Interesting design.
Have you looked at the Rebak style wood chunkers? One of our members built one, but they are also commercially available. It’s what I would use if I needed to build a chunker from scratch.
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Welcome to the DOW BramH.
Good you are approaching wood gasification from the make fuel standpoint.
Anything; and every system made up, whether raw wood or a charcoal system, is worthless without a sustainable fuel supply.
So first you must ask, “What does a small woodgasfier to make engine grade fuel want?”
For a raw wood input system it wants; clean, uniform, and very dry fuel wood bits.
Here in this video you will see a bucket of prepared fuel wood input for StephenA.'s system:
And he did make these with a three point tractor PTO driving a re-set disc chipper.
Described here:
All of his sites videos are down now as he stepped away from DIY woodgasification as of 2019.
But do read his discriptions. He only chips his hardwood sucker growths in winter no-leaf, sap down. He then screens the results. Rejecting out ~1/3 of his chipped production.
Pretty much making prepared fuel for a woodgasifer is a Garbage-In then you will have Garbage-Out situation.
J.O. and others are by hand hacking off first all of the fine twigs and branches first.
Otherwise you must then set up, and spend the additional time to do a lots of size screening, and size classifying. More equipment. More time involved.
Regards
Steve Unruh
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Bram, welkom.
Rebak hebben we hier ook. All the small stuff is processed through. You can build one with your gear but what Mr Steve said. What size do you need?
I have a diskchipper here that needs some TLC, something for you? Needs around 20-25 hp, I think. Stuffed in the back somewhere.
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Hi there Chris,
I was hoping to see some feedback from you.
Yes I have thought about the Rebak style wood processor. But first of all it doesn’t offer me the option to cut things a certain length. You sort of push the material in and it gets decimated into whatever size the machine is set up for. There is no control what so ever. I want to be able to make little bunches of sticks 1.5 ft / 45cm long. They will fit into our RMH perfectly and burn nice and bright, exactly what we need to charge up the mass.
Secondly, they don’t really work for me as a woodchipper. The material that will come out of the woodchipper I have in mind will be half an inch max in size. So if I throw in a branch that is a meter / yard long, I will get a bunch of fine woodchips. Closer to sawdust than ‘chunks’.
Thirdly I want to protect my little tractor. We don’t have a lot of money and the Rebak gets connected straight to the PTO. It looks fantastic in videos, but should something get stuck all the energy is going straight into the tractor. With my design the worst that can happen is that I burn up a few v-belts.
Do you think 30mm / 1.18 inches is sturdy enough for this type of chunker? There will be a bearing right behind it and I will ask the machinist to turn out thick flange that allows me to exchange the blade so I can experiment a bit.
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Hi Bram,
I also tried to design a chunker with a worm drive. But then I read somewhere that worm drives produce a lot of heat because of friction so they are not used for larger than 5hp. And I looked at things out there that I could buy, and it seems to be true. So then I tried to imagine and invent a worm drive that uses ball bearings or rollers, something like that. I don’t have any success with this.
I wish you success.
Rindert
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Bram,
I have experience running a wood chunker based on a square baler gearbox. You can see that project here:
It runs on a 5hp electric motor, but could easily be adapted to a small tractor. The heavy gearbox and 200 lb flywheel takes all the abuse, the motor just spins the flywheel back up via a double V belt.
I also have run a woodchipper/shredder behind a BCS 853 two wheeled tractor, Lombardini 11hp diesel engine. I understand being worried about overtaxing the small tractor. The chipper I used was made by Caravaggi in Italy, rebranded as the BIO-100.
It makes very small chips and then what you can’t push through the chipper (side opening) gets tossed into the hammermill-style shredder (top opening). If you push into the chipper too hard you’ll bog down the engine. If you throw too much in the shredder, it will stall and you can’t restart until it is shut down and cleaned out manually. Really a pain and to be avoided. Those units are driven by double V-belts, which do stretch and wear, and over time lose power transfer, which makes it even more prone to clogging. But the belt is an important safety stop, to avoid slamming the motor if you chunk a rock or steel by mistake.
