pulley sizing for motorized mil

hi, i'm going to build my own mill as a access to a few free parts has come my way, i currently use a converted pasta maker which works well but takes a long time and i have to stand there with a cordless drill to power it.

the mill is going to be either a 2 or 3 roller (4.5 inch by 10 inch) and powered either by a circular saw motor rpm,1800w,240v or a kenwood chef motor.
the kenwood chef would be my prefered option as it has already has an attached gearbox-currently faulty. the problem is if i fix it i've also fixed the problem and swmbo will want her kenwood chef back!, if i use the skillsaw motor it will require a large amount of reduction so i'm thinking it will require a 2 stage stepdown otherwise 1 wheel will be enormous.

any ideas how i work out the sizing to get from 4100rpm to 150 ish in 2 stages?
i'm hoping to source a few parts from old washing mavhines to keep the cost down.

The speed reduction is simply a ratio of the two sheave diameters. Reducing the rpm from 4100 to 150 or so will require large sheaves even with a double reduction with a jack shaft arrangement. I would try to find a lower speed motor if possible. I don't know what's available down your way, but up here the common AC motors are either 1725 or 3450 rpm. You probably have some equivalent to our 1725 versions and one of those would be much easier to deal with. Forget the Kenwood Chef thingy. It's not worth the aggravation from the lady. Have you considered using a large, cheap drill motor? That's the least painful way to go IMO. Other than that, consider buying a used gear motor of some kind. That's what I use and it makes for a simple and compact set up. It looks like you would need a a 20" sheave driven by a 1.5" sheave twice to get you down from 4100 to somewhere around 150 rpm. That would be a cumbersome configuration IMO.

I don't remember how you measure the v-belt driven sheave diameters in order to calculate the reductions, so the above examples are only rough approximations.

this is a good start

http://hbd.org/carboy/motorizing_a_malt_mill.htm

A compound arrangement using 2" drive and 12" sheaves would bring you to approx 114RPM resulting in 134 sfpm with a 4.5" mill.

thanks for the replies fellas,
i've come across these listings after a quick browse,the 24v motor seems to run at a good speed but i assume i'd need an inverter to run it,
the gearbox would give me an rpm of about 68-too slow?
http://www.trademe.co.nz/Browse/Listing.aspx?id=321820618
http://www.trademe.co.nz/Browse/Listing.aspx?id=320753387
i'm going to make a trip to the recycling centre to see if any pulley wheels are available for a new life on a roller mill,if anythings available i'll make a decision on which direction to take.

That would still be 80 sfpm which is a little on the slow end but not overly slow. Would easily still get the job done.