I am building a router/plasma table (big one) and need some long ballscrews. I need 2 12' travel screws and 1 8' travel screw. Where can I get these mammoths for a good price?

Ballscrews that long are going to have to be large diameter or you will get lead whip at even moderate speeds. Also leadscrews and plasma cutting do not play well together. IF you can find them at less than the price of a small car you will face a difficult task getting them mounted properly and keeping them clean.

You might want to rethink the leadscrew design and drop back to the favorite standby:
Rack & Pinion with belt reduction or it's close cousin the long belt drive.

Tom CAUDLE
www.CandCNC.com

Not a problem lenght as I see it, there are longer setups than that. But as Tom says, the plasma is a problem if you don't mount the screws on the sides. And then there are cheaper solutions.

Have you looked at the max suggested RPM for a 12ft ballscrew? Depending on the pitch (TPI) you need to work backwards to see how many RPM you need to travel 200 IPM for plasma cutting (400 IPM would be nice for rapids)

With a 5 TPI ballscrew you need to spin it 1000 RPM to get the min 200 IPM. You will find that RPM too much for even a 6ft leadscrew unless it's larger in diameter than 3/4".

In a big gantry you need to drive it from each side and that means two 12 ft screws.

The only way to get decent speeds with long screws is to fix the screw and spin the nut. That is an approach a lot of commercial table builders use on big precision tables.

The dirt and plasma dust problem is a separate matter and anything short of having way covers over the screws (bellows type tubes) will cause you to have to clean and lube the screws every few hours of use.....ask me how I know:D

You answered yourself, the screw doesn't have to rotate. :)

I am still considering ballscrews for their accuracy and strength. We are using MASSIVE linear ways on a table we are building. It will probly handle a 3/4 end mill buried in aluminum.