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Post by wrekinwanderer on Mar 16, 2014 12:38:41 GMT -8
Now, this is a call for help... The Peterberg Batch Box Dimension spreadsheet has been amazing! It's so easy to follow a recipe. I have always struggled with dimensions for the J-tube even though I have read, studied and gone over it a hundred times from the book....
Can anyone do a similar spreadsheet that calculates the requisite dimensions for the J-Tube?
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hpmer
Full Member
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Post by hpmer on Mar 22, 2014 5:44:09 GMT -8
Here you go (but you have to supply your own calculator)
1:2:4
feed tube:burn tunnel:heat riser
Burn tunnel length is 2x feed tube height, heat riser height is 2x (at least 1.5x) burn tunnel length. Same cross sectional area throughout.
Although 1:2:3 also works, a bit higher riser equals better draft.
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Post by smarty on Mar 23, 2014 12:39:40 GMT -8
I seem to remember that when Peter gave out these measurements at some point he took the points as measured to be from a line drawn through the centre line of the j tube. So if you draw a j tube seen from the side and then draw an imaginary dotted line through the centre of the j tube it is this imaginary line from the top of the feed tube to the centre of the burn tunnel, from the centre of the feed tube to the centre of the riser, and the centre of the burn tunnel to the top of the heat riser that has the proportion 1:2:4.
The next question would be what is the relation between this proportion to the System size? Is 1 the same as the system size?
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Post by smarty on Mar 23, 2014 13:50:00 GMT -8
Looking into it it seems like 1 in the proportion 1:2:4 is equivalent to about 1.5 system size. So in a 6" system 1 will = 9", 2 will = 18", and 4 will = 36" or if you use the 3.5 minimum it will be 31.5". I think I remember Peter saying he found he could slightly shorten the burn tube when he had the p-channel and trip wire in there, so you could take off maybe 1/2" off the length of the burn tube and then the riser could be a bit shorter too I guess.
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Post by peterberg on Mar 23, 2014 14:11:26 GMT -8
The next question would be what is the relation between this proportion to the System size? Is 1 the same as the system size? I'm inclined to say it could be, but this is unknown territory. When you would view this as a fixed proportion it isn't possible anymore to make the tunnel longer or shorter as need arise. Building a stove using a larger or smaller diameter barrel there ought to be some variation in the length of the tunnel I would say. So maybe it is something between 0.7 and 1.3 in the feed:tunnel:riser proportion of 1:2:4. We have to think this over, a simple spreadsheet is much better than trial and error. Maybe we could include the diameter of the barrel into the calculation? I've got the feeling there are probably more factors into play here. |
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Post by smarty on Mar 24, 2014 1:15:20 GMT -8
The next question would be what is the relation between this proportion to the System size? Is 1 the same as the system size? I'm inclined to say it could be, but this is unknown territory. When you would view this as a fixed proportion it isn't possible anymore to make the tunnel longer or shorter as need arise. Building a stove using a larger or smaller diameter barrel there ought to be some variation in the length of the tunnel I would say. So maybe it is something between 0.7 and 1.3 in the feed:tunnel:riser proportion of 1:2:4. We have to think this over, a simple spreadsheet is much better than trial and error. Maybe we could include the diameter of the barrel into the calculation? I've got the feeling there are probably more factors into play here. So would this be 0.7 = 1 measured from the centre of the burn tunnel to the top of the feed tube? This would make the burn tunnel on a 6" system 8.4" measured centre of feed tube to centre of riser, making the actual length of the burn tunnel roof only 2 3/8"?, and the height of the riser 16.8" measured centre of burn tunnel to top of riser. If we add 3" for the bottom of the tunnel that gives an overall height of 19.8" which is well below countertop height for cooking applications. If I have this right that's good news for anyone trying to use a j-tube to cook on. The j-tubes I've been thinking of using up till now have been just under 4 x system size measured end to end with a burn tunnel roof of 2 x system size. Have I got this right Peter, or have I got in a muddle? Here is a link to some drawings of various dimensioned 6" j-tubes based on your proportions. app.box.com/s/7mn9idb5tq5e9yypnjdb |
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Post by smarty on Apr 10, 2014 23:45:24 GMT -8
Hello guys just wondering if anyone got a chance to look at the link above on various J-tube proportions. I agree that it is a nice idea to have a few basic parameters for designing them and I'm keen to know if the drawings on the link are on the right track or not. If they are not I'll remove the link otherwise I fear it could cause confusion if anyone takes it as gospel.
