Main Discussion Area > Flintknapping
Getting ready to put together a kiln
iowabow:
Pm me for perfect ramp for novaculite. It has to be done just so or it will crack
iowabow:
Ok I missed the rate =temp to temp time. I was wondering how you would set rate.
Huntrick64:
IOWABOW, PM Sent
Huntrick64:
An Update:
Measured voltage at the dedicated 15A receptacle is 124V.
The old kiln has 4 elements and 4 switches. I removed all of the electronics (kiln-sitter, switches, etc.) To my surprise, all 4 elements were still good. Each one makes 3 complete wraps around the inside of the kiln and measured 9 OHMS. I think I'm going to try and use one or two of the existing elements in the center of the kiln with our setup. The existing elements are too brittle to modify without breaking ( I proved this on the kiln extension elements). The 9 Ohms is too little resistance and would provide 1700 watts (I like), but would draw 13.8 Amps ( a little too close to 15A for me). If I wire two of them parallel, then total resistance drops to 4.5 Ohms, and Amps jumps to about 28 (going the wrong way). I actually wired two of them serially and they measured 17 Ohms. Even though 7.3 amps was well within the safety zone, we are dropping to 905 watts. I'm hoping that this will still be enough heat given the insulating abilities of the kiln. If I can ramp up a full kiln at 20-30 degrees per hour with 900 watts, we should be fine. The inside dimensions of the kiln are 17.5" diameter X 18" high.
Does anyone have any experience with a kiln of similar size using only 900 watts?
Do you think this will work?
On kilns that hold 3 or 4 buckets of rock, other people talk about using two separate Robert Shaw switches and separate elements with 16.5 Ohms each. So they would be looking at two elements of 900W each where I would only have one, but I have no idea how quickly their kilns heat up. I'm thinking that their 16.5 Ohms is more of a function of making the Robert Shaw switch function properly instead of generating the correct heat.
Man, I'm not sure how this qualifies as "primitive", but I guess I also drive a pickup truck to the quarry to get my rock, wear modern clothes, eat processed food, etc.
Huntrick64:
UPDATE!
Got everything assembled and tested. Last night we set her off on her maiden voyage, and so far, everything is working perfectly. The ramp/soak feature is awesome. Now we have to see if the two serial elements can heat it up at 20 degrees per hour all the way up to 575. It had no problem ramping at that rate, completely full of cold rock, to 200. It is holding between 3 and 4 buckets of rock depending on their shapes. The PID is soaking it within +or- 1 degree F. You could actually watch it "auto program" itself to get better at activating or deactivating the element. When it first started it would be +or- 5 degrees. We used the 3M Fire Block FB-136 (Lowes) to caulk up all of the holes in the kiln and to plug the gap around the thermocouple.
Time will tell.
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