Should I bother with this kiln?

[zhyla]

Would the amp draw be the same if I was only using 2 of the elements?

It will be different and dependant on how the coils are wired. I skimmed over the manual and didn't see a schematic. I would measure the resistance at that NEMA plug with the two switches in different configurations. With both on high you should get 240 V / 26 A = ~ 9 ohms. You should see higher resistance with other knob settings the amp draw will be 240 V divided by the resistance.

I'd be tempted to apply 120 V (= 13 A) to it and see how well that works. It may heat too slowly.

The control is a timer and this deal they call a kiln sitter. Basically it's a lever that triggers a mechanical switch. You place a cone inside holding the lever up and when the cone bends it shuts the breaker off. I can control the 4 elements with the 2 knobs. 2 elements per knob, top and bottom independently. So yes you can just use 2 elements. There is not a thermocoupler

Ok, you definitely need a PID, SSR, and thermocouple. The tricky thing is finding a thermocouple with a high enough temperature rating that isn't pricy. I think I paid $30 for a 1000C K-type but it took some searching. You might as well get an additional PID, SSR, and low-temp thermocouple to convert a toaster oven for tempering while you're at it. And Stacy is right, you'll want a fan and heat sink on the kiln's SSR, that thing is going to get hotter than the sun.

 

[Stacy E. Apelt - Bladesmith]

Stacy, why is it you don't want to open top loading kiln while hot? I mean obviously its hot and heat rises so you need to watch out for that, but is it bad for the kiln as well? The reason I ask is I've been doing that for the last 6 months ...you've not steered me wrong in the past so I'm thinking I should probably look at modifying the top.

Opening a large kiln while at 1500F is not something most folks would want to do. The uprush of very hot air can set your clothes on fire, set off fire alarms and sprinklers, and if you suck in a breath of the hot air it could do serious internal damage. Additionally, it is really rough on the coil life.

The multiple coils aren't a problem. If you want to, you could turn on only one control, but that may slow things down, may cause uneven heating, and make it take longer to bring the oven up to fully soaked. The kiln draws about 6Kw/Hr, so that is about $1.00 an hour to run it.

The control knobs marked HI/MED/LOW don't vary the current or anything like that. They just switch the power to the coils on and off. The difference between the settings is the ratio of on/off time periods.

The kiln sitter is a shut-off switch that you don't need or want. It needs to be bypassed so it is always on. Just move the wire from one side of the to the wire on the other and screw them down together.....problem solved.

Set the control knobs on HI and let the PID turn things on and off.

As for turning it on the side, you have the problem of conductive objects that can fall on the coils and short things out. Also, making a platform/floor with it on the side will cover part of the coils, which isn't a good idea. You could rip out, replace, and re-configure the coils, but that would be a lot of work. They work just fine upright with a few holes in the top. I have a friend who does long blades and swords, and his Paragon HT ovens are stackable and are all run vertically.

 

[Sandeggo]

So I did a bunch of googling and came across a thread on here that led to a build on another forum. Jason Wilder converted the exact same kiln as this to a heat treat oven running off of 110v. I plan to do the exact same thing as the logistics involved with accessing my 220 in my shop are definitely not ideal. What size chamber should I shoot for? I am hoping to find some stainless sheet that I will skin this with, if not I'll just use some carbon sheet and tig it all together. He talked about the conversion on BF but posted the pics on knife dogs. hope its ok to link to it. http://knifedogs.com/showthread.php?21258-Convert-your-pottery-kiln-into-a-heat-treat-oven.

 

[zhyla]

I like his toolbox electronics enclosure, very clever.

I prefer to do blades in batches of a few. You can groove the floor or another firebrick to hold blades edge up to get more into a given space. My cavity is 4.5" x 4.5" x 15". If I had built it twice as wide like his it might be a little more flexible. If I ever want to do a Chinese cleaver I'll have to somehow put it in there diagonally.

The length is the real limiting factor. I would make it longer than you think you need. A 24" cavity may come in handy some day. My 15" cavity gets is just long enough to do the 12" gyuto I'm working on today.

I've heard that once your coils get up to temperature you don't want to re-bend them into a new shape. So you'll want to get new coils. Make sure stretch them, I screwed that up.

