Build bigger 3D printer using parts from smaller 3D printer?

I already have a PowerSpec Ultra 3D printer for 9 months. A drawback is the build volume of about 9 inches by 6 inches by 6 inches. Someone built a larger 3D printer using parts from a smaller 3D printer at http://www.instructables.com/id/How-...g-a-Smaller-3/ He printed out the frame instead of buying aluminum extrusions. I would use aluminum extrusions but I don't know the size of the lead screw used for Z-Axis. All I need are longer guide rods, longer GT2 belts, and longer lead screw. Any suggestions?

Can you clarify your question? Are you asking what the Z-axis screw is on your PowerSpec, or what was used in the instructable?

The instructable says he used 8mm 1.25mm pitch threaded rod for the z-axis "lifting screws". Other than the mechanical differences, firmware configuration should allow you to use pretty much any pitch you want. It's just a matter of configuring the steps-per-unit-of-movement properly. This is how some printers use 5mm threaded rod, 8mm threaded rod, ACME lead screws with two thread starts, ACME lead screws with four thread starts, etc.

I want to use the same kind of lead screw that came with my 3D printer but longer. I would like a build volume of 24 inches by 24 inches by 12 inches.