mtigges@NOSPAM.SHAW.CA on tue 14 feb 06
I received two replies to my odd and long message
On Tue, Feb 14, 2006 at 06:08:45PM -0500, Taylor, in Rockport TX wrote:
> My guess is your local expert's ring is more stable because it has one less
> joint with one less brick in the ring. I'm still trying to figure out if
> having the bricks stick their 'back ends' out would make it more stable,
> but I can't see it. The longer the butt joint the more stable I would
> think.
On Tue, Feb 14, 2006 at 08:05:59PM -0600, Vince Pitelka wrote:
> Your so-called local expert is wrong. The design with a smaller end-contact
> surface between bricks will be less stable, and will allow more flex in the
> circle of bricks. There is no way physically possible that it could be more
> stable. If he's building kilns like this, then he's getting away with
> making a larger circle with less bricks, but there's no advantage to it
> other than saving money in the manufacture.
You both say the same thing, and intuitively, it is exactly what I
feel. He quotes stability as the reason he doesn't use 12, but
repeatedly asking him why yields no answer. He's an engineer by
trade, and has been building kilns for 15 years, taking over for a man
who had built them for just as long. I can't disregard his advice, it
just seems really wierd. He said he tried 12 bricks once, but
abandoned it.
His response to the saving manufacturing cost is simply that he points
out that laying them on the flat demonstrates that he isn't interested
in that. It's a reasonable argument when most commercial kilns lay
with 4.5 inch courses.
> Maybe you are approaching the cutting of your bricks a bit
> differently than I would. I would not worry about measuring out hot
> face lengths. I would be focusing on the angle and making a jig to
> cut the bricks.
>
> If you think about it, the same angle is used for all the kiln
> diameters from the smallest (where the hot face is 0 inches) to the
> largest (where the butt joint lengths are 0 inches) when the ring
> contains the same number of bricks.
Yes, I know this. With 12 bricks the angle for each mitre is 15
degrees since each brick subtends 30 degrees in the approximation of
the circle. With 11 it's a trickier angle ... 360 / 22 = 11.3636 ...
so it's definitely a better idea to mitre the bricks based on the 6.75
inch hot face length. Moreover, you still need to make sure each
brick is exactly the same shape.
> All you have to do is build a jig that holds the brick at the
> correct angle to your grinding disk or saw blade. Do you think even
> a belt sander could shape the angles?
It could, but a mitre saw is easier I think. (The big problem with
grinding them is the dust.) Regardless of how you cut the bricks, you
still have to make sure that the hot face length is exactly correct.
My neighbour works at a sign manufacturing shop and has agreed to CNC
me a blank with which I can set my mitre saw stops.
I'm tempted to try first with some scrap mdf to see if I can
accurately cut the 'bricks' to approximate a circle.
> If you have good success with your kiln project, be sure to share it
> with us. I am almost tempted to try it myself.
I definitely will. No question. It will be a lot more detailed than
the kiln vent page. I also plan on putting up the software that I've
written that does the electricity calcs and the trig for cutting
bricks too.
> BTB, your last pic is a broken link.
My apologies, this link should work:
http://www.m2crafts.ca/r_11.49-l_6.75.jpg
That is the configuration that I'm planning on going with (for now).
11 courses, 5 circuits of 2 elements each element at about 14.4 ohms
(15 gauge A1) and the kiln carrying around 42 amps. I'm pretty
excited. With the 4.5 inch brick and one of fibre it will be far
superior to any kiln you can buy. And less than $1000 canadian.
> Love your vent fabrication. I'm planning on doing my own. Your
> page will be a fantastic help.
Thank you. I fired the first glaze firing with it yesterday and it
worked perfectly. It was stinky outside, and inside it smelled like
crystal clear fresh ... desicated rat remains. That's a whole
different story. And that firing yielded several beautiful mugs from
which I will have to choose for the mug exchange.
Thanks Taylor and Vince.
Mark.
