Vince Pitelka on sun 19 jan 97
>I had mine all bolted and tied with eye bolts over the top however as
>the kiln aged one of the bolts rusted thru and gave way during a reducing
>stage in my firing. I felt uneasy continuing the firing since the arch could
>collapse so I shut down and called a welder and had not fired since. Now that
>I am moving the kiln to a new site I regret that but am debating bolting vs
>welding the frame? Margaret T. Arial.
Margaret -
A bolted frame works OK as long as the tie-rods are heavy enough (at least
1/2" rod), as long as you are planning to use a stacked door. But a bolted
frame is inappropriate for a hinged door, because the kiln frame does not
have the necessary rigidity to support the weight of the door.
In my opinion a hinged door is the only practical choice for a variety of
reasons. In order to use a hinged door, the kiln frame must be extremely
rigid, and a welded frame is absolutely necessary. Someone else mentioned
using 1/4" x 2" angle for the kiln frame, and this is nowhere near heavy
enough. On the 45 cu.ft. downdraft we built several years ago here I used
1/4" x 4" angle-iron verticals and overhead cross-piece (high enough to
clear the outside top of the arch) in front, where the door will be hung,
and 1/4" x 3" angle-iron verticals and overhead cross-piece in back.
Connecting the front frame to the back frame were 1/4" x 3" angle-iron
horizontals at the appropriate height to support the skew-bricks which in
turn support the sprung arch. 2" flat bar was welded all around the bottom
of the kiln between the verticals to complete the frame. Horizontal tabs
were welded to the bottom of the corner-verticals, and these were bolted
securely to the concrete slab.
There are a variety of good door and hinge designs out there. For my door I
built a frame out of 1/4" x 4" angle-iron. I have a favorite heavy-duty
hinge design which works extremely well. The sleeve portion of the hinge is
made from 4"-lengths of 1 1/4"-diameter solid round-stock bored with a
3/4"-hole (this should be done on a lathe). You can get by quite well with
3/4"-inside-diameter black iron pipe as the hinge sleeve, but the fit will
be a bit loose. The hinge-pins are made from 7"-lengths of 3/4" hot-rolled
round stock (solid rod). The sleeve members were welded vertically to one
edge of the door frame near the top and bottom, spaced out from the frame
about an inch with pieces of 1/4" x 1" flat bar. The hinge-pins are welded
to one of the front verticals of the kiln frame, spaced out with pieces of
flat bar. Drill a 3/4" hole through the center of a 2"-length of 1/4" x 2"
flat bar, and slip it down over the top of the hinge-pin, so that four
inches of the 3/4"-rod stick up vertically from this horizontal surface.
Weld it in place on the under-side. This will form the
thrust-bearing-surface that the sleeve member will rest upon. The pin is
welded to the kiln frame with appropriate pieces of flat-bar welded to the
3" portion extending below the thrust-bearing. If everything is very
carefully placed and welded, the kiln door-frame can be lifted into place,
and the sleeve members will slide down verticall over the hinge-pins, with
the weight of the door resting on the thrust-bearing surfaces. The hinges,
especially the upper one, should be periodically oiled at the top of the
pin, and the oil will naturally work down into the hinge.
Obviously, the door frame and hinges must be designed and placed accurately
to accommodate the desired thickness of refractory. My favorite design has
a solid piece of 16-gauge sheet steel tacked inside the door frame, with
appropriate holes for the spy-holes cut with a fly-cutter (circle-cutter in
an electric drill). Make the holes large - 2" to 3" - you will make a
refractory collar for the spy-hole later on which will fit into this hole.
Inside the sheet steel is a layer of 1" fiber board, and then a single 4
1/2" thickness of 2800 softbrick. I find the 2800 softbrick to be much
sturdier than the 2600, and I use it in the trouble spots - doors, door
jambs, etc. This layer of softbrick closes against the front face of the
kiln, and the door frame must be designed large enough so that the softbrick
door extends beyond the door opening at least 4 1/2" in all directions. A
wise addition is a woven ceramic fiber gasket cemented to the front-face of
the kiln all around the door opening. This will minimize abrasion between
the kiln and kiln door surfaces, and give a tighter seal around the door.
Once the door frame is hanging in place on the kiln frame, and the
sheet-metal is tacked into the frame, place the layer of fiber-board. If
necessary you can cement it in a few places with a good ceramic cement like
AP Green Greenpatch 421. The brick is then mortared in place from the
bottom up, and of course you stagger alternate courses. Use a good
high-temperature mortar. The same Greenpatch 421, thinned to a thick liquid
consistency by adding water and mixing with a jiffy-mixer on a drill, will
make a very good mortar for these bricks. Do not use AP Green Sairset
mortar for a high-fire kiln. If the kiln is ever overfired, especially in a
reducing atmosphere, the Sairset will begin to break down and disolve the
softbrick, whereas the Greenpatch 421 will withstand much higher
temperatures. Dip each brick completely in water, and then coat the
appropriate surfaces with mortar, and IMMEDIATELY put in place. The
water-dip will prevent the porous brick from drawing the moisture out of the
mortar, which would prevent it from setting up properly. The consistency of
the mortar should be thin enough that all excess squeezes out as you put the
brick in place. It often helps to tap the brick lightly into place with a
rubber mallet.
