neilestrick

Not everyone wants to or is able to throw dinner plates on the wheel. I slab build my plates, and it is much faster than throwing and I don't have problems with humping in the middle.
@chris123 I think the issue is either with glaze tension as mentioned above, or it could be from uneven heating/cooling between the edges and the center or the top and bottom.
1. Does it happen with all of your glazes or just one?
2. What size kiln do you have, and what firing schedule are you using?

I'm afraid I kind of agree with BlueBird. If it has half dollar size holes in it due to corrosion, the rest of it is probably not structurally sound.
The non-pugmill option is to simply not wedge and not recycle. Most clay bodies are good to go for throwing right out of the bag.
I switched to slab building about a year ago after 30 years of throwing, due to bad arthritis in my hands. Gotta say I don't really miss throwing. I'm happy to still be working with clay, and the challenges and possibilities of working with new techniques have me more excited about ceramics than I have been in a long time.

There are other cost savings with firing to lower temps besides just the cost of electricity, big time if you're firing to cone 10 in the electric kiln.
- Extended element life. Firing just 04 will give you 2-3x the element life versus glazing at 5/6, double that vs cone 10.
- Longer kiln life
- Longer kiln furniture life
- Less energy removing excess heat from the studio (if you're running AC or fans)
Plus you can increase output with shorter firing schedules, and it's better for the planet.

So the metal rod is the stem? First you'll need to decide what size rod you're going to use. Then when you make the flower, make a short hollow stem at the bottom of the flower that the rod will slide into. Make it big enough to allow for shrinkage of the clay. Make the stem a couple inches deep, and thick enough to support the weight of the flower. Then after firing you can glue the rod into the pocket using marine epoxy.

I have seen freishly glazed pieces blow up in a raku kiln. Unlike a regular electric kiln firing, the kiln heats fast enough that the pots don't have a chance to dry out before steam happens. When I used to do raku workshops, newly glazed pots were set on top of the kiln to dry out before they went into the kiln. Once the kiln was heated up from the first firing, the bricks held enough heat that the kiln would rocket up to 800F within a minute as soon as the door was closed without even turning on the burners, so pots were set into the kiln with the door open for about 10 minutes to heat up slowly at first at get that last bit of moisture out of them. We also set the pots on cold pieces of soft brick so as not to shock the bottoms, pulling out the hot ones after each firing and replacing them with cold ones.

I usually fire my kilns at night so I don't really see what's happening with actual temps in the kiln, but today I started it up in the morning and was in the studio in the evening and got to see exactly what was happening during the cooling cycle. I do a slightly-slow cooling cycle to even out the results in my 3 kilns because they all cool at drastically different rates due to their sizes. I do a drop from the peak down to 2000F, then cool at 175F/hr down to 1500F. This gives me identical results from all 3 of my kilns. This firing I'm talking about here is in my 10 cubic foot L&L EQ2827-3, which has 3 zones, and was packed very tight in the middle. I was surprised at just how much slower the middle cools compared to the top and bottom. This photo shows how it's going part way through the initial drop from peak temp to 2000F:

As you can see, the middle and the top are nowhere close to each other. In a normal firing segment, a 73 degree difference would stop the firing with an error code. So why isn't it doing that here? It's because the cooling rate is set at 9999, or full speed. Any time you use 9999, whether it's climbing or dropping, the controller lets the kiln do its thing and doesn't care if the sections aren't even. Firing up or down at 9999 is the fastest, but you sacrifice evenness. As the temp continues to drop, we see this:

