When I was building my burn tube and got to the rose peddle funnel I saw that I had a bladder pressure tank with nice heads. Ya its not a cone but it is a bowl with some pitch but not enough. I suspect that as the wood above the nozzles in pyrolyzing and taring the pieces sitting on the almost flat portion of the head doesnt slide down into the burn tube. Then the wood above and behind also starts to tar and glue together so by the time the wood closest to burn tube finally resizes the rest is stuck together in one big mass. I have no other explanation or theory as to the bridging. Unless fuel that is lumber scrap that is flat and rectangular is a problem like 2x3x3/4". I have attached a cross sectional view of comparison as well as the build pic for your feed back. The plan is to install a cone over the bowl.
Hi Wes
I have a funnel setup on my gasifier. I can’t say I have had a bridging problem. The funnel stays clean because there is hot gas circulating on the underside, no tar buildup.
I use rough sawn timber in the same dimensions, never had it tar glued together. But it is rough sawn not smooth planed.
Hope this helps
Thanks Patrick
Wes, be sure to try some round wood before you decide to modify anything. I have usually had poor results with the 3/4" boards, they love to bridge.
Head for the woods and find some dead limbs, cut them up and run a hopper or two of that. You may be surprised!
My first firetube I had very short “rose petals” that had very little slope to the firetube. It did just as you said i.e glue together around this area however directly above the firetube in the middle stays warm and will flow, therefore I didn’t have major bridging problems, just lost some capacity of the hopper since the stacked/glued wood on the side essentially made there own funnel. Personally I will be going with a steeper funnel next time.
Welcome to the 75% club!
I have found thin (3/4"-ish) sawed wood can be problematic as well. Carl seems to be having good luck with it. (I don’t his stuff has the grooves on the under side though)
When I’m cutting up that kind of stuff… I set the saw to cut about 20? degrees off square and split some of it as well…
Irregularity can sometimes be your friend 
Like Cris said… Rounds usually work great.
I would definitely try them.
You may be able to mix rounds with the present fuel and get a good result.
If you have a reliable source of something… Looks like that’s flooring and could be really good! Just have to learn how to deal with it.
If ya have or can get a lot of that stuff… Cut up a bunch like ya did before… But make it odd shaped as I said above… Then make a pile, about 3’ wide trying to make it as tall as ya can, eventually the pieces will fall down the side… For a given width you can only go so tall before the sides won’t hold. If you make your angle steeper than that angle it… (usually around 60 degrees) With “that” material ya should be bridge free If ya have to modify the funnel go with that (your mileage may vary)
Won’t be long and you’ll be looking back and laughing about this…
Awesome work man!
Thanks for the Videos!
TerryL
I don’t like using dimensional lumber, the problem is flat sides, you throw it in as 1x4’s or whatever and they stack against each other and now you have much larger blocks gluing themselves together because air can’t circulate around them. It’s like anything else, they create there own challenges!!! I would suggest mixing at least half irregular with dimensional. It’ all about air flow and dry fuel wood!!! Herb
Good Morning Mr. Wes,
I agree with all the above replies and think first I would experiment with fuel in different shapes and sizes .
Some of the stages that happen in the hopper seem to be wet and slippery wood in the upper levels . On down where the heart is greater it seems the wood start to bake, form a crust and seem to adhere to all other surfaces . Just a little deeper and closer to the fire tube it begins to burn .
On the funneled shape the fist opportunity for the wood to get a toe hold to bring on bridging is the top of the top of the burn tube , but at this point the heat is enough to burn the wood. I think with the bowel design the wood might be finding a toe hold just before the heat is high enough to burn the wood.
One other thing to consider on the rose peddle type funnel it is flexible . Road condition and vibration may be letting the wood spring around enough that during the baking mode the wood don’t have the opportunity to bond .
As I mention above I think I would experiment with different fuel first. If no luck I would split the bottom of the bowel some where it would cause a spring board or flex.
wes I also have the same problem and almost thinking of a hopper shaker .its funey my ash flows fine almost to good just cant keep wood in the tube.if you find a fix please post maybe the funnel is it thanks paul
Paul,
Since I have switched from the bowl to the cone the bridging has for the most part become a thing of the past. I do use wood that is flooring scrap and just make sure it is no more than a 3x3. Every now and then I may see a temp climb in the hopper but then it will fall back down. I suspect if there is a fuel bridge it will only get so big and then collapse and the temp goes back down. It was an exponential improvement over the bowl. Too much flat on the bottom of the bowl for wood to just sit there and begin to pile up and stack around the perimeter.