Who Here Remembers Their Geometry?

Gary L
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Post Fri. Dec. 19, 2008 10:52 pm

Here is a pic of my stove with new fire brick installed.

**Broken Image Link(s) Removed**

I have a good tile saw and could cut the angles on the edges of each brick for a perfect fit but can't figure out the correct angles I will need.

Bricks are 1 1/8" thick and 4 1/4" wide. The round steel liner in the fire box the bricks fit to is 17 inches accross. I have 10 full bricks in there and that leaves a gap of 2" on the steel side and 1 1/4" on the coal side.

I don't know if this is necessary or if it would even make any difference to close the gaps. Just my anal nature and desire to make a job look and fit right. I also thought about refractory cement but that would make for a difficult repair if I ever crack any as I am sure I will.

My other option is to draw a 17 inch circle and start playing with my bricks to get the angle but I am pretty sure there must be a formula to figure this mathematically. I believe I might have slept thru that class or cut it alltogether while at the Woodstock Festival. :lol:

Gary

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CapeCoaler
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Post Sat. Dec. 20, 2008 12:33 am

How about just scribing one side of each brick, half as many cuts and no math involved.
This will make it just a repetitive cut to one side of the bricks
You may need to make a 'filler' brick if the gap is still too large.
You do not want a 'tight' fit when the bricks are cold as they will spall when heated if they don’t have some wiggle room.

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jpete
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Post Sat. Dec. 20, 2008 1:16 am

Seems like a "10 sided circle" should have ten 36* angles. So if you imagined all your pieces like a pizza, the angles around the center point would be 36*. And the sum of the interior angles is 180* so 180-36=144. Also assuming the stove is a circle(which it's probably not), then the two remaining angles are 144/2=74. Then theoretically, you should be able to make 37* cuts(74/2) on both sides of your bricks and to make a 10 sided polygon(decagon).

But don't hold me to it, it's 1am, I worked 12.5hrs today(I'm a machinist), ran the snow blower for an hour+ and am under the influence of Ny-Quil(I think I have strep throat).

Gary L
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Post Sat. Dec. 20, 2008 2:48 am

Good idea on cutting just one side of each to marry them together and do half the cutting. I would suspect that as the bricks heat up and expand so too will the steel cylinder in the stove.

36*/37* sounds about right and actually what I thought except for the partial eleventh brick that has me cornfused. Think I'll wait for you to feel better and me too. Got woken from a sound sleep this morning at 4:55 with the next door neighbors house burning to the ground. No injuries and not wood/coal related. Then we got hammered with a foot of snow and now it is freezing rain and I am still up and going at 2:45 AM and the Nyquill sounds pretty good to me.

Gary

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Westy
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Post Sat. Dec. 20, 2008 3:39 am

After some calculations, if you used 13 bricks,

each brick would be 4.068" on the outside, with an 13.8 degree angle on each end
Untitled.jpg
Last edited by Westy on Sat. Dec. 20, 2008 5:46 am, edited 3 times in total.

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Freddy
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Post Sat. Dec. 20, 2008 4:53 am

This isn't math, this is flop the stove & bricks on the computer & see what ya get. If you cut just one side of each brick they won't match up. I'm sure it'd work fine, but when the inspector stove fairies come in the night, they'll go "ewwwwww".

My best hack & chop guess is 104 & 64 degrees. Oh, and it looks like 14 bricks, not 10.
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Richard S.
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Post Sat. Dec. 20, 2008 5:05 am

If you take the triangle that is your gap, cut it in half, that's the material you need to remove from one brick. Just measure the length of the gap between the two corners of the bricks on the back, divide by two and the that's the width you need to cut at.

TimV
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Post Sat. Dec. 20, 2008 5:44 am

Wonders how many extra bricks will be needed to get 20 "perfect"cuts not to mention the amount of abrasive wheels required to do this job.
While your at it you might want a convex radius on the back fit them flush on the back.
When you get that done you can notch the bottoms on 6 bricks for me so my grate trunions don't push them upward when I use the full stroke of my shakedown lever. :D

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Freddy
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Post Sat. Dec. 20, 2008 7:01 am

TimV wrote:While your at it you might want a convex radius on the back fit them flush on the back.
When you get that done you can notch the bottoms
Time to make a mold & dig some blue clay. Bake them off next to the chocolate chip cookies.

hyway61
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Post Sat. Dec. 20, 2008 10:40 am

Look at the top of your bricks and the 'space" triangle....measure the base of the space/air triangle. From the inside of the brick measure off this triangle's base and scribe to the outside corner....measure the angle if you like. If you remove this wedge of brick it should coincide with the ones side of untrimed brick.

..hyway61

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Cap
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Post Sat. Dec. 20, 2008 12:54 pm

I'd fill those cracks with glass beads or something that can take the heat but if you do go thru the trouble to cut, make yourself extras. You'll be glad you did next season.

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Devil505
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Post Sat. Dec. 20, 2008 4:25 pm

Cap wrote:I'd fill those cracks with glass beads or something that can take the heat
From a stove safety/effectiveness standpoint I think the way they are is fine. Your stove wall is protected from direct contact with hot coal by the air gap anyway, or you could just fill each gap with coarse sand & save yourself allot of work.
Last edited by Devil505 on Sat. Dec. 20, 2008 7:03 pm, edited 1 time in total.

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Jim503RI
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Post Sat. Dec. 20, 2008 6:14 pm

If the angles are not the same, one edge would stick out. The line of angle will
be greater in length then the 90* cut. If your installing a handrail or crown molding, both
angles have to be equal. I don't know what size brick you need to create a circle , But if you measure the gap in back, divide x 2. That's the amount you would take off each front edge. If your gap is 3/4", You would
take off 3/8" off each front edge to 0" in the back. It's the no think methord .That's my 2 cents, spend it the way you want.

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grizzly2
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Post Sat. Dec. 20, 2008 7:02 pm

I'd like to help, but I got mad and dropped out of geometry class on day 2. The darn fool teacher tried to tell us that pies are square. If he don't know his shapes yet how in the hell is he gonna teach me geometry. toothy

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coaledsweat
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Post Sat. Dec. 20, 2008 7:56 pm

Here is a cure.

http://www.amateurgeologist.com/estwing-chipping- ... e3-wc.html

Chip across the center line of the brick along the thin side chamfering it. It doesn't have to be beautiful or fill all the gaps, just keep the live coals off the steel like the Devil said.

I just picked up 20 splits for $1.33 apiece at the brickyard. I like doing them with a hammer and chisel for the adventure! :) Looking back, I never broke one chipping from the thin side. It is always a face cut when you ruin them, so whack away. ;)

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