modification to cast core

Hi all; Just a small addition to the cast core. I am currently in the drying process on my core and I noticed that my feed tube edges were getting the worse for wear as I loaded wood or it was feeding itself. Small problem easly fixed with some clay . But the addition of some sheetmetal pieces has handily solved the problem. I intend to leave these in place as I cob over the burner as extra protection for the feed tube walls. More later Tom

wow that is huge tom. is this stove still in action?

Hi John; You sure found an old post... No, that core was my 1st and the feed tube could not hold up to the heavy duty use in the greenhouse. I have switched to using heavy fire brick in my cores, they take noticeably longer to come up to temp, and i don't get quite as hot at the barrel top , but you can't damage the feed tube. As far as size, it was the standard size recommended by matt walker in his video. My current core in the greenhouse is a heavy firebrick core surrounded by a clay brick outer with a firelay and perlite mix in between.

what materials did you use the first time / failure ?

Fireclay and perlite and a small amount of refractory. That core was the fastest ,hottest core I've ever built ! My feed tube started the season as a 7.5 "x 7.5" square with a 5 gal pail as a feed tube extension... end of season the feed tube was the size of a 5 gal pail. !!! I had to keep the feed tube partly covered to draft. In our greenhouse during the winter the fire stays going all day, many days my wife is in charge .... seems that if you force wood into a feed tube made of a soft substance it crumbles... therefore making more room for wood. My next core I used soft insulated firebrick ,thinking that they would hold up better than perlite... nope, seems that if you force wood into a soft firebrick you can make it wear also. My next core was my first with hard firebrick , but I did not bring the retaining walls up past the top of the feed tube... seems that you can break the bond of fireclay if you force wood into a 7.5" X 7.5" square hole without proper support ... my current core is hard firebrick and the clay brick surround is cemented and is above the level of the feed tube... winter is almost over and guess what seems that you can't force wood into hard firebrick feed tube that is surrounded by concreted brick ! Bottom line , the cast core was by far the Superior material to build with but... it is fragile ! In an insulated home where you are sitting near your rmh and your fire does not need to stay going 12 + hours a day it would work perfectly. If you search my posts you will find pictures of all rebuilds.

thomas rubino wrote:.....7.5 "x 7.5" square with a 5 gal pail as a feed tube extension... end of season the feed tube was the size of a 5 gal pail. !!! I had to keep the feed tube partly covered to draft. In our greenhouse during the winter the fire stays going all day, many days my wife is in charge .... seems that if you force wood into a feed tube made of a soft substance it crumbles... therefore making more room for wood. My next core I used soft insulated firebrick ,thinking that they would hold up better than perlite... nope, seems that if you force wood into a soft firebrick you can make it wear also. My next core was my first with hard firebrick , but I did not bring the retaining walls up past the top of the feed tube... seems that you can break the bond of fireclay if you force wood into a 7.5" X 7.5" square hole without proper support ... my current core is hard firebrick and the clay brick surround is cemented and is above the level of the feed tube... winter is almost over and guess what seems that you can't force wood into hard firebrick feed tube that is surrounded by concreted brick ! Bottom line , the cast core was by far the Superior material to build with but... it is fragile ! In an insulated home where you are sitting near your rmh and your fire does not need to stay going 12 + hours a day it would work perfectly. If you search my posts you will find pictures of all rebuilds.

you said you used a 5 gal pal but then at the end of the season the feed tube was the size of a 5 gal pail? or did you mean the burn tunnel ended up as big as the feed chamber?

this whole cast core fragile thing was one of my concerns and the reason i went with hard fire brick with a thick steel propane tank. the propane tank can take the beating but is only holding the wood and at times may burn up in side of it, the air flow is positioned at the bottom where the refractory cement was poured and the hole to the burn tunnel entrance even if it did deteriorate the steel it can only get as big as the hard fire brick burn tunnel. i have shown since the air tight wood magazine does not have air flow down through it and only through the bottom front air port the propane tank stays intact. believe me... i beat the snot out of my Rocket Mag Stove feed magazine. i use other logs to pound pieces down and jab it with the poker and slam the lid down and you would never be able to do that with a hard firebrick feed tube let alone a fireclay feed tube so propane tank with air tight lid is a must.

I believe a good compromise would be to cast most of the core with an insulating refractory mix, and cast firebrick splits (only 1 1/4" thick) as the liner of the feed tube and maybe part of the burn tunnel. Solid brick surrounding the top of the firebrick split feed tube should give enough strength to stand rough feeding.

Glenn i really beat my Rocket Mag Stove into submission, it needs to be able to handle a whoopin. coming in from the cold and accidentally dropping in an 8" log as it slams to the bottom would destroy a hard fire brick feed tube. For me, it has to be crazy tough. I buy and build everything extra tough and over engineered or it just wont last around me. If it can last a long time for me then its gonna last an eternity for a normal user and thats good stuff. i would hate splitting those tiny little stupid pieces for the normal 6" feed tube and dont get me started with the babysitting.... goodness.

I was not referring to your post, as I didn't see it until after mine went through. If your situation risks very hard use or abuse of the system, by all means use a metal liner for the feed. As a matter of fact, I have firebrick around the feed tube in my home RMH nearing completion, and will have a 10 gauge steel liner/top plate to allow P-channel air supply to flow around and cool the feed before injecting into the burn tunnel. This will of course strengthen the feed as a beneficial side effect.

Also, splitting fuel to very small sizes is a persistent notion that is not actually necessary. Small wood burns faster and hotter, but Ernie Wisner recommends wood of a size that only two or three can fit in the feed tube. For a standard house-sized 8" system, 3" to 5" pieces can work. There is no particular reason to cut big trees for firewood if you have a choice. Thinning smaller trees in a woodlot gives convenient-sized fuel with minimal splitting and lets you use all of the wood, some as kindling and some as long-burn fuel.

Glenn you are correct using a wood lot to prune is a good idea and i plan to do that if there is no fuel source for chainsaw use. Still... splitting 3 pieces to fit into a 8" system would bring it to 2" to 3" wood splits and thats just way to much splitting for my taste. matter of fact Ive been hand splitting wood since i was 7 and im about done with that. My back aint getting any younger.

An 8" feed can hold split wood like three 4" quarters easily, or a 5" round and a few 3" rounds. I suppose the bother of splitting depends on what size logs you have to start with... if I had 12-18" logs I would not feel like splitting down to 4"...