Ball Mill 101

[maximusg]

The Mill

 

A good idea for any moderately serious Pyro is to construct a device capable of turning coarse powders and compositions into much finer material. The most useful case for this is of course when manufacturing Black Powder. Black Powder that has been prepared via ball milling will always perform better than powder made with alternative preparation methods, such as using a coffee grinder or the CIA method.

 

I have seen a lot of cases where people have chosen to purchase their ball mill, spending upwards of $20-$150 in the process. Though with a little research and improvisation it’s extremely easy to build a high performance machine for a fraction of the price.

 

Most of the materials are quite inexpensive and easy to obtain, I happened to build my mill with out spending a dollar in fact…

 

The basic design of a mill consists of a Milling container filled with a milling medium, a drive shaft construct, a fly shaft/wheel construct and a motor capable enough to turn the heavy milling container.

 

This is where the improvisation comes in; here is a picture of my mill to get things started:

 

http://users.tpg.com.au/jholc/Ball%20Mill%20resize.jpg

 

Although this image depicts the mill running inside, it should be stressed that when milling any material, the mill should be placed away from buildings, people, animals etc. These pictures were taken inside as it was convenient at the time of writing, and there is no material in the jar. Thanks Canadian_Pyro for pointing that out.

 

As you can probably see, I have hardly taken the highly aesthetic route, but that’s not exactly important, and I did want to say that I built it for nothing

 

Scrap lumber was used, just some stuff that I found lying in my garden shed, to make the base and the uprights that hold drive shaft, it was put together with screws and is solid as a rock. The fly wheels are pivoting castor wheels that I had laying around unopened from a previous trip to the hardware store, they were inexpensive though, about $3 or so for both of them. They are rated at 20Kg each, which is more than enough for this application.

 

The drive shaft is a stainless steel rod that I purged from an old printer I had, it came with the rubber grip already attached which was also very nice. The motor can be hard to find for free, although less difficult to find for a few dollars from a scrap yard, washing machine motors are ideal as they are powerful and quiet, which is what my motor was used for previously. My mate happened to have that lying around and gave it to me.

 

I opted to use a direct drive system on the shaft to connect the motor. I rigged up a pseudo universal joint using garden hose and some hose clamps. It works a treat and will run smoothly even if the motor isn’t perfectly aligned to the shaft. I didn’t use any bearings because I didn’t have any lying around, so I just placed the shaft directly through the wood and used some high quality bearing grease that I did have. I measured the area with an infra-red thermometer after several hours of use and there where no major hot spots.

 

This is just one example and there are many other designs to be utilized depending on what materials you happen to have, you just have to remember the basic principles.

 

Milling Jar & Media

 

The milling jar is just the container that holds the composition and media during the milling process; it can be something as simple as a length of capped PVC pipe or cylindrical plastic container. Metal containers are not recommended, as they can spark during the violent rotation of the milling media and ignite the composition.

 

The milling media is the material used to crush the composition or chemical inside the jar during its rotation. When making black powder, Lead media is preferred as it is completely non-sparking and heavy enough to create an efficient milling environment.

Some Lead Milling Media:

 

http://users.tpg.com.au/jholc/Milling%20Media%20resize.jpg

 

It should be common sense but never mill friction sensitive compositions, such as flash powder. And if you are milling metals, you will need media that is made of stronger material than the material you are milling. Also when milling metals, you should open the jar and let new oxygen into the container every hour or so, as the rapid oxidisation of the newly exposed surface area can generate heat and ignite the metal.

 

I hope this little write-up is helpful for those newbie’s who are new to this. And it may be a good idea if people posted other examples of their mills, for design ideas.

 

http://users.tpg.com.au/jholc/Ball%20Mill%20with%20jar.jpg

[Mephistos Minion]

I think it's beautiful maximus. I like the way you've attached the motor to the shaft. I also like the word shaft. If I wasnt so padantic about looks or proffessionalism of my mill it would be built by now. Perhaps something I should keep in mind. One question, have you ever had problems with the drum coming off the casters? At the moment I use another rod which is held by the same barings as the drive shaft is, these barings are rather stiff for the mill jar to turn, but if casters work well I might just switch, and make another mill with the two other barings.

 

Good work explaining the safety tips when milling, don't want anyone milling flash now do we

[maximusg]

No I have never had problems with the jar staying secure The castor wheels acutally move and centre the jar to keep it rolling smooth

[Mumbles]

Does your motor actually turn at an acceptable rate. I had the problem of finding an appropriate RPM motor to use for direct drive. I opted to just get an easier to find motor and use a system of pullies to gear it down to an appropriate rotation. My motor actually came with the appropriate pullies when I bought it off ebay, which was nice.

