How do you program the cutting of a shape (star, gear, etc.) using just a circular axis (theta) and a linear axis (either x or y)? A simple example would be if I had a five pointed star and I want to trace the star's outline by rotating it and having a pen attached to the linear axis follow just the edge. I want to be able to use a .dxf file of the shape and run that through a cam program and output the commands to the two axis.
I want to use a hot wire on the linear axis to cut a foam gear on the circular axis. This is why I can't just use x and y axis to cut the shape. The lower arm holding the element will collide with the work holding device. That is why I need the chuck to rotate and the linear axis to move in and out and the two to be coordinated. In the past I have done this with a series of point to point moves for example when theta = 0 degrees, x = 2.0; when theta = 1 degree, x= 2.15, etc. The finer the moves the smoother the cut. This makes for a lot of code writing and thus my interest in some way to convert a .dxf file into the cutting path.

I think you need to convert the X or Y to polar values to run as A.  Cart to Polar conversions are fairly simple .

OR in you cam Have IT do the conversion for you.

Just a thought, (;-) TP

Thanks for the reply.  So you believe that this is something that the CAM software should be capable of doing.  I could go into, say, Bobcad Cam and set a few options and it would generate the correct code?

If I read your question correctly, you want to use a rotary table in the C-axis i.e., mounted flat on the table with its axis parallel with the spindle.

I wrote an app to do the conversion but it isn’t exactly as straight forward as I would have liked.  There are several things to keep in mind that may require some hand editing
 
For example, in rectilinear coordinates we are used to seeing arcs made up of short straight line segments, but in polar it’s the opposite. Straight lines consist of short arcs.  Your CAM software can probably break the lines into segments for you.

Another problem is feed rate.  (The feed rate for each block is dependent on the current radius.)  For the A-axis Mach will do this conversion. It uses the Z value to determine the radius.  Unfortunately this feature is not enabled for the C-axis. I had to use G93 Inverse Time mode which has its own drawbacks. It seems to require a (much?) faster PC than any other file that I have ever run.  It runs fine on my desk top (1 GHz) PC but bogs down to a crawl on the older and slower machine PC.  

I will attach the app and two short sample files, the original rectilinear and the other one converted to polar with the feed in Inverse Time mode.

See how it goes; if we can’t get this to work there are other fall backs.

Al