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akin4843

Sitter Shutting Off One Cone Before Supposed To...

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Hi guys. I have yet another question. I bisque fired some pots yesterday and used the kiln sitter for the second time. I put in a ^05 junior cone in it and had the witness cones at 06, 05, & 04. I usually babysit the kiln and shut it off myself when the middle witness cone falls. Yesterday the kiln shut off and when I looked in the peep hole I saw the first cone bend but the middle one (05) was only slightly starting to bend. Is this normal for sitters? Its only my second time using the sitter - kiln is a Skutt 1027 KS. The first time I used it, the same thing happened, but I was glaze firing so things still came out good. If it's not normal, I'm assuming the pieces got bisqued at 06, so is that a good temp for ^6 clay, or is it under-fired? Thanks in advance. I've learned so much from you folks already!

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Couple of things can cause this. Calibration of setter is off, cone being used is placed more toward the narrow end, or the drop rod has a bend in it. The first and the last are all part of one problem-calibration. When you got the kiln, the directions included a calibration explanation that you should follow to make certain the setup is correct. The setter had a calibration disc, that fits over the drop rod and the supports, with a screw driver you can readjust the counter weight on the outside of the drop rod.

 

The middle(cone placement) is easily fixed by moving the cone toward the fatter end more. However, for consistent firings with a setter move away from the cones to using bars for firing. These will consistently melt at proper heat work, even if place off one side to other. 

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Are you placing the cone in the sitter the same way, ie number facing down, each time?  Is there a shelf sitting very close to the cone set up of the sitter?

As Pres says use your calibration disc, and the angle of the latch on outside of the kiln may come into consideration.  Length and rate of firing the same?

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using minibars, which are cones that are made as rectangular "bars" of an even thickness, instead of pointed cones, will allow you to have more consistent firings.  AFTER you do the calibration mentioned.

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Ok, thanks I will try the calibration and get the bars....but also, if it shut off at ^06, did it under-fire? Should I just re-fire them to ^05? The pots don't look as "pink" as they usually do.

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As Mark says they will be bisqued fine, really don't need to rebisque, some people here bisque to 06 all the time. Pots will be slightly more porous, so glaze may need to be a little thinner, not a lot.

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Here is a quote from the instructions given by the manufacturer of Paragon kilns: 

"The cone used in the kiln-sitter will not react to heat in exactly the same way as a cone placed upright in the normal position. The weight of the actuation rod and the horizontal position will cause it to bend at a lower temperature than an upright cone. It is usually necessary to use one cone hotter in the kiln-sitter than the cone to which you wish to fire."

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