Picture/diary of my modifications to my electric (Skutt 1027)
kiln
Introduction (Last modified: 7 Jan 02):
For a long time, I was disappointed with my electric kiln's efficiency
and it's tendency to let the kiln temperature drop like a stone
causing poor glazes and dunting cracks. It took me a long time to get
the courage to modify the kiln, but once I took the plunge it was
incredibly satisfying. The modifications for me cost about $120 all
told and took 2 afternoons, one of three hours for the kiln lid, and
one of about 2 and a half hours (with a trip to the hardware store)
for the actual kiln modification. It's easy to see that the entire
thing can be done in a single day by a determined person. I have to
add that this is how I did it. This is not the
way to do it, if there is one, and following these steps will not
guarantee success. Don't sue me.
I've tried to build this page quickly (so it's not pretty) but also as
complete and easy to understand as possible. I'd recommend everyone
read through the page completely before attempting to modify their
kiln, and then read along while doing it. I'll try to cut out as much
wordiness as possible.
If you're looking only for the pictures, they
are cataloged also on a seperate
page. There aren't as many as I thought, but if you
should want a picture of a specific thing, email me and I'll try to
post it.
If anyone has questions or concernes, feel free to email me at
jwpennin (at) bellsouth.net, or ask on Clayart. Good luck with your
mods.
-Jonathan Pennington
Table of Contents
Tools and supplies needed
First let's talk about tools and supplies. Part of the reason that my
modifications were so cheap was that I relied mostly on used and cheap
materials. I'll include the list of materials, as well as the tools I
found necessary so that you can try to limit runs to the store and
stalls in work.
Tools:
- Screwdrivers: Phillips and straight (for removing hardware and
banding straps)
- Tin Snips: These are needed for cutting sheet metal.
- Bandage shears: I have the real heavy ones that'll cut
metal. Anything will do that you feel comfortable cutting kaowool
with.
- Pliers: For holding hose clamps while tightening.
- Duct Tape: Just because it's always nice to have around, even
if you don't use it :-)
- Twine: For holding bricks and for holding kaowool onto the kiln.
- Saw: For cutting firebrick to make second top.
- Drill: with a very thin bit, enough to put a small hole into the
steel jacket to start a screw.
Supplies:
- IFB: For making the second kiln lid, if you want to. I estimate
about 30-35 bricks for the second top, although I used scraps and
broken bricks, all second hand.
- Firebrick: This is probably not desired by most, but I used some
to make a wall around my kiln, about 4 inches away, because it's
outside (under a house on piers). This keeps a bit more heat in during
cold weather.
- Sheet metal: You'll need enough to go around the lid and as an
extension for the kiln's jacket. Because I use my lid atop the
original lid, I used flashing for that. For the kiln jacket extension,
I used a single section of 4 inch drier vent, it's cheap, and I had
some at hand. (Note: I don't know how this will hold up in the long
term, but it's doing fine so far, and easy enough to change).
- Hose Clamps: I used 12 6 inch (they are sold by the inch here) clamps for the kiln lid (two sets of
straps to go around and 6 per strap) and 6 for the back of the kiln
jacket. I'm sure there are other ways to do this on the lid, longer
hose clamps, banding straps, etc.
- Kaowool blanket: I used the next size up from 1in thickness (it
too is sold in not-metric thicknesses here), only
because that's what they had. Measure the outside of your kiln, then
get a couple feet more.
- Guts: Yeah, you'll need a large supply of these. I can't express
how scared I was to start cutting into my expensive kiln with tin
snips, knowing that Skutt would laugh at me if I called them in panic :-)
Modifying the kiln
Remove Hardware
In order to prepare your kiln, you will first need to remove
all the harware from it. Remove everything, the latches,
handles, lid hinge, controller or sitter. All of these screws actually
screw into the soft brick, so you'll need them out to move the
steel. See the picture.
If you want to place thin strips of kaowool between the sections of
the kiln (My kiln sections were pretty open), do it before you remove
the hardware. It's easier lifting the kiln sections with the handles
attached, and once the jackets off this step is nearly impossible to
do easily.
