Dale Neese on thu 14 dec 06
Ingeborg,
My plates are fired on the 12"x24" within the posts. I have to alternate
spaces, one plate on half the shelf with a smaller plate or square plate on
the opposite end. Most stacking of same height shelves share a post. One the
shelf next to that one it is reversed allowing the
rims to extend into the space on the adjoining shelf. So three 12x24 shelves
side by side is my stacking space. If the next level up is the same
configuration, 3 shelves,12 posts.
Larger shelves 24"x24" hold larger trays and platters up to 20 inches in
diameter, 8 post with no post in the middle.
Dale Tex
"across the alley from the Alamo"
San Antonio, Texas USA
Deborah Woods on thu 14 dec 06
I guess the title is most of my message. I have been buying THORLEY
shelves from my distributer. Of the first 8 I bought, 3 cracked, can't
remember. Had those replaced, all cracked. Then replaced with thicker
shelves, same brand, two cracked. So replaced with 3 more (I didn't want
one shelf a different thickness) opened the kiln, all three cracked. I am
quite certain this is nothing I am doing regarding loading, washing,
cooling, anything. I have heard I am not alone with this problem. I'm not
the only one at my distributor having this problem either. I'm fed up.
What brand should I try? I absolutely don't trust THORLEY any more.
Deborah Woods--going to cone 6 I should say.
Dale Neese on thu 14 dec 06
I don't think that you will find shelves that won't crack if the firing if
they are not posted to keep them from cracking. That is my first guess. I
don't suspect that it's the shelves. I've used the same Thorley shelves for
over 20 years and barely have had a couple develop cracks. Just added 6 more
new Thorley shelves couple months ago. Never have had a speck of kiln wash
on them. None have ever gotten wet. Whether it's cone 2 or 12, if the
shelves are not supported, they will develop cracks. Mainly I have all 12"x
24" Thorley shelves and a few 24"x24" all stamped 1978. When I post the 12"x
24" for bisque or for glaze firing to cone 10 plus there are 6 post on each
shelf. A post at every corner and 2 in the middle at the edges. Turn them
over next firing and there is no warping. You will say that posts take up
too much room so I only use 4 posts or one in the middle, 5 at the most. A
person I know just purchased all new shelves for the kiln he built. He was
so dismayed at the number of shelves that cracked. I asked how were they
posted. He said they were posted with 4 or 5 posts to save space like he had
always done before. Well yeah they do, but your shelves crack and slump. Not
fair blaming the cracking on supposing bad material or poorly manufactured
shelves. If you need more room then use larger properly posted shelves. I
can put flat plates, platters, wide bottom casseroles on my shelves and
suffer no losses.
I believe that you buy the best materials and equipment and take care of
them properly and they will last you a lot longer paying for themselves over
time and use. Let's see, I believe I read something like this just this
week....
Dale Tex
"across the alley from the Alamo"
San Antonio, Texas USA
Kathi LeSueur on thu 14 dec 06
Deborah Woods wrote:
>I guess the title is most of my message. I have been buying THORLEY
>shelves from my distributer. Of the first 8 I bought, 3 cracked, can't
>remember. Had those replaced, all cracked. Then replaced with thicker
>shelves, same brand, two cracked. So replaced with 3 more (I didn't want
>one shelf a different thickness) opened the kiln, all three cracked. I am
>quite certain this is nothing I am doing regarding loading, washing,
>cooling, anything. I have heard I am not alone with this problem. I'm not
>the only one at my distributor having this problem either. I'm fed up.
>What brand should I try? I absolutely don't trust THORLEY any more.
>Deborah Woods--going to cone 6 I should say.
>
>
>
>
This problem has been going on for at least three years now. As far as I
can tell, ever since Thorley was bought by Laguna. Until I hear they've
solved this problem I will buy NOTHING from Laguna. Even if they replace
the shelves what about the freight costs. I bought shelves from Thorley
for thirty years and never had a problem until the last shipment when
seven shelves cracked on the first firing. Cracked in the exact same
place on a diagonal with the cracks exactly the same length. It's time
to get this fixed. There is no excuse for a company to continue to ship
a defective product.
