It typically takes 15 to 25 minutes for a cone to bend, depending upon the cone number. The cone bends slowly at first but once it reaches the halfway point, it bends quickly. When the cone tip reaches a point level with the base, it is considered properly fired; however, the difference between a cone touching the shelf and a cone at the 4 o'clock position is small and rarely affects the fired results.
The Kiln Sitter® shuts off the kiln when a small cone (or bar) placed under the sensing rod receives enough heat for it to fully bend. Bending is caused by the weight of the sensing rod. Because the cone in the Kiln Sitter® is located at the kiln wall (closer to the heating elements), it frequently receives more heat than witness cones, causing the kiln to shut off early. Using the next hotter cone/bar may be necessary.
Thanks for any help!