In article ,
Tim Wescott wrote:

We have this big ol' pile of horse manure out back, which we can't
spread out in the pasture because it is full of rocks that are just
about exactly the right size for causing problems with horses feet
(according to SWMBO, at least). The sizes range from sand to 3-4 inches.

Since clean, rock-free horse manure is pretty easy to get around here,
I'm assuming I cannot give it away. So I'd like to build a sifter for
the stuff, to separate the good rocks from the good fertilizer.

I'm considering making a big drum with a 1/4" screen, rotating it with
either an electric motor or a Vibration & Stratton engine. I'll load in
dirty manure in one end with my loader, get clean manure out the bottom,
and occasionally dump slightly odiferous rocks out of the drum.

What I need to know is:

1. Is this a good approach?

Sort of... It's a "bad" variation on a unit called a Trommel-screen.

1a. How do quarries sift their rock?

Trommel-screen... Often a series of several of them with graduated size
elements.

1b. Is there something out there that I can get my hands on that does
this task? It doesn't have to look like what I think will work, it just
needs to separate the rock from the crap.

Trommel-screen. But unless you home-brew it, it's gonna be *REAL* pricey
- The smallest "ready-made" one I've ever personally laid eyes on was
used by the Mackinac Island dump/recycling center for *ALMOST* exactly
what you're looing to do - They started up a recycling/composting
operation there a few years back - Basic concept: Trash separation is
mandatory - You've got three containers: "Landfill", "recyclable", and
"compostable". You're welcome to buy only "Landfill" containers - at a
price intentionally set to "over the moon and then some" specifically to
discourage their use. Compost & recycle containers are practically free.
Misuse of compost or recycle containers for landfill means you get *NO*
garbage service whatsoever, and are legally obligated to transport it
all yourself (at exhorbitant prices) to get it off the island. Anyway,
long story shorter, "compost" bags get opened, spot-checked for
"illegal" trash, then run through a grinder. The output of the grinder
then gets mixed with some of the output from the 500-odd horses that
populate the island in the summer months, and stuffed into composting
frames. Once it's "cooked" enough (about 6 weeks from start to finish)
it gets fed to the trommel-screen, where any "chunks" that didn't
compost down nice the first time through get sent back through the
grinder for a repeat processing, and the "final product" that comes
through the side of the barrel gets sterilized and bagged for sale as
landscaping/topsoil material. (at premium prices, I might add! Even
though expensive, it is worthwhile if your're in the market for such
stuff)

2. Anyone have any suggestions for screen? I'm considering expanded
metal, but it looks like I can't get really thick expanded metal with
1/4" holes. I'm afraid that the 18 gauge that it seems I can get will
wear too quickly, particularly if I get a big rock bonking around in there.

There's where your plan goes bad...

Trommel-screens are more or less like the barrel of a cement mixer, only
tubular instead of conical, and open at both ends, with the size screen
needed to let "OK" stuff fall out along the length, while keeping the
"too big" stuff inside the barrel until it falls all the way to, and
eventually out through, the lower end, where it can either be loaded out
to a dump-site, or run into another Trommel-screen with a different
sized mesh for further size-grading if desired.

Basically, take your idea of the drum, make both ends open, cut out the
sides of the drum leaving a framework of "spokes" to suppot your screen,
and line the inside with plain old quarter-inch hardware cloth. Mount it
slanted so that the barrel can be spun on its long axis (doesn't need to
be very fast) and start shoveling stuff in at the top. "Clean" stuff
falls out through the screen, oversize "stuff" ends up piled at the
bottom end - Continuous cycle - As long as you keep feeding it, you keep
producing sifted stuff to be used, and oversized chunks to be disposed
of, with no need to stop to empty the barrel, and litle problem with
"big chunks" beating it to death, since they're only inside for as long
as it takes them to fall thorugh the barrel to the other end.

--
Don Bruder - - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
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