Kathi
threereeds1 on thu 14 dec 06
Deborah,
Had the same deal with fewer shelves. Read many posts from other victims.
Bought ten 12' x 24" Acne Marls/Dyson from Highwater. Their shipping was
surprisingly reasonable. Three posts per shelf. Happy camper. Other local
potters
have had the same shelves for 14 and 20 years. Happy campers.
Good Luck,
Tom King
----- Original Message -----
From: "Deborah Woods"
To:
Sent: Thursday, December 14, 2006 12:47 PM
Subject: I need kiln shelves that won't crack during firing
>I guess the title is most of my message. I have been buying THORLEY
> shelves from my distributer. Of the first 8 I bought, 3 cracked, can't
> remember. Had those replaced, all cracked. Then replaced with thicker
> shelves, same brand, two cracked. So replaced with 3 more (I didn't want
> one shelf a different thickness) opened the kiln, all three cracked. I am
> quite certain this is nothing I am doing regarding loading, washing,
> cooling, anything. I have heard I am not alone with this problem. I'm not
> the only one at my distributor having this problem either. I'm fed up.
> What brand should I try? I absolutely don't trust THORLEY any more.
> Deborah Woods--going to cone 6 I should say.
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
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>
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> melpots@pclink.com.
>
Ingeborg on thu 14 dec 06
Dale Neese said:
" Mainly I have all 12"x 24" Thorley shelves and a few 24"x24" all stamped
1978. When I post the 12"x
> 24" for bisque or for glaze firing to cone 10 plus there are 6 post on
> each
> shelf. A post at every corner and 2 in the middle at the edges."
Dale,
I've always been told to use only 3 posts per shelf...a triangle being
stronger than anything else. Now I wonder should I change my posting to six
per shelf. How do you fit large platters onto a 12 x 24 shelf with 6
posts? My shelves are old and slightly warped and need to be replaced soon.
Ingeborg
3058 Stringfellow Road
P.O. Box 510
Saint James City, FL 33956
http://www.thepottersworkshop.com
Vince Pitelka on thu 14 dec 06
> I've always been told to use only 3 posts per shelf...a triangle being
> stronger than anything else. Now I wonder should I change my posting to
> six
> per shelf. How do you fit large platters onto a 12 x 24 shelf with 6
> posts? My shelves are old and slightly warped and need to be replaced
> soon.
Ingeborg -
I'll second your question. I have never heard of such a thing as Dale
suggests. Six posts per shelf? Seems like overkill and a waste of space.
Three posts per shelf is the standard, and if multiple adjacent shelves are
at the same level, common posting saves space and gives a more stable set.
The only exception to the three-post standard at the Craft Center is in the
wood kilns, where we use four posts for added stability. Of course,
whenever you use more than three posts you must use wadding so that all the
posts touch and support the shelf evenly.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Randy O'Brien on fri 15 dec 06
Michael Wendt wrote:
> Deborah,
> I recently got new Thorley shelves and they have
> performed just as well as the old ones I still use
> from the early 70s.
> Please describe the kind of crack? Is it at a
> particular
> site? only on one face? starting near a post?
And I'll describe the cracks on my shelves. These are 10 sided 21" full
shelves 5/8" thick. The crack runs from the center of a straight side
to the
center of the shelf (radial crack). Date of manufacture stamped on the
shelves is 08/04/05. I have fired thousands of kiln loads and have never
cracked a shelf, until last year when I had 6 full shelves in a 12 hour
computer controlled cone 05 electric firing. 4 of the shelves were brand
new Thorleys. 3 of the 4 Thorleys cracked. Even the top cap shelf that
had nothing on it! I took a tile saw and cut all 4 into 5/8" high kiln
posts.
That is the only way I would trust a Thorley in a firing.
To be fair, my distributor did refund my money, although it took a year
of asking. This distributor has a sign over the cash register that says
no refunds on kiln shelves for any reason. They contacted Thorley
before giving me a refund, which makes me think Thorley is well
aware they have a problem. And they didn't ask for the shelves
back, so I have enough 5/8" kiln posts to last 3 lifetimes.
All my other shelves were purchased from Bennett's and I have
never had any problems with these shelves. Plus they were a lot
cheaper. I love Bennett's.
