Double duty chunker

Here are some ideas for a wood chunker made from a rear end, like one out of a standard 1/2 ton pickup truck. I would like to make two different chunkers using one rear end.

The plan is to use one side of the axle to make a drum style circular blade and anvil chunker like Mr.Keith’s… just scaled down a bit because I have to go pick the rear end from the junkyard and I want something that I can move around, so I will be planning to have it on wheels. I do not have a tractor with a PTO, but do have an old tractor motor, so I hope to power it with a 15HP Briggs and Stratton engine.

I plan to use a flywheel (something like a brake drum?) on the pinion of the rear end that will be driven by the motor using a small pneumatic tire off the motor pulley (friction drive). The motor would be on a pivot to “engage/dis-engage” the drive wheels to start or stop the chunker.

The other side of the rear end housing would be used to make a screw chunker that eats 6-8" poles as seen in the video that Woody found:
That is a serious industrial duty processor, but think the basic movement could be replicated using a rear end that is modified with a larger axle tube, like 6" diameter and the axle shaft could be used as a center for a ribbon flight auger similar to what David S has spec’d out on Dave O’s chunker thread at

I am still “on the drawing board” with this but I am planning to get the rear end soon so I can start with the Keith style drum chunker.
Seems like I will need to get a posi style rear if I want both axles to do work, right ?

I am not sure of the RPM for the motor to get the power it will need, but if it is turning at 1000 RPM and I get a 4.11:1 rear end, the axles would be turning at 4 times a second, which is still too fast. I can bring that down some more with a really tiny motor drive wheel and a larger diameter flywheel on the friction drive combo…or use a small/large pulley set.

Also have to figure out the details of the screw chunker, like the feed trough angle so it pulls the stock in automatically, and how to automatically clean the chunks out from between the auger blades once it makes the cut, and where to make the chunks exit (probably a hole in the right place and some gravity) any ideas/suggestions, etc ?

Really simplified drawing below:

I have the ribbon auger on order it should be here in a week or so. I was hoping to get it before the weekend meeting. I have the out side tube here already. I will keep all posted on how the project progresses. I like your idea. Wood processing has to be every bit as important as a gasifier in my book.
David S. PS are you coming to argos?

Hi David,
I have a prior commitment and will not be making the trip, although I had buy-in from the family. I will try to catch the next one, or try to meet up with some of the other regional gassers that do not make the trip.

On the topic of wood prep, I agree, and have been working with pellets while learning (for size and moisture consistency) until I can make some chunks for the larger unit.

I was wondering how the flights on the ribbon screw auger works with the base of the flight being so thick at the bottom… it seems the wood could pinch and get stuck in there unless the extra thickness is somehow working like a wedge to pop the chunks as the sharp outer edge is drawing in the piece and making a progressively deeper cut.

Are the flights symmetrical or are they made in a way to be flat on one side and angled on the other ?

I assume the chunks would somehow drop out of the bottom, because I have not been able to imagine a way to clean out the pieces from between the flights of the screw… what is your take on how it works ?

I looked at some Lamiet screw chunker videos and they have one model that is cone shaped insted of a cyliner. You are building a cyndrical one, right ?

After thinking about the drawing, I think if I have the motor and pulleys, etc on the pinion side, I should feed the stock from the opposite side.

HI David, the Keith chunker is self evident of it’s performance displayed. I think that the auger needs a few things that will become apparent over tests. First is the horsepower that it will require will be more in the range of an automotive 4 cylinder or up. Second, the blade width that is designed for moving dry or wet product, may not handle extreme twisting force. Third, the cutting edge of the auger blade should be hardened by a tool steel welded on tip or you’ll have a tapered clearance distance between the tube and the auger at the begining of the process. And one last thought that is possible, with those screw type splitters famous for making ridgid strands of 30 degrees or so angled tangents, would those chunks sit in a hopper and have gaps and or hook with each other?. Hope to see you this week. I have red hair…

The slow speed screw type chippers are made by a company called Laimet in Finland. They require about three times the horsepower of a traditional chipper for the given diameter of wood. So you need 100+hp for a screw chipper to do 7" material where you can get a 35hp drum or disk chipper to chip the same size material. Laimet’s 15" chipper needs 700hp compared to 125hp for a traditional chipper.

The difference is chip quality, size and consistency. I know I’m preaching to the converted but the goal is to reduce fines in the final product,

I notice that most of the commercial screw type chunkers feed the wood at an angle so as to not make a direct cross cut. Can anyone tell me if they think the W/K style chunker with a spinning wheel would benefit from feeding wood at an angle? Would this allow larger diameter wood per horsepower to be cut?

Good morning Doug,

I think the answer to your question would be yes. By angle cutting one could get more wood cut with less horsepower required.

However the gasifier seems to work best with fuels in a more of a block form. Example 1-1/2 x 1-1/2 , 2x2 , 2-1/2 x 2-1/2 , 3x3

The fuel seem to flow better when in more of a cube form plus more BTUs can fit into the fuel hopper.

I know it has been almost a year since you posted this message. Did you get the ribbon auger and get a screw chipper set up? Any pictures or more info on the supplier of the auger?

George, Good talking to you the other night on my chunker progress. Many got to see it at Argos and honestly is isn’t gotten any further along from there. So much to do and not enough time. I still have the Toyota to get fixed up. When I got home I modified my air valve linkage so it was more responsive I could fine tune my air mix better, went to light it again and now I have a major air leak in my ash can door. So mods need to be to that before I fire it again. I would post pics on my chunker for all to see on a blog or something if someone can help this computer illiterate guy do it.

David S

David, we would love to see more pictures. If you can get them to your computer, just scroll down beneath this box to the image-choose file-upload section. “Choose the files” that you want and press “upload” so it can be working while you type in the comment box. Takes a while to “upload” pics, and don’t press “save” till all your pics show. Hope this helps. Tracking down the little things seems to take forever, but you do learn too.