We have a brand new vertical CNC with an Oi-MC control. We had a workpiece set in G54 with a Z0.7940" work offset. We had to do another quick production job of 20 or so parts. So using G55 the work offset was Z1.0132". The first part ran without any problem, but when we put a new piece of material in and started the program the first tool crashed. Put a new drill in, started again. First piece no problem, second piece tool crashed. When we started to investigate we found it went .2192" deeper when it rapided in the Z axis. So with a reference height of only .100" above the work it was doing a rapid movement .1192" into the top of the workpiece. We relized that the .2192" was the exact difference between the G55 work offset and G54 work offset. Since the machine is brand new and under warranty, we have had a FANUC tech. here for three days and he's stumped too. What we did find out was that it would not happen if you used single block or pressed feed hold before the first negative Z axis movement or if the first tool of the program was already in the spindle. We tried many different work offsets for G54 and G55, if G54 was a bigger number than G55 then the tool would stay up and if G54 was smaller it would come down to far. The amount was always the difference between the two offsets. This will only happen on the first tool in the program, the 2nd and 3rd would go to the proper depth. We have tried numerous ladder diagrams and different edits of these ladders from machines that work fine and have compared the parameters to many working machines. I've checked all I have also contacted the MTB and they are baffled also. Has anyone ever heard of anything like this or have any suggestion what to try to fix it.