in calculating the tool path

[Robin Hewitt]

Thanks but yes you have misunderstood. It is the center of the tools position I am after when it is at the end of the straight bit.

Well you just subtract the tool radius from the arc radius and add the tool radius to the line y co-ordinates before you do the pythagorus bit.

I've just been writing code to do much the same thing, decided pythagorus was a lot easier than applying the cosine rule even if it meant rotating the chord into the vertical and then back again :whistling:

Just to make it interesting I also spiral down into draft angles and hemispherical sections which is taxing my brain a bit but I'm getting there. Slowly. The G-Code is a bit whacky, I define the arc centre using I and J but the end co-ordinates are not necessarily on the same radius as the start. Dubiously G-code legal. I had to mod my mill driving code a bit before it would accept a spiral