Happy Firing,
Randy
Tucson, AZ
Snail Scott on fri 15 dec 06
At 07:57 PM 12/14/2006 -0500, you wrote:
>I've always been told to use only 3 posts per shelf...a triangle being
>stronger than anything else...
Three things arranged trangularly do not
make a triangle!
A triangle is NOT stronger than anything
else for this purpose, since in fact there
is no actual 'triangle' involved. Nothing
is being cross-braced here (that being
the canonical example of 'strength of
triangles'). Shelves are merely supported,
and the relative locations of the posts
in a triangular relationship is irrelevant
to 'strength'. Three is simply the smallest
number of supports which will produce a
stable surface; this is why it is popular
as a stack arrangement - efficiency, NOT
strength.
For low-fire and even mid-range work, a
three-post support structure should be
adequate, as shelves are not very vulnerable
to warping at these temperatures. For higher
temperatures, added supports will be more
worthwhile for resisting warping. The higher
the firing temperature and the heavier the
work, the greater the vulnerability of
shelves to warping.
Four posts (or more) are not always helpful,
as posts and shelves are seldom perfectly
level. The shelf will rest on the three
highest posts anyway, so if only three
points of support are actually used, they
may as well be in a triangular arrangement
to get the most even distribution of support.
However, a little kiln wadding will nicely
level any number of posts, making a stack
which is actually (and not just apparently)
well supported.
Whether added posts are beneficial depends
on your shelf type, your firing temperature
(heat-work) and the kind of objects you are
making.
-Snail
Michael Wendt on fri 15 dec 06
Deborah,
I recently got new Thorley shelves and they have
performed just as well as the old ones I still use
from the early 70s.
Please describe the kind of crack? Is it at a
particular
site? only on one face? starting near a post?
When I visited the Thorley plant on my yearly trips
to L.A. I got a chance to meet and talk to long time
plant manager Robert Haecker(sp.?, now retired).
He showed me photos someone sent him of their
kiln stack complaining of the poor quality of the
shelves and cracking.
I was amazed the whole load had not collapsed since
none of the posts were in line one above another.
Those shelves had performed way above the call of
duty considering their abuse.
These were the rules Bob told me:
1. 3 posts per shelf (if you use more, use wad clay)
Why only 3? it takes three points to define a plane.
If you try to place more posts, some may not touch
or may be too tall creating cantilever loading on the
shelves and while they can support such bending
moments cold, when they are hot, they crack.
2. All posts must line up directly over the post below
so that the loads introduced by the shelves above are
transferred to the hearth plate directly without
creating
any shelf bending. It is always wise to level shelves
with
a small torpedo level in all directions. Use shims
or wad clay.
3. The first few times you fire new shelves, slow
down a little. Each time you fire Thorley shelves,
the crystal structure grows a bit so if you keep
using them, they get stronger and stronger.
I add my own personal favorite advice:
no kiln wash. If you fire runny glazes, make cookies
or throw setters like mine to keep the shelves clean
so they can be turned over as soon as they show
the slightest bend.
For the record, I fire very fast... in by 10 am
over by 5 pm to cone 10 and we cool quickly too
to improve cycle rates.
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Kathi LeSueur on fri 15 dec 06
Michael Wendt wrote:
>Deborah,
>I recently got new Thorley shelves and they have
>performed just as well as the old ones I still use
>from the early 70s.
>Please describe the kind of crack? Is it at a
>particular
>site? only on one face? starting near a post?>>>>>
>
I'll describe the cracks on my shelves. These were 14" x 24" shelves
3/4" thick. Each crack started on the long side 13 inches in from the
center, continued on a diagonal line for nine inches. If you took those
shelves and laid them on top of each other the crack was identical.
I've also visited the Thorley factory and spoke with the late Mr.
Hacker. I've gotten small cracks over the years that I just ignored with
no problem. But, when these cracks ran more than half way through the
shelf I was concerned that they would collapse. One of the things I did
notice was a deformation of the surface. The shelves look like they had
been extruded and at some point the extrusion got hung up causing a wavy
look to the surface. This was on all of the shelves that cracked. Don't
know if it mattered. It seems that lots of people are having problems
that were non-existance before.
