I bought an old cement mixer. *About 24" in diameter, about 24" deep. *Old,
old, old. *Has new big pulley on the end of shaft, and motor plate. *What
horsepower would you recommend so as to handle a good days work, and not
overload it or kick the 20 amp breaker? *

Do you know for sure it was electric? A bunch of the gas ones used
6:1 reduction motors, so 600 rpm or so, usually 3 or 5hp (about a 1hp
electric equivalent).

According to their website, my HF mixer has a 1/3hp "1500rpm" motor,
and turns the drum at 30rpm, but it doesn't take much overloading to
stall it. Drum size is a little smaller, 22" dia x 18", so I'd guess
at least 1/2hp or 3/4 if you have it, and 1hp is probably not out of
line. I'd guess 1725rpm but that would depend on your gearing, of
course, and what sort of drum speed you want.

Your drum size is about 6 cubic feet, so as a rough estimate I'd guess
it was designed for a "half batch" (half a 94lb bag of portland, 1
cubic feet of sand, 1-1/2 of gravel, and 3 gallons of water) to allow
room for mixing (a full batch would probably choke your drum, but you
can always adjust your batch size once you see how the thing mixes).

My little HF one (nominally 3-1/5 cu.ft.) works pretty good if I start
with a square-shovel-ful of portland, two of sand, three of gravel,
and a gallon of water. I mix to consistency, so sometimes have to use
a little less or more water to adjust for how wet my sand and gravel
already are. It's only when I start trying to push my batch size to
try and speed things up that I run into problems with the motor.

Hope that helps,
--Glenn Lyford