I think there's a limit to the skill level that you will be able to get from your workers. If I were a fast thrower, with good skills, why would I put in that type of effort into make someone else's pots? like John said, maybe for a year or two to pay the bills right out of school, but I would much rather be putting the effort into making and selling my own work. So you're either going to have a lower production rate than you want, or have to be training new people quite often.
To keep labor costs down, I would look into forming methods that require less skilled labor, like jiggering, casting, etc. New people can be easily trained on how to run the machines. Get away from the idea that things need to be made the way you made them when you were producing alone. You can't expect others to produce at the same rate you did, nor can you expect them to have the same passion about what they're making that you do. The vast majority of very skilled potters I know are not necessarily the fastest throwers. But they demand good prices for their work, so it all works out for them.
Seriously look at getting bigger kilns. Loading and unloading kilns takes a lot of time.
The kiln sitter is a mechanical device, and therefore has the possibility of not working. If any parts of the sitter stick, then it won't shut off. That's why they started putting backup timers on the sitters. Of course, if you set the timer too long then it doesn't do any good, and it's also possible for the timer to fail since it is a mechanical part as well. The only way to be 100% sure that a sitter kiln shuts of properly is to be there in person to check it. If you're not willing to do that then you have to accept that at some point your sitter will possibly fail and you will ruin some pots and/or the kiln itself.
The worst I have ever seen was a firing where a post or pot fell over onto the sitter tube and prevented the sensing rod from dropping and shutting off the kiln. It was an old sitter and didn't have a backup timer, so it kept on firing until the pots melted, then kept on firing some more until the shelves warped like potato chips and collapsed into a pile at the bottom of the kiln. The kiln was destroyed. The whole bottom half of the kiln was a melted mass of shelves and pots fused to the wall bricks. Luckily it was a really old kiln that needed to be replaced anyway.
For a digital kiln to over fire, a relay has to stick in the 'on' position, and the kiln has to be packed in such a way that enough heat is trapped in the section controlled by that relay that it can over fire. A section probably can't over fire in a cone 6 firing, but it is theoretically possible that in an earthenware firing a section of the kiln could over fire a little bit. In a two section (18" high) kiln where there are only two relays, one sticky relay can cause the entire kiln to over fire a little. I've seen that happen. I have never seen more than one relay stick 'on' at a time, however I have seen two relays fail 'off' at one time. Again, the only way to be sure is to be there to check that it has shut off.
I was thinking it should be possible to do cone 04 soda with the addition of other fluxes to the bomb, shouldn't it? I've seen mentions, but does anyone else have a line on a good resource? Could be really nice with the use of terra sig.
Low fire salt does not produce the glazed surface that it does at higher temperatures. It can give some great colors, though, similar to pit firing. Lots of reds and yellow and oranges. I used to do pit firings with wood shavings soaked in salt water (then dried), and got some fabulous results.
Didn't I read somewhere here someone recommending using , rubber bands? or ???? around the pins if the bat holes are worn? I have a bat system, with a square for smaller inserts to go in and the holes on the base have worn. so I'm interested in this.
If you put the second dip on while the pot is still saturated from the first dip, it is likely to crawl. The first dip should not be totally dry, but dry enough that the pot can take in the water of the second dip without ruining the grip of the first dip on the clay.
That raspberry recipe likes to crawl. It needs to be on kinda thick to get good color, but that thickness tends to cause crawling with some glazes.
That's cracking, not exploding in that photo. Exploding is hundreds of little pieces, shards in the element grooves, a total mess. It's really, really, really hard to blow up pots in an electric kiln that have already been bisque fired. They have to be fairly moist and fired really fast. The only time I have seen it happen is in raku firings where pieces weren't quite dry after glazing.
What's your firing schedule? I'm thinking that either the second firing is too fast either heating or cooling. Try slowing it down and see what happens.
It is definitely possible for the glaze to crack the pot, especially if it was only glazed on one side (inside or outside), or if the glaze is very thick on one side (in or out) compared to the other. Differences in COE between the clay and glaze can also cause cracking.
Here's another recent thread that has had a lot of discussion on this subject:
When I was trying to figure out pitcher spouts way back when, I threw 6 pitcher necks (about 4 inches tall) and pulled 4 spouts out of each one. By the time I got to 20 I had it figured out pretty well. Then I wedged all that up and threw some actual pitchers.