Here you can see that the top section (TC1) has started firing again. The set point for this segment was 2000F, at which point it should start cooling at 175F/hr, yet the top section passed that by about 20 degrees before the relay kicked on and the controller stopped the drop. Why did it let it get so far below the set point? Because it's averaging the 3 zones. Once the average of the 3 zones hits the set point it will start to fire each section again as needed to match the set point.
I get a lot of questions from customers about error codes and cooling cycles. The biggest problem is that the kiln can't always keep up with the programmed cooling rate. There are a number of firing schedules out there on the internet that people are trying that use a rate of 600F/hr or more for the fast drop portion of the cooling cycle, and many kilns simply cannot cool that fast, especially the middle section. When you have a specific rate programmed, the controller will send out an error code if the kiln can't keep up with that rate. So if you want a really fast drop you should use 9999F/hr, not a specific rate. For most people doing slow cooling with cone 6 work it won't matter if the sections are not totally even during the drop. If you do need more precision, like if you're firing crystalline work and it's important that you don't overshoot any target temps, then you'll want to put in a slower drop rate that the kiln can actually keep up with, and the controller will keep the sections even and not overshoot set points.

In my experience, self-supporting cones can stick to the shelf if you overfire them just a little. They’re not supposed to, but it happens! As @Bill Kielb said, if you kiln wash your shelves, this is not a problem. I do not kiln wash my shelves, so I have had to chisel off some stuck cone bits. 
My solution to this is to use cone plaques, the kind that have holes in one side for holding non-self-supporting cones at the correct angle. I use the underside that doesn’t have holes, put kiln wash on that surface, and place my self-supporting cones on them. Any small piece of old or broken kiln furniture will work too.
 

Tiny tips one may have never seen, read, or heard 'bout before.
Flexible metal rib, ideal (almost) for moving insects on the surface of water/glaze/liquid to outside the Studio.
Tiny spiders, gnats, et cetera land on the surface tension - timely removal can prevent a tiny insectoid blob (and the bug can live on!). The rib's edge, just on the surface, allows the bug to change footing without wetting, nor harming them. Step outside, blow the bug gently off the rib, onto a rock, plant, or somewhat. Note the tiny antennae nod of thanks.
Using actual real chamois leather chamois*?
Is it floppy - stretched out - slimy and soft? When next you pour hot water into your throwing bucket, note that your chamois, when exposed to hot water, will shrink and "tighten up" considerably! ...maybe too tight? Don't worry, it will loosen up after while...
It's not rainy today!

*We have an actual leather chamois that was a gift promotion from an auto parts store, decades ago.
I've been trimming strips off of it for pottery use over the last six+ years...

@Retxy How much of what we're seeing is rusted metal vs old clay? If it's all metal, then the metal is in really bad condition and I wouldn't touch it. If we're looking at a bunch of clay on the surface and the metal underneath is still decent then I think sandblasting is probably the best way to go. Do not put any sort of coatings on the auger or in the hopper. They won't survive. Just leave the interior raw. Paint the exterior if you want to.

So the metal rod is the stem? First you'll need to decide what size rod you're going to use. Then when you make the flower, make a short hollow stem at the bottom of the flower that the rod will slide into. Make it big enough to allow for shrinkage of the clay. Make the stem a couple inches deep, and thick enough to support the weight of the flower. Then after firing you can glue the rod into the pocket using marine epoxy.

L&L just recently changed their recommended first firing schedule from cone 5 to cone 04. Either will work fine.
Probably because they still have a bunch of cone 5's to use up. Use them when you do your first glaze firing.  I'll talk to them about getting some 04's instead.
Personally, I would do an empty glaze firing (just shelves) with the 5's because if your glaze firing is running hot or cold you can ruin a lot of work.

Luckily there are a ton of online resources to help people do their own kiln maintenance. It's a lot less daunting than before the internet. Most of the kiln manufacturers have good online videos showing how to test, diagnose, and repair kiln issues. It's a good time to be a kiln owner!

It's not just a knob. It's specific to the Sitter, as it has a piece on it that triggers the shutoff. Google 'kiln sitter timer knob' for sources.

It's not just a knob. It's specific to the Sitter, as it has a piece on it that triggers the shutoff. Google 'kiln sitter timer knob' for sources.

It's not just a knob. It's specific to the Sitter, as it has a piece on it that triggers the shutoff. Google 'kiln sitter timer knob' for sources.

