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A Simple Ball Mill

A ball mill is a device used for grinding materials to a very fine powder. It is probably the best way to produce black powder and other compositions. It consists of rotating rollers on which a round container is placed containing the components to be ground and and some 'milling media', usually lead balls. When left running for three to four hours, the materials are ground to a very fine powder.

Most designs need a fairly well equipped workshop to produce them. This one is designed to be made with only basic woodworking tools. The rollers and bearings can be quite complicated to produce but this version uses a conveyer-belt roller which comes complete. You just have to produce a wooden clamp to hold each end in place.

To avoid complications of gearing the drive you can use a geared motor. This one rotates at about 60 rpm. The speed could be varied by making the driving pully bigger or smaller. This pully is a commercial toothed pully which has had a groove filed around it to stop the belt falling off.

The belt is obtainable in continuous lengths. To make it into a closed loop cut it slightly shorter than you need (to let it stretch tight) and join it by melting the ends over a gas flame (till they almost 'run') and then pushing the melted ends together and holding them still to set. You can clean it up with a sharp Stanly Knife. If it breaks you can clean up the ends and join it again. After a few goes it's easy and you can make belts any length you want.

These jars are old medicine bottles. You can use any wide mouth plastic bottle. If you have any doubt about the security of the lid put a turn of tape around it before you start milling. I have had lids unscrew themselves owing to the pounding thay get from the milling media. If the jars slip you can produce a couple of 'O-Rings' from the plastic belting and put them round the jars to give a more positive drive.
You can probably get the parts from a good engineers supply house, but in case of difficulty RS Components stock them all. They will sell to the general public on credit card. I have appended a list of the parts they stock. The motor is the most expensive part. If you know where to look you can sometimes get cheaper ones on the surplus market. Otherwise you will have to gear down a faster motor - much cheaper but more complicated. Make sure it's continuously rated and runs on the correct voltage for your local mains supply. Also that it's enclosed so spilt composition won't fall inside.
RS Components are at http://rswww.com
DescriptionRS part Number Price (plus VAT)
500 mm roller 213-1314 9.01
5mm belting (5M long) 309-8218 9.05
60W 68 RPM geared motor 717-607 139.10!!

In the light of experience

Having now run this mill for several years I can say it is very satisfactory. However, there are a couple of modifications which may prove useful.

The first is very simple, and is to fit a ball race at one end, as shown in the picture. The jars always wander to one end of the rollers and either rub, or can even jam. This simple mod stops any problems of this sort.

The race is about 3/4inch diameter and held in place with a wood screw and a spacer beneath.

Wanting to mill larger quantities I made a much larger jar from 4inch waste pipe and fittings.

This can mill about 600grams of black powder but needs a charge of about 12 pounds of lead balls!

I found that although the motor had plenty of power, the plastic drive belt did not have enough friction and slipped.

In order to fix this, I have fitted a toothed drive belt that cannot slip.

This involves fitting a new pulley to the motor shaft and getting a toothed belt.

The tricky part is fitting a pulley to the roller as it has to drive from the outside. Fortunately the larger sizes of toothed pulleys are made from solid aluminium and you can machine (or drill and file) the middle out to make a ring that is a tight fit over the roller. This is then fixed in place with epoxy. You may have to raise the rollers a bit or cut a slot below the new gear to give you clearance.

Belts and gears from RS.

This is a mill made by Peter Hoare based on the above design.

Peter has used this small model makers motor to drive his mill.

I thought it would not be powerful enough, but he has since extended his mill to 4 rollers and shown me a video of it working - must be a very tough motor and much cheaper than the heavy duty mains one. Thanks for the pictures & information Peter.