It's begun....

[EddyCurrent]

Could it be anything to do with one of these ?

10.7.28 Set Feed Rate Mode - G93, G94 and G95
Three feed rate modes are recognized: inverse time, units per minute and units per
revolution of spindle. Program G93 to start the inverse time mode (this is very infrequently
employed). Program G94 to start the units per minute mode. Program G95 to start the units
per rev mode.
In inverse time feed rate mode, an F word means the move should be completed in [one
divided by the F number] minutes. For example, if the F number is 2.0, the move should be
completed in half a minute.
In units per minute feed rate mode, an F word on the line is interpreted to mean the
controlled point should move at a certain number of inches per minute, millimetres per
minute, or degrees per minute, depending upon what length units are being used and which
axis or axes are moving.
G and M-code Reference

Using Mach3Mill

Rev 1.84-A2
10-32
In units per rev feed rate mode, an F word on the line is interpreted to mean the controlled
point should move at a certain number of inches per spindle revolution, millimetres per
spindle revolution, or degrees per spindle revolution, depending upon what length units are
being used and which axis or axes are moving.
When the inverse time feed rate mode is active, an F word must appear on every line which
has a G1, G2, or G3 motion, and an F word on a line that does not have G1, G2, or G3 is
ignored. Being in inverse time feed rate mode does not affect G0 (rapid traverse) motions. It
is an error if:
♦ inverse time feed rate mode is active and a line with G1, G2, or G3 (explicitly or
implicitly) does not have an F word.