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Homemade ball mill

Svimmer

By Svimmer
in Tools and Tooling

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PeteyPyro Newbie

PeteyPyro

Posted
Posted
Sounds a little fast and looks fast for anything over 4 or 5 inches in diameter, which would be tiny indeed. What is the jar's diameter?
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Svimmer Newbie

Svimmer

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Sounds a little fast and looks fast for anything over 4 or 5 inches in diameter, which would be tiny indeed. What is the jar's diameter?

 

Its not more then 2.9 inches

OldMarine Newbie

OldMarine

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Posted

That looks like around 150 rpm which I think is pretty close to optimum for a 3" jar if only a little too fast. Lloyd has the formula to figure all of that in his book but I have no idea how to type that math crap. I'll see if I can get him to chime in.

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Col Newbie

Col

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Needs to be around 108rpm if its half full of media, it looks like its going quite a bit quicker than 108rpm.

Curiosity got the better of me, its doing 200rpm ;)

Edited by Col
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PeteyPyro Newbie

PeteyPyro

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That looks like around 150 rpm which I think is pretty close to optimum for a 3" jar if only a little too fast. Lloyd has the formula to figure all of that in his book but I have no idea how to type that math crap. I'll see if I can get him to chime in.

I can't type 'scientifical' stuff well, but I found a pen and paper. ..post-21112-0-43536800-1513911223_thumb.jpg This equation from Lloyds book is to calculate the 'critical speed'. You'd probably want to run at 'optimum speed' for dry powders, which is about 65% of critical speed. With the diameter of your media (1/2" balls ?) and the INTERIOR diameter of your mill jar, you can calculate the critical speed required, and the by multiplying this by 0.65, you'd arrive at a reasonably optimum speed. I should have asked you what size your jar's interior diameter and media size are, in order to give you a more responsive reply.

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Svimmer Newbie

Svimmer

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Jar diameter: 3inch

 

the rod its spinning on is 1.2 inch

 

Atm i use marbles as media because thats what i had.

 

and 50% media.

Edited by Sondre
Boophoenix Newbie

Boophoenix

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Sounder, marbles have been linked to more than a few oopsie's if I recall correctly. Please be sure to set this up remotely away from you and most especially others should you be milling BP if you choose not to change media.

 

If you're going to continue to use the marbles after being warned slow the mill way down. To the point you barely get a cascading effect of the media if any at all to help prevent chipping and shattering the marble. This will cause a loss of efficiency and extend milling times. This may could help with the down sides some, but I wouldn't count on it.

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Svimmer Newbie

Svimmer

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Sounder, marbles have been linked to more than a few oopsie's if I recall correctly. Please be sure to set this up remotely away from you and most especially others should you be milling BP if you choose not to change media.

 

If you're going to continue to use the marbles after being warned slow the mill way down. To the point you barely get a cascading effect of the media if any at all to help prevent chipping and shattering the marble. This will cause a loss of efficiency and extend milling times. This may could help with the down sides some, but I wouldn't count on it.

I thought glass marbles was ok to use but not the best ?

MrB Newbie

MrB

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I thought glass marbles was ok to use but not the best ?

Where is BB, and his missing marbles when we need him?

 

Anyway. Just... No. BB used glass marbles, and had the mill go boom on him, if i recall right, when emptying it. Don't mill live compositions with marbles. And don't mill chems you once milled with marbles, as a part of live compositions.

 

Edit

Ok, i made a quick search, but i cant come up with the thread.

BurritoBandito used glass marbles, had run a milling pass on BP, and was emptying the mill. Seeing BP clumped together, sticking to the walls of the jar he shock it, and it grenaded in his hands. Lost a pinky, but survived mostly scared, rather then "actually" harmed. Having a bomb go of, shooting glass marbles in all directions, just losing a finger isn't really that bad. Staying alive, is something of a miracle. Which is why i would suggest switching from glass media...

/Edit

Edited by MrB
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Svimmer Newbie

Svimmer

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Where is BB, and his missing marbles when we need him?

 

Anyway. Just... No. BB used glass marbles, and had the mill go boom on him, if i recall right, when emptying it. Don't mill live compositions with marbles. And don't mill chems you once milled with marbles, as a part of live compositions.

 

Edit

Ok, i made a quick search, but i cant come up with the thread.

BurritoBandito used glass marbles, had run a milling pass on BP, and was emptying the mill. Seeing BP clumped together, sticking to the walls of the jar he shock it, and it grenaded in his hands. Lost a pinky, but survived mostly scared, rather then "actually" harmed. Having a bomb go of, shooting glass marbles in all directions, just losing a finger isn't really that bad. Staying alive, is something of a miracle. Which is why i would suggest switching from glass media...

/Edit

Alright im going to get some leadballs

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PeteyPyro Newbie

PeteyPyro

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The thread that I remember from Dagabu about BB's accident:

 

https://www.amateurpyro.com/forums/topic/9798-ball-mill-explosion/?do=findComment&comment=128158

Col Newbie

Col

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Hardened would be better as they dont wear. With a small mill jar i`d go for ceramic cos you dont need a lot.

