Minimum kiln depth for drop ring?

[smallbitz]

I have been fortunate to try and experiment with just about everything in my 15/6 Jen-Ken kiln - except a drop ring. Is it possible to do one in such a shallow kiln? If so, would I take out the shelf to do it? Put thin-fire directly on the kiln floor? Unfortunately, I can't turn off the top elements, which I know presents a problem. Hmmm.

Has anyone done this in a 15/6? Any suggestions for schedules, set-up or whether I should even give it a try? Thanks in advance for any help!

Smallbitz

[Brad Walker]

We routinely do five inch drops in a six inch deep Olympic 146 kiln. The key is that you must fire with side elements only, no top elements.

I don't know if the Jen-Ken kiln you have has the capability of firing without top elements. If it does, you can do the drops. If it doesn't, I'm not sure that you can drop as far as an inch less than the height; with top elements, you will need to be further from the top and fire very, very slowly, and even then it's a risky firing.

[smallbitz]

Nope, can't turn off the top elements. Should I remove the shelf to give myself a little more room?

[Brad Walker]

Nope, can't turn off the top elements. Should I remove the shelf to give myself a little more room?

Absolutely remove the shelf, you need as much space as you can get. Put a small piece of fiber paper on the floor beneath where the piece will drop. Start with the top of the glass two or three inches from the roof. Fire very slowly -- about 100dph -- stopping at around 500F for ten or fifteen minutes on the way up to 1100F. Then fire from there up to where you do the drop. If that first drop survives the firing without cracking on the way up, do another one a bit closer to the elements. You could go even slower -- 50 dph if you want -- to reduce the likelihood of failure even more, but that really increases the length of the firing.

And above all, don't do this with a piece you really like. Practice on a piece that won't make you cry if it cracks.

[JestersBaubles]

I have a Fusion 14 that is only 1/2" "taller", has only top elements, and I have had good success with drops. Everything I have read says you should be fine as long as the glass is 1" away from the elements, and this has been my experience. My schedules are not as conservative as suggested. (200/hr advanced rate).

Just my experience, YMMV, and all that!

Dana W.

[smallbitz]

Many thanks! I think I'll give it a try on a test piece. Very curious to see how they will come out!

[Bert Weiss]

Understand that the more even the heat the glass sees, the faster you can heatup without a thermal shock. Conversely, if your heat is quite uneven, you have to slow down enough to avoid the dreaded pop.

[Brad Walker]

My schedules are not as conservative as suggested. (200/hr advanced rate).

We usually fire 1/2" thick pieces at 200 to 250 dph, but that's aggressive (doesn't work 100% of the time). If I have the time to spare, I'll go 100dph to be safe and succeed all of the time.

But every kiln (and every sheet of glass) is different.

[Pat K.]

I've done it in both of my Skutt kilns - I think they're 6.5" deep. Your glass should be a little thicker than normal too - about three pieces of glass - then the sides don't get too thin as it drops especially if you plan to slice off the lip. You don't get as much flow for the short drop, so it's not quite as dramatic, but I still like them. I've done from 1 inch to four inches with good results. I'd really like to do a deeper one, but don't have the deeper kiln

Good luck.

Patty

[Bert Weiss]

There are way too many variables to come up with a universal schedule, unless you get real slow. The theory I work by, says that heat evens out, at a depth, somewhere between the distance between the elements and the height of an equilateral triangle, with legs that distance. Any closer than that, and you need to start compensating for unevenivity. Another theory is that heat radiates evenly for about 12" and then begins to fall off. You also have to compensate when the glass is supported by a mold that makes it heat unevenly. A shelf is relatively even. A bowl mold, not so even.

My kilns heat very evenly as elements are straight wires set less than an inch apart. I have always been able to heat at 600dph with little mishap, until I started to cast circles of broken tempered glass. To slump these, reliably, I have to slow down to a crawl.

[smallbitz]

I think since I'm already starting out 'in the negative' with such a shallow kiln to try this in, I'll play it safe and go 100 dph. I'm in no hurry - learned the hard way 'hurry' and 'glass' don't mix well!