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3 or 4 point posts under shelves -- my vote is ?

updated tue 3 aug 99


nikom chimnok on mon 2 aug 99

>At 16:54 29/7/99 EDT, you wrote:
>----------------------------Original message----------------------------
> T'would make a fascinating "read" if anyone wants to try to explain why
3-posts should be better -- I'm sincerely curious!
>Ellen Baker
Hello Ellen et al.,

I wish to begin with the definitions in Euclid's Elements (not the
company, the 2000+ year old book about geometry) where it is stated, "3
points determine a plane". Now it's true that 4 points may also determine a
plane, but they also may determine 2 planes, looked at in one way, or a
tetrahedron, looked at in another. And I have seen many a kiln shelf (a
plane), when loaded heavy enough and fired hot enough, turn into 2 planes
(that is, break), just as predicted by old Euclid.

I think there are mitigating circumstances. First, if you load your
kiln perfectly: the floor of the kiln is a perfect plane; the posts are of
exactly the same height; the wash on the shelves is perfectly even. Second,
the load is not very heavy, and is not stacked very high, and the shelves
are thick enough to have a large margin of strength. Then you can get away
with a 4 point load.

However, I have a friend up the road who was firing 4X4 relief
tiles, stood on edge (heavy!), around 10 layers high, as I remember, and she
was sloppy about cleaning shelves and wadding off posts, and in less than a
year she had broken every shelf in her kiln. Using 4 posts per shelf.

Whereas we fire 8X8 mural pieces, up to 4" thick, on edge, (even
heavier), load them sloppy as children (industrial, you know: time is
money), with unground glaze runs plastered over with kilnwash on the corners
of the shelves, and posts that are only tiny points at the top, they're so
battered, and virtually never break a shelf. Using 3 posts per shelf. And
you should know this is a relatively big kiln, with a footprint of 24
shelves, so we're often firing 96 or 120 shelves at a time. If we were
breaking a lot, I'd be trying something new, you can bet.

So there you go, my best argument, first theory and then practice.
And you may also be interested to know that I have also built 3 point
buildings on Alaskan permafrost, which heaves and sinks as it freezes and
thaws, and tears traditional 4-or-more point buildings apart, whereas the
3-pointers are naturally, geometrically indestructable. I now live in a 3
post house built on expansive clay, and after 10 years it is doing just
fine, while all the buildings around me are crack city.

Please note too that airplanes have 3 wheels, or possibly 6, but in
pairs, and the lunar lander had 3 legs. There is a sound engineering reason
for all this, and it all starts with Euclid's remarkable observation that 3
points determine a plane, no matter how it tilts.

So that's my vote: 3 points forever.

Pedantically yours,
Nikom in Thailand, where if it ain't raining the RH is 80%, and since the
pots won't get dry I have nothing better to do than yammer away on the old