Smithy CNC Mills - Manual (Page 93)

SmithyCNC Programmer’s Reference Manual: Tool File & Compensation 9-11
diameter given in the tool table to be tangent to the contour at all points of the
contour.
In particular, the interpreter treats concave corners and concave arcs into which
the circle will not fit as errors, since the circle cannot be kept tangent to thecon-
tour in these situations. This error detection does not limit the shapes which can
be cut, but it does require that the programmer specify the actual shape to
be cut (or path to be followed), not an approximation. In this respect, the inter-
preter differs from interpreters used with many other controllers, which often
allow these errors silently and either gouge the part or round the corner. If cut-
ter radius compensation has already been turned on, it cannot be turned ona-
gain. It must be turned off first; then it can be turned on again. It is not neces-
sary to move the cutter between turning compensation off and back on, but the
move after turning it back on will be treated as a first move, as described
below.
It is not possible to change from one cutter radius index to another while com-
pensation is on because of the combined effect of rules 4 and 11. It is also not
possible to switch compensation from one side to another while compensation is
on. If the tool is already covering up the next XY destination point when cutter
radius compensation is turned on, the gouging message is given when the line
of NC code which gives the point is reached. In this situation, the tool is already
cutting into material it should not cut.
If a D word is programmed that is larger than the number of tool carrousel
slots, an error message is given. In the current implementation, the number of
slots is 68.
The error message. "two G Codes Used from Same Modal Group," is a generic
message used for many sets of G codes. As applied to cutter radius compensa-
tion, it means that more than one of G40, G41, and G42 appears on a line of
NC code. This is not allowed.
First Move
The algorithm used for the first move when the first move is a straight line is to
draw a straight line from the destination point which is tangent to a circle whose
center is at the current point and whose radius
is the radius of the tool. The destination point of the tool tip is then found as
the center of a circle of the same radius tangent to the tangent line at the desti-
nation point. This is shown in Figure 9. If the programmed point is inside the
initial cross section of the tool (the circle on the left), an error is signalled.