Smithy CNC Mills - Manual (Page 98)

program with tool zero selected, and it draws a line at the actual part's outline.
(see figure below) Then, I select a tool with the diameter of the tool I intend to
use, and run the program again. (Note that Z coordinates in the program may
need to be changed to prevent plunging the pen through the platen.) Now, I get
to see whether the G41 or G42 compensation that I specified will cut on the
desired side of the part. If it doesn't, I then edit the opposite compensation
command into the program, and try again. Now, with the tool on the correct
side of the work, you get to see if there are any places where the tool is 'too
fat' to fit in a concave part of the surface. My old Allen-Bradley 7320 was pretty
forgiving on this, but EMC is a complete stickler. If you have ANY concavity
where two lines meet at less than 180 degrees on the side that a tool of finite
size cuts on, EMC will stop with an error message there. Even if the gouge will
be .0001" deep. So, I always make the approach on the lead-in and lead-out
moves such that they just nip the corner of the part a tiny bit,
providing an angle just over 180 degrees, so that EMC won't squawk. This
requires some careful adjustment of the starting and ending points, which are
not compensated by cutter radius, but must be chosen with an approximate
radius in mind.
The operative commands are :
G40 - Cancel Cutter compensation
G41 - Cutter Compensation, Tool Left of Path
G42 - Cutter Compensation, Tool Right of Path
Here is a short file that cuts one side of a part with multiple convex and con-
cave arcs, and several straight cuts, too. It is to clamp a high speed drilling
spindle to the side of the main Bridgeport spindle. Most of these commands are
straight from Bobcad/CAM, but lines N15 and N110 were added by me, and
some of the coordinates around those lines had to be fudged a bit by me.
N10 G01 G40 X-1.3531 Y3.4
N15 F10 G17 G41 D4 X-0.7 Y3.1875 (COMP LEAD IN)
N20 X0. Y3.1875
N40 X0.5667 F10
N50 G03 X0.8225 Y3.3307 R0.3
N60 G02 X2.9728 Y4.3563 R2.1875
N70 G01 X7.212 Y3.7986
N80 G02 X8.1985 Y3.2849 R1.625
N90 G03 X8.4197 Y3.1875 R0.3
N100 G01 X9.
N110 G40 X10.1972 Y3.432 (COMP LEAD OUT
N220 M02
SmithyCNC Programmer’s Reference Manual: Tool File & Compensation
SmithyCNC Programmer’s Reference Manual: Tool File and Compensation 9-16