Received this question over the weekend. Here's a quick answer:
condition that has a work piece that is completely flat on both sides (top
& bottom) so that the machining nozzles can both be set to within under
0.008” (set to 0.020” on Makino). This close setting of the machine
nozzles, which is very sensitive and critical, is done with the aid of a metal
shim or gage. In addition to the work piece being completely flat, their
must also exist a 0.200” wide zone of material all the way around the working
geometry/shape to maintain seal-off and maintain flushing pressure, and their
can be no thru or cross hole interruptions during the machining process (work
piece and cut are thru completely solid materials). Any changes in any of
these conditions will contribute to part inaccuracies, wire breaks, and greatly
reduced machining speeds.
That really begs the question - what is a poor flushing conditon?
A poor flushing condition is any cut or process that does not allow one or
both of the machining nozzles to be set to within the “optimum” nozzle setting
of under 0.008” to the work piece. Poor flush typically involves
non-flat work pieces that may include changes in part thickness, machined
steps, thru holes, cross holes, counter-bores, etc. Poor flush can also
occur in a completely flat work piece as a result of the work holding
setup. It is quite common to see a completely flat work piece not allow
one or both of the machining nozzles to be set to within the “optimum” flush
condition height as a result of the nozzles needing to be raised away from the
work piece to provide clearance for work holding and clamping.