Mark Tigges on tue 14 feb 06
I have a question that a local expert has me wondering about. He
builds custom electric kilns. I want to build one for myself. The
plan is to build with a radius of 11.5 inches, and 11 courses (each
course is 2.5"). Powered by 10000 watts.
So, these are parameters which are very similar to one of the kilns
said expert builds.
When you do the math, the kiln should logically look like this:
http://www.m2crafts.ca/r_11.5-l_6.16.jpg
- radius of 11.5 inches, and hot face brick length of 6.16 inches.
12 bricks is kind of the minimum (more later) that can be used to
approximate a circle.
Now, to me, 6.16 inches is very difficult to cut, so I set the hot
face brick length to 6.25, and compute the radius as 11.66.
http://www.m2crafts.ca/r_11.66-l_6.25.jpg
- no appreciable difference, just easier to cut the bricks.
Here's where it gets strange, this local expert claims this is
superior:
http://www.m2crafts.ca/r_11.5-l_7.47.jpg
- he uses 10 bricks.
He claims that this is more stable. I don't understand it. He fixes
the radius, and tries to cut a very strange length accurately, so I
think that the short butting lengths make it easier for him to fudge
it a bit. Three hundreths of an inch aren't a big deal, but you have
to be bang on to approximate a circle well.
He is unable, or unwilling to explain to me why it increases
stability.
He clads the kiln in 1/2 (or 1) inch of fibre so those notches end up
being a closed air space, and likely fairly insulating, so I don't
think they harm the kilns efficiency too much.
Playing around a bit, I figured out that one can get away with 11
bricks:
http://www.m2crafts.ca/r_11.49-l_6.5.jpg
Here seems to be the best of everything! Almost 11.5 inch radius with
6.5 inch hot face lengths.
The outside of the bricks get rounded (that's the dashed circle) so
that the fibre wraps nicely. And the rounding gets rid of the notch.
Perfectly economical use of bricks.
So, the reason I have written this email is that I find myself in
disagreement with the expert. I see no reason (other than to save a
brick per course) to use 10 bricks. Maybe I just need another expert
to convince me he is right. Hence, this appeal to clayart.
All opinions welcome, what would you do?
Regards,
Mark.
Taylor, in Rockport TX on tue 14 feb 06
Hey Mark:
I'm just spit balling here if you don't mind.
My guess is your local expert's ring is more stable because it has one less
joint with one less brick in the ring. I'm still trying to figure out if
having the bricks stick their 'back ends' out would make it more stable,
but I can't see it. The longer the butt joint the more stable I would
think.
Maybe you are approaching the cutting of your bricks a bit differently than
I would. I would not worry about measuring out hot face lengths. I would
be focusing on the angle and making a jig to cut the bricks.
If you think about it, the same angle is used for all the kiln diameters
from the smallest (where the hot face is 0 inches) to the largest (where
the butt joint lengths are 0 inches) when the ring contains the same number
of bricks.
All you have to do is build a jig that holds the brick at the correct angle
to your grinding disk or saw blade. Do you think even a belt sander could
shape the angles?
If you have good success with your kiln project, be sure to share it with
us. I am almost tempted to try it myself.
BTB, your last pic is a broken link.
Love your vent fabrication. I'm planning on doing my own. Your page will
be a fantastic help.
Rock on,
Taylor, in Rockport TX
On Tue, 14 Feb 2006 12:40:23 -0800, Mark Tigges
wrote:
...>
>So, the reason I have written this email is that I find myself in
>disagreement with the expert. I see no reason (other than to save a
>brick per course) to use 10 bricks. Maybe I just need another expert
>to convince me he is right. Hence, this appeal to clayart.
>
>All opinions welcome, what would you do?
...
Vince Pitelka on tue 14 feb 06
Mark -
Your so-called local expert is wrong. The design with a smaller end-contact
surface between bricks will be less stable, and will allow more flex in the
circle of bricks. There is no way physically possible that it could be more
stable. If he's building kilns like this, then he's getting away with
making a larger circle with less bricks, but there's no advantage to it
other than saving money in the manufacture.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
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