After removing the hardware, you should look at the elements and
thermocouple area (remove the thermocouple too). There should be a
second piece of sheet metal about 2-3 cm away from the jacket. It's
there to hold the thermocouple and (I imagine) the ceramic parts of
the elements. There is a picture of
the sheet metal cut to remove it from the elements, and a picture of the top sheet metal
removed, but the bottom piece still present. There is also a picture of the element wires without
the sheet metal.
My Skutt kiln's elements are permanantly attached to the wires. In
order to slide that extra sheet metal out, I would have to remove the
wires from the elements, which would involve cutting them- I'd then be
forced to install new elements. Instead of doing this, I used tin
snips (Heavy sissors for cutting sheet metal) to cut the small piece
of sheet metal away from the elements. Be careful! You do not
want to accidently (as I almost did) cut an element wire, and you want
only to cut the small piece of sheet metal, not the jacket.
After you remove the sheet metal extension, you should have only the
metal jacket and the element wires on the outside of your kiln. Find
some things that are about the same height as the various sections of
the kiln, two per section. You are doing this because you still cannot
remove the sheet metal jacket completely away from the kiln (due to
the elements), so when you loosen the clamps at the back of the
jacket, you will be essentially opening up the kilns jacket. By having
something the same height as the sections, you can rest the steel for
each section on it, away from the kiln, and not have it hanging down
and putting stress on the element wire. It sounds a bit complicated,
but when you do it you will see exactly what I mean. Now open the
kiln jacket and see your kiln in all it's naked beauty.
Ahh! Wait! Watchout!!!
That's just what I said. Don't make the stupid mistake I did and
assume the kiln company mortared those bricks together. The jacket to
the kiln is the only thing holding them together. I found that they
are still pretty stable (I was rather rough with my kaowool), but at
one point I actually leaned against the kiln and the entire top row of
bricks shifted out of alignment. Be careful, don't jar things
unnecessarily. It's easy enough to put them back in place, but I
cracked two bricks by being clumsy.
At this point, you can install the kaowool blanket (fiberboard,
pepperoni pizza, whatever you're using). The hardest part is figuring
out how to get the area around the elements sealed well. The steel
jacket is about an inch away from the kiln wall in this area, and the
elements are permanantly mounted, and staggered. I decided to make
this the seam of my blanket, since it's going to be broken anyway.
To fit the wool snuggly into the seam, I took some heavy bandage
shears and cut into the kaowool so that I could then slide the kaowool
into the elements. (I couldn't take a picture of this, so I'll try to
explain.) The elements are spaced about every 4-5 cm, so if you make
cuts into the end of your kaowool about every 4-5 cm you should be
okay.
If you want to get closer, I found that sliding the blanket in
between the jacket and kiln wall, as if you were installing it, then
pushing hard against the element wires will actually dent the end of
the kaowool enough that you can pull it out and cut it right where the
elements hit it. Because the elements are staggered, you'll only cut
spaces for every other one this way. You can either cut in between
them for the other elements (leaving the other end of the kaowool
blanket uncut) or do the same thing with the other side of the blanket
and have the seem of the blanket in between the elements. I choose the
latter, and I've made a drawing of
what I'm talking about showing the elements and the kaowool. The cuts
I made are drawn in red. This puts the seam of the blanket in between
the elements. You'll have gaps in there, I filled them with strips of
kaowool packed in. The nice thing about this step is that the steel
piece that you removed earlier is about the same thickness as the
kaowool. This means that when you slide that blanket into the
elements, the ceramic tab on the element sits near perfectly on the
surface of the kaowool, and the thermocouple is the same distance from
the kiln wall as before. I thought that was serendipidously sweet!
