Here is a simple guide to making an extremely simple ball mill. The point of this project is to create small amounts of powdered metal and charcoal. It is not meant to make Kgs worth of ground material, and although it is possible to tumble and shine rocks, there is going to be a very low limit to the weight this particular build can handle. That said, it does offer 2 major advantages. The first being that it’s compact (not exactly the definition of light, but it is portable) and the second being simplicity (most of these measurements are there only to be a rough guide,as most of them were decided on the spot rather than following a set plan).
Disclaimer: this is a mix pot of some of the materials just lying around my workshop. If you want a mineral tumbler (or a ball mill, the two are basically the same thing) and are planning to buy the parts you need, then this may not be the best approach. I recommend you do some research on what acceptable components are.
The materials used:
- A windshield wiper motor (I have no idea how standard these motors are. Good luck.)
- Wood plank, approximately 2cm thick(The two pieces I used were: 20cm x 11cm and 13cm x 11cm)
- Wood screws of the appropriate length
- Thread bar and nuts (5mm)
- PVC pipe (110mm)
- Two threaded access caps
- Plain end cap
- PVC glue
- General tools
- Saw (In my case, a drop saw)
- Drill bits (Have a couple of sizes handy)
- 90° straight edge & pencil
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Step 1: The Long and Short of It
The base was extremely simple: two pieces were cut to a length big enough to make sure that the whole set up wouldn’t tip over (either forward or backwards) due to weight. If that sounds too vague, here are the sizes I used: the base board measured in at 20cm, with the motor mounting board being screwed in place 7 cm in. The wood piece used to mount the motor was 13cm by 11cm and was cut at 25° to give a slight slant to the tumbler’s drum. The tilt was included to reduce the force the motor had to deal with, and because this tumbler will only be used for small amounts of material. Thus, the tilt forces the stuff being tumbled to condense in one area.
First the hole for the central shaft was marked out and drilled (there was no way of knowing what size was the best to use, so I just worked my way up from the smallest size I thought would work. The key here was to have the transmission shaft fit snugly,and then to mark out the holes for the 3 screws (note that the actual electric motor is housed on the side, so the weight distribution should be taken into account.). Once those are done and drilled, use a bit that is 2-3 sizes larger (1-1.5mm) and increase the size of the central hole.With the other holes already present, the drive shaft should be centered(give or take).
*A side note on the screws: I ended up using a thread bar because I did not want to figure out how deep I should drill to fit the screw heads, so I opted for a lazier approach (which ended up being roughly the same amount of work.)*
The larger part of the reasons not to use rails was because of the access caps, which had notches on the sides, most likely for grip. The choice was then to either use plain end caps (which are hard to take off and are not physically attached to the drum) or to find an alternative way to spin the drum. Considering that you’ve read this far, you probably know which route I took.As much as the access caps may have been a problem to work around at the start, they ended up being the saving grace: the threaded end could be attached to the back of the drum-to-be and the cap could serve as the mount for the drum itself.
The rest is pretty simple. I cut a stretch of 110mm pipe to fit to the base of the end cap and access cap. In the end the pipe was a bit too long, but that was not a problem since it was not going to have any impact on the end result.Using some PVC glue I attached all the parts and set it aside. A access cap now needs to be mounted against the end cap so that the drum can be screwed on the base. The access cap’s threading needs to be somewhat centered, but don’t worry about getting it perfect. While that was curing, I cut a hole in the cap meant to be mounted. The advantage here is that the motor has a rectangular key at the front which is made for an armature,and thus is meant to exert a good bit of force. So I CAREFULLY cut a hole for it to fit into, after which a washer and nut were added(the washer was there for extra support but is not deathly necessary).
If that is done the next part is to finish the assembly, and well, job done.
This is the part where you may realize that this is a DC motor and that it needs a 12v supply. It may seem simple enough, but supplying this thing with power for the amount of time that it needs to run will prove problematic unless you have a dedicated power supply or battery. Another problem is that I don’t feel comfortable with running the motor for an extended period of time. Like every other motor, there is a byproduct of heat which will build up, and if left on too long it will burn out. Therefore I resorted to the egg timer method of making sure that it did not run for too long. Those times I was around the time could be managed more carefully, asI could feel how hot the motor was and potentially increase the run time and decrease the down time. Adding a fan might be a good idea, but I did not have one handy at the time. Using some ball bearings and a good deal of time I was able to make some fine charcoal powder which proves that it works(at least for the moment).