Craig Martell on fri 14 sep 01
Hello Klyf:
I learned to make kiln shelves about 20 years ago. My teacher was Harry
Davis. Don't get your hopes up too much though because I haven't made too
many of my own.
He suggested using a body of 50% fireclay and 50% crushed
hardbrick. That's what we used during the class. I would think that
additions of kyanite and pyrophyllite would help thermal shock and durability.
Harry made angle iron frames for the forms. He had rectangles, squares,
and round ones as well. You place the claybody in the form and beat it
with a large wooden mallet. We used one that was about 6 to 8 inches in
diameter covered with a canvas sock to keep it from sticking. So, you just
beat the clay fiercely into the form and then level it off with a big bow
wire cutter. Then, lay very wet newspaper over the form and roll it very
smooth with an iron pipe. I think the beating down of the clay is what
will eliminate the possibility of warping. The body you use will affect
this too.
Let the shelves dry in the form and take them out when you can handle
without distortion. You can do a bit more smoothing too, especially the
underside. I used to oil the frame a bit to aid in removing the
shelf. I'll take a look at The Potter's Alternative and see if there's
anything else about the shelves. If there is, I'll send another post.
That's about it, Craig Martell in Oregon
Klyf Brown on fri 14 sep 01
Does anyone have a recipe for mulite or equal or better kiln shelf
material? Does anyone have any experience extruding kiln shelves
and posts? Extruded tiles are supposed to warp less than slab rolled
ones, so I am hopeing that it is also true of kiln furniture. The planned
use is Raku and a mid range stoneware kiln. Any tips on fireing them?
Stack them up like bricks?
Any info would be appreciated.
Klyf Brown
New Mexico
william schran on sat 15 sep 01
Klyf - I'd advise against creating your own kiln shelves. Trying to
form them, dry & fire without any warpage will be very difficult.
Firing them high enough for stoneware firings may be beyond what your
kilns are capable of doing. Making small shelves for raku firing are
certainly possible, but I think the cost of manufactured shelves are
worth the price.
Bill
Michael Wendt on sat 15 sep 01
Shelf users:
If you have a potter's wheel, you can make your own kiln shelves. I throw
special shapes needed on the wheel. Start with a weighed out amount of clay
and throw a simple flat disk the thickness and diameter needed (allowing for
shrinkage). Smooth the disk with a large blade putty knife (I have also
coated the surface with alumina hydrate at this stage and worked it in
well). Wire it loose and dry in your damp box. When leather hard, flip it
over and burnish the wired side with a metal rib. Crack propagation is the
main cause for failures so take the time to shine the surface up as smooth
as possible for strength. You can make round shelves any size you like and
cut off the facets to fit various electric kilns although round works fine.
Composition is not hard either. Many ceramic suppliers sell ground mullite,
kyanite and other low expansion refractories so all you need to do is find a
proportion of kaolin, ball clay or fireclay that will hold the refractory
together for forming. Use the highest proportion of refractory you can
while still maintaining forming ability.
I fire my shelves flat, centered in the hottest part of the kiln so they
take up almost no load room. They last for years, work really well, stay
flat and are fast and cheap enough to make for limited run production jobs
where no commercial shelf size exists. If a commercial size exists, I always
use it rather than make my own since pots are worth a lot more than shelves.
I have tried rammed posts in cardboard tubes with some success, but posts
are very cheap an uniform so why make those? Use your time to make pots
whenever possible. There lies your source of income.
Regards,
Michael Wendt wendtpot@lewiston.com
Klyf asked:
Does anyone have a recipe for mulite or equal or better kiln shelf
material? Does anyone have any experience extruding kiln shelves
and posts? Extruded tiles are supposed to warp less than slab rolled
ones, so I am hopeing that it is also true of kiln furniture. The planned
use is Raku and a mid range stoneware kiln. Any tips on fireing them?
Stack them up like bricks?
Any info would be appreciated.
Klyf Brown
New Mexico
David Hendley on sat 15 sep 01
In my (vast) DIY experience, it is not practical for a potter to try
to make kiln shelves for stoneware firing.
My homemade 27" diameter half-round shelves would not even hold
up to bisque firing in my electric kiln, and cracked after a few firings.
If you are thinking about small slabs, small enough to be extruded,
that could probably be done, but I would not call a slab 6 or 8 inches
wide a 'kiln shelf'.
Kiln post are another story. It is very practical to extrude your own
posts. Simply use a small square 2-part die with a small washer
for the hollow center.
Make guides, adding extra length for shrinkage, out of thin boards
for cutting them to length.
My recipe for refractories is approximately equal parts by volume
of ground-up (window screen mesh) used insulating fire bricks
and fire clay.
I bisque fire and high fire new kiln post along with regular firings,
sticking them in where there is extra small space. After that first
stoneware firing, they are ready for use.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
----- Original Message -----
From: "Klyf Brown"
To:
Sent: Friday, September 14, 2001 8:15 PM
Subject: DIY Kiln shelves
> Does anyone have a recipe for mulite or equal or better kiln shelf
> material? Does anyone have any experience extruding kiln shelves
> and posts? Extruded tiles are supposed to warp less than slab rolled
> ones, so I am hopeing that it is also true of kiln furniture. The planned
> use is Raku and a mid range stoneware kiln. Any tips on fireing them?
> Stack them up like bricks?
> Any info would be appreciated.
> Klyf Brown
> New Mexico
>
Jeff Lawrence on tue 18 sep 01
Neighbor Klyf,
I've got a broken bag of kyanite that's yours for the taking if you can meet
me in Pojoaque. I think it was a 100# bag and I'd bet there's 80 there.
Might be some Mullite, too.
Jeff
in Los Alamos but usually headed into Santa Fe once a week.
Michael Wendt on tue 18 sep 01
Klyf,
Many years ago, when Richard Haecker was plant engineer at Thorley's in
California, I toured their refractory plant and saw what they do to make
kiln shelves. Most notable is the firing cycle. It is very long and slow so
that the mullite spinel structures grow long and strong. He told me how long
they fired , but I have forgotten,... seems like it was days long. As
potters, we don't really have the means to equal the quality of good
commercial shelves. I buy all but a few shelves from Thorley and have
shelves that are nearly 20 years old ( they dated and gave blunger batch
numbers on each shelf in the old days before they went from hand molded to
hydraulic pressing).
Both the grog and the clay matrix would need to be mullite composition. The
most recent ACERs bulletin had an article about the composition of mullite
refractories, might help, but why do it when they are so cheap?
Good luck,
Regards,
Michael Wendt wendtpot@lewiston.com
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