JO’s Rebak is running off a 5hp motor, belt driven with no flywheel. You could belt drive yours as well, to save the tractor. I think the Rebak design requires the least cutting effort for making proper sized wood chunks. Less power input is probably easier on your tractor and all the drivetrain.
It takes quite a bit of power to grind a long branch into 1/2" pieces for mulch. I believe that is a very different tool than a wood chunker to make gasifier fuel.
Making the blade style chunker work, either cylindrical like mine or flat blade like your design, will need a heavy flywheel to complete the cut. This should be spinning fast to provide any advantage, so before the gearbox. The gearbox must be able to take the pounding of chunks being cut and released, the gears inside will load up and release over and over. This is why I used a square baler gearbox, they are designed for this exact purpose and cadence while packing hay into bales. Very heavy duty, and easy to find in the US. Maybe not so much where you are at.
One final question I wanted to ask, your Bertollini has a driven wheel trailer, making it essentially 4 wheel drive, correct? Meaning the PTO turns faster or slower as the wheels go faster/slower, in different gears, etc. Is that a separate PTO than the normal implements would use, like a tiller? It appears to be in the same spot as your tiller would attach. Usually PTO is independent of the wheel speed. How does that work on a Bertollini? I would love to have a driven wheel trailer, but they won’t work with BCS because the PTO is independent only, same speed regardless of wheels. Perhaps when EV drive motors are cheap enough, I’ll build a push trailer.
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Hey hoi, leuk om een Nederlander hier tegen te komen.
The Rebak is not really what I want. I responded to Chris with a bit more detail. And I have never really liked the disk chippers because they don’t draw the material into it. This is more what I have in mind.
What do you think, is the 30mm shaft strong enough for a chunker like this?
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Cheers I will have a look. Right now I am not looking at any woodgasifiers, just firewood and woodchip production. But if the time comes and the zombies are at our door, I will probably be happy I already created step one! 
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This makes a big difference! I misunderstood what you needed to create. Sorry if I misread your original post.
In that case the disk chunker you have designed will probably be fine, but what I said above regarding flywheels and gearboxes is still important. You also have a speed mismatch between the disk and the chipper, one wants to go slow and make slices, the other wants to be faster and get through chips quickly.
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BramH. when you say you desire “firewood” what does this mean?
30cm to 50cm lengths cut to work in a bulk wood stove? Fireplace? Or a specific whole house furnace like J.O., JanA and most recently newest Premium member DavidP had pictured up using to heat his home.
Or cut stems and branches cut like in your reference video for use in an Eastern European type auger fed furnace?
In none of these is twig ends and small branches with leafs, or needles covered; wanted, or desirable.
Feed these in, and most chippers and shredders will bind up and clog stopping.
UNLESS hugely flywheel effect oversized, and oversized engine brute force powered.
This is just the reality of it. Same-same anywhere in the world.
Steve Unruh
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He’s talking about a Rocket Mass Heater SteveU. I have one in my greenhouse. Just a feed port that small pieces of wood stand in and burn from the bottom. I never worried much about the size of my fuel length. Smaller diameter is better but requires pretty much constant feeding. For those not familiar, here is a link.
If I were going to build another one I do one of these batch designs.
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Wow! That’s a lot of responses all at once! 
I don’t know if I can answer all individually so I’ll just make a general post that addresses all of them (I hope).
Yes I am only looking at making fine woodchips and firewood in terms of bundles of medium sized branches. Gasification is something that I might look at in the future but it’s not an immediate goal.
Normally people burn branches that are smaller than a wrist in a big bonfire. But our Rocket Mass Heater burns that kind of stuff happily. If you want to see a video of our specific RMH, check out this video. I hope to produce bundles of about a shoebox in size, maybe a bit longer. Those bundles I can just plunk into the RMH it’ll save on a lot of handling.
