#21  
Old 06-14-2010, 01:49 PM
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Default Re: just about to start a build

Make sure your flue is outside the oven rather than inside it. A flue inside the oven is simpler and gives you more floor space but doesn't work nearly as well. I tried this kind of design for my second oven and found the trditional design with the flue outside the oven door far superior.
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  #22  
Old 06-14-2010, 02:02 PM
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Default Re: just about to start a build

http://www.davespizzaovens.com.auYour 9.5" door height is correct for your stated oven dimensions and a 5" flue should be enough for your oven size. A flue outside your oven door would be far superior. Also try to arrange some volume under the flue pipe so the smoke funnels into the flue pipe. I tried the flue in the oven for my second build but have since found the traditional flue outside the oven door far superior. Have a look at the cross section drawing on my "drawings" page.
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  #23  
Old 06-14-2010, 04:31 PM
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Default Re: just about to start a build

Man, I'm loving the beach ball form!

Have to agree with David - flue should vent from the tunnel, with the door fitting behind the flue.
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  #24  
Old 07-11-2010, 06:04 AM
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Default Re: just about to start a build

Sorry for the interlude in time , this work thing just keeps getting in the way, anyway I have a few spare mins so thought I would up-date with the progress (or lack of it ) so far.
Having read the last couple of tips I Have decided to alter the fiber glass mould a little and extend the door passage a couple of inches so that the chimney will fit better into it,I now have a couple more questions that I would love some guidance on,
would a 4 inch internal pipe do or would I be better finding a 5 inch one?
and for my first casting I am thinking of using up some stuff I have to hand , I have plenty of fire clay , fondue cement , sand and saw dust . From what I have read if I get some rough grog and mix it to the aforementioned this should make a reasonable refractory , should I mix in anything else or omit any of the ingredients ?
and lastly I have read that you can use chicken wire to help hold the together and act as a bit of an armature, would you recommend this ?
Many thanks for your help so far and looking forward to any replies to these questions so that I can get back on with the build in the next couple of weeks when I find that all illusive time.
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  #25  
Old 07-11-2010, 10:07 AM
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Default Re: just about to start a build

Mixing a bit of this and a bit of that, using experience and common sense, may be a good plan for cooking, but with concrete, particularly the ruinously difficult to work with refractory concretes, you're trying for a rather specific chemical reaction. Guess work, and trial and error just won't do it.

And a four inch flue won't fly with any sort of oven. It may keep some of the smoke out of your face during actual cooking but plan on smoke pouring out the door on start-up. The smallest flue system available around here is 6 inch id.
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  #26  
Old 07-11-2010, 01:42 PM
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Default Re: just about to start a build

Because your oven is small (24") the 5" flue should be fine. I think 6" for this size oven is overkill. Getting the first casting off the mould can be difficult. For release agent I use equal parts kero and motor oil brushed well onto the fiberglass. Make sure there is a release. That is a slight angle at the base rather than vertical. If you need to thicken the mould around the base to do this you can make a paste by adding microspheres to the resin. Leave out the sawdust in your mixture. This will only burn away leaving voids and a less dense final result which you don't want. The fondue is expensive so don't mix up too much in one go as it goes off pretty fast.
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  #27  
Old 07-12-2010, 02:08 AM
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Default Re: just about to start a build

thanks for the info , I wasn't planning on just mixing up the ingredients in an experimental way , rather finding a mix that has been tried and tested using these ingredients as a staring point , thanks for the ideas on a release agent for the mould and also the chimney size,
I found a link to an artist potters mix for refractory cement and would love to be directed to any other mixes people have used, also does anyone know where to get kyanite ( does this go by any other name ) in the UK,
many thanks,
Mark
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  #28  
Old 07-12-2010, 03:58 AM
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Default Re: just about to start a build

Mark,
I used chicken wire on my first cast dome, but because it is embedded there is no way of knowing how it is performing short of destroying the dome to inspect it. There is some doubt about using galvanized wire because of zinc's relatively low melting point (420C)
The industry standard is melt extract fibbers (stainless steel needles) They are expensive and many say that they're not needed, although I always put them in the mix.It is the rapid increase in temp rise that stresses the material, but who has time to fire the oven up at a safe 100 C per Hr?
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