Making form for Casting a J tube. Lego style.

Making form for Casting a J tube.   Lego style,   I intend to make this so I can put different risers or fireboxes with this J Tube design.

I am a bit confused, what are you going to do exactly?
What it that thing wrapped in cardboard and cling film?

Are you actually planning on a restriction in the bend between the two tubular cardboard sections? If so, why? It is recommended to make the bends in the core sharp for beneficial turbulence which causes good mixing.

The burn tunnel is typically made square rather than round for better fuel exposure to air; coals on the floor are not bunched up and smothering the bottom ones.

Do you have a plan for getting the form out after casting? If it is all paper or wood, it can burn out as long as there is an initial channel for draft, but you don't want any plastic in there.

What dimensions are you planning for all the elements?

Glenn Herbert wrote:Are you actually planning on a restriction in the bend between the two tubular cardboard sections? If so, why? It is recommended to make the bends in the core sharp for beneficial turbulence which causes good mixing.

The burn tunnel is typically made square rather than round for better fuel exposure to air; coals on the floor are not bunched up and smothering the bottom ones.

Do you have a plan for getting the form out after casting? If it is all paper or wood, it can burn out as long as there is an initial channel for draft, but you don't want any plastic in there.

What dimensions are you planning for all the elements?

I think it will be easier to show you the finished product.     This is the mold that I will be putting refractory mix.  

Is the white fluffy stuff ceramic fiber?

It may be just me, but that structure doesn't look strong enough to hold up to even one casting, let alone several.

The white stuff is plastic bags,   The castings I have done so far do not stick to the plastic bags and are very easy to remove.

Yes it is flimsy and meant to be so for easy removal after the casting is made.      This is one of several proto types, each time I make them I learn how to make them with cheap materials, what works, and what does not.

Thanks for your input.