Here's a little bit of what I learned during the planning and construction of a 24"x 42" mill I built this Spring.
- Length to diameter ratio should be almost 2:1.
-You'll need grinding media. We're using forged steel balls in 1", 1.5", 2". A fairly even split between the three.
We bought them from Legend Mining, Nevada. As they wear down (which is happening VERY slowly), we'll be adding new media to maintain the ball charge.
-I built a screen out of 1/2" punch plate with a poly chute below that to rinse the ore from the balls. The cleaned media funnels into buckets on the right and the ground ore funnels into buckets on the left. A water hose does the rinsing.
-My mill is driven by a 24hp Kohler from a riding lawn mower. Belts and pulleys rotate the barrel.
-Large dump/clean-out door at 6:00 and a smaller door at 2:00 for hose/rinsing access makes clean-up easy.
-The drum is approx 48 RPM and works brilliantly.
A full load is 330lbs of media, 15 gallons of 3/4 minus quartz ore, approx 10 gallons of water, one decent squirt of Jet Dry. I had planned for a batch to take about 45 minutes to grind. Testing showed that we have ground down to a very consistent sand with about 1 cup of oversize in 20-25 minutes. Full load is about 650lbs.
One interesting and useful thing I learned during testing is that the mill is actually pretty quiet when you start a load. The crushed ore tends to soften the impact of the balls against the drum. As the ore is reaching the size of sand, the noise level goes up noticeably. This provides an easy indicator that the batch is done.
For our needs, this thing does a ridiculously good job. The only thing is, it's too slow to clean out and reset.
My plan is to modify it. Right now, it's rotating on 2500lb trailer stub axles and only runs one batch at a time.
Load, grind, rinse, re-load, etc. Plan B is to upgrade to 3" pillow block bearings and 3" OD tubing as axles.
This will allow a continuous feed loop and should take it from approx 1.5 yds per day to approx 4-5 yds per day.
That's all I'm coming up with...Good luck on your project.
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