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ghetto3jon

Kiln Temp Too High...Even At Lowest Setting?

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I just bought an old manual kiln (SNO Industries, 15"x15" inside, kiln sitter), and it seems to work well. Perhaps too well. I bisque fired a single pot as a test (2hrs low, 2hrs medium, high until 05 cone bent), and the pot broke during the firing. On a hunch, I used an oven thermometer to check the internal temp with the dial set to the lowest temp, and it said 400f. Isn't that too high for the lowest setting? I'm assuming that the lowest temp should be lower than 212, to allow water to leave the pots without breaking/exploding? I'm new to this, so any advice is appreciated.

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Yes you are correct. Anyway that you can slowly warm things up and keep them  about 200 degrees is ideal. Automatic kiln controllers allow a preheat cycle which is a slow ramp up to about 200 then hold  at or under  for as long as the user specifies. Folks with manual kilns often turn their bottom elements on low and crack the kiln lid several inches to let out the steam and keep the overall temperature from increasing. So two hours low with the lid cracked  might be the ticket. You have the correct idea so now you will be able to figure a combination that gets you there.

in a pinch I have even microwaved a piece or two five  seconds at a time checking it at each cycle  until all the water was gone and making sure it never got too hot. A bit desperate, but you get the idea, anyway to slowly get the water out is just fine.

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Thanks for the reply. I did have the lid cracked about 3 inches during the low and medium part of the fire...perhaps I should try again with the lid opened more. Is there anything wrong with doing the candleing with the lid all the way open? I have to shave off some major degrees.

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Nope, as long as you don’t mind wasting the energy. If that gets you there then that is what you do. Drying everything out thoroughly before the firing is also another option but often is not possible.

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23 minutes ago, ghetto3jon said:

The test pot that blew up was thrown in 2015...so it was about as dry as it was going to get.

When you say blew up, like it shattered into shards or ? If it's cracked a picture of the crack would help. Little kilns can fire super fast, might just need to leave it on the low and med settings for longer if the pot was bone dry going into the kiln. If it's thick, like more than about 3/8",  then definitely lengthen the time spent on low.

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Hmm, looks a bit thick but now I know that it was completely dry this changes things a bit. Some of the old snow industries kilns used infinite switches for the low medium high element control. These switches are the same as those used for electric range burner control.

If you have these, then there is the distinct possibility that your speed issues are a result of a faulty switch. These switches are capable of dialing back to 22% of full fire so this could be a thing in your case. These switches almost always provide a means  to calibrate their on / off duty cycle as well.

send a good picture front and back of the switch and I should be able to tell you how to check it’s operation and give you a Robert Shaw equal that should work. 

No guarantees  but a realistic possibility,  we will give a go if you are interested.

Edited by Bill Kielb

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Even bone dry pots have some moisture left in them, which must be driven off before it turns to steam. With thick pots, the moisture isn't driven off as quickly as with thin pots, so you have to fire slower at the beginning of the firing. Those look like typical thickness blowouts to me. Small kilns can heat up really fast- it's easy to get a lot of power into them for their size, and there's less mass to absorb heat.

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It is indeed a single infinite rotary knob that controls the temp. Although, I am seeing a consistent increase in temp through the full travel of the knob...so I don’t *think* it’s faulty.

 

One thing to note: I found the manual, and it says to leave the cover completely open during the early stages of a bisque firing. Seems inefficient, but perhaps that’s required for this kiln.

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A decent pyrometer can be had for about $130 (that's what I paid for mine!), which gives you feedback on current temp and - given you check it periodically - the rate of change as well. Although (likely) you wouldn't want to depend on it for reaching your target temp + "heat work" it is better than nothing if your cones fall over, aren't visible, etc., and can also guide you through critical heat ranges, e.g. ~212F, where good ol' water flashes to vapor - "live stem" (see "Sand Pebbles" with Steve McQueen). Per regular forum contributor Glazenerd, there are a few other temperature ranges to pay attention to, particularly in bisque firing...

That said, I'm cranking all three elements to high the night before and then shut them down before 212F is reached - doesn't take long, just some minutes; still warm the next a.m., first thing I start up without much worry about wet pots, and finish firing much sooner.

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yes, i use my household oven occasionally to dry out a piece to meet a deadline, not as a normal thing.   but i would NEVER expect to fire anything that thick.   if you want to improve your skill level in throwing, feel the thickness of that pot with one hand and the thickness of one of your kitchen dishes with the other.   (just be sure it is not a very heavy pfalsgraff or however they spell it,  plate.)

i turn the oven on for 15 minutes with a timer.  the temp is 170 F.   leave the pot until i am ready to take it out.  if it needs another few minutes i do it again.  that is if it is a real emergency.

Edited by oldlady

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Standing around doesnt mean dry..a figure I fured for a friend had spent years inthe house and on a covered verandah blew in a v. Slow firing.

I think it would have dried quite quickly initially thus sealing in moisture.

 

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16 hours ago, ghetto3jon said:

Anyone ever use a standard kitchen oven to dry out a pot before you put it in the kiln (couple hours around 180)?

Yes, after taking dinner out, also use the airing cupboard.

 

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Oven thermostats often have a large deadband or to put it another way it’s common to find they heat 25 degrees above setpoint before shutting off and cool 25 degrees below setpoint  till they turn on again. Depending on your ovens accuracy you may want to set the dry out temperature setpoint  to a safe low setting staying reasonably under the boiling temperature of water.

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Hi, I just bought a used SNO Industries Model P11. The interior is 11 x 11". It didn't come with a manual, did yours come with it or did you find it online?

I am totally new to firing by myself and would love some tips for getting started. Thanks!

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