Kathi
>
>
>
>
Deborah Woods on fri 15 dec 06
Thank-you to everyone who has responded thus far. I truly don't believe it
is a problem with my post support. I too only use three posts per, and I
have never had a problem until now, including 5 years in college. I too
heard that this has been a problem since Laguna bought out Thorley. I have
to say, my distributer, Portland Pottery, in Portland Maine has been very
supportive. They have replaced every shelf thus far, no shipping, nothing.
But I think they are growing tired of this. It is my understanding that
they are sitting on over a 1,000 $ of shelves right now that they have
replaced for people, while trying to get this resolved with Laguna.
Frustrating. I am told you can fire with the cracked shelves, and I do
between replacement, but am waiting for a very loud crash. I can't even
imagine if I hear it.
Michael Wendt on sat 16 dec 06
Deborah,
Thank you for your response.
I checked the date on the last shelves
I got from Thorley and they are 2001
so that probably predates their purchase
by Laguna.
As a result, I tend to agree with you
that the problem is with the shelves rather
than the way they are being used.
Old Thorleys were blunged and moist
formed (that is what the BL 1 stood for),
while the newer ones are dry pressed.
It may be that this is the source of the
failure.
Sorry they have not been responsive to
the complaints,
Regards,
Michael Wendt
Wendt Pottery
2729 Clearwater Ave
Lewiston, Idaho 83501
USA
wendtpot@lewiston.com
www.wendtpottery.com
Deborah Woods on sat 16 dec 06
Michael,
As far as stacking my posts all line up over eachother. Al of the
shelves until the last batch cracked the same way. My kiln is 10 cu. ft.
electric. Half shelves for that size kiln (I'm drawing a blank on the
dimensions without going to measure). They all cracked on the long side of
the shelf, pretty much right in the middle, going straight towards the
center for as much as six-eight inches. The latest surprised me.
One cracked the same way, although the fissure was noticeably wider
this time. One cracked on the opposite small side of the shelf, and one
cracked on the long side, but about a third of the way from the edge.
Originally I ordered 5/8 inch shelves, and the first time I replaced them
I replaced them with 1 inch shelves thinking this might not happen with
them and two of those cracked the same way.
Perhaps it's not the shelves, although that would lead me to wonder
why I am not the only person having this problem. Why is it happening so
much to ME? I do not know. I work in my basement. Do they absorb dampness?
Lots of people work in their basements. I do use kiln wash, but it was
dry, dry, dry before they went into the kiln. I set up shop lights over
the shelves to make sure (no I didn't do this with all the others so it's
not the reason they cracked) I was just trying to rule out the possibility
of damp kiln wash as a culprit. I really don't fire heavy things right
now. 3 pound pieces max on average, pretty evenly stacked. About 10 hours
to cone 6 I think (without consulting my records). I always ramp-fire
down, so no crash cooling.
Ingeborg on sat 16 dec 06
Dale Tex said: Ingeborg,
> My plates are fired on the 12"x24" within the posts. I have to alternate
> spaces, one plate on half the shelf with a smaller plate or square plate
> on
> the opposite end. Most stacking of same height shelves share a post. One
> the
> shelf next to that one it is reversed allowing the
> rims to extend into the space on the adjoining shelf. So three 12x24
> shelves
> side by side is my stacking space. If the next level up is the same
> configuration, 3 shelves,12 posts.
> Larger shelves 24"x24" hold larger trays and platters up to 20 inches in
> diameter, 8 post with no post in the middle.
If this has been working for Dale for many years, what really is the best
way to post shelves? Dale sent me a picture of his loaded kiln. He has
posts everywhere and I must say he is a very very neat person. All posts
are lined up perfectly like they should be distributing the weight.
My first kiln came with instructions to post 4 to a shelf. I ended up with
major warping very quickly. I then switched to 3 posts per shelf and still
get warping, albeit very slowly. The warping is directly related to the fact
that I rarely flip the shelves. (too labor intensive - removing kiln wash,
spraying new wash etc.)
