neilestrick

Any kiln will get to cone 018, it's the hotter stuff that's an issue. If you plan to fire to cone 5/6, your elements can only wear a little bit before they don't work. You end up changing the elements a lot more often.

Cone 10 porcelain does not have to be fired in reduction, but 99% of people who fire in a gas kiln do so in reduction.

Thinner brick use slightly more electricity, but they cool faster. The other potential issue is that they radiate more heat because they aren't insulated as well. Depending on your space and how it is vented, that may or may not be an issue. If a kiln is rated to cone 10, it will get to cone 10, regardless of the brick thickness. I rarely sell new kilns that aren't 3" brick, but 2.5" brick is not a deal breaker with a used kiln at a good price IMO. L&L's most powerful kilns, the JH crystalline series, are rated for cone 12, but are built with 2.5" brick. The thinner brick allow for faster cooling times, and more precise temperature control.

You do not have to have 3 inch bricks to get to cone 10. It's a little easier with 3 inch, but not necessary. Most any kiln that's rated for cone 10 will be the same rating in both the 2.5 and 3 inch models.

There's very little reason to fire to cone 10 in an electric kiln. Your glazes won't look the same as pots fired in a gas kiln to cone 10, because you can't do reduction in an electric. You might as well fire to cone 6 and save the wear and tear on your kiln. There are really nice vitrified, translucent, cone 6 porcelain bodies available from most clay suppliers.

A cone 6 kiln will only get to cone 6 when the elements are in perfect condition. That may mean only 30-50 firings. You could contact Skutt and ask them about using different elements that would allow that kiln to go to cone 10. That would mean that the kiln would pull higher amperage, though. Typically in an 18x18 kiln they pull 24 amps, which means you'd need a 30 amp breaker. You would probably need a new power cord to handle the higher amperage, and the internal wiring may need to be upgraded as well. All of that is pretty inexpensive, though, if you can do it yourself. If you got the kiln cheap, and the bricks are in good condition, it would be worth it.

Glazes may be garbage. If they're dried out, add some water, let them sit overnight, and use a stick blender to mix them up. If they don't brush well, you can add some CMC gum. If it's a weird plug, but it's in good shape and the cord is good and it's the proper amperage, yes, you can use whatever plug matches. The lid can be taken off. It's a simple hinge. The bottom is not attached. The two body sections can be moved individually. There are several ways to make it into a digital kiln. Olympic makes a controller system that replaces the sitter, assuming that's not the really old style sitter. Post a picture of the control boxes. You can also buy an external digital controller that it plugs into.

Not bad. Find the serial plate and see what the amperage draw is. You'll need a breaker that's 25% greater than the actual draw. Most kilns that size pull about 24 amps and need a 30 amp breaker. If that's the case, it may have a 30 amp cord, or it may have a 50 amp cord because they like to use the same cord on all their kilns. That's not the original cord, so take a close look at it and see what kind of condition it's in, and if it's the right size wires.

There must be something in the air. I ruined a batch of 20 mugs two weeks ago! @LeeU Cooking spray works great for keeping non-porous stamps from sticking. I had a batch of sprigs to do last year with very fine raised letters and detail in a plastic stamp, and after trying everything I could think of, cooking spray worked beautifully.

Today I threw the bodies and necks for some tall bottles. I really enjoy assembling these. The bodies are 3lbs of clay, 12" tall. The necks only require 1lb since they're so narrow. I'll lose about 3" to shrinkage, so the finished pots will be just under 18".

I'd use porcelain. The lower the absorption rate the better.

I shoot for 18 inches from flammable walls, 12 inches from concrete. Wood floors are okay if you put down two layers of cement board that extend at least a foot beyond the edge of the kiln. I once worked on a kiln at a school that was on a carpeted floor in their paper storage room. We had a nice discussion about not endangering the lives of hundreds of children. The worst part, though, was that the manual for their old kiln didn't say anything about what type of flooring the kiln should sit on. When I built my gas kiln at my last shop, the fire marshal and building inspector didn't care at all about the safety systems on my kiln burners, probably because it was a concrete free-standing building. What they did care about, however, was the venting system. They considered air quality to be much more of an issue than the flame, because it can hurt/kill you without you realizing it.

It's not that we are held accountable, we're just supposed to do our best to make things safe, based on the knowledge we have. We aren't expected to know everything, and the terms of use say to use the information on the forum at your own risk. We're just trying to make it less risky. @jbruce I still think this is a great project, and like I said before, it's even better because we are discussing the safety issues. Carry on!

