This is a ball mill used for refining materials into a fine powder. [Jpoopdog] built it in two parts, a base and the tumbler chamber. The base itself is build using LEGO wheels as rollers. The motor and controller from an NXT kit is used to drive the rotation, with programming to stop the mill every so often so that the raw material can cool down. That’s important because this can be used to make substances like aluminum powder, an explosive substance sometimes used in pyrotechnics. We don’t recommend producing your own explosives (or making your own propellant) but if that’s what you’re after [Jpoopdog] did build in a safety feature. The chamber,which is constructed from PVC, has a fail safe to prevent an explosion. A hole has been drilled in the end cap and plugged with hot glue. In the event the milling material starts to overheat the glue will melt and alleviate the built up pressure.
21 thoughts on “LEGO Ball Mill”
PVC seems very static prone to me.
Built something very similar ages ago. Unfortunately I learned pretty soon that the + shaped axis aren’t exactly good for hours and hours of turning without bearing. Not that it made my mill fail (it worked very nicely until I retired it) but after a few days there was visible wear on the lego.
Wait, so is he concerned about heat or pressure? If the aluminum is set off by heat, a glue ball melting out isn’t going to cool it down. If the stuff is so hot that the temperature is increasing the pressure, then he should be looking at active cooling. If there’s guaranteed to be offgassing of some kind, he needs a gas-permeable vent, not an emergency blowout valve.
Just seems like he’s got a mistaken idea of how safe his machine actually is.
And yeah, if he’s actually planning to make pyrotechnic chemicals, it seems like he should be taking all the regular precautions like using wooden vessels and brushless motors and so on.
Yeah, I wouldn’t trust a PVC mill for doing any kind of pyrotechnic work. Way too much likelihood of static buildup/discharge.
The glue plug isn’t to cool it down, it is so the chamber goes off like a rocket and not like the ball bearing filled pipe bomb that it is.
A lego motor will burn out long before a ball mill does anything useful.
On top of that, ball milling in a pvc tube is moronic. I’m not normally a huge stickler for safety but there is a major reason why PVC is never used for pyrotechnics. If something goes off inside the tube a tiny hole isn’t going to stop the pvc from shattering.
Gunpowder and aluminum powder aren’t going to slowly pressurize as they gently heat up – they are happily grinding one second and shoving pvc shrapnel into your eyes the next.
He seems to completely misunderstand the risks as well. His stupid glue covered hole is useless and won’t prevent any of the possible catastrophic failures he seems so intent to reproduce. Periodically stopping the ball mill so it can “cool” is both unnecessary and hilariously misinformed.
I could go on, but this is getting redundant.
I have never complained about the safety aspect of a story before but this one is beyond comprehension. Its like a kid told me he is going to try skydiving and drilled a hole in his backpack so the parachute doesn’t tangle up.
I don’t see this as particularly unsafe, rather uninformed. PVC isn’t that much of a hazard – If you were to buy a “pyrotechnic” ball mill, it would have a chamber made of HDPE – Much tougher than PVC, and used for the same purpose – IF it explodes, it is likely to tear rather than shatter, and the relatively low density means that the fragments will only be lethal for a short distance (versus metal or hard woods).
As for the “vent,” it’s simply stupid. The danger from ball milling generally comes from two things – sparking and oxidation. Take sparking first – Your milling media must be non-sparking, regardless of what you’re milling. Brass, lead, and a few grades of steel are the preferred media – Whether they are hitting eachother, metals in your mill, or the walls of the container, they won’t spark. This is especially important for making black powder meal, and when milling anything potentially flamable (look up “grain silo” explosions).
When milling metals, a vent is good – But it needs to be an air-permeable membrane. The major pyrotechnic metals, aluminum and magnesium, oxidize incredibly quickly in air. This is a heat liberating reaction, meaning that the shit gets hot. Now, imagine milling – you’re breaking your metal up into smaller pieces with unoxidized surfaces being exposed. Open up the container, air rushes in, and it oxidizes…And heats up… Standard practice, when using an efficient mill, is to open it every six hours – This allows oxidation to take place periodically, rather than all at once at the end. There have been many amateurs killed or sent to the hospital because they weren’t aware of or simply ignored this hazard… Search the apc forums for some tips and horror stories if you’re interested…
If you have to resort to using kiddie toy legos to “hack” something – get a new hobby.
