I picked up the controller from
Auber Instruments as well as my K-type thermocouple. They have good prices and good products. You may want to opt for a little higher model than my simple PID controller. Maybe their unit with ramp/soak control so you can control ramp/holds/etc. and do controlled temperature descent for annealing.
I used pretty thin guage weld steel for the body. Really, the insullation effectiveness in is the brick, and the body serves just to hold the bricks together in proper position. That being said, once the oven is heat saturated, the sides and top get pretty hot. Definitely want it on legs, and later on, I ended up placing my oven legs on some long scraps of bar stock I had laying around to better disipate the heat coming through the legs and protect the table. It wasn't burning the table, but I thought it better to be safe than sorry. You can touch the sides of the oven very quickly, but if you leave your hand there for any length of time when the oven is fully heat soaked, you will probably burn yourself. Definitely not as insullated as an industrial oven. Actually, the door may be the best insullated portion of the oven and gets warm, but rarely too hot.
One thing I learned the hard way is to watch your electrical connections at the back of the oven and the coil. I had originally bent a loop into the end of the coil and attached it to a stainless bolt by sandwiching it between two washers. This unfortunately created some very narrow spaces in which an electrical arc was able to form and burn through the coil over time. I changed it by actually drilling a small hole through the stainless bolt, passing the end of the wire into/through the hole, and tightening up a nut against the wire. That eliminated my arcing problem.
Keep in mind that once the oven has been in use a few times, the coil will stiffen up and become more brittle. Make sure your grooves in your brick hold it well and use some "staples" made from the kanthal wire to anchor the coil into the brick to prevent it from jumping its grooves. Also, if the wire touces itself, it will short and take the shortest path to complete the electrical loop, effectively bypassing whatever is in between the two touching segments.
I have the thermocouple entering the middle of the oven and the tip of it very near the center of the oven chamber. This allows me to get a reading that is more accurate to the space where my knife will be sitting. A sheilded thermocouple may actually give you a more accurate reading because it is less effected by radiant heat from the coils as they cycle on and off. I believe Auber also sells the sheilds for the TC.
Anyhow, good luck, and have fun. Build in some sort of safety to cut the current to the coils when you open the door. I didn't use an interrupter switch, but I do always flip the master power off when I am removing or inserting a knife. Those coils are live at 220 and pushing 15 amps. All it takes is one small wrong movement to ruin your day.
--nathan
