View Full Version : Kiln converted to HT oven

LR Adkins
05-07-2010, 11:34 AM
I apologize for not getting this up sooner. It seems several people are building HT ovens right now and could benefit from any info they can get. I said I would show how I did this awhile back but it has been slow going. The wife has kept me busy landscaping our new house. Planting the garden has taken forever. Yada, Yada , yada, anyway I haven't had much time to devote to the shop.:mad:

Ok, I started with and old kiln I had laying around for years. I played around with it for awhile trying to figure out a way to use it without tearing it apart. I turned it on it's side and it collapsed dumping the firebrick on the floor breaking several bricks and both heating coils. Project over!! Not really, I had another larger kiln waiting to come to the rescue.

I carefully disassembled the kiln, starting with the lid first to get it out of the way so I could get to the heating coils. The heating coils had been used one time since being replaced in this kiln so I wanted to use them instead of spending money on new ones.

Heating coils are a pain to remove without breaking them. You have to heat them and remove them while they are hot because they get very brittle after they have been red hot, just like a knife blade after heat treating.

I removed the control box from the kiln so I could get to the wires to disconnect them. Where the heating coils come through the wall of the kiln they are twisted around the bolts they are connected to. They have to be straightened before you can pull them through the kiln wall. I used a small propane torch to heat the bent end of the heating coils and while they were red hot I straightened them. Next I went to the inside of the kiln and heated about the first foot long section of the coil and while it was hot I gently pulled it through the hole and gently removed the 1 foot section I heated from the groove in the firebrick. Again I heated about a foot of coil and gently removed the coil from the groove in the firebrick. I continued to do this until the heating coil was removed from the grooves in the firebrick.I didn't get many pictures of this because I was too busy playing with hot stuff.

First pics is showing where I started on the outside with the end of the heating coil. Second pics shows what happens if you don't heat the coils. I broke one.

LR Adkins
05-07-2010, 11:49 AM
After I got the heating coils removed and set aside in a safe place I could remove the bricks. Next I checked everything out to see what I could use. I decided to use
the stainless steel shell
some of the wiring
the control box
small bolts and screws
the porcelain insulators where the coils go through the wall
the heating coils
the firebrick
Here's a picture of the small stuff I decided to use.

LR Adkins
05-07-2010, 01:08 PM
Now that I had an idea what I needed I ordered these parts.
From Auber Instruments:
1/16 DIN PID temperature controller
25 amp SSR
K type high temperature thermo coupler

from the hardware store:
20 amp fuse and fuse holder
1 amp fuse and holder
I also ordered some Kastolite refractory cement to fill some of the grooves in the firebricks.

The kiln I used was round and I am building a square HT oven so I had to square the ends of the firebricks. After squaring the bricks, their dimension was 4 1/2" wide, 2 1/2 thick and 7" long. I wanted the inside of my oven to be 14" deep. I figured that would cover about any knife I would want to make. The inside width ended up 7 1/2". I stacked the bricks in the configuration I wanted so I could get the outside dimensions for my frame. I stacked two 7" bricks and two 5 inch bricks for the back. Then I added the sides two 7" bricks deep and two 7" bricks high. That made my inside 14" deep by 7 1/2 wide by 9" high. The outside ( adding 2 1/2" for the bottom and 2 1/2" for the top ) is approximately 14" high by 12 1/2" wide by 16 1/2" long.
I used my bandsaw with an old blade to cut the bricks, they are very soft. It made a gritty mess of my saw and was a bear to clean it up. The rest of the trimming I did with a hand saw.

LR Adkins
05-07-2010, 01:47 PM
I used the top and bottom from the kiln for the top and bottom of my oven because they were solid pieces and easier to use than loose brick.

I made a angle iron frame to hold the bricks together allowing a little extra for the thin SS shell I scrounged from the kiln. I welded a angle iron bracket on the bottom right side of the frame to mount the control box. I made it long enough to keep the control box 4" away from the oven to keep the control box from absorbing so much heat from the oven.

The grooves were already in my bricks from the oven so I didn't have to deal with that but I did have to cut round grooves from one groove to the other so the coils didn't have sharp bends. also I cut slanted grooves in the back bricks so the coils could transition from one groove to the other. Not sure how to explain it but you will see later when I show the coils installed.

LR Adkins
05-07-2010, 01:51 PM
I'll add more later, I have to throw some steaks on the barbie.