Hi @mattb, and welcome to the forum. It would help if you could draw a picture of your plans. Here are some questions I have based on my understanding of the project:
You're making it a downdraft, correct?
What is the btu output of your burners? Powered burners or venturi? Natural gas or propane?
What are you using for a safety system on the burners- Baso valve?
Why do you want to run everything through the electronics bay? Seems like a lot of hassle to work in there, and you'll be restricting airflow for the burners.
How do  you plan to construct the chimney?
Use 16x16 shelves. It needs space to breathe.
You can rewire the control transformer to run the controller on 120V if you want to use the thermocouple. I'd put the thermocouple in a protection tube or it won't last long if you plan to fire in reduction.
You can put the flue opening between the burner ports. Make the flue opening equal to the total area of the burner ports. You can always damper it down.
The bottom shelf will need to be above the burner ports. Have a bag wall for each burner under the shelf. Target bricks can just be a brick leaning against the wall at the end of the firebox, or a brick set upright but turned at an angle to the burners about 2/3 of the way from the burner.

Bring the burner in along one wall, and have the flue opening centered on the opposite wall. Put a target brick about halfway in.

CFM of the blower will depend on the btu output needs, but for something small like this a little 50cfm squirrel cage blower would probably work. You'll want to have a rheostat on it to slow it down. The nice thing about a power burner is you can resize the gas orifice and get a really wide range of output without making any significant changes to the setup. If you really want to make it safe, put a solenoid on the gas line and connect to it a high limit shutoff, in addition to the Baso pilot system.

This is one of a pair of burners I built a long time ago for a gas kiln I  no longer have. About 450K btu each. Baso, solenoid, rheostat, high temp shutoff, timer. About as safe as I could make it with off-the-shelf parts and without getting into complex and expensive control systems. These can get pricey by the time you buy all the parts, but they work well and are quite safe. 
Ward Burner Systems is a good resource for burner info.

I've seen that kiln, which is why I don't think the electronics bay is suitable for the burners. It's probably too shallow to house the burners, and I don't know how you'll be able to get to them to make adjustments during the firing if they're enclosed. Plus you don't want anything to restrict air flow around the burners. I would cut out a big panel from the right side of the cabinet from kiln floor level to the top so you have a nice open space to work within. Make the chimney a full brick thick (4.5"), and put in a damper about 1/3 of the way up from the bottom.
Baso with a simple thermocouple and pilot light like an old school water heater will work well and be a cost-effective safety system.
Just thought- if you make a power burner (with a blower) you'd only need one, and it would also eliminate the need for a very tall chimney. The chimney height is the number one issue we see here on the forum when it comes to successfully firing converting kilns. Most of those use venturi (n/a) burners, which are cheap but require a good dose of secondary air to fire properly, which comes from a taller chimney. With a power burner the chimney doesn't need to be any taller than the top the kiln. Having the front wall of the controller cabinet would also allow for mounting a rheostat for the blower.
This kiln is a much better candidate for conversion than the majority of kilns we see here. It should work well.

Luckily there are a ton of online resources to help people do their own kiln maintenance. It's a lot less daunting than before the internet. Most of the kiln manufacturers have good online videos showing how to test, diagnose, and repair kiln issues. It's a good time to be a kiln owner!

Nestle 

So the metal rod is the stem? First you'll need to decide what size rod you're going to use. Then when you make the flower, make a short hollow stem at the bottom of the flower that the rod will slide into. Make it big enough to allow for shrinkage of the clay. Make the stem a couple inches deep, and thick enough to support the weight of the flower. Then after firing you can glue the rod into the pocket using marine epoxy.

