Smithy CNC Mills - Manual (Page 87)

SmithyCNC Programmer’s Reference Manual: Tool File & Compensation 9-5
The effect of this is that in most cases the machine
will pick up the offset as a ramp during the next xyz
move after the g43 word.
9.4 Cutter Radius Compensation
By Jon Elson
Cutter Diameter Compensation (also called Cutter Radius Compensation) is
something that was obviously added onto the RS-274D specification at the
demand of users, as it is VERY useful, but the implementation was poorly
thought out. The purpose of this feature is to allow the programmer of the tool
path program to 'virtualize' the tool path, so that the control can, at run time,
determine the correct offset from the surface to be cut, based on the tools
available. If you resharpen the side cutting edges of end mills, then they will
end up smaller than the standard diameters.
The problem is to describe to the control whether the tool is going to be cutting
on the outside of an imaginary path, or on the inside. Since these paths are
not necessarily closed paths (although they can be), it is essentially impossible
for the control to know which side of the line it is supposed to offset to. It was
decided that there would only be two choices, tool 'left' of path, and tool 'right'
of path. This is to be interpreted as left or right 'when facing the direction
of cutter motion'. The interpretation is as if you were standing on the part,
walking behind the tool as it progresses across the part.
9.4.1 Cutter Radius Compensation Detail
By Tom Kramer and Fred Proctor
The cutter radius compensation capabilities of the interpreter enable the pro-
grammer to specify that a cutter should travel to the right or left of an open or
closed contour in the XY-plane composed of arcs of circles and straight line seg-
ments. The contour may be the outline of material not to be machined away, or
it may be a tool path to be followed by an exactly sized tool. This figure shows
two examples of the path of a tool cutting using cutter radius compensation so
that it leaves a triangle of material remaining.