What is a Kiln Sitter?

Before the invention of automatic kiln controllers, the kiln sitter was a major innovation in kiln control technology. Introduced in the 1950s, a kiln sitter is a mechanical device that automatically shuts off a manual kiln when it has reached a specified temperature.

Unlike digital controllers, which utilize thermocouples, control algorithms, and microchips to precisely monitor kiln temperature and regulate power, kiln sitters utilize more primitive technology to determine when the kiln has reached temperature: melting and gravity!

Components of a Kiln Sitter

Before explaining the mechanisms of how a kiln sitter determines when to shut off power to the kiln, it’s important to understand the various components of a kiln sitter:

Cone Supports: Two cone supports in the interior of the kiln are used to support the sitter cone.
Sitter Cone: The sitter cone (or witness cone) is a small pyrometric cone that is placed on top of the cone supports and used to prop up the sensing rod.
Sensing Rod: The sensing rod is a metal rod that connects the interior of the kiln to the exterior components of the kiln sitter. On the interior side of the kiln, the sensing rod is propped up on top of the sitter cone. On the exterior side of the kiln, the sensing rod is connected to a claw assembly that holds up the weighted latching mechanism.
Weighted Latching Mechanism: The weighted latching mechanism, on the exterior of the kiln, is connected to the sensing rod at the top of the latch. The bottom of the latch is a weighted hinge that will naturally fall unless held in place by the claw assembly.
Timer: A timer on the exterior of the kiln sitter shuts off the kiln when the timer hits its allotted time.
Plunger: Situated within the weighted latching mechanism when the latching mechanism is flipped up into the on position, the plunger is depressed so that the timer is initiated.

How a Kiln Sitter Works

On the interior of the kiln, the sensing rod is propped up by the sitter cone. While the sensing rod is propped up, it lowers the claw assembly to hold up the weighted latching mechanism on the exterior of the kiln, allowing the kiln to be powered on.

However, as the kiln heats up, the sitter cone begins to melt at a specified temperature, allowing the sensing rod to move lower under the weight of gravity. As the sensing rod lowers, the assembly claw is lifted. When the sitter cone melts to a 90° angle, the sensing rod is fully lowered, the assembly claw is fully raised, and the weighted latching mechanism falls, causing the kiln to power off.

Illustration of the position of the sensing rod when the sitter cone is melted. — **When the sitter cone has melted to a 90° angle the sensing rod is fully lowered, and the kiln is powered off.**

How to Use a Kiln Sitter

Using a kiln sitter is extremely easy. Below is a step-by-step guide:

Select a sitter cone that matches the pyrometric cone temperature rating for the ceramic or other material you’re firing. Different materials have different firing temperatures. Select a sitter cone that matches the cone temperature of your material. This ensures that your sitter cone will melt and power off the kiln at the correct temperature.
With one hand, hold up the weighted latching mechanism and attach it to the claw assembly. Make sure that there is proper clearance between the weighted latching mechanism and the claw assembly (usually 1/16th of an inch). The two should not be touching at the start of the kiln firing.
With your other hand, insert the sitter cone between the cone supports and the sensing rod. Make sure the sitter cone is placed evenly on top of the cone supports. It’s also important to center the sitter cone on top of the cone supports (unless you’re intentionally aiming for an abbreviated or a prolonged fire).
Once the sensing rod is situated on top of the sitter cone, set the timer of the kiln 30 to 60 minutes passed the projected time it will take your sitter cone to fully melt. This is to ensure redundancy in case there is an error with the kiln sitter.
Power on the kiln and press the plunger to initiate the timer. You’re ready to go! At this point, the kiln sitter should make sure the kiln powers off at the proper time – but the timer switch is there as backup just in case.

Limitations of a Kiln Sitter

When it was first introduced, the kiln sitter was a major advancement in kiln control technology. However, that was over 70 years ago, and there have been major advancements in kiln controller technology since then. While a kiln sitter is adequate for simple firings, such as those for pottery and ceramics, it is not nearly as precise, versatile, or handsfree as the most advanced digital kiln controllers.

Limitations of kiln sitters include:

Incapable of complex kiln firings with precise ramp rates and multiple setpoints, such as those needed for glasswork.
Leaves room for user error – for instance, improperly positioning the sitter cone and cause the firing to go on for too long or not long enough.
Doesn’t provide extensive diagnostic insight into failed firings.
Requires the kiln operator to manually check the status of their kiln.

Automatic kiln controllers, on the other hand, perform all the functions of a kiln sitter but with a greater degree of accuracy, control, insight, and less need for direct oversight or manual intervention.

How Hard Is It to Upgrade Your Kiln Sitter to an Automatic Controller?

The good news is that you can upgrade your kiln sitter-controlled kiln to automatic controls without having to replace your kiln or make significant modifications. Standalone kiln controllers make it easy to upgrade your kiln sitter – check out our step-by-step guide for DIY standalone kiln controller installation!

Choose the Most Advanced, User-Friendly Automatic Kiln Controllers

If you’re tired of the limitations of a kiln sitter, the TAP and TAP II Controllers by SDS Industries are the most advanced, precise, and easy-to-use automatic kiln controllers on the market today. With responsive touchscreen controls, an intuitive graphical UI, and integration with the TAP Kiln Controller Mobile App, TAP Kiln Controllers can pair with any relay-controlled kiln or oven.

We invite you to explore our selection of automatic kiln controllers, standalones, and conversion kits on our online store. You can also purchase TAP Digital Controllers or TAP-Controlled Kilns and Heat Treat Ovens through one of the following distributors:

Scott Shannon