I usually fire my kilns at night so I don't really see what's happening with actual temps in the kiln, but today I started it up in the morning and was in the studio in the evening and got to see exactly what was happening during the cooling cycle. I do a slightly-slow cooling cycle to even out the results in my 3 kilns because they all cool at drastically different rates due to their sizes. I do a drop from the peak down to 2000F, then cool at 175F/hr down to 1500F. This gives me identical results from all 3 of my kilns. This firing I'm talking about here is in my 10 cubic foot L&L EQ2827-3, which has 3 zones, and was packed very tight in the middle. I was surprised at just how much slower the middle cools compared to the top and bottom. This photo shows how it's going part way through the initial drop from peak temp to 2000F:

As you can see, the middle and the top are nowhere close to each other. In a normal firing segment, a 73 degree difference would stop the firing with an error code. So why isn't it doing that here? It's because the cooling rate is set at 9999, or full speed. Any time you use 9999, whether it's climbing or dropping, the controller lets the kiln do its thing and doesn't care if the sections aren't even. Firing up or down at 9999 is the fastest, but you sacrifice evenness. As the temp continues to drop, we see this:

Here you can see that the top section (TC1) has started firing again. The set point for this segment was 2000F, at which point it should start cooling at 175F/hr, yet the top section passed that by about 20 degrees before the relay kicked on and the controller stopped the drop. Why did it let it get so far below the set point? Because it's averaging the 3 zones. Once the average of the 3 zones hits the set point it will start to fire each section again as needed to match the set point.
I get a lot of questions from customers about error codes and cooling cycles. The biggest problem is that the kiln can't always keep up with the programmed cooling rate. There are a number of firing schedules out there on the internet that people are trying that use a rate of 600F/hr or more for the fast drop portion of the cooling cycle, and many kilns simply cannot cool that fast, especially the middle section. When you have a specific rate programmed, the controller will send out an error code if the kiln can't keep up with that rate. So if you want a really fast drop you should use 9999F/hr, not a specific rate. For most people doing slow cooling with cone 6 work it won't matter if the sections are not totally even during the drop. If you do need more precision, like if you're firing crystalline work and it's important that you don't overshoot any target temps, then you'll want to put in a slower drop rate that the kiln can actually keep up with, and the controller will keep the sections even and not overshoot set points.

Luckily there are a ton of online resources to help people do their own kiln maintenance. It's a lot less daunting than before the internet. Most of the kiln manufacturers have good online videos showing how to test, diagnose, and repair kiln issues. It's a good time to be a kiln owner!

Gas combustion made simple! At about 10:1 air / fuel you will get a nice blue efficient flame (natural gas, propane not so much), plenty of oxygen for efficient combustion. A nice blue base of the flame is a reasonable indication of an oxidizing fairly efficient flame so the answer to your question is basically yes it’s a decent indication enough primary air is coming in. . Venturi burners are sort of self calibrated within a pressure range of operation so the more gas pressure, the more primary air is sucked in by the Venturi effect. Your burners do not appear to have a primary air shutter and that is ok really. A nice blue color, devoid of yellow indicates you are operating within a reasonable efficient pressure  range for this burner.  
About 50%:of the air for combustion comes from the primary air and 50% secondary air. The secondary air enters around the burner or the hole in the bottom of the kiln where the burner penetrates.
when closing the damper there will be an absolute best position for a given gas pressure where you are losing the least amount of heat but still allowing enough secondary airflow through the kiln for all the gas to be burned efficiently. Close it more and flame efficiency drops, less secondary air comes in the holes around the burners.
Folks often set their gas pressure -  then find the point where performance begins to drop and open their dampers slightly more from there to get near that perfect balance. Every increase in pressure generally requires a slight opening of the damper so patience is key until you learn about where the damper needs to be for a given pressure for your kiln.
Your stuff seems to be working as designed, I would’ suggest testing with a damper first, it seems you are close ……. before making changes to the original design. Meaningful fine tuning  damper adjustments start about 1000 degrees btw.
There always seems to be a lot of confusion with combustion
Simple Bunsen burner pic below we use to teach primary and secondary air and a fuel air chart showing efficient mixtures you might find helpful.