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having issues recalibrating my kilnsitter?


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I have been reading many other threads on this forum, and you guys/gals are great, I've learned a LOT. 

So, Covid lost me my firing source. They literally closed down local branch, and moved to headquarters 2.5 hours away. No way I'm gonna try and transport 50+ greenware that far! So the hunt for a used kiln finally found me an old American Beauty AB-18 that looked quite used, but fired up great and seems to have good integrity to brick. Only had to get a new sensor tube for it! This is my temporary stopgap until I can save up for a new kiln (guessing its about 3 years away).

Got electric run and did 2 bisque firings... just bowls and stuff that was easy to recreate if there was disaster. First load sang nicely (no thunks) and feels like its about an 05 surface (used 05 in sitter). Second load was already firing when I finally found a manual online on how to adjust. It seems fine like first load.

Both loads , it actually overfired (sitter cone is more of U shape than L shape). Made adjustments, did test firing to cone 020 (just happened to have on-hand for MOP!). Since wares fired were bisque loads, I didn't use witness cones, although I do have them ready for my first glaze firing 5-6-7 (shooting for 6).

BUT this last adjustment / test fire I think maybe we made it TOO sensitive? Claw seems perfectly adusted, so now were down to dealing with adjustments to trigger plate. We did a fast heat (kiln empty) and it was shut off before even an hour went by? Hubby just got brave and opened the kiln, it UNDERfired this time (sitter cone still in position and unbent. Are sitters always this finicky getting them adjusted? They suggest recalibrating every 30 firings.

I do have a high quality gauge to test temps inside kiln through a peep (we're retired from a field related to HVAC CO testing), and when I checked on test fire at 45 minutes, was planning on getting internal temp but kiln had already shut down... and reading was only about 630F.

 I have 6 more bisque loads to fire, and then a boatload of glaze loads... but until I get this thing to not over-fire, afraid to ruin a glaze load.

Anyone else have a manual kiln from the 70's and have the same woes? Its a K type sitter. I'll probably try one more test fire tonight, gonna drive my husband crazy trying to get this beast adjusted.

We marked the spot where things were before adjustments started... if we cannot get the two adustable pieces just right, would putting them back into old position work if we dropped down to 06 or 07 in the sitter (letting it overfire to get us to cone 05?) and if that is a viable alternative, would we need to drop to 4? or 5? for glaze firings when we intend 6?

Ugh. So much to learn. ~ Dawn

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Hi Liz!

Just wanted to suggest placing witness cones (for bisque, one may be enough), two reasons, a) gives you a clear idea of the heat work accomplished, b) allows you to relate your pyrometer reading to cone position.

On "a" - the cone, or bar  (the small cone allows you some adjustment/leeway; the bar is, obviously, same section all the way across. I use small cones) is subject to the force the rod is exerting. My (limited) experience indicates the kiln sitter trip doesn't quite match up with witness cones. I'm shooting for cone 5, but place a 6 in the sitter, which is fairly close - your results may vary, of course!

On "b" - you might start out watching (use protective eye wear - against harmful rays and hot bits!!) witness cones through the peeps for glaze firings. Once you've watched (take good notes) the pyrometer feedback and compared against the cone achieved, you may not feel it necessary to watch the witness cones as closely.

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(sitter cone still in position and unbent. Are sitters always this finicky getting them adjusted? They suggest recalibrating every 30 firings.)

Does your kiln have a shutoff timer feature on the sitter ? The cone bends and sitter shits it off so if the cone is not bent how did the kiln turn off?I'm assuming your timer turned kiln off  to early before cone bent and turned off kiln/

A bit more clarity whould help

I have a manuel kiln with a timer and sitter for shut off.I usually adjust the sitter once in a few decades-I bisque to 08 but 06 is standard. What are you using the 020 cones for?

 

take all the advice adjust sitter per sues instructions and put some ones all arount in bisque to see whats going on everywhere .A MM is a lot of adjustment .

I also assume you have the sitter setup template for adjustments? (small roundish thing)

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If you're using small cones, not bars, then be consistent about the placement of the cone in the sitter. Keep it centered under the rod. Closer the cone tip vs closer to the base and it will bend differently. 

I have found the calibration disc to be a good starting point, but it often needs adjusting after that. 

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Yes, I think we have it adjusted now. Per Sue's instrux, we had 2 additional adjustments we had to tweak.

Mark C - no timer on my k type sitter. Just 4 power switches. Guessing circa early 70's. Upon inspection, cone did start to bend, but only about 10%.  Just enough to shut off because we were off on trigger plate height.  I do understand the complete mechanics of how the sitter works. (Not offended at too many details btw). And using 020 for tests because they are my lowest temp small cones, fastest test fire method. Yes I have the calibration plate.

Neilestrick - yes, very consistent with small cone placement. Haven't tried the bars yet, are they more accurate for sitters because of their shape? My supplier in Columbus was out of them.

A little background on me since I'm a newbie, I grew up around ceramics, my mom had a shop, specialized in porcelain. I am a 4th gen artist & musician. Also an advanced quilter and pattern designer (quilts & crochet). Played on/off with pottery at college, and also on base in Hawai'i (my ex was USMC). Just recently picked it up again in 2019. Retired graphic designer, so I'm super finicky about consistency (like placing cones), but learning to let go of my perfectionism because pottery's charm & beauty is not perfect. Happy we kept some equipment from a closed biz (HVAC related) because I have digital testing meters already equipped to handle temps over 2k degrees, and we can monitor any CO as well in our kiln room. Pottery and quilting are my creative outlets for retirement. Covid kind of gave us the push to setup the studio completely (had wheel already)

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