AC Speed Controller for Lathe: Meat or Accident?

Swarfer-breatheren,

I seemed to have (accidentally) bought myself a massive big old lathe
at an auction. When I picked it up however, I found that the motor
was some horrid 3-phase electical fire with a rats nest in it, so I
dropped this and decided to just buy a new one of ebay. However: as
I'm now missing the belt-drive and motor assembly I'll have to make
this up.

I thought this would be the best place to ask this: I'm thinking
about building my own AC motor speed controller (with some
thyristors) and just leaving the motor belted on one setting or the
other. I was wondering what advice people would have on this? I'd
have asked this on another forum, but as you all are so terribly
nice, and experienced with this type of thing I thought I'd ask here
(and hey! I'll probably convert the lathe to CNC in the future
anyway. :) )

So what's the deal? Is this good science, or bad science? Will the
lower voltage mean the motor will turn really slow, but also have no
torque what-so-ever? Should I use some other kind of circuit? Or is
this is all just a terrible idea that's going to wreak havoc on the
electrical grid for blocks around as I throw rude-pulses at a 2KW
motor? Should I use a DC motor instead? (I want to do this on the
cheap, really)

BTW> This is a BIG old lathe! 5foot long and weighs.. well.. the
tailstock weighs about a third of my weight. :P

Thanks for your advice!