Coding an Arc on a Lathe

This is an example of coding an arc for a normal front tooled lathe.

To cut the arc on the rondelle I first move to the start point X1.0 Z0.0. To figure the arc offsets look at the drawing and see the arc center. Subtract the arc center from the start point and that is the X offset which is programmed using the I word. The offset is on the minus side of the start point so it is a negative offset. Next is the Z offset which you can see is on the plus side of the start point so K is a positive offset. The other gotcha is a normal lathe the imaginary Y axis positive end is under the lathe so viewing from the top arc directions and tool offsets are on the opposite side. Using radius mode for the lathe you generate the G code as follows:

G8 (radius mode) G18 (XZ plane)
T1 M6 G43 (load a tool)
G0 X1.0 Z0.1 (get close)
G1 Z0.0 F10 (move to start position)
G3 X0.500 I-0.250 K0.1219 (Z is the same at the end so is not needed)
M2 (program end)



John