Michele Hoskin on sun 3 jan 99
Hi everyone! Hope you all had a wonderful holiday season. It was a good
break for me from the pre-Christmas clay rush and now I am looking forward
to getting muddy again.
I have noticed that my bottom kiln shelf is cracking and I moved a post
right underneath the crack for support but wonder how long I can fire with
this shelf as is. Can it be repaired or do I need to replace it?
Thanks in advance,
Michele Hoskin
Toronto
(where the snow is piled high)
Bill Williams on mon 4 jan 99
Michele: I am new, but have experience with a cracked bottom shelf. My
bottom shelf cracked during a cone 6 firing because I had it propped up off
the bottom of the kiln on stilts laying flat, with a center support. Big
mistake. Anyway, I repositioned the stilts that were laying down so that
the cracked shelf was supported (mine cracked right down the middle) in the
center and the 2 now separate halves were solid. I have used the cracked
shelf for a year now and it hasn't cracked any more and as long as it is
solid, it works fine. Connie(billwms....etc.)
-----Original Message-----
From: Michele Hoskin
To: CLAYART@LSV.UKY.EDU
Date: Sunday, January 03, 1999 12:46 PM
Subject: Cracked kiln shelves
>----------------------------Original message----------------------------
>
>Hi everyone! Hope you all had a wonderful holiday season. It was a good
>break for me from the pre-Christmas clay rush and now I am looking forward
>to getting muddy again.
>
>I have noticed that my bottom kiln shelf is cracking and I moved a post
>right underneath the crack for support but wonder how long I can fire with
>this shelf as is. Can it be repaired or do I need to replace it?
>
>Thanks in advance,
>Michele Hoskin
>Toronto
>(where the snow is piled high)
>
Ray Carlton on mon 4 jan 99
you can't really repair it micheal but on the bottom well supported it will
last for a while....i have used shelves with cracks in them for
years...eventually it will breakand probabbly take out a few pieces with
it.....weigh up the cost of the replacement shelf agaiinst a damaged
piece...then consider that the shelf may last for many firings but it may
not see out another
itAt 13:45 03/01/99 EST, you wrote:
>----------------------------Original message----------------------------
>
>Hi everyone! Hope you all had a wonderful holiday season. It was a good
>break for me from the pre-Christmas clay rush and now I am looking forward
>to getting muddy again.
>
>I have noticed that my bottom kiln shelf is cracking and I moved a post
>right underneath the crack for support but wonder how long I can fire with
>this shelf as is. Can it be repaired or do I need to replace it?
>
>Thanks in advance,
>Michele Hoskin
>Toronto
>(where the snow is piled high)
>
cheers Ray Carlton
McMahons Creek Victoria Australia
Brad Sondahl on mon 4 jan 99
Large full shelves for electric kilns seem to crack frequently. I use
them until they are cracked nearly halfway across without ever having
them fail during firing. Sometimes I'll continue the crackwith a chisel
and hammer to make two halfshelves if they aren't too warped. I do
prop them at the crack, to support both sides, but wonder if this might
not increase the pressure in the crack area and the likelihood of
failure.
--
Brad Sondahl
http://www.camasnet.com/~asondahl/bradindex.html
Sondahl homepage http://www.camasnet.com/~asondahl
Original literature, music, pottery, and art
Bruce Hunter on tue 5 jan 99
I looked for a way to cut the shelves in half, not wanting to have them
fail in a bad spot. I found that if you put them on the bottom of the kiln,
and just stack on top of them, in a few firings, ( at .06 ) they break
themselves and then you have two half shelves,
Suzanna,In Pa. Where no snow is in sight.
>
lpskeen on tue 5 jan 99
Brad Sondahl wrote:
> Large full shelves for electric kilns seem to crack frequently. I use
> them until they are cracked nearly halfway across without ever having
> them fail during firing.
I don't have cracking problems, I have BENDING problems. My (new)
shelves are bowed down in the middle, which makes my plates interesting
at best....
--
Lisa Skeen ICQ# 15554910
Living Tree Pottery & Soaps http://www.uncg.edu/~lpskeen
FAILURE IS NOT AN OPTION!!! It comes bundled with the software.
The Bill of Rights - (void where prohibited by law)
the cat lady on tue 5 jan 99
Brad Sondahl wrote:
> ----------------------------Original message----------------------------
> Large full shelves for electric kilns seem to crack frequently. I use
> them until they are cracked nearly halfway across without ever having
> them fail during firing. Sometimes I'll continue the crackwith a chisel
> and hammer to make two halfshelves if they aren't too warped. I do
> prop them at the crack, to support both sides, but wonder if this might
> not increase the pressure in the crack area and the likelihood of
> failure.
>
I had some kiln shelves (2) crack almost 1/2 through about 6 years ago.
These are round shelves that fit my 7 cube kiln. I still stilt them the
exact same way - 3 stilts - and both still work fine for me. I don't flip
shelves as they are kiln washed (if this makes a difference) and use my kiln
to both bisque (06) and glaze (10).
