the fourth factor is the final required mesh that you plan to mill down to. since the balls basically come in one size, and i haven't measured them, they are about 3' diameter. there are sources for small milling balls for milling pigments and small batches in small ball mills i.e. bench-top mills.
first run ran six pounds of rock in my small homemade ball mill 14 x 12 for two hours,rock was reduced to flower fine dust. nice pay day in gold too luck on your next hunt. chuck
depending on how much you ran it through the ball mill before, it is possible that the gold is already in smaller specs than the sand. as i understand it, it's like this: you have ball bearings that are larger than the sand and the gold. the gold 'may' collect on the steel balls and flatten out.
ball mills. ball mills have been the primary piece of machinery in traditional hard rock circuits for 100 years. they are proven workhorses, with discharge mesh sizes from 40m to <200m. use of a ball mill is the best choice when long term, stationary milling can be justified by an operation. sold individually or as part
stawell gold mines is excited to announce that commissioning of the ball mill successfully occurred on wednesday morning. sgm millconstuction ballmill commissioning construction production gold
tomcat you are describing a rod mill. work like a ball mill but usually they are not expected to grind as fine. works great and sometimes easier to get rods by cutting scrap hardened steel like axles etc. one inch works pretty good in mills in the 12 to 18 inch diameter. you can convert a larger rock tumbler into a rod mill quite easliy.
that being said, here are a few links i found for building your own ball mill, a rod mills would be build much the same but using heavy rods instead, old truck axles would be a great source for a small rod mill, with a ball mill or a rod mills having different sizes of grinding medium would work better than having all of the same size balls/rods.