I have a vintage 5 HP DeWalt 16" GE radial arm saw which was operating at 3 phase, 240/480 volt. Can I operate this saw at 1 phase, 240 volt. If so what has to be done to the saw.
Thanks

What you need is known as a "Phase Converter".

These things basically convert the single-phase input to the 3-phase that the saw wants. It is not a perfect science, but it works in many cases.
Be aware that a 5HP unit will not be cheap!

There are two basic types of phase converter:

Static - Cheaper, but not as good. Still...works in many applications
Rotary - Higher cost, but better performance. Should work anywhere.

Here are a couple of links for more info:
http://www.phaseconverter.com/
http://www.phase-a-matic.com/

I don't recommend these guys, they were just the first hits I found in Google.

Good luck,
WallyH

You also need a circuit beefy enough to handle the current.