactly the same place you found home (with M92). That way you can troubleshoot by running another M92, and seeing whether the encoder count goes back to zero.

Yea, thats the way it was, It just bugged me that it stayed all the way up and all the travel was negative. Hass mills come off the z home switch and go to tool change height on power up for initial zero. My Zero now is the same as G28 G30 at -5.175 . Got a million hours running the Hass mill here sitting next to this one and wanted to keep things consistent and close to same setups.

If you want it to go down to carousel level after it is done homing, you can just put "G91 G28 Z0" at the end of your homing macro.