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Col Newbie

Col

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Posted

Best to shop around, £17 for a kilo with delivery.is a little steep

MrB Newbie

MrB

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The thread that I remember from Dagabu about BB's accident:

 

That's the one i couldn't find. Thanks.

 

 

Hardened would be better as they dont wear. With a small mill jar i`d go for ceramic cos you dont need a lot.

 

Don't wear as much. Lead is still a consumable as milling material. I think my BP balls lost 2 mm over the last year. I'm at the point where i will have to recast them soon. I'm using 50/50 wheel weights, and commercially recycled lead from Boliden Bergsöe. (pretty much as pure as it gets, i suppose. Just happened on a bar, if i was paying for it, i would have gone with a 6% antimony variant.) Anyway, the lead hardens pretty well, but i have no real way of measuring it. Just comparing water quenched vs slow air cooled by pressing them, and such.

I'm sort of considering switching to ceramic, mostly for environmental reasons. Less lead in the end product, so to speak. Not entirely sure what i would do with all my lead at that point. I don't need THAT many lead hammers.

 

Also... If someone ends up buying lead that isn't hardened, but does contain antimony / arsenic to let it be hardened, could simply toss it in the oven at 225c, or so, and then drop them in to cold water, to set them of.

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Col Newbie

Col

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Hi B.

doesnt wear as fast is what i meant ;) Lead and ceramic have their own plus`s and minus`s so the best option is to have both in seperate mill jars.

Svimmer Newbie

Svimmer

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Well overall i think the mill can work pretty good for the money :D

 

Cost me under 4$ to make lol

calebkessinger Newbie

calebkessinger

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Can't argue with the price!
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stix Newbie

stix

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I can't type 'scientifical' stuff well, but I found a pen and paper. ..attachicon.gif15139111699272028247215.jpg This equation from Lloyds book is to calculate the 'critical speed'. You'd probably want to run at 'optimum speed' for dry powders, which is about 65% of critical speed. With the diameter of your media (1/2" balls ?) and the INTERIOR diameter of your mill jar, you can calculate the critical speed required, and the by multiplying this by 0.65, you'd arrive at a reasonably optimum speed. I should have asked you what size your jar's interior diameter and media size are, in order to give you a more responsive reply.

 

I thought you also need to know the RPM of the motor that's driving it?

 

[EDIT]: Just checked some old notes, It looks like the RPMs aren't required for working out the "critical speed", but would be needed to work out what size pulleys/drive shaft to work out what RPMs you originally have.

 

For the record the Metric version for critical speed is worked out the same as Petey posted above except for the numbers:

 

The critical speed (rpm) is given by: nC = 42.29 / Sqrt of D, where D is the internal diameter of the Jar, minus the media diameter (in meters).

Edited by stix
Boophoenix Newbie

Boophoenix

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Posted
Sonde, check with Ken at Pyro-Gear.co.uk Or Caleb at https://www.woodysrocks.com for some media. Either should have good for pyro usage. Don't skimp to much this is an art where sometimes to much bang for your buck is bad, but other times great. Keep your bang where ya want it.
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  • 3 weeks later...
Madumi Newbie

Madumi

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Posted (edited)

Sorry to hijack the thread a bit (I'm a new member & don't have thread creation ability yet)...

 

Thanks so much for the info about glass marbles, after reading on jacobsrocketry that he was using them, I wondered how safe they might be (I remember playing with quartz rocks as a kid--creating sparks, which can't be far off from a silica composition like glass).

 

couple quick questions:

1) I've seen people milling with dual sized media (eg .5" lead balls together with something smaller, maybe .3" lead balls). Is that a good/bad idea?

2) is there a good way to estimate how much media would be needed. I'm starting out with a very small mill, one quart & figured probably 300x .5" lead balls would fill it half way (but my math is not the best, so I thought I'd check).

 

Thanks!

Edited by Madumi
OldMarine Newbie

OldMarine

Posted
Posted

Welcome Madumi and after that post you now have the ability to create your own topics. Your mill jar should be half full of media and will process a quarter of the capacity of the jar of comp efficiently. Lloyd Sponenberg who is on this forum has published a bok on the subject and if you PM him he will give you much better advice than most here can.

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Boophoenix Newbie

Boophoenix

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Posted

According to information from Lloyd different sized media causes excessive stress on the media. The media will wear much quicker than if all the same size.

 

Your count on media seems fairly close. The rebel jars are 5 quarts. So the media needed for a rebel decided by 5 should put you right into the ball park. I use to have a formula I worked out the hard way for calculating the media amount, but had it scratched onto an envelope a few years ago. I’m sure it’s made it to never never land. I used weight and mass to figure out the actual count. A fella better with the math stuff than myself did a formula calculating the volume, sphere size, and void space. We were within about 10 pieces of each other in our end numbers for a rebel if I recall correctly.

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