 

[Sandeggo]

I decided to jump into this after considering many different avenues.

I got three of the elements out without issue. The fourth has a bunch of staples holding it in that I did not see, so I broke it a couple times.
Trying to decide on chamber size

I'm going to use a single element wired for 110v with a pid, ssr, and thermocouple.
What do you think about the chamber size? It's 14.75" deep 7.25" wide and 4.5" high

 

[zhyla]

That will get you a decent max length of 16", if that's enough then you're good to go.

 

[Stacy E. Apelt - Bladesmith]

I would consider that good for 12" blades. The problem I see is 110VAC. You really should go with 220VAC. That chamber is just too large for 110 to do the job well.

 

[Sandeggo]

I would consider that good for 12" blades. The problem I see is 110VAC. You really should go with 220VAC. That chamber is just too large for 110 to do the job well.

Single or dual element?

 

[Sandeggo]

I cut a top out of the old lid with a sawzall and got the front all sanded and flat. I'm gonna frame it all with angle and try to reuse the old stainless skin from the paragon.

Doing some reading and saw that most industrial ovens use 6000k per cubic foot. I am right at .27 cubic feet with this build. So that means I could use 1500-1600 watts to efficiently heat this?
Then I took my multimeter and read the ohms of the elements I pulled from the kiln. I got readings from 9-15 for the full length elements.
Calculating this all out
115A/9O= 12.77 amps
12.77x 115= 1469 watts. That's awful close to 1500 watts.
8 ohms gives me 1653 watts at 14amps
7 gives me 1889 at 16amps
Am I way off base?

 

[Stacy E. Apelt - Bladesmith]

You can run it on 110V, but 220 will perform better with less load on your wiring. I would shoot for 2500-3000 Watts drawing about 10-13 amps a leg on 220V. One coil or two is up to how the run is done. The total resistance will be the same.

I would also highly recommend you NOT using the old elements. The chances that they will fail very soon ( if not immediately) from removal and re-installation is nearly a guarantee. The coil diameter is going to be determined by the channel size in your bricks. A new element based on the length and resistance needed would be cheap and much better than trying to re-use the old ones. Use a piece of 1/4" rope to do a test fitting of you coil run and then measure the rope. That is the extended/stretched length of the coil. Use the desired wattage to calculate the resistance needed for the coil. Use the length and resistance to pick the right coil from one of the Kanthal element suppliers. Important - Remember that the extended length is usually about three to four times the coiled length.

 

[Sandeggo]

I've read all the advice on over building the controller. I plan to get a 40 amp ssr. Ok now another question, I'm looking at pid, ssr, and thermocouples on ebay. A lot of them have many different limits. One ad says it's 0-1800*C temperature range, then you scroll down to the bottom and it says that Detective temperature range is 0-400*C. Which do I need to pay attention to? Do the pid and ssr have temperature ranges or is it the thermocouple that determines the output?

 

[SunsetFisherman]

thermocouples have a specific range that they are very accurate at and then accuracy drops off as you get further away. So assuming detective range is talking about that more accurate range, that one works at 0-1800 but is only highly accurate around 0-400. You would want one that has your working/soaking temps within that detective range.

 

[Sandeggo]

Got further along on the oven, started the base and skin

Then threw an element in there and measured the ohms.

The bad news it that it's only 6 ohms.
At 220 it would be 36amps and 8066 watts
At 115 it would be 19amps and 2200 watts.
Neither will work. How do I up the ohms to get this usable?
The elements from the paragon are .060 so 16 ga

 

[Stacy E. Apelt - Bladesmith]

You use a different coil size. The wire diameter and the wire length determine the resistance. Start with the desired resistance and calculate the wire size/length. The simple way is to do what I suggested and purchase the right size coil new.

 

[Sandeggo]

You use a different coil size. The wire diameter and the wire length determine the resistance. Start with the desired resistance and calculate the wire size/length. The simple way is to do what I suggested and purchase the right size coil new.

Thank you for all the help Stacy. Now I am going to try and figure out element info.

 

[Stacy E. Apelt - Bladesmith]

Don't over-complicate things by trying to do too much math.