05-07-2010, 03:12 PM
I have a question on the K type high temperature thermo coupler I read on another link where some folks place this inside a ss tube to help protect it do you see any harm in this also where are you going to place it in the kiln?

LR Adkins
05-08-2010, 08:18 AM
Doug, the SS tube is probably a good idea, just make sure the end of the TC sticks out of the SS tube about an inch so it can read the true temperature in the oven.

I placed my TC just above center coming in from the back. It needs to be high enough that your knife rack doesn't hit it or touch it when you take your knives out.


LR Adkins
05-08-2010, 09:41 AM
where was I?

Hmmm, my computer is being stubborn this morning, it doesn't want to give up my pictures. Maybe it's me, I'm plump dumb when it comes to electronic gadgets.

Ok, I'll try to get this going. I have my frame made and my firebricks cut to size, and the grooves cut that I had to add to the bricks. Now it's time to assemble everything and see what kind of monster I have created.

Assembly was much tougher than I imagined. I was a little sloppy with my measurements and cuts so I had to trim a little here and there to get the bricks and the SS sheet metal to fit inside the frame. I should have used a bigger hammer. :D
I mixed up some refractory cement and filled all the gaps and the grooves that weren't needed. Then I went to the back of the oven and drilled the holes for the heating coil connections. The stainless steel sheet metal I used to cover my oven came from the old kiln and it already had holes in it for the connections to the heating coils and the thermo coupler so I made sure this section went on the back of the oven. That way I didn't have to drill large holes in the SS. Next, from the back, I drilled 1/4" holes through the bricks from the center of the holes in the SS to the center of the grooves inside the oven. I can't seem to get my head wrapped around this project this morning, I hope I'm explaining things well enough.
I drilled the hole for the TC at this time too being careful not to drill into one of the grooves for the heating coils. I don't remember what size hole this was but you can measure your TC and decide on what size hole you need.

Next I installed the control box on it's bracket and it will be ready for wiring the oven. I haven't wired the oven yet so I will add that later. Same thing with the door, I haven't had a chance to get that done so I will get on that today. I'm sorry I didn't get enough pictures of this project to make everything real clear. I would get so wrapped up in what I was doing and forget to take pictures. Here's what I have.

LR Adkins
05-24-2010, 08:21 AM
I apologize for not getting this finished. Haven't been to the shop in a while. Both my legs have taken a crap on me ( old war injury ) and I'm pretty much house bound. The pain killers keep me pretty fuzzy so I won't touch power tools, I hurt myself enough when my head is straight. Hope to get back at it soon.


LR Adkins
07-04-2010, 09:01 PM
Well I finally got the HT oven finished. My buddy came over and wired it for me and I finished buttoning it up Sat. I copied the operating instructions from Aubers Instruments and now I'm trying to figure out how to operate the oven. I still have to get a dedicated 220 line set up for it.

I have about 20 fire bricks left over from the kiln if any one is interested. they have the grooves already cut into them. I have 3 final pics of the oven and I'm finished with this project.

If any one has any questions I'll do my best to answer them.


07-05-2010, 07:39 PM
Larry that looks great let us know when you get it fired up. I ordered the same controls so I would like to here how well they preform. All my stuff is still in box's I just can't seem to stay away from the high lakes the trout keep calling me back.

Stacy Apelt
07-09-2010, 08:51 PM
The only thing I see missing is a heat sink for the SSR and maybe a cooling fan blowing through it. I also would put some sort of cover over the SSR and all that exposed 220VAC wiring.

LR Adkins
07-11-2010, 01:40 PM
The only thing I see missing is a heat sink for the SSR and maybe a cooling fan blowing through it. I also would put some sort of cover over the SSR and all that exposed 220VAC wiring.

I was considering a heat sink and a fan to help keep the SSR cooler and last longer. The SSR has a clear plastic cover and I have a cover for the back of the HT oven, just left it off for the picture. Also have a bracket to install to keep the wires further away from the oven. I have a pacemaker and am very careful around electricity.:D
Thanks for the advice though, Stacey


LR Adkins
07-11-2010, 01:53 PM
Larry that looks great let us know when you get it fired up. I ordered the same controls so I would like to here how well they preform. All my stuff is still in box's I just can't seem to stay away from the high lakes the trout keep calling me back.

Hey Doug ya just gotta take time for fishin' :D
It may be a while until I get the oven fired I just lost $1200 per month income and still have to get the new line ran for the oven. If the oven is built tight, it will work fine. Build it.