No bump, just grind

February 10, 2024 6:09 AM

I would like to grind oyster shells, mussel shells and other hard stuff. I thought a blender would do it, but it looks like I would need one for hundreds of dollars. What options do I have? Are there industrial ones like for crushing stone etc? Ideally with replaceable blades I guess?

I would like them to be ground to pretty much a powder to be mixed into a paste. I don't have unlimited funds to throw at this as the users will probably break it before too long anyhow.

Is power the only consideration or are there structural things I should consider.

posted by Iteki to Technology (15 answers total)

Best answer: Grinding up mussel shells can be very dangerous, because they’re full of toxins that can build up in the body if inhaled. If this is something you’re thinking of doing frequently, you should figure out what kinds of safety measures you need in place.

Here’s a horror story for you.
posted by AAAA at 6:19 AM on February 10 [33 favorites]

There are "grain mill" stand mixer attachments, which ought to be able to grind smallish hard stuffs.
posted by glibhamdreck at 7:31 AM on February 10

Mod note: Hi ya folks, several comments removed. Please just focus on answering the question per the Content Policy, thank you!
posted by Brandon Blatcher (staff) at 9:11 AM on February 10

How about a cast iron mortar & pestle? Depends on the quantity I suppose...
posted by nkknkk at 11:14 AM on February 10

Crushing oyster shells (for the soil) using simple tools. If you have a car, put the shells in layers of bags (zip-lock sealed envelopes for the innermost layers, & remove air from bags) and drive over them a few times? You'll still have big chunks and shards; after sieving, you'll have powder for your project. And please, observe all safety measures (masks, eye protection, gloves, etc.) when emptying the bags and making your paste.
posted by Iris Gambol at 12:40 PM on February 10 [1 favorite]

Yeah, I think you'll have more luck crushing them than grinding them. On a smaller scale, try a sledgehammer and a makeshift anvil (e.g., piece of railroad rail, scrap of metal plate, etc.).
posted by bricoleur at 2:02 PM on February 10

I'm interested in crushing/grinding charcoal. I went to a local metal recycler/yard (not for cars, and they allow wandering through). I ended up with a cast iron grate from a wood stove, and some sections of iron bars I plan to attach to 2x4 boards. Elsewhere I found a sturdy plastic case/suitcase thing. I'm hoping this provides the start to a workable system.
posted by amtho at 2:12 PM on February 10

Response by poster: I appreciate the warning, thank you I will be even more careful about methodology going forward. I also appreciate the mortar/pestle/mechanical crushing suggestions. I would love some answers more in line with what type of electric grinder/crusher/blender properties I need to take into consideration, like is the wattage more important than the material of the blades or what.
posted by Iteki at 3:14 PM on February 10

Building on Iris Gambol’s comment above: I used to live in a big oyster producing town in France, the shells were used as an aggregate to fill and surface local back-roads. Over time cars would reduce them to a coarse sand consistency. So… one strategy if you have many shells and are willing to wait.
posted by rongorongo at 3:19 PM on February 10 [1 favorite]

Iteki! I'm back with news from the online trenches.

Apparently, straight-up oyster shells will kill the blades of most consumer-grade food processors and blenders; one outlier on a hobby site touted their "old Blendtec" as getting the job done. Try: boiling and/or baking the shells, then breaking them into smaller pieces (bag, and bash -- via rolling pin, vehicle, or energetic offspring). These bits go into a less-dear, single-purpose burr coffee grinder (Krups $20, 200 watt example & Cuisinart $50, 500 watt example) or food processor (Hamilton Beach $50, 450 watt example). Or maybe thrifted appliances suit your purposes? (Separate devices to grind different materials, until the blades and/or motors give up the ghost.) Some people use a mortar & pestle at this stage, and still screen after that.

These are tips from around the web, from gardeners (oyster shells to amend soil or discourage pests) and chicken keepers (ground oyster shells add calcium to the chicken diet), including a DIY "rock grinder" and ready-made products like oyster shell flour (50 lb for $15) and oyster-shell "feed" (4 lbs "flaked" shell for $20; 5 lbs "crushed" shell ["for Laying Hens or Slug Deterrent'] for $10).
posted by Iris Gambol at 7:00 PM on February 10 [1 favorite]

Best answer: The appropriate tool for this job is a ball mill. This is what ball mills are for: it is their core purpose. Reducing hard, brittle materials to powders. That’s what a ball mill does.

They’re not cheap new, you might be able to find an affordable one used.
posted by mr_roboto at 12:18 AM on February 11 [5 favorites]

The appropriate tool for this job is a ball mill. This is what ball mills are for: it is their core purpose. Reducing hard, brittle materials to powders. That’s what a ball mill does.
...
posted by mr_roboto at 3:18 AM on February 11 [1 favorite +] [⚑]


Cool idea! The illustration of a ball mill looks very similar in principle to a hobby rock tumbler, aside from being directly driven by a shaft vs having a drum resting on spinning rollers. So, perhaps a rock tumbler and some large stainless steel ball bearings might be just the thing?
posted by Larry David Syndrome at 5:15 AM on February 11

Response by poster: Yeah, mr_roboto do you think a rock tumbler might do it, I was thinking of getting one anyhow!
posted by Iteki at 8:24 AM on February 12

Rock tumbler would be worth a try... my main concern would be burning the engine out if you ran it for too long. I would probably use steel ball bearings. You want to include a variety of sizes: check out the chart on this page for an example.
posted by mr_roboto at 1:07 PM on February 12 [1 favorite]

Curious to find out if you've found a solution!
posted by mr_roboto at 6:15 PM on June 6