John Hesselberth on sun 20 may 01
Hi Everyone,
I just got another reminder of why it is a bad idea to use a Kiln Sitter=AE t=
o
turn off your kiln. I don't. It is strictly a safety device to prevent
gross overfiring so far as I'm concerned. Here's what happened.
I normally fire to cone 6 tip touching. I put cone 9 in the sitter as a
safety backup. Last night as I was watching cone 6 get to 4 o'clock my
sitter tripped. No it hadn't really reached cone 9. All three cone 6s in
the kiln confirmed that I was approaching cone 6. I had not calibrated my
sitter in some time and it had drifted that far off!! 3 full cones!!
Had I been using a cone 6 in the sitter to turn off the kiln, like I know
many people do, I would have shut off at Cone 3. In fact in parts of the
kiln it probably would have been only cone 2 since when you fire this way
you often don't pay attention to top-to-bottom uniformity either. In my
opinion, this is one of the biggest reasons why glazes don't travel well fo=
r
people who use electric kilns.
Since I was right there and figured out what had happened I overrode the
sitter and finished at a perfect cone 6 top to bottom in the kiln. And,
yes, I know I've harped on this before, but I shudder when I see people
still using their sitter to turn off their kiln so they don't have to "sit"
with it themselves.
I hope this reminder helps someone. Even though I knew this was a problem, =
I
didn't expect a 3 cone difference.
Regards, John
P.S. My sitter is now recalibrated per factory instructions (it only takes
5 minutes), but I bet it is still at least a cone off.
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
John Hesselberth on mon 21 may 01
>
> << My sitter is now recalibrated per factory instructions (it only takes
>
> 5 minutes) >>
>
> I don't know how to calibrate a cone sitter. Any hints? I got my kiln used
> and there was no instruction book.
>
> Marion
Hi Marion,
Don't know if I can do this without being able to sketch it or not, but I'll
try. There are two adjustments to be made on the front of the sitter. You
need a small alan (hex) wrench to loosen the set screws.
First, though, you have to slip the little calibration gauge/bracket, that
came with the sitter, over the prongs (on which the cone sits) and the rod
(which sits on the cone). If you don't have one of these, most pottery
supply stores carry them. They can't (or maybe I should say shouldn't) cost
more than a dollar or so.
Second when you hold the trip lever in the up position pushed back toward
the kiln as far as it will go, there should be 1/16" clearance (front to
back or horizontal clearance) between it and the L shaped hook that sits and
"hooks" over it. You adjust this by loosening the set screw on the L shaped
hook and sliding it one way or the other. Then retighten.
Third, you adjust the clearance between the L shaped hook and the trip lever
so the trip lever just clears the L shaped hook when the calibration gauge
is in place. The set screw to do this is on the trip lever.
Retighten both set screws, remove the calibration gauge and you're done. If
this isn't clear maybe someone else can do a better job of describing it to
you.
Regards, John
John Hesselberth on thu 24 may 01
> From: vince pitelka
>
> If the kiln-sitter is well
> maintained, then it is extremely reliable, and any small fraction of risk is
> well worth it.
Vince,
I don't disagree with this. But I think this is a mighty big "if". I have
seen an awful lot of kiln sitters that haven't been calibrated or maintained
since the day they were bought. Try running an experiment and ask in
studios you visit if they have a sitter calibration gauge. You will get
quite a few "Huh? What's that?" responses.
While some people do an excellent job of maintaining their equipment, a lot
of others don't even know they should. Hopefully this discussion has raised
the awareness of some to this need.
Regards,
John
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