Now I have a question about kiln shelf position, My kiln builder (non
potter) told me to always leave space between the shelves to allow for
proper air/heat movement. He said it is ok to occasionally have a platter
span the air space but not to cover the entire area. I seem to do more and
more large platters that don't fit onto a 12 x 24 shelf especially when you
take the posts into consideration. How detrimental is it to butt the
shelves tight to each other sharing posts and have more air space
surrounding the shelves? Any consensus on this?
I fire in a downdraft car kiln to cone 10 loaded with 3 12x24 shelves on
each level.
Ingeborg
3058 Stringfellow Road
P.O. Box 510
Saint James City, FL 33956
http://www.thepottersworkshop.com
William & Susan Schran User on sat 16 dec 06
On 12/15/06 7:39 PM, "Deborah Woods" wrote:
> I am told you can fire with the cracked shelves, and I do
> between replacement, but am waiting for a very loud crash.
Try to position the shelves/posts such that a post is under the crack.
I believe there is a manufacturing and/or material issue with these
cordierite shelves, so I don't fault the users, but I also think many folks
are using shelves that are too thin for the temperatures they are firing to.
I don't know if this might contribute to cracking or not.
I would suggest firing to ^6 in a 29" diameter kiln requires 3/4" cordierite
shelves and this thickness may be needed in 23" kilns.
At school I have seen thinner 26" half shelves warp from ^6 firings, but our
3/4" shelves have remained flat. There is a very slight warping in the 21"
full shelves that have been fired to ^6 for many years.
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
John Dellow on sun 17 dec 06
I am wondering if a trick a German potter in Australia showed me could
help. He was cutting a nick about 1/8 inch mid-point on each side of new
silicon carbide kiln bats which were being used in an electric kiln ( I
know one is not supposed to use them in an electric kiln). I also came
across a potter in Kobe doing the same,but using the silicon carbide
bats in a oil fired reduction firing.
John
John Dellow "the flower pot man"
From the land down under
Home Page http://www.welcome.to/jkdellow
Ivor and Olive Lewis on mon 18 dec 06
Not being in the market for shelves at the moment I have not really =
followed this thread. But the mention of "Cordierite" and the fact that =
I was having a look at Plate 3, System MgO-Al2O3-SiO2 of the ACS Phase =
Diagram Wall charts, this morning made me inquisitive.
Given the position and composition of this mineral in the diagram, any =
impurities in appreciable quantities might have a catastrophic effect on =
service performance.
What advantages does Cordierite have over good old fashioned Mullite or =
Sillimanite refractory materials ?
Best regards.
Ivor Lewis.
Redhill,
South Australia.
William & Susan Schran User on mon 18 dec 06
On 12/17/06 11:56 PM, "Ivor and Olive Lewis" wrote:
> What advantages does Cordierite have over good old fashioned Mullite or
> Sillimanite refractory materials ?
Ivor,
A web search resulted in the following:
http://www.morganadvancedceramics.com/materials/cord.htm
Seems like low coefficient of expansion, thermal shock resistance,
electrical resistance and low cost are major factors for its use.
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Ivor and Olive Lewis on wed 20 dec 06
Dear William Schran,
Thank you for nugget of information. Did Morgan qualify that with facts. =
In view of the reports about such material breaking it would seem =
Mechanical Strength is not on the list of desirables.
Must have a look. Thanks for the URL
Best regards,
Ivor
Paul Borian on thu 21 dec 06
Larkin Furnace in Conyers, GA is getting another large shipment of silicon
carbide shelves from China some time in late Feb. and their prices are very
reasonable - much less expensive than high alumina's from england, for
example.
i have heard from a few potters who use them with no problems and i plan to
pick up 24 of them (18" by 24" shelves) when the shipment arrives. I spoke
with people at Larkin many times and they said they have had very few
problems with them and have sold thousands of them to potters and schools.
They also assured me if they do crack early on i can get a refund - of
course i can not be 100% sure of this but it is reasonable to believe them
since they are a reputable company.
Although there is a lots of junk imported from china, they have been making
kiln shelves for a long time and i find it hard to believe, at least for
now, that shelves would be made any better in england.
The ones i am getting are $50/each and they probably still have other sizes
in stock, probably worth looking into.
-Paul
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