Why not just use a rock tumbler? They run about $40 at harbor freight?
Yeah, the hot glue filled safety feature is useless.
Also, why do people think ‘alum’ is an acceptable abbreviation for aluminum/aluminium?
The suggestion to put aluminum and the grinding media in a plastic bag to prevent the aluminum from sticking to the inside of the barrel seems a little suspect. I’m curious to know if he actually did this. I would think the bag would get beaten up pretty quickly.
United Nuclear uses neoprene in their barrels… http://unitednuclear.com/index.php?main_page=index&cPath=25_35
Yes, this is moronic. Using PVC ensures only that you accumulate static, and that when the shrapnel enters your body and you subsequently end up in hospital, the radiologist trying to find the pieces inside your body is hindered or unable to do so due to the lack of transparency gradient (PVC appears similar to body tissue under X-ray).
Use HDPE. It doesn’t
fragment when it overpressurises, and is used by pyrotechnics professionals for the purpose. It would have been better if I actually finished that sentence before posting it…
Ok, a little FYI from someone who has made and used Aluminum powder.
Aluminum is HIGHLY reactive and will oxidize almost instantly forming a microscopically thin layer of aluminum oxide which stops the process as it forms an airtight barrier. So when your looking at something aluminum what you actually are looking at is a thin coating of aluminum oxide.
To make the powdered aluminum I would suggest replacing the air with an inert gas, Helium works well is cheap, non-flammable and easy to acquire.
Say you want to make thermite (a mixture of Aluminum powder and iron oxide(rust). A VERY fine aluminum powder and Iron oxide powder with a binder(I used wax) and an ignition source hot enough to start the reaction. A small strip of magnesium works well and can be ignited with a small hand torch or good “turbo” lighter.
I “make” my iron oxide powder using water a DC voltage and an iron nail. This works well and makes a fine powder. Dry the powder thoroughly in a toaster oven. The aluminum powder must be a very fine dust.
Warning Thermite is basically imposable to stop once it starts to burn (water wont put it out) can ignite material that you wouldn’t think could burn (alloy rims and bicycle frames!) and will melt through almost anything else. I have used it to “spot weld” and to cut holes in 2″ thick steel plate so it does have some very useful properties. Eye protection is a must(welding mask) but I have burned a hole through some asbestos rings and gloves so keep your distance.
After reading my post I realized I wasn’t satisfied with the level of WARNING I gave.
Aluminum powder is one of the most dangerous things you can make.(big period) It’s not just flammable it’s downright explosive and will ignite on contact with the air. It’s less dangerous when it’s made with a constant air source which makes it sealed in it’s own little microscopic aluminum oxide cans, but it’s still a lot more dangerous than most people would think it is.
THIS IS A VERY DANGEROUS THING TO DO.
Yea I have done it(more than once) But I’m more than a little crazy.
If you really, really, really want to live you might want to skip this one.
YOU HAVE BEEN WARNED!!!!
seriously guys, step 4:electrics.
this guy is pretty much retarded.
Yeah, umm, these lego parts are going to have some MAJOR durability issues with this. They are toys!!! This is not a good idea unless you are building it for the “concept”, but not building it to actually *use* it.
Come on, HAD. It’s pretty easy not to fail like this.
I don’t think this is actually something intended for use although he saids he’s making aluminum powder with it. It’s probably a good thing it’s made of cheap material as a more ruggedly built system would be quite dangerous(read my post about aluminum powder) As it is the powdering is probably so slow that the aluminum oxidizes without making to much heat and would not ignite when he opened the container and the air rushed in.
Lego’s make good design tools for concept. Now he can make more durable parts and have a fair idea how they will fit and work together. Obviously the pvc barrel and lego motor wont stand up to polishing rocks much less for pulverizing metal.
If you read the author even mentions the idea that this is a DESIGN and mentions scaling it to a bigger dimension. Rating the design (not the material used for this demo) it seems that it it were made of more durable materials it would be quite useful.
I would add a way to ventilate the barrel and a decent ground! we don’t need static buildup for an ignition source, some machined parts(not legos) and a hefty motor(sealed type no need for sparks and dust). By placing this entire device(again made more durable) in an enclosure filled with an inert gas for magnesium aluminum powder etc.
