Sciencemadness Discussion Board - Small Scale Ball Grinder

Small Scale Ball Grinder

the_grungler - 24-6-2025 at 08:00

Hello, Internet Denizens.

I'm building a ball grinder with the intent of turning silica sand (particle size ~ 1mm diameter) into smaller silica sand (particle size <100μm). So far, I've got a chunk of 3" diameter PVC pipe with end caps on either side, and inside I've got about 250 mL of sand (~1 cup if you like nonsensical units of measurements) and a handful of various sized ball bearings. I've scavenged a bunch of parts for it, so a lot is jerry-rigged and/or 3D-printed. At the moment, it looks a lot like a pipe bomb, which I am taking as a sign of real progress. It's mounted on a set of skateboard wheels and I have an old AndyMark CIM motor hooked up to my bench PSU for power.

I am mostly looking for advice on where to go with this. I had belts made of a bunch of materials, but my best so far have been long rubber bands.

Here's a short video I took of it running, and why it's really not working that well. Note the chunks flying off as it spins: google drive video link

I don't really know where to go with this or how to make it better

The rubber bands only last 12-ish minutes, which is nowhere near enough time to actually grind down the sand. I'm currently working on 3D printing some sprockets for an old chain I dug out of a scrapped robot arm, in the hopes that'll do better.

If any of you all have suggestions, or perhaps a different grinding topology I could try out, please let me know

I am not terribly attached to this model and would be more than happy to throw it out if there's a better setup or belt I could use.

Thanks so much,
- The Grungler

Fulmen - 24-6-2025 at 08:37

Good work so far, just keep on improving it.

Try round PU belts:
https://www.amazon.co.uk/High-Performance-Urethane-Belting-P...

These can be heat welded to the desired length.

[Edited on 24-6-25 by Fulmen]

chempyre235 - 24-6-2025 at 08:58

If you 3D print a planetary gear reducer (designs and models are readily available online), you'd avoid the need for a drive belt. These can be printed as a single component (with some fine-tuning) and make decent bearings, too. A modified version of the planetary gears using herringbone teeth keeps the gear assemblies from coming apart. A friend of mine printed a fidget toy for me this way, and it's sturdy and works well, even after extended use.

[Edited on 6/24/2025 by chempyre235]

bnull - 24-6-2025 at 09:32

Some ideas:

old printers have belts to move the printing head to and fro across the paper. They look like they would last much longer than rubber bands. If not possible, try cutting your own from old inner tubes (from bikes or motorbikes). You can have them for free if there's a hole in them.
the downside of using PVC is that sand will scratch away a lot of PVC. Besides the damage to the tube, there's the need to separate fine sand from PVC powder. You can try a steel paint can (with its cover) instead and use a magnet to remove the steel grains that mix with sand. The steel can will last longer than the tube.

By the way, is it aquarium sand?

the_grungler - 24-6-2025 at 09:41

Quote: Originally posted by Fulmen

Good work so far, just keep on improving it.

Try round PU belts:
https://www.amazon.co.uk/High-Performance-Urethane-Belting-P...

These can be heat welded to the desired length.

[Edited on 24-6-25 by Fulmen]

Thanks so much!! These look exactly like what I need. I'll update later once I get my hands on a few.

the_grungler - 24-6-2025 at 09:43

Quote: Originally posted by bnull

Some ideas:

old printers have belts to move the printing head to and fro across the paper. They look like they would last much longer than rubber bands. If not possible, try cutting your own from old inner tubes (from bikes or motorbikes). You can have them for free if there's a hole in them.
the downside of using PVC is that sand will scratch away a lot of PVC. Besides the damage to the tube, there's the need to separate fine sand from PVC powder. You can try a steel paint can (with its cover) instead and use a magnet to remove the steel grains that mix with sand. The steel can will last longer than the tube.

By the way, is it aquarium sand?

I've got a few dead printers actually, I'll look into this.

As for the sand question, no, it is not aquarium sand. I bought some refractory silica sand off Amazon, and I'm planning on hitting it with an acid bath later on anyway to get all the metal salts and other garbage out after the particulate is small enough. I've also got a metric ton of PVC pipe, and I've got the dimensions recorded so if it crumbles, so be it. I only need a few liters of this stuff to go thru anyway.

Is there any reason I should use aquarium sand?

[Edited on 2025-6-24 by the_grungler]

the_grungler - 24-6-2025 at 10:04

Quote: Originally posted by chempyre235

If you 3D print a planetary gear reducer (designs and models are readily available online), you'd avoid the need for a drive belt. These can be printed as a single component (with some fine-tuning) and make decent bearings, too. A modified version of the planetary gears using herringbone teeth keeps the gear assemblies from coming apart. A friend of mine printed a fidget toy for me this way, and it's sturdy and works well, even after extended use.

[Edited on 6/24/2025 by chempyre235]

Oh. This would be really neat actually! I'll give it a shot, my PU belts won't be here for a few days. Thanks so much!

bnull - 24-6-2025 at 12:14

Quote: Originally posted by the_grungler

Is there any reason I should use aquarium sand

None at all, unless you have a lot of it. Refractory sand didn't cross my mind.

[Edited on 24-6-2025 by bnull]

MrDoctor - 24-6-2025 at 16:25

i would avoid gears altogether, they will get trashed. small rollers to big barrel ratio is best and what most ball mills use anyway. when i made a ball mill from PVC, i also found that it was impossible to produce a perfectly symmetrical setup so the barrel kept drifting up or down the rollers, so consider that you might need to add something for the pvc to push up against without grinding it down or friction heating.

If possible though i would suggest using a belt(s) in order to make both rollers spin.
lastly, brushed motors arent built for this kind of duty, the main reason to avoid them is if doing flammables like BP or metal powder, but, they really just dont like being run non stop like this. try finding an induction motor to do it, like one out of an old fan, otherwise, if the scale is small, a servo like you see on 3D printers is brushless, though they are low power relative to their size, or, get a low KV brushless DC motor for like RC cars or whatever, i got one i never ended up using, was like 600-700W continuous, 700KV (rpm/v) cost $15

Twospoons - 24-6-2025 at 17:51

Quote: Originally posted by MrDoctor

lastly, brushed motors arent built for this kind of duty,

Nonsense. Just don't use an undersized motor and you should be fine.

[Edited on 25-6-2025 by Twospoons]

clearly_not_atara - 25-6-2025 at 14:08

Wouldn't grinding sand inside of PVC grind the PVC?

the_grungler - 30-6-2025 at 12:49

Alright! I have good news! The polyurethane belts work wonders

Thanks to everyone who helped out!!