Thank you. I've never used one of those, so I wasn't sure how it was powered. To clean up the box: 1. Replace the power cord with a 6ga 3 wire cord. You can reuse the plug, just get a new cord. I buy the SEOW cords from McMaster, about $35 for a 10ft length. They're super flexible and easy to work with. Use a cord grip, or just a simple clamping cable connector to hold the cord securely in the hole in the box. Use a snap-in plastic grommet to hold the TC wire, and another for the controller power supply. You'll have to figure out which sizes you need for each cable. They not only protect the cord from the sharp edge of the hole, but keep the cord from pulling out if you accidentally snag it. 2. You can go with the single leg SSR if you add in a mechanical main relay. Every kiln system I've seen uses a definite purpose contactor (DPST-NO) for the main. Because it is big and your controller has low voltage output, you'll need an intermediate relay (pilot relay) between the controller and contactor. So for the pilot relay you'll need something that has a coil that will work with your controller, either single or double pole. L&L uses their standard 25 amp 2 pole 12VDC coil relays for the pilot. In the Skutt KM-1 external controller, they use a small single pole relay and just run the power for the other side of the coil directly off the main power. I've attached a wiring diagram of the KM-1 which should give you a good idea of how you can do yours. Either way works. The contactor, then, will need a 240 volt coil. You'll have to set up your programming to turn the main relay on and keep it on when the kiln is firing, and off if there are any error situations, or at the end of the firing. The most important error would be to shut it down if the temp is climbing too quickly, which would indicate a stuck relay or TC issue. 3. Make sure you ground the box. 4. If this was my project, I would use a larger box so it's easy to work in, put in a terminal strip where the main power comes in, and distribute everything as needed from there. It'll make the wiring much simpler to deal with, and easier to see what's going on. Terminal connections are much easier and cleaner than wire nuts. I think we're all on the same page here. You've got the thing working, which was the hard part (congrats!), now it just needs cleanup and safety concerns addressed, which is mostly just busy work. It's a great project. @liambesaw I had a small test kiln last year that got really hot during firings. Because the kiln and box were only about 10 inches tall, there wasn't enough draft created in the box to keep it cool like it would in a taller kiln. The controller was getting very close to its max operating temp. So I installed a little computer fan in the bottom of the box, and it made a huge difference. I agree with @Bill Kielb that it would be good to avoid adding in more parts, but it will definitely work if it comes to that. I've also attached a pic of a Skutt with SSRs. You can see the big cooling fins on the box.

@jbruce Can you tell me how the controller is powered- is it running on 240VAC, low voltage DC, or is it powered by the computer connected to it? What is the output voltage for the relay?

I agree that this is a great thread. No denying that seeing someone build their own controller is very cool. But I do have a responsibility as a moderator to point out things that could be dangerous to others who would copy what's being done here (it's actually in the rules), and for the safety of the person posting. I don't know when a member isn't aware of the safety issues, or is just working through it fully aware that the final product will be done differently. Either way, I think it's good for things to be discussed, for the education and safety and knowledge of everyone involved. I don't think any of it diminishes the value and hard work of what's being done. In fact, I feel like to adds to the project, because it fleshes it out more. As I said before, I wasn't aware of the parallel feeder method, so I have learned something, too. So on that note, I have seen the charts for chassis wiring, and I don't think what you have there qualifies, because those cords are power wires, not chassis wires. Chassis wires are very short single wires connecting parts within the appliance, which are not bundled and therefore can dissipate heat well. What you've got there are power transmission wires, which require a much larger gauge and can be bundled. The chart that Liam posted is a good one to go by. If you look at all the wire gauges recommended by the kiln companies, they go with the 60C column because it doesn't hurt to be on the conservative side. The danger of using them as a parallel system is that if any of the wires in a bundle comes loose, the others will be overloaded and overheat. There are a lot of rules about how parallel systems must be installed because of that, and they're limited to use in very high amperage systems where it's impractical to use large single wires. It's a code thing, not a personal preference. The fact that they're not overheating means that they are, in fact, performing as a parallel system should, but that doesn't mean it's safe. The prototype Skutt SSR kiln I saw had a big heat baffle mounted to the front of the control box just like yours. And their control box was mounted on the kiln. So it seems you're definitely on the right track there. You don't necessarily have to have a fuse in the system, since it's under 50 amps. Once you get over 50 amps you have to have branch fusing in the system. It's another reason production kilns are more expensive than hobby kilns of the same size. More parts, more engineering. Definitely have a fuse on the controller path, but you don't have to have one on the power path. If you do decide to put one in, size it with the breaker. I would put in a mechanical safety relay to kill the whole system in the event of an SSR fusing 'on'.