[Chris]

Does your motor actually turn at an acceptable rate. I had the problem of finding an appropriate RPM motor to use for direct drive. I opted to just get an easier to find motor and use a system of pullies to gear it down to an appropriate rotation. My motor actually came with the appropriate pullies when I bought it off ebay, which was nice.

I had a smiliar problem with my new motor running too high RPM. My solutions was to connect a commerical halogen dimmer before the motor. I had to replace the fuse with a 16 A fuse. I havn't used the setup since, so I can't be sure how well the rheostat itself tolerates the higher current. I will know when build my 2nd mill.

[maximusg]

It turns at a very efficient RPM... The motor is rated at about 1400 RPM (I forgot the exact standard) There is a 16:1 turning ratio between the shaft and the milling jar. So it spins at about 85 RPM

 

Here is a short video of it running. It has no audio, but you can tell by the sound in real life that there is alot of "smashing and crashing" and that the media is not simply turning with the jar.

 

http://www.weewaautemuster.com/Pyro%20Shiz...Ball%20Mill.MOV

[Canadian_Pyro]

Running a stainless steel shaft difectly on wooden "bushings" is not a good idea. The capacity of your jar appears to far exceed a gallon, and a properly charged gallon jar holds around 30 pounds of lead media. That is alot of load to place on a wooden surface. If your bushings are not severly worn by now, your jar is probably undercharged. The media must occupy 1/2 of the jar's volume for optimum efficiency, and to prevent wear on the milling medium. The composition to be milled should occupy 1/4 of the jar's volume.

 

Also, it appears that you are running the mill in a building, probably a shed or a garage. I cannot stress to you how important it is to mill away from all buildings, people, and animals.

 

I used to use a Rock Tumbler with higher gearing and a more powerful motor to mill my BP. It turned the 4" by 4" jar at around 100RPM, and milled around 200 grams of powder in 3 hours using around 150 canadian pennies as the media. Truley an improvised mill, but it worked. Then I built my current mill, which has a one gallon capacity, and mills 2lbs of BP in 3 hours using brass cylindrical media. I still use the good old rock tumbler for smaller batches of powder, usually when I want to test charcoals or make blackmatch. Pennies work surprisingly well in this little mill, and the quality of the BP made in the small mill equals that of the BP made in the large mill.

 

Usually, the media is the most expensive part of the build. I bought 15 feet of brass round stock for $40 at a scrap metal dealer, and it has served me well. Mills just as fast as lead, and there is no toxic contamination of the milled powder.

[maximusg]

It may look different in the picture, but that container is much smaller than a gallon! It's roughly one litre, which is about 1/4 gallon I think. I only mill about 300 grams at a time and the jar is half charged with lead media.

 

The load on the system I have designed that best fits my application is minimal... I have been testing it for weeks, and it still runs perfect with hardly any major vibration. And it would have worn it considarably, but thats why I used some high quality bearing grease... It spins easily.

 

Yeah it is indoors at the moment... But that was only for the purpose of writing this tutorial, as it was late at night. There is nothing in at the moment I normally undertake any milling out side.

 

I will add some more of those points to the original post. Cheers for pointing those fact out.

[Canadian_Pyro]

What is the diameter of the shaft you use to drive the jar? Unless it is 1/4" in diameter, you will not get a 16:1 reduction AND have a jar capacity of only a liter based on the length of your jar. Unless of course the jar walls are incredibly thick. My 1 gallon jar is 6" in diameter and 9" long, yours appears to be much larger. I am tired, so it is possible that my eyes are decieving me.

[maximusg]

I measured it, the jar is exactly one litre. Here is an image of it next to a 1 litre ethanol container for scale purposes. There is a 16:1 ratio, I dont have the measurements handy, but im afraid your gonna have to trust me

 

http://users.tpg.com.au/jholc/Milling%20Jar.jpg

[brainfever]

I'm a supporter of a more direct driven ballmill setup like this one:

 

http://ci.cambridge.md.us/brainfever/pics/ballmill/ballmill_4.jpg

 

This setup needs an engine, a reduction gear and an optional frequency drive.

As clamping mechanisch I welded a cross with 4 aluminium "claws" to be attached directy on the reduction gears' shaft.

 

I like my frequency set at 23 Hz, which is 1400/7/50*23 = 92 rpm.

 

Anything faster then 2 rotations per second is too fast.

 

More pictures of this setup can be found on my site in the link below this post.

[Star_Roller]

I still say the best ball mill in the world is my treadmill........

I have like 25 containers all for different materials and well it pwns...

[lnstantkarma]

I was about to buy a ball mill when the pump for my well started to give and it was replaced. So now I have an extremely powerful motor and almost no practical electronics knowledge. Here is all the important looking info on the motor:

 

HP 1.5

Hz 60

Volts 230

Amp 5.0

Kw .37

RPM 3450

S. F. max amp 6.0

PH 1

 

It would be really cool if I could use this for a star rolling machine too if I can use it for anything. Thanks anyone who can tell me what I need to begin with.