I wouldn’t trust the apparatus of someone who writes 4 lines and 11 commas in one unstoppable sentence, and can’t spell most of the words right.
It reflects the work of someone that doesn’t stop to think.
Oh and about Instructables, please make it stop.
It’s a freaking website making money from stupid user content, and the birthplace of artsy-hippies praying the blue led god (throwable).
Seriously, it’s premise is about hiding the information that someone gives for free to the world, and makes you become member to see it.
Isn’t that against the principles of hardware hacking? You know.. breaking information free.
It’s like hiding half of a turd, and making you pay or eat spam to see the other end.
Is HAD affiliated with that site?
hello everyone, i am jpoopdog, as the creator of this i think i should mention that the description was misleading, in the ways as follows
1. i am not using a nxt motor or pack, to allow the mill to cool, it isnot programmed at all in any way, it works exactly the same as a comercial hobby mill. what i said about letting it cool was to allow the motor and the dc power pack to cool down, as they heat up over time, like any motor or power pack, so they dont melt, which is an issue i had twice.
the actual milling barrel will never heat up much, because the only heat mine has ever gotton, was radiated from the motor, which i might add has not burnt out, even after 3 days nonstop running.
2. the fail safe works by melting before the pipe gives way from an explosion, as it is the weakest point in the barrel.
i have done tests, purposly milling flahs powder, with rocks, to make an explosion, which oddly enough took a very long time, and after 3 explosions, in which the pipe ends just blew off,
i got a failsafe that would melt before the pipe blew up. though those barrels all melted, and are not the same ones in the picture, but the main barrel, (not the endcaps) are the same. and
the failsafe will do exactly what was said, it will shoot off like a rocket, or slowly release presure when the hot glue melts so it does not produce a shrapnel explosion, now what i did forget to mention is that i have only ever milled alum powder in the mill itself, all other chemicals wee made in a ziplock bagg within the barrel, and for gunpowder milling, i used a static proof chemical container. the only possible source for ignition within the mill when making alum is a spark from the ball bearings, thats it, which will ignite airborn alum powder, which will cause an explosion, but not strong enough to , rocket off per say, like an actual rocket, but at least its safer than an explosion. i have never had issues with static within the mill, though i will admit, after a few days of milling, all the alum foil does stick to the sides of the barrel, with static electricty, this goes awya once the first small amount of alum is made, (after 2 days, no more gets made for a long time after though).
3.yes , the lego does show a small amount of were an tear, though this only takes the form of a very light white dust. ill point out that lego no longer make + shaped axels, they all all a bit more ounded now, though still, vaseline will fix that permanently.
4. yes it is a design, something you can base a bigger mill off, or smaller for whatever reason.
5. i check the mill ever 3 hours or so, so i how far its gone, i must do this as if i just plainly mill it for ages , once its a powder, it leaks from the barrel, as alum power is microscopic, once it is powder, or partly powder , i add ductape to the barrel, to avoid leaks, i do this only when its a powder as i think ductape will make static electricty.
6. i am making aluminium powder with this, and i have made alot of it. though with aluminium, i had no issues, also ill point out i add a small amount of charcoal to this, to reduce the hazard of an explosion.
7.about the bag, it does work, and remarkabley, does not get beat up to bad, though i am using chrome stainless ball bearings, that come from a train (thanks to my grandpa who is a train mechanic).
im sure i said it before though, the ziplock bag i used was a freezer bag, which is thick and quite strong, though i used two bags . now though i just use that barrel that is already stained for alum, and different barrels that are clean, that have a ziplock bag inside, for everything else.
please post any other questions and concerns about this mill, and i promise i will respond, both here and instructables.
lastly ill point out that i said, that you SHOULD use a genuine milling jar for this, but i prefer to use pvc as im a cheapskape.
i am not retarded, im just simplifying it, because believe it or not, there actualy are people who dont know how to connect a battery two wires and a light bulb (with two wires pre-attached). such as me, only when i was 8, at which time i could read instructions on how to build things from electronics kits, but i didnt have a clue on how they were actually working, but i still built it, though at the time i was more a lego person, as i am still now,
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