gCode

GCode has a couple codes for cutting arcs and circles: G02 and G03.  I have spent a lot of time trying to figure out how to use it and I think I have figured it out. (No, I am still having trouble figuring this out.). In both cases, you specify the destination position and the radius of the circle.  (There is an i, j variant of this command which is supposed to be better at checking for consistent radius but I am hard pressed to see the advantage and the radius version is obvious.). G02 goes clockwise and G03 goes counterclockwise (or is it the other way around)?

Anyway, you are at xs, ys. You specify the destination xe, ye and a radius of the circle or arc.  It then cuts from xs, ys to xe, ye so as to describe a circle or arc around that radius.  The inner diameter will be r-mill diameter; the outer diameter will be r.  This matters if you want to cut a hole in the workpiece of size r-mill diameter or cut a circle r diameter.  If your destination is your current position, you get a circle.  

It seems to be a bit less exact than I expected.  I have been working in scrap acetal. 

G00 x.4375 y.4375 f5 (position at one side of the circle)

G03 x-.4375 y.4375 r .4375 f1 cuts an arc that it .8720" across.  I need to cut a hole .875" diameter in a piece of carbon fiber, so I will try this with r.4380 in a piece of acetal first and see what i get for diameter.