Oztrain Kiln: Firebox Construction

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The Bourry downdraft firebox is discussed here, and the floor of this one is shown here. It has some advantages compared to a simple  anagama style cross-draft firebox: easier to stoke, easier to control the ember bed, and if you subscribe to a theory of Steve Harrison's, provides more fly ash because the burning wood products have to drop through the flame path on the way to the ember bed. On the other hand, the wood has to be cut to a restricted range of lengths in order to rest on the hobs. Too short and they fall down onto the ember bed, too long and they will not fit into the fire box at all.

In the image above the steel work for the Bourry box has been partially and temporarily set up,  arch bricks for the throat arch have been assembled, and a piece of weldmesh  to be used in the arch formation has been put into position where the arch will be located.  The final position of the arch is higher than shown in this image. In the final configuration of the steelwork the throat arch will have to be braced at each end to prevent it collapsing.
Bracing to constrain the arch has been added and the arch propped up into positon,using bricks and bits of wood under the weldmesh strip. The shape of the skewbacks needed to support the arch was determined  at this stage. Final arch position is higher than shown here.

Three skewback bricks were needed on each side but with just one on each side the arch was stable enough to lock into position without  mortar. Final arch position is higher than shown here.

The skewbacks were cut from ordinary firebricks using a masonry cutting disk in a 9inch circular saw. Final arch position is higher than shown here.

The walls of the firebox have been built up to the final height, with the hobs constructed to form ledges to support the wood.

1. Primary air holes
2. Secondary  air holes
3. Lower door
4. Mousehole
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