Awesome strange!!! lose position then get it back randomly!!!

[Scramjet]

Hi
I have a small CNC im leveling the aluminium table plate to get it flat to make PCBs as it is a little rougly.

I noticed something strange:

It suddenly loses position in the passes along X, about .03 inch ( .762mm) i notice it in the unbrushed corner, makes a line pass then it gets back to the original posotion with great precisión, makes like 20 straight lines of 1ft of lenght, then suddenly again loses that .03 inches, sometimes makes it in 2, 3 or 8 following lines then it corrects itself, again and so, but this happend randomly, sometimes is every 40 lines of 1 feet, sometimes 15, or 50, is random. Dont know what is it, is something very strabge, since i know could be backlash, but happens is not acumulative, as it always comes back to same position in randomly moments.

Im using Mach3 as program control, the pc has 2.2 GHZ amd sempron, 1Gb ram, running XP sp2, i searched for virus and is clean, i checked wiring , interferences all seems is ok, checked the machine transmision, some slip in the couplers, all is tight!, but cant find the reason of the problem.

Using step motors, with mm setting on motor tuning, 125 step/mm, vel 2500 mm/min, accel 300 mm/s/s.

I settled the kernel on Mach3 to 25 KHZ, and in motor tuning i set to 2us.

The machine always come back to the exact initial point after the 10000 code lines, i mean like 1 hour making all "brushing" to the aluminim bed with an 3/32" end mill, but i can see the edges of the square (1x1 ft) than randomluy is the .03" (.7mm) eaten, sometime in 1 only line or sometime 5, 8 continuos, in random distance each.

Thanks in advance for any help you can give to me to discover the cause of the prloblem and fix it.

[Superman]

Thanks in advance for any help you can give to me to discover the cause of the prloblem and fix it.

More Tequila to make it go away ??

Have you tried to switching into single step as it happens ?
Could it be a lag in the graphic card updating the screen position display ?

[Scramjet]

Tequila is not helping anymore

I tried with a softer material (wood) to see if was a bending issue.. same

Is not a graphic cards update problem since it happens in real cut and on screen all seems perfectly drawed, but allways comes back to same position!, even is steppers.

Will try changing PC maybe that helps.