Hope this helps.
--
sam - alias the cat lady
Melbourne, Ontario
SW Ontario CANADA
http://www.geocities.com/paris/3110
scuttell@odyssey.on.ca
"Thousands of years ago, cats were worshipped as gods.
Cats have never forgotten this."
Vince Pitelka on wed 6 jan 99
>I looked for a way to cut the shelves in half, not wanting to have them
>fail in a bad spot. I found that if you put them on the bottom of the kiln,
>and just stack on top of them, in a few firings, ( at .06 ) they break
>themselves and then you have two half shelves,
>Suzanna,In Pa. Where no snow is in sight.
Seems a strange way to end up with half shelves. I have never liked the
whole round or multisided shelves for use in toploader electrics, except in
the smallest kilns. The whole shelves seem awkward to handle in loading the
kiln, and then of course you have the greater likelihood of cracking on a
such a large flat shelf.
But if you have whole shelves, and you want to cut them in half, it is a
simple matter, as long as they are high-alumina or mullite/cordierite
shelves (the standard electric kiln shelves.) Get a masonry blade for a
skillsaw. Draw a line on both sides of the shelf where you want to cut it.
Wet the shelf well, allowing the water to soak in. Blot off all excess
water. Wear a good dust mask and face shield. Set the skillsaw to cut
about 1/4" deep, and cut a groove on each side of the shelf along the line.
With a little tapping along this line the shelf will snap neatly in half
with only the slightest roughness, which can easily be ground smooth with an
angle grinder equipped with masonry stone. Depending on the porosity and
hardness of the shelf, you may even be able to cut all the way through it
with the masonry blade. The professionals use a diamond saw with a water
jet to cool the blade and take away the grinding residue. Soaking the shelf
helps a lot, as long as the shelf is porous. Good luck -
- 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
Roger Korn on thu 7 jan 99
Vince's remarks are right on the mark. Masonry blades on Skilsaws work
well and are cheap. I take all the broken shelves I can scrounge and
make small shelves posts, props, flame targets, etc from them. Be really
careful about dust protection. Mullite is probably as bad as it gets re:
silicosis.
For portable use, I just got a cordless Makita 9.6V trim saw (~3 1/2"
blade) for $US 45 (Factory Reconditioned), a diamond blade for $27 and a
water-drip accessory for $25, all made by Makita. It is a slowww but
effective cutter for mullite/cordierite shelves, tile work, and
rockhounding (I take it and a couple of battery packs in my knapsack),
it recharges in the cigar lighter in my pickup, cuts (scores) hard
brick, building brick, and IFB very cleanly, with NO dust.
Roger Korn
McKay Creek Ceramics
rkorn@europa.com
William Gellow on tue 20 sep 05
Crack in kiln Shelves.
During the ^5 test firing of my new kiln I had 4 of the 8 half round shelve=
s develop a hairline
crack about 2=94 in all in the same place. I fired slowly, as per the direct=
ions , over 10 hours. Each
shelf was supported with 4 post each, and the bottom shelf was almost fully =
supported with posts
on their side.
All the cracks are in the same place on the shelf, regardless of support (th=
e fully supported base
shelf crack too). No cracking occurred in the other shelves located in the o=
ther half of the kiln. The
cracks occurred one section to the left of where the peep holes are located.=
The kiln vent was on during the cool down, could that have contributed?
Could opening the peep holes in each section created a cool draft that cause=
d the cracks?
Did I fire too fast?
Was the placement of the support posts insufficient? If so, why would the ne=
arly supported base
shelf crack?
Or does this seem like a shelf defect?
Thanks, in advance for any insight you might have.
William
PS. UPDATE - I called my supplier, they admitted to having a bad batch of sh=
elves and they are
exchanging them for me, for which I am glad, BUT I'm concerned that it was s=
omething I did - so
please send some insights if you might have them. Thanks again.
Michael Wendt on tue 20 sep 05
William,
Unless the peep hole plugs are very tight, they leak air when the vent is
on. Worse, the cold air stream gets faster as the aperture gets smaller (up
to a point).
It is possible that this contributed to the cracks. I have seen wares also
crack from this.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
William wrote:
Crack in kiln Shelves.
During the ^5 test firing of my new kiln I had 4 of the 8 half round
shelves develop a hairline
crack about 2" in all in the same place. I fired slowly, as per the
directions , over 10 hours. Each
shelf was supported with 4 post each, and the bottom shelf was almost fully
supported with posts
on their side.
All the cracks are in the same place on the shelf, regardless of support
(the fully supported base
shelf crack too). No cracking occurred in the other shelves located in the
other half of the kiln. The
cracks occurred one section to the left of where the peep holes are located.
The kiln vent was on during the cool down, could that have contributed?
Could opening the peep holes in each section created a cool draft that
caused the cracks?
Did I fire too fast?
Was the placement of the support posts insufficient? If so, why would the
nearly supported base
shelf crack?
Or does this seem like a shelf defect?
Thanks, in advance for any insight you might have.
William
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