I already own a very similar chipper to what Chris posted about, the kind that speed up to 2500rpm or so and chip the branches through a spinning disk with blades or with a hammerlike drum. And yeah my experience also has been that they tend to clog up pretty fast. Also the chute on mine is so narrow that it doesn’t take branches that are slightly twisted.
But what I have in mind here doesn’t care about high RPMs, both the chunker and the chipper can operate at a relatively low RPM. The 60ish RPM I’ll get after the reducer should be fine because both the chipper and chunker work on torque. The chipper blades I posted above are from a garden chipper that specifically runs at a low RPM and doesn’t produce noise. It just pulls the material into itself and with a bunch of torque, munches up the branches. If you’ve ever seen those high torque shredder machines that eat up whole cars? That’s kindof how this chipper worked in the original setting. The original machine had 3hp fed into a small reducer. Mine will be 12hp, reduced via the PTO and then again through the reducer. I estimate that it’ll have anywhere from 60 to 100hp in terms of torque.
Lastly Chris asked about my tractor and the trailer that can attach to it. So I wanna say that my tractor only came with a rotortiller, those videos in the playlist are from other people. But it has two PTOs coming out the back. One is the regular kind of PTO which spins clockwise and has two speeds and neutral. The other PTO is slightly smaller in size, has no gears and spins counter clockwise. This is what the people connect the trailers to from what I understand.
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Good details. Able to use good sized wood also.
Thanks for showing the made up door in the front for going cold draft safety. And the bypass into the chimney to insure up drafting starting and later going bed for the night.
No thin burn through sheet metal.
So not a barrel drum enthusiast “Hippy Killer”.
Steve Unruh
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Correct. I recently found out my Agria has a broken PTO. We are using the small one 
without knowing it is for driving. Strange things happen when you go backwards with a mower . Well, no one told me…
Blockquote If you’ve ever seen those high torque shredder machines that eat up whole cars ?
Blockquote
Here is a 3 kW version. Works ok. And in another corner of the shed. Replaced by a 18 kW Gross shredder. Interested in the small one?
edit, just watched your riserless core. You are a do-er. You will just fit in here.
35 mm is ok!
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Yeah my wife and I just didn’t want a big oil barrel in the room. Ever heard of the term fugly? Besides that, this version allows you to see the fire and you can cook on it. Which is a nice backup to have when winter is the time we have the most power outages.
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So in general the consensus is that this 30mm/1.18inch axle should be sturdy enough to run the chipper and chunker?
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Good Morning BramH.
I think no one knows. And being uncertain with your different approach none willing to say anything.
Here is a link into a topic that may give you guidance:
https://forum.driveonwood.com/t/branch-logger-stekovac-wood-processor-design
Has an embedded YouTube of one of the only other examples of a single shaft system. Most are building using opposing blades two shaft systems. Note that the flywheel is on the power working side of the for-safety belt drive.
Scroll up and Tom Collins was able to post up manufactures dimensioned diagrams of a commercially made system.
Maybe someone else finished actually working system in this group of 35 topics can give you shaft sizing direction.
Users say it would be really really nice to be able to power reverse to more easily clear out clog/binding jams.
You can click on “Wood Chunkers” in the headers anywhere in this topic to open up the 35 topic listings.
Try reading “Axle for clunkers” Feb 21 started by Low-and-slow.
Steve Unruh
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Bram,
There are many, many sample calculations out there. Search: shaft torque calculator. Those numbers mean something to me because I used them many thousands of times.
But in your case I cannot say anything because I am not familiar with your machine. For you I would recommend not to use numbers. Think like a farmer. Compare your machine to other machines you see that use similar torque and cyclic loading. If you want to save weight, a hollow shaft can deliver more torque at the same weight.
Rindert
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I like screw type chunkers because of lower cyclic loading.
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