JO´s Rebak Chunker

Hi JO,
Thank you for the diagram and the link. It certainly does a job on those branches. I was looking for a winter project.
Pepe

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Watching the video it is way cool but sticking your hand in the shoot to push it in scared the crap out of me. I think I would add a spring loaded feed roller set like a wood chipper has. Would be safer and power feed would allow you to walk to the wood pile while it chunks and get the next peice.
This makes me want to look at my wood chipper and see how hard it would be to convert I never actually liked it as a chipper it tends to make long strands and plug up.

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Hi Jan,

finaly I decided to build a chunker inspired with your great rebak.
The plan is for it to make chunks below 3,5cm wide and 3.5cm long.
l do know how this operates, but l dont know where to obtain the nessesery components. So, a few questions.
have you got a idea on where apropriete gears culd be acuired? And, allso the blades. Where did you get them? I guess they need to be at least high carbon steel, if not something better.
I have acces to bearings and other things, so those are my last missing peaces

Thanks!

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Kristijan,
The gears were just a lucky find in a local machining shop. They were made for one of their customers but rejected. You may find similar gears on old farming aquipment.
The blades are flat pieses of SS I found in the dump at work. Another lucky find.
I’m sorry but I can’t give much advice other than that. I’ll get back to you if something comes to my mind.

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Is SS hard enough for the job?

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I am also building a rebak. I was lucky to find an old cracked 54" saw blade from a sawmill. It should supply good steel for my blades. I wasn’t as lucky with gears so am using 100 roller chain and 3 sprockets. The drive sprocket is below and slightly in front of the 2 sprockets on the knife shafts. The chain goes under the drive sprocket and up around the front of lower kinfe sprocket then between the lower and upper knife sprockets, over upper sprocket and back to the drive sprocket, just missing the chain on the front of lower knife sprocket. Will let you know how it works in a week or so and if I can figure out how, post some pictures.

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Well, it was what I could come up with at the moment. It’s certainly harder than mild steel, but the sharpened edges still get a bit bent sometimes as you can see in post 40.

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Whats the thickness of it?

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If you were asking me, the saw blade is 1/4" or about 7mm. Sence you are probability asking JO maybe he could tell me the best angel to grind the blades. Thanks Fred

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Mine are about the same. 6-7mm.
Kingfred, I don’t know about the angle. I did them on free hand with the angle grinder. Maybe somewhere between 30-45. I guess it’s a tradeoff. Sturdy vs sharp.

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I have been wondering how hard it would be to convert a chipper to a chunker. Seems like everything is there just need to make the output longer. I have a chipper that tends to not do so good more of a stringer then a chipper and the blade is a nightmare to adjust.
Anyway if you could find a used chipper on Craigslist it might be most of what you need. And once you figure out how to make it chunk let me know so I can fix mine… lol

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The reason I’m building a rebak instead of using a chipper is the rebak seems to use a lot less power to process the same amount of wood. Other than the engine I don’t think much of most small chippers could be used in a rebak though. Without seeing your chipper I can’t say for sure though. You might look at JO’s diagrams and pictures in this post and at your chipper and get some ideas. Good luck, Fred
Oh almost forgot the big reason for the rebak, chunks for a gasifier. When I know what size they are, it should be easier to size the gasifier, I hope.

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Hi Jan,

a question again on the rebak. What is the optimal lengh of the blade?
Allso, l bought gears with a diameter of about 10cm. Looking on the youtube, people tend to use bigger ones. Is there a catch on it?
And finaly, how did you make the rectangular-round transition for the bearings? l am thinking to get a 3x3cm full steel bar and lathe it round on the ends, but l dont have a lathe… Do you think it will be strong enough?

Hi Kristijan, I guess you mean width. Depends what you’re aiming to chunk. Branches with lots of curves or wide slabs may need some width but narrow blades (short shafts) will make a sturdier machine.

10 cm dia with 4 blades per shaft is perfect for making our size chunks. Bigger will use less force (better cutting angle) but longer chunks. Mine are 12 cm dia. The chunks get a little longer than I like (close to 3") when I’m chunking thin material (less than 1" dia).

I didn’t. I used square tubing and pressed bearings into the the ends. The shafts are 20 mm dia bolts and they don’t spinn. Only the square tubes do. They are attached to the gears. No bearings on the frame.
I’ve never seen anyone else go this route, so I had to try :smile:

3×3 cm solid shafts may be strong enough if you find a way to attach the blades from all 4 sides without weakening the shafts to much (drilling holes).

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Hi Jo
What size of wood can your rebak take?

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Hi Thierry
2" material is OK if it’s green. A bit more if it’s soft wood.

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Is the engine (power) limiting to two inches? Or the height of the knives?

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I use a 3 hp motor now and it’s more than enough. Knife hight and the single belt are my limitations.

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Hi Jo

What type of steel you used for the knives ?

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Hi Tierry,
I used 6 mm flat ss plates. That was just what I happened to find in the bin at the moment.
I think worn out circular saw blades should be acceptable material, if not too thin.
Have you started a rebak build? We wouldn’t mind a few pics if you have :wink:

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