mel jacobson on mon 2 dec 02
many statements about kiln roofs.
caving in
bricks falling
one more firing.
propping up, fire again.
it is like getting into an aircraft, the tail is falling
off. `hell, i can get in this last flight, or maybe i can
duct tape the tail back on`.
that is not how it is done.
it is not the fault of the roof technique. flat tops do
not by themselves drop bricks. it was how the kiln
top was originally built. incorrect tension.
when the first brick dropped, that is when you make
some hard decisions.....redo the top.
i have seen dozens of arch roofs sagging. they were not
built correctly.
has anyone questioned the brick? i have seen some old
a.p. greene bricks that cracked into 5 or 6 pieces. no,
it has to be the flat top design.
it is not the engineering technique, it is the builder or the brick.
kiln roof maintenance is critical. flat tops as per instructions
are to be re tightened on a regular interval.
very few do this.....and it is often said, `hell, i did not know that.`
read the instructions, follow them.
the tail fell off the plane. the plane crashed. cessna is at fault.
sue them. but, then, who checked the tail? no one.
mel
`got a great deal on a kiln...three phase...course it cost
a thousand dollars to convert it`. hmmmm. boy, i want in
on that kind of a deal. `you can buy a new army jeep, still
in the packing case for 200 dollars.` hmmm, wanna bet?
From:
Minnetonka, Minnesota, U.S.A.
web site: my.pclink.com/~melpots
or try: http://www.pclink.com/melpots
L. P. Skeen on mon 2 dec 02
----- Original Message -----
From: "mel jacobson"
> it is like getting into an aircraft, the tail is falling
> off. `hell, i can get in this last flight, or maybe i can
> duct tape the tail back on`.
Hey mel,
When I was getting my pilot's license, I knew a guy who owned an old
tail-dragger Cessna. He had duct tape on the tires after the tread wore
off, to keep the air in 'em. We called it "200 Mile-an-Hour Tape". ;0)
(Not a joke, true story, but I did not fly with him.......)
L
Tjo62@AOL.COM on wed 4 dec 02
I built my MFT three years ago. Within the first 6 or 8 firings, I began to
have a sagging roof. I had not tightened the roof. So, I gave it the boost
I described to the woman wanting "one more firing", and it was good for 5 or
6 more firings. I boosted again and fired 5 or 6 more--I did tighten from
time to time. Finally, I took it all off, got about a 100 new bricks to
replace any cracked, and rebuilt it. It looked better than it ever had. It
had a nice gentle doming, and this time I did tighten regularly. It lasted
one year (about 10 or 12 firings). This time boosting would not help. I took
it all off and rebuilt again and got one firing before two bricks fell out (I
was shocked). I then did my boost and got one more firing (two bricks are on
the ground) to finish off what I needed for holiday sales. At this point, I
intend to let it rest till spring and build an arch. However, I am not
blaming the design. I did not say one word to place blame anywhere. I have
heard too many GOOD things about the design of this kiln. It is my
understanding that there are many MFT kilns that are working perfectly.
Unfortunately, I have just not gotten it right yet, and at this point, I am
ready to try something else, that's all.
John Britt on wed 4 dec 02
Tjo62@sol.com,
I don't think you should be so afraid to question the design. You are
certainly not the first person to have problems with the roof falling in.
And you should definitely not have to spend your time tweeking, snugging
and fixing your kiln. If this were the Frod motor company they would have
to recall it.
Arches are a beautiful thing. You can build an sprung or a catenary arch
kiln and then fire stuff in it. No fixing, no tweeking, no mess not muss.
Archetectual principles that have been tested for centuries are very hard
to argue with. Let's face it, a large horizontal expanse(albiet slightly
arched by pressure)is very difficult to maintain.
Make the switch,
John Britt
Fredrick Paget on wed 4 dec 02
MFT kilns are called flat tops but the roof must not be flat. It is really
a dome section with the outer downward sloping part of a large dome omitted
and replaced by the rods and ironwork. The dome has a weight that causes
it to want to expand outward and get flatter. If it goes all the way flat
it has only the friction and adhesion between the bricks to prevent them
from falling in. And fall they will.
Consider the dome of some huge structure such as some the Romans built. The
6 x6 foot section of one of these at the very peak has only a small rise if
considered alone. Yet has stood for centuries.
It is essential to keep those rods tight
On my flat top I have placed stacks of Belliville Washers under the nuts
and tightened up to compress these springy washers. This bulids up to
sufficient tension and yet allows the rods to avoid stretching when the
kiln is hot since the washers allow a little give while maintaining
tension. Really heavy truck valve springs might work too.
The other component of flat top design with flat bricks is to fill up the
gaps in the top side of the top after it is jacked up with a fireclay -
sand- sodium silicate slip. This makes those flat bricks behave like arch
bricks after it has dried out and been fired.
Fred
>It is my
>understanding that there are many MFT kilns that are working perfectly.
>Unfortunately, I have just not gotten it right yet, and at this point, I am
>ready to try something else, that's all.
From Fred Paget, Marin County, California, USA
don hunt on wed 4 dec 02
You might give some thoughts to a fiber module roof. The modules are
end stack 12 x 12 They are installed alternating 90 degrees. Because
of these factors there is very little shrinkage. The roof is 10 inch
thick. I have about 15 firings on it and it looks great. It was pretty
easy to install if you make it separately and then get 4 or 5 guys to
lift it up and put it on.
Don Hunt
Jennifer F Boyer on thu 5 dec 02
Where do you get fiber modules?
Jennifer, thinking about a car kiln door rebuild....
don hunt wrote:
>
> You might give some thoughts to a fiber module roof. The modules are
> end stack 12 x 12 They are installed alternating 90 degrees. Because
> of these factors there is very little shrinkage. The roof is 10 inch
> thick. I have about 15 firings on it and it looks great. It was pretty
> easy to install if you make it separately and then get 4 or 5 guys to
> lift it up and put it on.
>
> Don Hunt
>
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Thistle Hill Pottery Montpelier VT USA
http://www.thistlehillpottery.com/
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