cameo/templates/mkmk-simple: introduce Z0 parameter; clean up Z calculation

This allows the setting of the "tool down" position, e.g., when varying
the thickness of the support or of victim material under the PCB.

cameo/templates/mkmk-simple

@@ -9,6 +9,7 @@ PATH=$PATH:/home/qi/cae-tools/gp2rml
 # X0, Y0	lower left corner of raw board, default: 0mm 0mm
 # X, Y		position in array, default: 0 0
 # XN, YN	number of boards in X/Y direction, default: 1 1
+# Z0		tool height when in contact with the surface
 # ROT		board rotation, default: 0 degrees
 # DRILL		drill diameter range, default: 13mil,14mil
 # MILL_IN	diameter of mill for work inside the board, default: 35mil
@@ -31,6 +32,7 @@ fi
 : ${X0:=0} ${Y0:=0}
 : ${X:=0} ${Y:=0}
 : ${XN:=1} ${YN:=1}
+: ${Z0:=-57.4}
 : ${DRILL:="13mil 14mil"}
 : ${MILL_IN:=35mil}
 : ${MILL_OUT:=35mil}
@@ -70,8 +72,7 @@ $rot
 align 1 $X0 $Y0		# align relative to board corner
 translate 4mm 4mm	# move to PCB zone assigned to project
 array +3mm +3mm `expr $X + $xi` `expr $Y + $yi`
-z 0 -58.9mm		# board surface (tool fully retracted)
-z 1.5mm			# slack for extending the tool
+z 0 ${Z0}mm		# board surface (tool extended)
 z -$BOARD_Z		# board thickness
 z -0.5mm		# tool extra depth
 clear
@@ -118,7 +119,7 @@ drill:
 		PORT=/dev/ttyUSB0 \$(SPOOL) drill.rml
 
 cng:
-		\$(CNGT) -57.4 20 mill.gp
+		\$(CNGT) $Z0 20 mill.gp
 
 plot:
 		echo 'set size ratio -1; \