Radius Compensation---Leadin

Hi all:

Can someone explain Lead-in's on radius compensation.

If I have a program which cuts a sqaure contour for example.

X10Y0
X10Y10
X0Y10
X0Y0

and I wish to do it in Radius Compensation, ex.
G42D1
X10Y0
X10Y10
X0Y10
X0Y0 What would be my leadin values after G42D1. As it is I get a proper cut except for the start and I suspect I don't understand the Lead-in values. (This all assumes a 6mm bit is in Slot1) . Shouldn't I get a nice Square with rounded edges with a 3mm offset.

Thanks,
Art


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