Fredrick Paget on mon 15 nov 04
>i would avoid a flat top/hard brick kiln.
>use the arch.
>
>the entire system of flat top kilns is designed
>around soft brick. weight is a big issue...and you
>should not vary the design or brick of nils' kilns.
>i think by over engineering, 3/4 inch all thread, with
>heavy heavy angle iron one could pull it off.
>but, then, maybe i would not trust it. you would have to use
>a six foot wrench to torque it down. no, stupid.
>arch...............mel
You have to remember that if its done the way Nils says you jack up
the roof of the flat top a couple of inches into a shallow dome and
fill the gaps between the bricks at the top with a slip of fireclay
and sand etc.
That makes it a section of a dome.
Since you have not completed the dome to the shape is a true half
sphere but in fact have built it only part way down you have a lot of
horizontal thrust . The clamping arrangement takes this thrust. Think
of it this way - in order to fall down those center bricks have to
crowd the outer ones out of the way. The outer bricks would have to
move outward and the clamping arrangement prevents this. However if
the movement due to thermal expansion is enough to permanently
stretch the all thread it loosens up on cooling and the dome is
unstable.
When I was building my flat top I put stacks of Belliville washers
under the nuts of the all thread to make stiff springs, This allows
the kiln to expand without stretching the all thread and keeps it
good and tight. Belliville washers are spring steel and slightly dish
shaped. You stack them up rim to rim in sets like maybe 3 left 3
right so they get the stiffness you need and the amount of give you
require. They are usually kind of expensive but I got 100 for 10
cents a piece at a surplus place in Orlando Florida.
Since arch bricks are available it is no doubt the best way but
since nobody these days builds a complete arch you still have to use
iron work to take the horizontal thrust from the arch bricks.
Fred
--
From Fred Paget, Marin County, California, USA
fredrick@well.com
mel jacobson on mon 15 nov 04
i would avoid a flat top/hard brick kiln.
use the arch.
the entire system of flat top kilns is designed
around soft brick. weight is a big issue...and you
should not vary the design or brick of nils' kilns.
i think by over engineering, 3/4 inch all thread, with
heavy heavy angle iron one could pull it off.
but, then, maybe i would not trust it. you would have to use
a six foot wrench to torque it down. no, stupid.
arch.
i have tried, and failed with hard brick.
we built a mini flat top with hard brick, but
that is not a good test. worked fine. small span.
when you start spanning 6 feet...soft only, or
stick with the proven arch.
mel
we will be putting a soft arch on marta's residual
soda kiln. hard brick on the inside, soft on the outside.
k23 out. probably a layer of kaowool on top.
flu liners, coated with itc 100.
she cannot make smoke, so this will be residual.
small pots of soda in the base of the kiln. we have had
the plans for a small flat top drawn in cad. it will run
soon in pmi.
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
new/ http://www.rid-a-tick.com
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