Start with the current/power desired...say, 10 amps at 220VAC = 2200 watts.
Determine the installed coil length by using a rope....say, 80".
80" expanded is about 20-25" tight coiled.
Look at the coil charts of available coils and get a 2000-2500W coil that is in the 20-25" length ( tight coiled).
Install it and your kiln will draw 10 amps at 220VAC.

 

[Sandeggo]

Don't over-complicate things by trying to do too much math.

Start with the current/power desired...say, 10 amps at 220VAC = 2200 watts.
Determine the installed coil length by using a rope....say, 80".
80" expanded is about 20-25" tight coiled.
Look at the coil charts of available coils and get a 2000-2500W coil that is in the 20-25" length ( tight coiled).
Install it and your kiln will draw 10 amps at 220VAC.

Thanks for dumbing that down for me. I'm anxious to finish this thing up because this is how it sits right now.. Not too bad for a $24 kiln so far. I'm going to get some kaowool to use on the door and the lid as a sealer.

Don't worry about the door falling when I undo the vice grips, I welded one of the hinges a little cattywhompus so the door doesn't move on it's own

Well I just ran some paracord in there and whattayaknow 80" just as you guessed

 

[zhyla]

I've read all the advice on over building the controller. I plan to get a 40 amp ssr. Ok now another question, I'm looking at pid, ssr, and thermocouples on ebay. A lot of them have many different limits. One ad says it's 0-1800*C temperature range, then you scroll down to the bottom and it says that Detective temperature range is 0-400*C. Which do I need to pay attention to? Do the pid and ssr have temperature ranges or is it the thermocouple that determines the output?

The thermocouple will have an upper limit, and that obviously has to bee high enough to withstand the temperatures you want to harden at. The random Chinese PID controllers don't seem to say a whole lot. The one I have says it's good to "9999", but it actually wouldn't go past 1400 F without changing it to Celsius. But it did work so here are the Amazon titles for what am using:

"IMAGE® 25A SSR-25DA Solid State Relay with Heat Sink+ Manual/ Auto-tuning PID Temperature Controller SNR"

"K-Type Wire Thermocouple PK-1000 Temperature Sensor Probe w. High Temperature Fiber Insulation 1832F or 1000C"

If you have any inkling at doing stainless, D2, A2, etc you may want to invest in a higher temp thermocouple. Also that PID can use many thermocouple types. I went with a K-type because it seemed the most common but it was hard to find a K-type over 800C.

I'm going to get some kaowool to use on the door and the lid as a sealer.

It may not be needed. There's a healthy 1/8" door gap on mine and no heat comes out of it. Plus you can gaze at the 1500 F glow .

It was pointed out in my oven build thread that I didn't have a door safety. You might want to consider it, especially if you are absent minded. The original kiln might have had one?

 

[Sandeggo]

The thermocouple will have an upper limit, and that obviously has to bee high enough to withstand the temperatures you want to harden at. The random Chinese PID controllers don't seem to say a whole lot. The one I have says it's good to "9999", but it actually wouldn't go past 1400 F without changing it to Celsius. But it did work so here are the Amazon titles for what am using:

"IMAGE® 25A SSR-25DA Solid State Relay with Heat Sink+ Manual/ Auto-tuning PID Temperature Controller SNR"

"K-Type Wire Thermocouple PK-1000 Temperature Sensor Probe w. High Temperature Fiber Insulation 1832F or 1000C"

If you have any inkling at doing stainless, D2, A2, etc you may want to invest in a higher temp thermocouple. Also that PID can use many thermocouple types. I went with a K-type because it seemed the most common but it was hard to find a K-type over 800C.



It may not be needed. There's a healthy 1/8" door gap on mine and no heat comes out of it. Plus you can gaze at the 1500 F glow .

It was pointed out in my oven build thread that I didn't have a door safety. You might want to consider it, especially if you are absent minded. The original kiln might have had one?

I'm reading everything I can right now. I just ordered a 2000w element that was 25" long, it didn't state the ohms in the ad, but it was 6$. We will see when it gets here. I dug through some older threads and it seems people double up the ssr's for 220, so I plan to order 2- 25 amp ssr's. I'll add a door switch to the list.