For most of these steps, if you don't have someone helping you (I
didn't), you will have to find ingenious ways of getting the kaowool
to stay against the kiln without falling out. It was a bear, but I can
give you some tips. Don't use the duct tape! The tape will only stick
to the outside surface of the blanket. The blanket is made of fibers
that are essentially tangled together. The blanket will still fall and
you will be left with a piece of duct tape with kaowool stuck to
it. You can try to tie the blanket on with twine- I thought of this
after the fact, so don't know if it works easily. Tie the kaowool to
the kiln by wrapping the twine around the bottom, then make your cuts
into the top and slide them into the elements. Then tie the very top
to hold that section in place, remove the twine from the bottom and
make the cuts there. It seems like this would work alright. If you are
one person you can also (as I did) cut the blanket in half and have a
seem at the elements and one in back. It might make it easier to
handle half the kaowool at a time. I did this without thinking about
the twine method though- I'd choose tying it before cutting it.
As for the orientation of the blanket with respect to the kiln wall, I
placed my blanket so that was more or less even with the top of the
kiln. There will be a good bit of extra at the bottom, but I just cut
that off (I think I have just enough left over to build a small raku
kiln).
Leave the twine holding the kaowool a while while you build your
sheet metal extension and re-wrap the kiln. For the extension, I used
a 4 inch drier vent pipe. Another thing sold by the inch here- did you
know the US Congress officially switch the US measurment system to
metric somewhere around 1900? In 2001 I still have to by drier vent by
the inch, ridiculous! At least it's cheap.
Take the drier vent and open it up by pulling it, stepping on it,
yelling at it, whatever. You're looking for a fairly flat piece of
metal. The ridged part at the bottom will prevent it from opening up
fully, you're going to cut this off eventually, so do it now if you
want, you can also measure the height of your kiln and cut the piece
to size now, otherwise you'll have to cut it with tin snips while it's
on the kiln.
Now you're ready to rewrap the kiln. Take your hose clamps and attach
them to one end of the jacket, place your sheet metal extension into
the space and loosly screw the hose clamps into the other side just
enough to hold them from falling.
The problem with this method is that placing the kaowool between the
jacket and kiln wall makes the jacket larger and screws up the
alignment with the element holes and peep holes. I decided that proper
alignment with the elements and thermocouple was paramount. While the
jacket is still loose, shift it so that the elements are sitting fixed
in the holes of the sheet metal, and not pulled to one side or
another. Then tighten the clamps enough to hold the blanket in place.
I think this tightening is important. It seems to me that some of the
insulation benefit of the kaowool comes from trapped air in the
blanket, so you don't want to tighten this in a death grip or you will
compress the blanket. I took a philosophy from my Aikido instructor
and tightened it like I would hold a bird- just tight enough so it
wouldn't get away, loose enough that I won't kill it. There is a
bad picture and a good picture of the extension
and hose clamps. It's close to a wall, so getting a good picture was
hard. There is also a rather blurry picture of the kiln with the
kaowool installed.
Thermocouple reinstallation
Now that the kaowool is installed and the jacket's in place, you'll
want to clean things up a bit. Let's start with the elements area. The
first thing you'll do here is reinstall the thermocouple. The way I
did this is pretty simple, and keeps a bit more insulation. Take the
thermocouple and insert it into the original hole inside the kiln,
then hold your hand against the kaowool around the original
thermocouple hole and push the probe through the blanket. It'll take a
bit of a push, but the probe should pierce the blanket nearly in the
center of the original hole for the probe. Now take the probe out of
the kiln and stick in the proper side of the blanket, as if you were
installing it correctly. Looking into the kiln, the probe should
extend just about as far as it originally did. Now mark and drill tiny
holes in the sheet metal for the probe housing, then screw the housing
to the sheet metal. No, mounting the probe against the sheet metal is
not as stable as driving screws into the bricks, but you don't need it
that stable.
I don't know anything about how the kilnsitters work, but for those
who have the kiln-mounted controllers, you will not be able to
re-mount the controller on the kiln. I originally mounted mine onto a
wooden stand next to the kiln, with holes in the rear for the element
wires. I'm changing that now and will eventually mount it another
way. right now, it is resting on firebricks right next to the
kiln. You should be fine as long as things don't get in there and
short the lines.
Peepholes
If you want all of your peepholes back, you'll have to cut the kaowool
away from them. However, because of the new orientation of the sheet
metal, the holes in the metal do not quite match up with the holes in
the kiln wall. You can deal with this as you like. I cut a bit away
from the sheet metal of the top peephole and left the bottom ones
alone for now.
