AvidCNC suddenly out of calibration with no changes by me or on the machine

Hi All,

I have had this machine running for years. I bought it when Avid was still CNCRouterParts. It is based on the LeadShine MX4660 with Nema 23 Servo's and I have the Pepperl and Fuch's proximity sensors for limit on X and Y and for squaring on the A axis. It was calibrated to within .001 on all axis' and the backlash was set properly as well.

I am running via a parallel port with a PC running XP that has never been connected to the internet or even a local network so no virus challenges possible.

I do a lot of setups where I have to set locating pins up to flip parts to cut on the other side. It has been working flawlessly for months of this kind of work. I can drill locating holes a little over halfway through the stock, flip it over, rerun the same program and the holes line up perfectly.. there are no witness marks in the holes.

Every day that I use the machine I RefAll home it in all three axis' and I can send it to a predetermined spot on the table and it always lines up perfectly.. until yesterday!

Yesterday I go through the exact same processes as I do every other day. No one else had access to the machine but me and today, it is -.030 off in the Y and -.044 off in the X. I have not measured the Z yet but it might be off as well.

After findng this out, I drilled a couple of 1/4 holes .75 apart of both X and Y directions and measured 1.253 in Y and 1.245 in X

So today, I have gone thought recalibrating the steps per cycle and have X and Y within .001 but when I go to send it to the predetermined spot on the table it is off in the other direction.... I haven't measured it exactly yet but I just know it's off to the positive side in both directions.

I have also reloaded past configurations that I had saved and also did the Restore Settings option in Mach3 to no avail.

I am very confused by this.

Anyone have any thoughts? What would make this thing go out of whack by that much pretty much overnight with no changes to anything on the machine or computer???? (a friend asked about the temprature since it is colder now but the proximity sensors are rated to -25C so that is not a problem and if that were the case you'd think they'd be off the same distance in each direction.... )

Thanks in advance,

Mick