Hello all,

I am working with a small group of university students on a custom CNC rotary plasma tube notcher. The intent is to cut and scribe the tubes used for our Baja SAE chassis. We have very little CNC experience, so we are complete newbies to Mach4, so please excuse our ignorance! Our machine runs on an Ethernet Smoothstepper, and we are using SheetCAM with the rotary plasma plugin, and of course are using Mach4 Hobby to control things if it matters.

Onto the inquiry! Our machine has a tube workspace of ~20" that is long enough to cut most of our tubes, but what we'd really like to do is cut arbitrarily long tubes by doing the following:

1. First end of the tube is cut
2. The tube is manually pushed through the machine, with a rotary encoder tracking the displacement
3. The machine then cuts the second end of the tube.

We are not 100% sure about how to accomplish this, and because we are newbies, we are not sure about what tools and limitations that Mach4 has for us at our disposal. Is it possible to write custom g-code subroutines? i.e. in the SheetCAM post processor, if the tube needs to be manually repositioned gXX is called which Mach4 interprets as a subroutine for us to move the tube a certain amount, and then the new position is updated automatically through the rotary encoder? Is something like that possible?

If someone would be willing to point us in the right direction, it would be greatly appreciated! We are not asking for anybody to do any grunt work for us, but just to maybe offer a bit of handholding to get us going.

Thanks so much in advance!