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[Aug. 21, 2018]
In the picture, from left to right: Furnace controller (green), electronic thermometer (yellow/orange), furnace/kiln (gray).
I purchased the small furnace (kiln) at an estate sale for $30 (shown on the right hand side in the picture above). I believe it was used as a small ceramics or jewelry furnace, but I plan to use it for heat treating metal. Unfortunately, the kiln did not have any kind of temperature control, so I decided to build a controller.
The furnace is fairly small; internal dimensions are 6.5" W x 4.25" H x 6"D. I do not know what the wattage is, but jewelry furnaces of similar size are around 1500 Watts so it is probably somewhere near that.
I purchased all the controller parts in a "kit" from ebay (details at bottom of page); a heat sink for the electronic relay was purchased separately. I also purchased locally an electrical socket, power cord (and strain reliever), and used other misclennaeous parts from my shop (wire, crews, etc).
I built an enclose of wood (with an aluminum back) based on the dimensions shown below; I made it with a sloping front to make the controller panel more easily visible in use. Note that the dimensions shown are the internal dimensions, so if you copy these plans be sure to allow for the thickness of the wood you use.
Heres a picture of the completed controller. After completing the wood enclosure, I painted it with spray primer (2 coats), followed by "hammered green" spray paint.
Another view of the enclosure.
Here's the back of the controller. The heat sink for the electronic relay is mounted to the aluminum plate; holes are drilled at the top for venting (there are also vent holes in the bottom of the enclosure. The holes for the power cord strain reliever and the thermocouple socket (yellow rectangle, lower right) were made by drilling and filing.
The bottom of the enclosure, showing vent holes.
Closeup showing the controller panel.
Furnace Heating Test
Furnace Heating Test
As a test if how long the kiln takes to heat, and how hot it gets, I set the controller to 2,000 degrees (F) and recorded the actual temperatures as it heated up (see chart below). To summarize, it took about 100 minutes to reach a maximum temperature of about 1,650 degrees (F).
To complete the testing, I reset the maximum temperature to 0 degrees and allowed the kiln to cool, again recording the temperatures at various times (chart below):
Details on the controller parts
Details on the controller parts
The parts were purchased on ebay as PID Temperature Controller Kiln Thermocouple SSR Relay Electric Oven Jewelry F°C.(cost about $75 including shipping in 2017). Since the original listing may disappear at any time, I've included a copy of the specifications from the listing page below.
In addition, here is the manual for the PID DTX controller : https://drive.google.com/open?id=1E816EY2ZCcUaBfsPSp27TeL4Rkd5Mrw4
Parts provided in the "kit" - clockwise from the top these are the PID temperature controller, the SSR relay, and the thermocouple with mounting block.
Purchased separately - Aluminum Alloy Heat Sink 80 x 50 x 50mm Mountable For Solid State Relay
Purchased separately - Panel Mount K-type Thermocouple Miniature Socket and Plug Connector MPJ-K & plug
Listing for the kiln controller "kit" :
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