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Post by peterberg on Apr 11, 2014 7:55:13 GMT -8
Hi Smarty,
I simply forgot to look at it because my Chromebook can't read .skp files. Your best one at first glance would be the one top right. I had to translate the dimensions first and the proportions truned out as 1:2:4 exactly. In some circumstances using the same method the ratio could be 1:2:3, provided there's an adequate chimney stack.
When there's a need for a longer burn tunnel the riser will be longer as well, that's a good thing. The feed tube will be larger as well but not as much by far as the riser.
This looks like a useable method, I would say.
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ebt
New Member
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Post by ebt on Jun 3, 2014 4:49:31 GMT -8
Smarty, is there any chance you could post those drawings as a pdf. On a mac with googles latest version of sketchup I cant open them. (seems to be a compatbility issue between windows sketchup and mac sketchup)
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crisp
New Member
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Post by crisp on Jul 18, 2014 10:39:11 GMT -8
For the burn tunnel length, do you measure from the end of the riser to the end of the feed tube, or just the length of the horizontal portion between to feed tube and the riser?
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Post by smarty on Jul 23, 2014 12:04:21 GMT -8
The burn tunnel length is either measured end to en horizontally or centre of feed tube to centre of riser horizontally. Depends on which system of measuring you use. If you are using bricks and designing on the hoof the first method is probably easier, but I find the second is easier if designing the thing on paper, or computer, such that it can fit into some other thing such as a cast iron cooking range where the ratios need to be worked out in relation to the particular dimensions of the thing you are trying to design the burner to power.
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gjh42
Junior Member
Posts: 61
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Post by gjh42 on Oct 7, 2014 10:12:37 GMT -8
Is there any guidance on cross-sectional proportions of the feed tube and burn tunnel? Are they best made square, or is there any advantage to making the burn tunnel taller than wide or vice versa? Obviously the feed tube should have the same width as the burn tunnel for fuel loading and combustion flow.
Building with firebrick makes the question relatively moot as modular dimensions have to be considered, but cast cores can have any shape or proportions desired.
I have seen mention of making the shape taller to facilitate access for cleaning or inspection. Peter's description of sloping the top of the burn tunnel to be slightly higher along the centerline would turn a 7" square into sidewalls shorter than the floor width; is this good or bad? My cob kiln-building experience has been that a wider firebox allows the fuel more exposure and better combustion, but this is with sticks laying flat on the floor/ash bed. That may not be applicable to the vertical feed with the burn tunnel essentially just a gas channel.
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Post by Donkey on Oct 10, 2014 9:32:14 GMT -8
I have noticed that long, narrow rectangular feed boxes tend to smoke back more often than square sections of the SAME CSA.
This wasn't arrived at scientifically, just an observation that has repeated over time.
I would like to see someone check this in a methodical way.
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gjh42
Junior Member
Posts: 61
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Post by gjh42 on Oct 10, 2014 18:19:44 GMT -8
Here is a jpeg of the .skp file for those who don't want to install Sketchup just to see an image...
Oops, I get a message "This forum has exceeded its attachment limit. There is no more space to store attachments" or similar wording. Can anything be done about this?
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Post by PNW Dave on Oct 10, 2014 19:43:16 GMT -8
Hi gjh42, you'll need to upload the picture to some other hosting site, like Photobucket, then post the link in your reply.
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