[Machman85]

I have a milltronics retrofit. A fryer MB11 bed mill with a centurion 1 control. Recently the Z axis has been doing a plunge before moving in a positive direction. For example I was circular interping some counter bores and when I rapid out of the hole it dose a quick plunge about .005 deep before moving up. I'm thinking its an encoder. Even in handle jog once I reverse direction it jumps down. Dose anybody have any experience with this or know what this could be?

[ZZZZ]

I think I would start by looking at backlash since it appears to occur when you change directions. Tighten up all the possible mechanical places things can get loose, then set the Backlash parameter to zero and check for the actual value you can't remove. Re-set the parameter to the value you found and check it again.

I hope this will help.

[Machman85]

So i posted the Z axis problem a few years ago and have been working around it. I want to add that this only happens when working close to the table.(not near the limits tho) after i get to a certain spot on the z axis close to the table...say touching off a tool, then on the reversal it jumps down .1 on the first "click" of the hand wheel then jumps back up and recovers to the right position on the second click. If i move up a couple inches everything works fine. I checked the "per inch backlash comp" and they are all zero ish. I'm tempted to try a large comp at the Z-17" comp setting.

[ZZZZ]

Well, since it has been 2 years and 8 months since you first posted, it can't be that much of a problem for you. What diagnostics have you done? Are you sure it only happens down low? Does it do it in Jog? How about in a program? Put an indicator in the spindle and write a program that moves up and down to check several heights of gage blocks. Does it go to the right places?

There isn't a "per inch" backlash compensation. There is a Ball Screw Compensation table; the Z axis table is called BSCREW3 and it is in the RAM folder.
Go re-name that file to something else and re-boot the machine. Jog or Handwheel back down to where you think the area is and try it. If a corrupted or wrong BallComp table is causing the move, this will eliminate it. If not, something else is going on.

[single phase]

It only does it at lower z values? Can you do a study to determine what z value is the cutoff? That is an odd problem. Could it be a corrupt ball screw compensation file?

[Machman85]

Thanks ZZZZ and Single phase for you responses. So I ended up re-checking the ball screw comps. They are set up for adjustments for ever 1/2"... all where set to zero. So seeing how for some reason i could not open the "ram" folder on the floppy disk on my pc. I decided to just turn off the ball screw comp on the Z axis since it didn't appear to have any values. I did test the axis with an indicator after, and it looks good, at least at that position range. Once I did this everything worked perfectly. So Thanks guys. And just for reference the magic Z number where this all started was Z-18.3321. Also the ball screw comp table started at 18.500 even tho i have 20" of travel. I was able to get around this for so long because I was doing mostly vise work and that raised me out of that faulty zone. It came to be a problem again as i'm roughing on a sub-plate and as you probably know a long holder chatters like crazy so once i was forced to use that stubby holder i had to fix this. Thanks again.