the doctor,
NOT trying to rain on your parade, but the J Code plug in is for recording Axis movements.
There is a work around: You can do a "Teach" with VB, you can bring in your encouders and set up there positions as vectors, and as each of the 3d Vectors change, you can record the new point to your Teach file, with an Append, you would have to put this in a "While" loop that watches a "Record" user LED, when your finished you would push the "Stop Record" button, that would close and load your Teach file in your G code window.
Or, you could do it in a Plug in, like above but it would be done in C++.
NOTE: Max resoulution would be no greater than 1/10th of a second since that is the update loop time of Mach3
scott
Commercial Mach3: Screens, Wizards, Plugins, Brains,PLCs, Macros, ATC's, machine design/build, retrofit, EMC2, Prototyping. http://sites.google.com/site/volunteerfablab/