The more I learn the harder it gets.
So a circle must have hundreds/thousands of calcultions?.
But I get the principle.

Graham

So a circle must have hundreds/thousands of calcultions?.

To get the feedrate of each axis at any given time? Well it depends on how you command your circle. If it's "hundreds/thousands" of G1 moves then yes but if it's G2/G3 then no.

I hesitate to ask but how does it do a circle under g2/g3?

Graham

If the circle is made up of straight lines then Mach has no idea it's a circle and plans each individual move just as if it was a "random" sequence of moves. If it's a G1/G2 then by definition Mach knows it has to produce a circle (or part of i.e. arc). In that case the relationship between the X and Y axes is a simple formula that holds for the whole arc/circle. Each axis simply describes  simple harmonic motion where one is a sine and the other a cosine.

Thanks Rich and Stirling for your explanations.
It helps me to understand the complexity of what goes on when I enter a command into Mach 3.

Graham