I’m hoping I won’t have that issue, these saws are carbide tipped. I’m also going to be extra careful about nails. I have a magnet pickup rod but I need to get some stronger magnets. I was thinking of putting a long magnet bar on my sifter.
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Cody,
Thanks for the offer. I’ll reimburse shipping. I am still contemplating trying to build the rock crusher design. I’ll try your design first.
I’d like to avoid a large percentage of fines. Tom Holton’s 20 percent by volume seems like much more than I get pressing the charcoal through a piece of expanded metal–probably less than 2 gallons for 20 gallons of uncrushed charcoal. I would think the rock crusher design would minimize fines, but I don’t know. Minimizing crusher construction complexity is worth something, also–especially to me.
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For the enclosure, make it as tight fitting as you can. I think I have a 1/8" gap between the saw teeth and the front and back walls, the sides you can’t do much about, I just let the nuts on the side act as spacers. I’ll toss in some pillow block bearings that I had ordered with it, but you might need to add some tape to the allthread so they’ll be tight in the bearing, and drill some witness holes for the grub screws. Maybe the screws will bite in enough. They’ll need some grease of course.
I need to drill out the wooden holes for the axle some more, the threads want to bite into the wood and shift it sideways. I’d go with a 3/4" hole in the wood to make clearance and the bearings will hold them true.
I might do a temporary setup with the electric motor to see just how much comes out as dust when it’s spun.
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Sounds great. I’ll need to make an additional donation for all that. Do let me know what seems to work best for you. That way I can learn from your mistakes instead of mine. Ha! Ha!
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Maybe “super thin” tile-cutting blades (used/discarded?) would be a possible compromise between aggressive carbide tipped saw blades and “very sharp discs”? https://www.amazon.com/Diamond-Porcelain-Cutting-Granite-Marbles/dp/B07MTYJNFS/ref=sr_1_18?crid=2M0GR4L44YHAB&keywords=7%2Binch%2Bdiamond%2Bblade%2Bfor%2Bwet%2Btile%2Bsaw&qid=1691507147&sprefix=diamond%2Btile%2Bblade%2Caps%2C1119&sr=8-18&th=1
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Hi Bruce, that is something i thought about too, i haven’t found the pic’s of the “industrial” crusher yet, but i will look for them.
Another thought i had is those blades used in “machines” for cutting ham for example, in Sweden those was popular in household (for cutting sausages and ham in thin slices, for sandwiches) in the -70s, can be found dirt cheap on garage sales and thrift stores, terrible sharp blades, with round edge, or small teeth, running backwards.
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Do you mean the blades that have teeth like a bread knife?
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Yes, some of them have inverted teeth, where the “sloping back” are the sharp edge.
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My brackets are arriving today, if I don’t get rained out like yesterday I’ll see if the grinder works better in forward or reverse.
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“running backwards” reminds me of the trick of putting a fine tooth plywood blade in the circular saw backwards to cut vinyl siding without cracking it.
Or maybe the thin blades should be free wheeling with little nubs forcing the charcoal sticks and pieces to break against them. Which produces the least fines and dust, sawing, slicing or cracking? And at what optimum speed and flow-through?
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Okay so after my initial test.
Motor spins at about 2500 RPM at 240v.
I used a 3" pulley on the motor and a 6" pulley on the grinder.
So I’m spinning at roughly 1250 RPM.
I’m getting what I’d say is an acceptable amount of dust, but I can’t help shake the feeling it would run better a bit slower.
Before I try reversing directions I will run it again at a 3:1 reduction. Just need to get a 9" pulley.
At this speed, it wants to fling chunks back out the hopper. That’s another reason I want to slow it down, perhaps it will be less violent. I had to put a cover on the hopper.
Another thing I could do is replace the 1/2" screen with a 3/4" screen considering the gaps between the blades are around that distance. If I do this then I definitely need to add filler spacers between the blades to prevent long pieces slipping through.
I’ll take pictures of the results, I was too excited to try it that I didn’t weigh my input and output. I’ll run a proper test tomorrow if weather permits.
I left the sides of the bottom screen open, so some bigger pieces do slip past but they’re well within engine grade spec. I finally got some 1/8" screen so I managed to not waste any usable char. This machine definitely grinds on the finer side.
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Over the years i have mentioned what i have been using since almost day 1 of my journey on the dark side , From memory not many people have ever been that interested in what i have and how well it performs , but just in case you missed it before I use a small wood chipper /mulcher, it originally had a 5hp B&S engine on it , i took the belt off the engine and mounted a wheel chair geared motor onto the frame and and used that to drive the hammers on the rotor , now the motor will run at 12 or 24 volt kinda works like a speed control the 12 volt spins the hammers at around 70 revs per min , the hammers do nothing really its the shaft rotor they are attached to that seems to break the charcoal up , i have a 1 inch screen and nearly all of the charcoal that drops through onto my Shute underneath is around half inch , works bloody great and the charcoal is so uniformed in size , i will get a photo of the charcoal for you to see if you want .
Dave
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Yes please, and a photo of the “machine”, i remember you using a wheelchair motor, but i cant remember seeing the set-up? 
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I’ve tried wood chippers, the issue is with the electric one I had it was killed by all the charcoal dust. Burned up the motor.
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Some charcoal crushers industrial- wartime.
From the Swedish department of machine/equipment testing.
Still looking for the “cutting/slicing” types
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There is a film of a cross made by Lars a little further down on this page. seems to work well, he has a magnet on the grill that takes the nail.
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I will get some photo’s of the crusher later today weather permitting , i will also see if i can remove the lid and take a video of the inside while it is crushing , these types of machines can be found at the side of the road or for very cheap money on line ,i turned down a larger one last week with a 13 hp engine in hindsight i should have grabbed it as this old one of mine has sat out side in all weathers now for 10 years even the belt is just holding on .
Dave
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Here’s what a hopper of large char chunks classifies into. It’s sitting in some 1/8" hardware cloth. I think this calls for a trommel.
The hopper is roughly a gallon and a half, and with anything bigger than 1/2" I filled it up most of the way. It looks like I’ve got almost a gallon of char.
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Goran,
Those are great illustrations of charcoal crushers/grinders. They are a good source of construction ideas. I would think that they were designed with a goal of minimizing fines. I assume they were intended to produce engine grade charcoal fuel.
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I’m not entirely sure if the dust is because I’m using mostly pallet wood for feedstock, or if it’s the grinder. I have one more trick up my sleeve to slow the machine down. I have a 12vDC power steering motor that I know spins a lot slower than this 2hp motor.
I might yet try using two axles of sawblades. If that works better, Steve, I’ll put one together for you. I’m also trying to minimize dust, I’ll already have tons of it to use in the garden.
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