Key to making dense charcoal is heat the wood as slowly as possible. Heat it fast and the stean eacaping will produce a poppcorn effect.
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I have watched a program on how some remote Japanese people on making their high quality charcoal used for heating and cooking. They cook it very slowly for hours in a open fire kiln. The charcoal comes out and tingles like glass. It is a art to make high quality charcoal.
Bob
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very good point and observation.
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Hereās one method, a bit more modern than other Japanese kilns. Iwasaki style. Intent is for blacksmithing charcoal.
The heat from the fire drafts through what becomes charcoal and out the opposite end. Not sure on the % full converted though.
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Beware of Binchotan charcoal though, not sure how true it is but Binchotan makes less carbon monoxide and is allegedly safe to use indoors.
Binchotan is the glassy metallic charcoal, itās practically graphite.
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Wallace,
That was an obscure reference, I admit! 
Here is the link to the @f_pal topic:
Recumbent bike with motorized gas trailer - Projects - Drive On Wood!
I am working on the article he linked to in post #4, The link does not work and I found it the hard way. Article is in French, I am working on translating because it is interesting. To cut to the chase, carbonite is ball-shaped compressed chunks of coal dust and powdered pitch (wood tar) as a binder. I am better at finding translating tools now. Soon a text fileā¦Here is a previewā¦ 
Click on the jpeg screen shot and it will clear up a bit.
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I made some coke from good shiny anthracite a while ago. I had to mix the anthracite with wood to make it in a tlud. After a bunch of trial and error, it worked with about 80% wood 20% anthracite. The coal had a LOT of water in it. Much more than the 20% wood has. And the few pieces of coke I managed to make were very low density, like puffed wheat, or maybe cheese doodles. Coal was formed in ancient swamps, so naturally, it contains a lot of water.
Rindert
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This guy is from my neighborhood, an extreme athlete and a good innovator, he and my brother Paul cycled on recumbent bikes and debated a lot about construction, ā¦ now he lives somewhere in America.
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Long time ago there was a price for the first person hitting the 100 km/h. I dont dare to look how long agoš
Topsport!
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Iāve become a bit dissatisfied with my current charcoal crusher. Iām finding that it lets long pieces slip between the teeth and isnāt purchasing on the big pieces to break them.
Iām going to make a few different crushers to compare them. My next one will be using these cheap saw blades I got on eBay. I bought 10 blades for about 60 dollars.
Using two lengths of 5/8" allthread rod, washers and nuts Iām going to see if this design will work.
One side will be spun and the other just freely rotating.
Waiting on some pillow block bearings to arrive,
Between the nuts and washers I think the blades will be spaced apart about an inch, and with each blade between the other, maybe a half inch spacing.
I know Bruce has made something similar, his Ab Roller design and the saw blade plus hammer mill. I donāt know if he tried making a double saw blade crusher, though.
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Donāt forget to bring your spacers between blades out to just clear the blades on the other side. I used gears for counter rotating by hand. Maybe I should have just let one side freely rotate like you suggest. If you find that you need counter rotation, using motors powering each shaft separately might be easier than gears.
Iām looking forward to seeing how yours works.
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Good idea, Iāll cut out some wooden discs to go over the nuts. That should help keep longer pieces from slipping through.
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You might put a pipe or wedge under the rotating drums to help keep the long stuff from slipping through as well. It is just to make sure it bends, and breaks. But it may also increase jamming.
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One thing I could do is put a 1/2" or 3/4" screen cupping the underside, so if a piece does get beneath it could give the blades a chance to grab again.
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Hereās how far apart the blades are on one of the axles.
Iām starting to wonder if I can just make a hammer mill screen and only spin this one axle?
Iāll play around with this idea.
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You could just make a hammermill. I saw one that shells corn, it was a barrel or metal 5 gallon bucket and then just a shaft with chains on it. then I forgot what they used for hammers. They use them for biochar a lot. but you would just need a bigger screen.
This is actually a pretty good, cheap idea. he is using pvc pipe for the barrel.
I would actually use screens instead of slots in it. so you can switch them outā¦ worst case scenario, you have a machine that can process grains. It is pretty much the same design as the others I have seen. Usually you put the feed shoot offset so stuff doesnāt fly out the hole. If you use a larger barrel, you could have a larger feeder that could process sunflowers with it as well.
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Okay so hereās what Iāve found today.
With a 5/8" rod, a wash on either side of the blades, and a 5/8" nut on either side, in a confined box with a small hopper: Iām getting engine grade charcoal with minimal dust.
I need to tighten the heck out of these bolts some more, when it slips the blade thatās caught freely spins. Brands will just simply get cut instead of smashed.
I have a 1/2" square mesh screen beneath the blades with maybe a 1/2" gap, I should probably try to tighten that gap.
This setup wants speed and a lot of char in the hopper. The more you have the more it helps in the crushing. I have a 2000 RPM motor that I might try to use, with a 3:1 reduction.
Hereās a 2" pipe nipple for scale.
I will probably take this apart and put some wooden spacers inside as well to prevent char from getting stuck between the blades, but the way I see it the jams clear themselves with higher speed.
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that looks -really- good.
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I wager it would also work using bicycle gearing, something overdriven.
Not bad for a No Weld design!
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