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Post by matthewwalker on Jan 10, 2014 10:19:21 GMT -8
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Cramer
Junior Member
Posts: 129 
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Post by Cramer on Jan 10, 2014 17:26:25 GMT -8
Wow Max! Thanks for going through all that trouble and all the calculations! Math was never a strong point of mine (I actually loved math, it just didn't love me back, didn't like English much but it had some affinity for me. Strange things happen in life). I know what a corbel is but in the manner you speak of it I am construing it to mean a recess in the top of the bell to hold the RSJ? Or would one affix a corbel of some kind on the inside of the bell to support the joist? I have been mulling over shortening the bell lengthwise and using firebrick pillars in the center of the bell to support the plates at their midpoint, thus having all four sides of any one plate with support under them at their edges. The pillars would add to the ISA of the bell (9 inches by bell height times 4) of course and that is the reason to shorten it by (at least) one brick length (9in or ~22.9cm). EDIT: Just thinking, how would I seal between the two plates then? ... back to RSJ.
Having trouble with this... what do you mean 2.5in slabs? 2.5in thick? That would be one very hefty piece of steel! I fairly followed all the rest and I agree wholeheartedly about building in safety factors in the calculations. Much better to over rather than under engineer. Which is why this particular part of the build is so important. EDIT: Disregard, I read and reread what you were saying an now understand you meant the weight of the fire brick on top of the RSJ. But now I am still wondering what thickness and type of metal to use on top of the RSJ now that I know the RSJ will be good to go. Leaning toward four plates of 1/2 inch steel since 3/8 for Patamos have done well without signs of warping. I found a steel provider near me with a search. It may be a good idea to go consult with them. I will probably purchase materials rather than try to collect them. I am not much good at scavenging.
Vortex, wow, I would have thought the thicker metal would have caused fewer problems not more!
Patamos, well I was thinking of 1/2 inch so that is good information to have for sure, thanks for the correction!
Matt, those look very nice. I wish dimensions had been given for these but I could find none. Dimensional data was given for some of the others but not these specifically. I will have to do a search for some of the right size for my application if I do not use just plain old steel plate (mostly covered in fire brick for heat retention purposes! Thanks!
ALL: I had no idea the top of the bell would turn out to be so complex! Maybe I will just throw a piece of high temperature plywood over the whole thing and be done with it! (Tongue planted firmly in cheek guys, don't take that comment seriously!)
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Post by satamax on Jan 10, 2014 22:43:10 GMT -8
Cramer, i was thinking about 6/10 of a mm for the steel plate, just held in place by the sheer weight of the firebrick slabs (you can use stone too, or may be even some type of concrete) May be a 1/32 of an inch does exist where you are or may be 1/64th. The plan is to use the sheet metal just for making the bell airtight in this case. And put a thick metal plate where you want to cook, on top of that, or a griddle as Matthew showed. Far better for cleaning imho. You could skip the steel sheet, but the problem is, how to make the joints airtight. One option would be criss crossing some thinner slabs.
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Post by Vortex on Jan 11, 2014 2:52:24 GMT -8
Cramer: wow, I would have thought the thicker metal would have caused fewer problems not more! A thinner metal sheet is more flexible so it just expands up into a dome over the hottest area, but with thick metal it cant do that and so the whole thing twists. A square cut-out above the hottest part allows for enough expansion to stop this happening. Weld a slightly larger piece of 5mm on top of your 10mm or 12mm and it'll sit nicely in the hole, a square is better than a rectangle because if the cut-out warps slightly you have 4 possible positions you can reseat it in to find the best seal. |
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Post by grizbach on Jan 11, 2014 12:30:33 GMT -8
Vortex has it right about having the most intense heat on a separate plate. You can see in this build pic that I have my "hot plate" welded to a column for more rigidity. donkey32.proboards.com/attachment/download/381Since then I have welded support bars to the corners because I was still getting a little flex. You can also see on the top plate the 10" discoloration ring from the heat. |
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 12, 2014 7:05:16 GMT -8
Thanks griz! I saw this build, quite impressive by the way! I don't think the attached picture is the one you meant to attach here though, it is of the bench portion of your build. Did you mean to post the top, where the heat from the riser impacts the top of the "drum" (for lack of a better term for it)? In the picture you cannot see the burn ring you are speaking of.
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Post by grizbach on Jan 12, 2014 11:51:49 GMT -8
Cramer, I don't have a good pic showing the heat ring. Here is a blowup of what I meant to show on that pic. The second half of the pic, the top is just oiled up,so you cant see the heat ring but it shows the support bars.  |
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 12, 2014 15:10:13 GMT -8
Ok Griz, I see it clearly now! That is a really nice looking unit you have there!
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 12, 2014 16:03:35 GMT -8
Okay, I have pretty much figured out what I am going to do with the top thanks to all of the input. Now one last thing. I said I was working backwards now to the riser. I don't know where those nifty pre-made insulated risers came from that I have seen on Peter's builds and I think Matt might also have one. Would they support themselves if they were recessed into a cast burner (at an angle) without any support? as soon as I can arrange some time off I will be picking up castable refractory cement for the burner. Before making the mold for the casting though I need to know what I am going to do about a riser.
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Post by matthewwalker on Jan 12, 2014 16:48:18 GMT -8
Yes.
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 13, 2014 3:15:15 GMT -8
Thanks Matt! Can you tell me where I might get one?
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 13, 2014 3:22:34 GMT -8
I did a burn in the prototype again yesterday. Similar results to the first burn but the wood was even wetter than before. It still drafted well with just a quick blow on a bunch of pine straw and continued to burn well for about an hour. The perlite had gotten wet and did not afford as much insulation value so it didn't rocket as well and took much longer for the smoke to clear up. Even with a slight breeze down the riser tube I got very little smoke back even under the less than optimum conditions.
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Post by matthewwalker on Jan 13, 2014 10:30:00 GMT -8
Your local refractory supplier can surely supply these. They are extremely common in the foundry industry. I could tell you my local supply but shipping will kill you as they only do pallets. Do some digging, you will find a local source.
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Cramer
Junior Member
Posts: 129
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Post by Cramer on Jan 13, 2014 15:38:23 GMT -8
Cool, thanks Matt! Do you know what they are called? I mean, is there a name like refractory insulation tubing or something of the sort I should ask for (you know, so I don't sound completely in the dark about what I need)?
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Post by matthewwalker on Jan 13, 2014 20:08:23 GMT -8
Try "riser sleeves" or just "formed ceramic fiber", you'll find something.
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