Orion/Baker on fri 30 jan 98
Geez, Mel. Such a "dreamy" tome! One has to know how to weld to build a
kiln arch? (NOT) And, oh, my -- what? -- what if the builder is a woman?
Double "geez"!
Here's some straight information for those who may feel a bit too
"scientifically challenged" to sort the wheat from the chaff in this
debate:
(a) By definition, an "arch is a structure built to support weight above
an opening." The debate of "how flat an arch should be" is the issue at
hand. Basically, arches range from catenary to sprung to flat.
(b) A "catenary" arch can be fully self-supporting. By its very
definition, "the curve of a catenary arch is the curve assumed by a heavy
uniform cord or chain hanging freely between two points in the same line."
Visualize a cord drooping between two level walls; flip it over, you have
the profile of a self-supporting catenary arch. Its geometric formula can
be found in just about any dictionary, encyclopedia, or geometry textbook.
(c) The next most efficient form of arch is a semi-circle that spans and
rests on a level gap. Such an arch exerts little outward thrust as most of
its weight is directed downward in harmony, or at least cooperation, shall
we say, with gravity. Such an arch requires little or no buttressing or
frame to remain sound and strong.
(d) The shallower (flatter) an arch is, the more force is exerted outward
<---->, and of course more restraint is required to contain the structure.
Whether they be real flat, sort of arched, or suspended blocks of fiber,
gravity is "not kind" to flatter arches.
(e) Designs that require metal rods or frames for suspension or support
are ALL vulnerable to metal fatigue and/or corrosion in the long haul.
Steel (and any other metal) expands and contracts at rates different from
the rates that hard brick, soft brick, fiber (and yes, even "rigidized"
(IFC'd) ones) expand and contract. These differences (differentials) cause
gradual material breakdown. For this reason alone, I cannot see anything
"best" in designs that rely heavily on metal support even when they're
brand new.
(Of course, it's already been established that a catenary or well designed
sprung arch do not not require metal for support.)
Personally, I don't think that "all designs are created equal." Kilns will
vary immensely in evenness and efficiency due to differences in insulation,
power/heat
delivery (whether gas or electric), circulation characteristics, and degree
of control. Circulation under a flat roof is not necessarily worse than
circulation under an arched roof (not to imply their characteristics are
the same, they're not). But when it comes to planning for a minimum of
maintenance and long-term wear, I think there's "no contest" in favor of a
good, strong, all-brick arch.
Finally, when it comes to kiln operations, l go you one better, mel. I'll
suggest that that with reasonable instruction, a well-built kiln should
"fire perfect in the hands of a NEW fire person," and time after time after
that.
The best, as always (and I'm definitely a "fire person," myself -- even if
I AM a woman)
Ellen Baker - Glacier, WA
orion@telcomplus.com
Virginia (Virginia Gibbons) on sat 31 jan 98
Let me add my voice to the swelling chorus of those protesting your
bland assumption that kiln building must beyond the ability of those of us
who are female and - heaven forbid -"alone"..... I am a 61 year old
hobby sculptor. I am just finishing up an 80 cu. ft. car kiln with a sprung
arch. I could not afford to buy the size kiln that I needed so I bought an
existing kiln, took it down, moved it about ten miles to my property and
reassembled it. I did have some help from friends (female) with the
move, but, overall, have done about 95% of the work myself. It wasn't
easy and I don't know yet how it will fire, but it sure wasn't as hard as I
had been led to believe - and I have learned a hell of a lot.
Vince Pitelka on sat 31 jan 98
>(e) Designs that require metal rods or frames for suspension or support
>are ALL vulnerable to metal fatigue and/or corrosion in the long haul.
>Steel (and any other metal) expands and contracts at rates different from
>the rates that hard brick, soft brick, fiber (and yes, even "rigidized"
>(IFC'd) ones) expand and contract. These differences (differentials) cause
>gradual material breakdown. For this reason alone, I cannot see anything
>"best" in designs that rely heavily on metal support even when they're
>brand new.
Ellen -
Just a comment on your good explanation of arch systems. A proper steel
framework, with expansion space for the bricks inside, will last almost
indefinitely (except perhaps for salt-kilns). Most people tend to
underbuild kiln frames, so that the whole thing can flex and shift with
time, and then breakdown is inevitable. The investment for heavier angle
and channel for a really heavy frame is a small price to pay. And once you
use heavier steel, it is a simple matter to build a hinged door, or even to
make the kiln self contained so that it may be moved with a forklift should
the need arise.
>(Of course, it's already been established that a catenary or well designed
>sprung arch do not not require metal for support.)
This statement is a bit misleading. It is certainly true that a catenary
requires no external framework. But there is no such thing as a brick
sprung arch or Roman arch spanning system, with vertical walls beneath it,
which requires no external butressing support, metal or otherwise. For a
single sprung-arched chamber, a welded steel framework is certainly the most
space-efficient system in contemporary terms. Brick or stone butressing
wings were common on European Medieval and Renaissance kilns. Adjacent
arches will buttress one another, as in the Japanese noborigama. The arches
on groundhog kilns and many anagama are buttressed with earth or rock fill.
Some sort of buttressing is essential.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
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