[tentacles]

That's way too much motor for a first ball mill.. Maybe if you were doing a mill using 30 gal drums as jars.

[frogy]

Really... I have a motor with these specs...

 

HP 0.1

Hz 60

Volts 115

Amp 2.6 (max load)

Rpm 60

PH 1...

 

That turns a (10 lb.+) barrel easily...

[rocket]

Look at the RPM of the motor its 3450 which is way too fast, mine is 1400 and I have enough trouble trying to get that to mill of direct drive. Your best bet its to try and gear it down a lot.

[tentacles]

That seems more like it, if it's only 60 RPM you would want it to drive the barrel directly, though 60 RPM is a bit slow for most first mill sized barrels. Keep in mind that 10 lbs is about a 4" pvc pipe sized barrel. enough to mill 200-300g of BP.

[lnstantkarma]

I thought 3000 rpm might be too fast to gear down. Oh well maybe I'll look on ebay.

[frogy]

That seems more like it, if it's only 60 RPM you would want it to drive the barrel directly, though 60 RPM is a bit slow for most first mill sized barrels. Keep in mind that 10 lbs is about a 4" pvc pipe sized barrel. enough to mill 200-300g of BP.

Lol... I have a 4" pvc barrel and I do 200 gram batches of bp\stars normally...

 

If this is up... look here:

http://frogy.is-a-geek.com/pyro/ballmill.php

 

If not....

Empty Jar

Jar with Media

Side of Jar

Front of Mill

Back of Mill

Top of Mill

Nailed Idle Wheel

 

 

Notice I do a direct drive... but the rollers are like 7.75" so it actually nocks my rpm up in the 110 range... the optimal for my 3.998 ID barrel w\ .53" media....

 

PS: I'm not the same guy... I think you might have confused that earlier because I used the same template for specs...

[FrankRizzo]

I thought 3000 rpm might be too fast to gear down.  Oh well maybe I'll look on ebay.

LOL..yeah, that's a bit much...not even a big gear reducer will bring it down to usable speed. You want a fractional horsepower (1/4 - 3/4HP)AC motor with 1425-1725 RPM. To give you a bit of perspective, most rock tumbler motors are ~1/20HP.

 

Also, TEFC (totally enclosed, fan cooled) motors that are rated for "continuous duty" should be the only ones you consider purchasing. Your mill jars *will* leak at some point, and you don't want dusts inside the motor.

[frogy]

I highly doubt that rock tumblers are 1/20 hp...

 

Because my 1/10 hp motor is wayyyy more than 2 times stronger than a rock tumbler... It is geared down internally, so I bet it has more torque...

 

Really all you need is a 1/10 - 1/6th hp motor with 1725 rpm... Preferably 110 volts, 1 phase, fan cooled, and continuous duty...

 

Mines a 1/10 hp continuous duty Dayton 110v AC motor... It's like 2.6 amp (max load) [so like 260W max load]... It's 60 rpm output is ramped up to like 100 rpm with a 7.75" wheel to my 4.7" OD jar (with the rubber coat)

[lnstantkarma]

Okay there is an overwhelming number of 1/6 hp 1700 rpm motors on ebay so unless there is anything else important to know about that my next issue is how do I power it? I don't really understand how to pick out what transformer I would need or anything like that.

[tentacles]

Transformer? You should buy a motor that will run on regular household voltage - 110V (120, 130) in north america, or 220(230,240)V in europe. Then wire on a power cord and plug it in. I agree, too, that 1/10-1/4 HP is plenty of power for nearly any ball mill. Maybe if you're swinging an 8 or 12" drum, you may need more, but I doubt it. Most clothes driers are only 1/4HP and can swing a 50 pounds in a 30" drum. I hear they make good mills, too.

[FrankRizzo]

I highly doubt that rock tumblers are 1/20 hp...

 

Because my 1/10 hp motor is wayyyy more than 2 times stronger than a rock tumbler... It is geared down internally, so I bet it has more torque...

Well, I'm not talking about those POS units from Harbor Freight, but my point is that you want something quite a bit more substantial.

 

Remember that an average 1gallon mill jar optimally uses ~32lb of milling media. It's much better to err on the side of too much power. If your mill jars are 4" or smaller, I see no reason why a 1/6HP wouldn't work.

 

I use a TEFC 3/4HP GE motor on mine, but I got it cheap from Surplus Center.

[lnstantkarma]

Okay I could spend 40 bucks and a lot of time working out the kinks or I could just buy a nice ball mill for $70 and I've got a birthday coming up so I think I'll go with the latter. Thanks for all of your advice I now appreciate how much work goes into constructing a ball mill.