Sorry SD this is an old post that has been brought forward.
Yes the 75 is the speed, but note that it is derived from the speed of the spindle and the diameter (or radius it is cutting at) This means it must be told where it is to start (see previous line).
The code Graham has included there works first time. The only problem was that I wanted to cut from the centre outwards - and I couldn't seem to get that to work the same way. I set the thing going as per Grahams program, have it travel in, the cut outward, and it worked perfectly. (up to the speed limit of that set of pulleys)