# Ball Mill Project



## snail (Dec 1, 2022)

I am considering building a ball mill. I assume diameter is a major factor.

I am thinking 15 inches in diameter. I assume the diameter has a major affect. Any advice on the diameter and horsepower required would be appreciated.
Dale


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## goldshark (Dec 1, 2022)

You got to figure hp requirements via the following formula. One HP = lifting 36,000 lbs, 1 foot, in 1 minute. I don't have my canned engineering specs in front of me, but you need to turn it at a rate which is just short of freefall, 32 ft per second. You didn't mention length of mill, which will need to be figured into the equation. Other factors will include ball load, pulp density, trunnion material ( for friction loss).
Long story short, I will not do an equation based on too many variables. It would take all the fun out of you learning about physics, math, welding, etc. I will be happy to do all that for you, at the rate of $200 an hour.


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## eaglekeeper (Dec 1, 2022)

What type of material you plan to mill might be important also.


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## snail (Dec 1, 2022)

Not ore, have access to a couple of drums of used crucibles, and have some pyrolized old military boards. 

Also thought it might be useful for blending flux with my bucket of incinerated filters.

Trying to get a wish list of components together for the project.


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## AlaskaLes (Dec 2, 2022)

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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## olawlor (Dec 3, 2022)

snail said:


> Not ore, have access to a couple of drums of used crucibles, and have some pyrolized old military boards.
> 
> Also thought it might be useful for blending flux with my bucket of incinerated filters.
> 
> Trying to get a wish list of components together for the project.


Have you considered using a cement mixer? For the price, they have quite well tuned and balanced motors, gearing, and bearings.


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## eaglekeeper (Dec 3, 2022)

AlaskaLes said:


> -You'll need grinding media. We're using forged steel balls in 1", 1.5", 2". A fairly even split between the three.



If your on a budget and have junkyards near by, you might be able to get a bucket full of trail hitch balls and cut off the threaded end. Not sure if the chrome plating would be an issue or not.


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## snail (Dec 4, 2022)

Thank you all for your replies, much useful information. 

I’m an old scrapyard guy that loves scrounging, you can’t beat the value. Time to ponder what I can find and need to purchase. Working out a plan should keep my mind busy during my idle time at work. 

I will not be in a hurry, the perfect items seem to become available if I wait a little. Have to love the power of intention, the universe is amazing!

Thanks again 
Dale


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## AlaskaLes (Dec 4, 2022)

The forged balls weren't crazy pricing compared to what I'd priced elsewhere.
I just checked and a mixed 20lb charge of 1' and 1.25" balls is about $34.
A tiny mill wouldn't need much media.

Ours was quite a bit more...lol.
We ordered enough to run it and enough to keep adding as the balls wear down.
We bought 630lbs and with a buddy helping to save on shipping to Alaska, it cost us just over $1800.

I was admittedly a little nervous, hoping that the machine I built would actually work and not be a serious waste of money. When the first batch finished in 20 minutes, I was ecstatic.

The things that would make me think twice about using cut ball hitches:
- the time to break those seized-on buggers loose.
- the time to cut the shanks off. 
-You wouldn't want too sharp of an edge where you cut them as it could chew through the mill.
-The size of the 2" ball is going to have larger voids between the balls, than the 1"/1.25" would and the larger the voids, the less comminution you will achieve. Comminution is the action of turning large chunks into tiny ground up bits.


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