I converted a heavy duty overarm mill to cnc and am prepping to make the first part!  I have off and on worked on setting up the axes, etc but have a nagging question.  My y axis has only 5 inches of travel and sometimes I
will want to make a wider part.  I understand that an intermediary point can be selected as a reference say, halfway across the part to re-orient the machine after moving the piece (actually in my case, moving the stationary overarm cutter head)- here's the million dollar question....how do I make the g-code (whether using a CAM program or simple 2D batch files within Mach3) to stay within the limits of the machine, but still make the bigger part?

Do I have to make 2 complete parts in code, which just happen to coincide?

Thanks so much, soon I will be cutting parts!

Yup, you will have to make two G-code files. When you make the files, you might want to add location divets that you can zero the tool to once you move the part.

Brett

Thanks, that's what I figured.  Real simple when making 2D parts, but how does one go about modeling in a CAM program for a single 3d part, to be dissected into 2 machining operations? 

I may be way off line here, because I don't have a good cad/cam program, but what I would do when I had finished modelling the whole part is to then divide it in two with a wall across where your 5 inch limit is. My turbo Cad program could do this so others should.

The wall can be the smallest thickness measurement your program can take, but should extend out from the main piece by a reasonable amount all round.

When your program then converts this to GCode it should do one side of the wall before climbing over and doing the other side.

If you insert an M1 in the code to stop the program, you can then move the part by a set amount.
As Brett says if you have some locating lugs on the part, you can then move it quite precisely.
Reset the DRO's on Mach 3 to the new location (i.e. 5 inches up from where you were) and let the program carry on.

The wall, if very thin, will either clean out easily, or break off in the general machining, particulary if you allow for the thickness whn moving the part.
I don't know whether this will work but I've read it over again and it sounds reasonable.