You took both the handle and the hinge off the lid, so at this point
you'll need to decide how you want to handle your kiln lid. Right now,
I'm lifting mine by hand, but that's not going to last. I'm thinking
about building a rigging into the sides somehow that will allow me to
create a block and tackle like system in the ceiling. The problem with
this is that in the tiny crack that exists between the upper (new) and
lower (factory) lid, I can see red while the kiln is firing, which
means that the entire factory lid is red hot. I'm worried about
putting anything into that lower kiln lid because it may fail. The
upper kiln lid is pretty cool though, I can rest my hand on it
comfortably when the kiln is as 1206 deg C. That's a pretty nice
feeling!
One potential problem, especially with the
second lid, is that the envirovent has to have
holes in the top. Unfortunately (or perhaps, fortunately) my kiln top
doesn't seal perfectly. I can look when the kiln is at temp and see a
small gap between the kiln wall and the kiln lid. For this reason, I
just set the second lid atop the first and didn't worry about covering
the holes in the kiln lid because there's plenty of ventilation. I've
considered trying to change this, but am not sure quite what to do.
I'm in coastal South Carolina right near the salt water marsh. Our
house is on a flood zone, and therefore on piers. My kiln is in under
our house, which to us is a basement, but to most other people is on
the ground floor and outside. In this picture of the kiln without the
hardware, you can see 2cm wood slats in the background with about a
2cm seperation between each. That's sunlight reflecting in the
background. The kiln is essentially outside, and I wanted an
additional level of protection from the cold wind that sometimes
steals more heat from my kiln. I decided to build something of a
portable kiln room.
I took a bunch of old firebrick that I
bought used for $.10/ea and built a wall around the kiln, about 4-5 cm
away from the jacket. This provides a second barrier against the cold,
but allows the heat to escape before becoming a danger to the jacket
and element wires. Even when it was below freezing on the outside of
those bricks, it was over a hundred degrees in between the bricks and
the jacket. I don't know what that translates to in dollars and
kilowatts, but every little bit helps. It's loose and laid dry
now. soon I'll mortar it. I'll mortar it in sections, so I can move it
if I need to, but it's a bit more stable and effecient. There's a picture of the kiln with the wall and the
controller.
This section is for adding stuff that I should think of later, or
stuff that people email me about.
- Here's a picture of what
happens to the kiln when you wrap the kaowool, however loosely, around
the outside of the kiln jacket. That dull gray mess at the top
is what happenend to the kiln lid holder. It melted down and across
the kiln!
Making a second kiln lid
This is a much easier accomplishment than the modification of the kiln
itself. It is also something that many people will want to do
differently. However, in the interest of completeness, I'll describe
it shortly.
I used many used IFB that I bought for $.25/ea. I laid them on their
sides and approximated the size and shape of the original kiln
lid. Then I placed them onto a piece of 3/4in plywood in the correct
orientation, set the factory lid on top of them, and used that as a
guide to cut the bricks to the same shape.
After this, I removed the original lid, took pieces of metal flashing
and cut them to go around the lid, then tied this all together with a
piece of twine to hold it in place. Then I took the hose clamps, it
took 6 to go around, and put them together, then put them on the lid
and tightened as much as I could.
That's it. It's laid dry and held by compression. I poured some kiln
cement over the top as a sealant, but I don't think it worked very
well and wouldn't do it again that way. If the hose clamps
are tight, and your cuts were clean, you should be okay. However, I
have not used this lid as my primary lid, and would not unless the
bricks are mortared. Eventually, I will buy some new brick and mortar
a nice lid together and use it as the primary lid, but until then,
having this as a secondary is nice, and holds a hell of a lot of heat
in. There is a top picture of the
new lid (with my hand for scale) and a side picture of both lids together
(Also with my hand for scale).
What I'm thinking of doing is building a drylaid lid in a square with
bricks laid on their ends. That would allow me to use turnbuckles to
tighten it, and mount hardware on a block and tackle from the
ceiling. For this, however, I might just wait until I build my gas
kiln.
Temperature tests and effeciency numbers
I'll get some numbers here as soon as I can.
