Speed control AC motor from old cement mixer (northern tool I think)

Hi,
i have a motor from an old cement mixer (smaller sized 1.5 cu feet from northern tool and supply or harbor freight or somewhere else cheap like that) and I've removed the motor to drive my compost trommel. It spins at about 1,200 rpm i think (based on specs from similar looking mixers online). There's no labeling on the motor - it's so old it's all fallen off or faded away. 

Ive been trying to gear it down using pulleys and belts, but it's got a 9/16" key way shaft and buying pulleys and belts is getting to be more expensive that I wanted this thing to be. 

Is there a cheaper way to control the speed of this motor and slow down the rpm?

ive seen where other people use light dimmers on similar things, but I don't know if that will work here. I do happen to have a voltage output controller but I don't want to use it if it will damage the motor over prolonged use. 

Mac

Those motors are often with a capacitor so no speed regulation possible.
Take an old 24 gear mountain bike and use the sprockets and chain for your reduction - if you do it in reverse the reduction should be quite massive on the lower gears.
Get the gear set on your drive shaft and weld in place with a single spot to check if it is working for you - if it does weld it permanently.