JD18-JH Update: Calibrations w/ Cone Readings.

admin | Kilns | Thursday, December 20th, 2007

Before reading this, you may find it helpful to review the post on Studio Kiln Thermocouple Calibrations.


While waiting for the modified Bartlett V6-CF Controller, I fired the JD18-JH using the motherboard from my JD230/3 –and it performed great. But now that the new controller is here, I’ve been having some issues getting my kiln to fire to a perfect cone.
Hey- it happens! The thing is, most people fire their kilns without ever taking into account that it may be uneven. For many, it doesn’t matter too much –but when you’re still cooking a glaze that’s already been melted for several hundred degrees, you need all the accuracy you can get.

Once Dave Myers (Bartlett Instruments) informed me that “18″ was the TC offset baseline for an L&L DynaTrol, things became a whole lot clearer.
TCoS:18 still resulted in over-fired cones however, and the bottom zone achieved slightly more heatwork than the top… but at least I have a place to start.

The following information shows how I’m attempting to calibrate the TC readings, using Bartlett’s TCoS function…

Firing 12.16.07
TC offset was set to TC1: 16 , TC2: 16.
The rate of rise during the last 150°F was keyed in: 108°/hr, within a “write your own cone fire program“, with ^10 set as the peak.
Cone 10 was reached in the bottom zone at TC reading: 2335°F.
Cone 10 was reached in the top zone at TC reading: 2342°F, about 4-5 minutes later.
This was not during a hold. It never reached this temperature because the controller’s calculation of ^10 was scheduled at 2351°F, and I skipped step out of that ramp to prevent over firing.

***I was going for a “^10 and a half “, by soaking at 2350°F until the desired bend. So the cones in the following image don’t show a true ^10, but rather what the cones looked like when I skipped stepped out of the last ramp (once my desired level of heatwork was achieved). But one thing they do relate very well, is the slight difference in heat work.****


According to the controller, the rate of rise was maintained at around 108°F/hr.
So if one compares the temperature when cone 10 was at a 90° bend, then zone 1 was too hot by (3°F + offset:16 ) 19°F.
Zone 2 was too hot by (10°F + offset:16 ) 26°F.
And there you have it — too hot and a difference of 7°F existed between the TC1 & 2 readings to boot, easily accounting for the cone measurements.

An educated guess at this point is that an offset of TC1: 19 and TC2: 26 might bring things true and even. I’ll know for sure tomorrow…

I have to add that I’m looking forward to getting the 4-1/2″ ring powered and into the game. The idea for that ring was originally to give me a place to cut a spy hole that you could actually view cones through. This would really help right now, as Bartlett’s limit for a Cone fire program is ^10. Because of this, I’m having to calibrate the TC’s by comparing the controller’s ^10 calculation to a self-supporting ^10, and then continue to hold (soak) to push ^11&12. That’s a problem, because it’s extremely difficult to see more than one cone in that itty-bitty little 1″ spy that electric kilns are typically made with.

1 Comment »

  1. Jesse - what is the ” 4-1/2″ ring” that you refer to above. How did you configure this “ring” to create more functional spy hole space? Since the above post is December 2007 - I assumed you have long since solved the limited spy view problem. You help to understand your solution is much appreciated.


    Comment by Dan Weaver — July 22, 2009 @ 4:43 pm

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