It sounds like you are thinking of building something, and those grinders on the video links are pretty awesome.
If you are more interested in getting from bark to powder and less interested in the
project of building the grinder,
here's a few things I have around the house that might do this job, at least for a small quantity:
1) Connie Vandyke crushes oystershells, nutshells, and other materials by leaving them in the driveway to drive over. She puts them between some sheets of
cardboard or plastic or whatever, so it's easy to collect the residue later. Not super-fast, but very little extra expenditure of effort in the course of everyday life.
Should work fine for cooked soup-bones or bark; raw bones might be harder.
2) Most saws makes sawdust. Grinders make a lot of bits of all kinds. Planes make cool thin shavings.
I am currently collecting sawdust from sawing
firewood in order to use it in an epoxy wood-filler for a later project, so it occurs to me that a tablesaw, or a hand-held grinder, could make any chunk of bark into dust pretty quick if you just 'saw' a kerf-thin section off the end, again and again. You could run a bundle in together if you are careful.
(I am using a thin-bladed saw because I want the firewood more than I want the sawdust; but there are very thick tablesaw blades that look like many blades stuck together, that could rip a 1/2 inch or an inch or more at a time.)
Power saws or grinders would work on raw bone as well as bark. A flywheel-style treadle grinding wheel, like for a blacksmith's shop, might be useful too, and you might be able to get a beat-up or almost used-up grinding wheel for nothing, (it wouldn't be much good anymore for tools if it was getting toothy
enough to be useful for chunking up debris; you could probably cut grooves in one, but don't wreck a fancy new one this way).
3) Along the same lines, a rasp, or one of those micro-planes like a hollow rasp, will shred things pretty quick. I could see maybe setting a couple of cheese-graters or microplanes as the sides of a funnel, where they reciprocate back and forth, kinda like carding wool.
4) For chopping up
straw, we often use a weed-whacker in a barrel or trash can. I believe you can get heavy-duty chain or cable instead of plastic string for a similar, but heavier, effect - they make them for the highway department to cut brush alongside the roads. This will be a nasty destructive weaponlike object, but might be very easy to scrap together. I saw somebody's chain thresher that worked on this general idea.
I would use a heavy plastic barrel or a barrel-lined pit in the ground, as the chain would make an awful racket in a metal container, and tear up any thin-walled container pretty quick.
5) The extremely slow but easy solution - bin the bark it up with some convenient and hungry insects, then wait a year or two. Removing the insects to use the powder ... lots of options depending on your location, and what you plan to use it for. I would probably use prevailing weather (
solar cooker, spread it thin when it's sub-zero, or salt-water rinse if you live coastally.) There is a fair amount of powder at the bottom of our woodshed, a good sifting would get enough for most projects, if you can avoid the cats using it as a winter litterbox.
For bone, a 'bone-fire' will reduce most of the bone to
ash, and brittle chunks that can be ground easily or absorbed in-situ by plants.
Likewise around our place, I use whole big bark chunks for medium-tough jobs like lining paths, or as roofing material for birdhouses, bee
shelters, etc. Smaller chunks might be useful as horse bedding or for dry footing when the thaw is turning their favorite paths into puddles.
If I want powdery
wood debris, I go for the shop-sawdust pile, or a duff log with lots of powdery punk that I can easily crumble in my hands.
Interested to see what you come up with, and what it's for.
-Erica
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