Once all of the brick is mortared in place from bottom to top, take an angle
grinder with a standard 1/4"-thick grinding disk mounted on it, and
carefully grind a 1/2"-deep groove into softbrick along the vertical edges
of the door-frame from top of bottom. Cut an appropriate length of 1/4" x
3/4" flat bar, and slip it into that groove, and weld it to the door frame.
This will hold the refractory into the door very effectively. It is only
necessary to do this along the two vertical edges of the door frame.
For latches, weld two short pieces of 1/4''x2" flat bar, near the top and
bottom of the edge of the door frame, close to the kiln face, and parallel
to the kiln face, on the opposite edge of the door from the hinges. To the
corresponding front surface of the vertical member of the kiln frame, lining
up with the centers of the two tabs on the door frame, weld horizontally two
short lengths of 3/4" I.D. black iron pipe, spaced out from the frame with
appropriate pieces of flat bar (you will have to decide this as you design
and assemble the latches). There should be at least a one-inch space
between the inner end of the pipe, and the closest edge of the tab on the
door frame.
For the moving part of the latch mechanism, cut two appropriate lengths of
3/4" round stock. Cut off two 1/2" lengths of the same 1 1/2" round stock
that was used for the outer members fo the hinge (or cut and finish two 1
1/2"-diameter disks from a piece of 1/2" steel plate). Weld these disks
off-center on one end of each of the two lengths of 3/4" round stock,
forming a cam or eccentric. Slide these into the two horizontal pieces of
3/4" I.D. pipe, with the cam at the end closest to the tabs on the door
frame. On the opposite end of the round stock, weld a length of 1/4" x 3/4"
flat bar for a handle. The round stock must be long enough so that it will
move sideways approximately one inch when both the eccentric cam and the
handle are welded on. As you assemble the latches, you will have to
determine the position of the handles in order for the eccentric to work
properly. In operation the horizontal latch slides outwards away from the
kiln door, so that the eccentric disk clears the tabs on the door as the
door is opened and closed. When the door is closed, the horizontal latches
are slid toward the door, so that the eccentric cams slip in front of the
tabs on the door. The handles are then drawn downwards, and the rotating
eccentric cam presses inwards on the tab on the door frame. If properly
designed, especially with a woven fiber gasket, when the handle is swung all
the way down, and the eccentric applies the maximum amount of pressure, the
door will just be closed snuggly against the gasket. This will prevent the
possibility of overtightening. If, with time, the fit becomes loose, it is
an easy matter to cut the tabs off the door and re-weld them to make the
latch close tighter. Does this make sense to you?
The spyholes can be drilled with a masonry bit, and then enlarged and shaped
with a piece of threaded rod used like a file to abrade the hole. I like to
have my spy holes quite small at the outer end - 1"-diameter, so they can be
easily plugged. Have them taper to 2" to 3"-diameter at the hotface, and it
will be easy to see the cone packs. Once all the refractory is in place and
the spy-holes are drilled and shaped, carve away the fiber board out to the
diameter of the hole in the sheet metal, and use Greenpatch 421 to form the
outer end of the spyhole. This will form a very durable collar, which will
withstand the repeated abrasion of removing and replacing the spyholes. A
good alternative is to throw the outer collars on the wheel using a good
refractory clay, fire them, and cement them in place with Greenpatch 421.
A well-designed door is such a joy to use every single time you open and
close it. After you load a glaze-fire, and you swing the door shut and latch
it, you will remember all thost times you bricked up door openings, and it
will inspire you to go relax and have a beer or a cup of coffee.
Good luck.
-Vince
Vince Pitelka - vpitelka@Dekalb.Net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts, Smithville TN 37166
Marcia Selsor on mon 20 jan 97
Margaret,
I agree with most of what Vince says about needed solid support for an
arched door. The two sides of my frams are solid welded frames with a
diagonal part that has an adjustable treaded section that goes from the
lower back to the top front where the weight of the hinged door
would pull. I still like the ability to adjust the frame on the arch.
Before I take the frame out when setting a new arch, I adjust the
pressure and lift the arch off the frame by tightening the threaded
rod. I think it is cool. Free standing arches inspire like some
religious experience. IMO.
Someone always has an opinion. As long as they're all right, it's
amazing.
Marcia
--
Marcia Selsor
http://www.imt.net/~mjbmls/
mjbmls@imt.net
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