That's how Nabertherm wires their kilns- one big main mechanical relay coming off the controller safety output, and SSRs cycling the elements. Most brands have not switched to SSRs because it's a more expensive setup than just using mechanical relays, and it would require a redesign of the control box layout to fit everything. That plus most customers don't care enough about it to justify the price increase. I know Skutt has a prototype out there somewhere, and L&L has considered making it an available option. I know they've used them on customs kilns before. Good thread.

I wasn't aware of this practice before now. After reading up on it, I know why- it's only allowed by code for wires over 1/0, which I've never dealt with. And even then there are a ton of rules. Some potential safety issues with that method.

I ran into a kiln like that once, where the previous repair guy had put a Bartlett controller on a Nabertherm and didn't do it right. I got a nice little shock when I tried to push an element in, even though the controller wasn't actually running. Luckily the teacher at the school had never gotten shocked. This is why two pole relays are used. Switching only one leg, the element won't heat up because the circuit loop isn't closed, but when you touch the element and ground it out you'll get hit. @jbruce I'm also worried about the extension cord wires. Those wires are only rated for 12-20 amps, depending on the size of the cord. How did you arrive at it being large enough for 4 times the 40 amps? And if the kiln pulls 40 amps, the wires should be rated for 50 amps, which means you should have 6 gauge wire in there.

Drill bits are less likely to crack the piece, since they remove material as they make the hole. Hole cutters force the clay to expand to make room for the wall thickness of the cutter. If the clay is too firm, or the hole is too close to an edge, it will crack. The biggest problem with all holes, and one that many, many people do not address, is the sharpness of the edge of the hole. Rubbing out the edge with a sponge or finger takes forever. The simplest solution I've learned is to use a countersink LIKE THIS ONE. Just twist it lightly in the hole once it's just past leather hard, and it will knock off the sharp edge. I use this on all my colanders, and I can do all the holes in a matter of a minute. It puts a nice little bevel that looks rounded once it's glazed.

Just so you have a point of comparison, I fired my E18T-3 yesterday, a fast bisque firing with a 4 hour preheat, and it averaged about 2,600 relay cycles per kiln section. These are typical mechanical relays. Because SSR's have a longer lifespan, it's okay to have them switch more, plus all that switching can increase element life. When relays switch less, the element has greater variation in temperature. That is, it heats up and cools down every time the relay turns it on and off. The longer the time period switched off, the greater the variation in the temperature of the element. As we know, metal expands and contracts as it heats and cools, and that movement decreases the life span of the element. By switching more often, the element can maintain a more constant temperature, which increases its life. So why don't all the manufacturers use SSR relays? Because they cost more, require an additional safety relay (even more cost), and most people don't care enough to justify the greater cost.

I've only ever heard reduction cooling to mean reducing during the actual cooling cycle, not heating slower. Yet another confusion bit of terminology in the ceramics world. So what would you call maintaining a reduction atmosphere during the cool down?

So that's different than firing in reduction. More like what we call reduction cooling. Firing like the Fallon would not reduce the clay body. No reason you couldn't use his system to reduce going up, though. In grad school I studied under John Neely, who is known for his exploration of reduction cooling techniques, both in gas and wood firings. In those firings the kiln would be fired up in reduction like a typical firing, then also cooled in reduction. In a typical firing, the surface of the clay reoxidizes during cooling, giving the toasty brown colors to stoneware bodies. In reduction cooling, the body can't re-oxidize, so the iron stays black. In bodies with around 4.5% iron, you can get a totally black surface. With short periods of air introduced during cooling it will flash bright orange, red, and yellows. Susan Harris does a lot of really nice reduction cooled work. https://www.artworkscedarcity.com/susan-harris-1

Google error codes for Skutt or L&L and you'll see that there are a ton of error codes that will shut the kiln down. Most are there so that the kiln doesn't try to keep firing when it's not able to, wasting time and electricity. The commonly seen is Error 1, which simply means the kiln isn't getting hot as fast as the program wants it to. Most of the others are variations of that, with slightly different parameters like whether or not it was during a ramp or cool or hold. Other important codes are if the kiln is hotter than it should be, or one section is hotter than it should be, which indicates a relay that is stuck in the 'on' position. Shutting down the firing with the controller won't stop the stuck relay, but it will shut down the other relays, which will usually prevent an overfiring situation. If you're using a single relay system in an external controller, though, it's not going to help, so second 'safety' or main power relay would be good.

When clay freezes and then thaws, the water will often migrate toward the outer edges of the block, so get a block that is sloppy wet on the outside and stiff on the inside. It just takes wedging to get it back to normal, but that's more work. Better to avoid the freezing in the first place if at all possible.