It rained so some inside work on the sprung arch

It rained all day so i figured it was a good time to figure out the arch details. Darn angles got me so messed up I enlisted my engineer hubby for some help. When his calculations started to look like this I was a little lost again. lol.

My thought was to figure out what span and what rise I wanted, draw an approximate curve. Draw a curve exactly 4 1/2 inches above (height of adapted brick) and parallel to that one . Figure exactly how many bricks I needed for the upper curve (the length divided by the width of brick, pick the closest number of bricks and this becomes my number of bricks per arch curve). Measure the length of the lower curve and divide it by the number of bricks I was using. I figured I needed to trim the sides of the brick by that amount on each side. Which maybe would have been fine if I had remembered to divided that number by 2 (for each side of the brick, duh). Yup, even I confused myself . Russ finished his angle calculations and we both drew it, then gave it a go. He even made a small metal jig I could use on the saw for consistent angles.

Hhhmmm...this will make a circle before reaching the span! Yeah, complete mess up. 

That's when I realized I hadn't divided my number by two for trimming BOTH sides of the brick? (I think.) And maybe my hubby did the same? So back to the drawing board and a new jig made. And a bunch more cutting...(we halved the angle and voila!)

Now that looks better! Pretty sure we didn't do it the "right" way but this is the correct size. Trial and error can usually get you there if you can't figure it out! It spans 31 3/4". My actual kiln opening is 31 1/4" at the widest so these will just fit over the edges. Which is another thing I went back and forth on. Should the arch fit just AT the edge or just OVER the edge? Please comment if you have feedback on this. I'm not sure it really matters if I have done my skewbacks properly and if the iron support is done right?

The rise is 4 3/8" which makes it 1.6" rise  per foot of span so all is good! (Recommended guideline said minimum of 1.5" rise per foot of span.)

Cut out a paper template and folded in half to check for symmetry on each side. All good and ready to use it to build the wooden arch support to build the arch onto the kiln. I also made a paper template for the skewback brick. All great as long as my dog doesn't make off with my paper patterns. :) There will be a layer of ceramic fiber and then IFB over this arch once I get that figured out.

Why am I cutting such funny brick sizes? Well, my firebrick I just picked up (I'm out of my nice even ones) are very uneven sizes and shapes. The most consistent thing is the width and the thickness. I can use partial bricks and trim 4 sides. This eliminates my roughest areas with the least amount of waste. Again, not ideal but making the best use of what is available to me. I don't mind doing the cutting with the saw along with using the metal jig. Bricks fit tight and are very consistent. Goes pretty quick but I would NEVER attempt this without the wet tile saw. Oh, and about this batch of hard fire brick. It was tested in a kiln before I purchased it which is good as a potter just shared her horror story of her newly built kiln melting the first time she fired it up!
Quick safety note about using the wet tile saw: always wear goggles, mask, and ear protection is good too, and be careful! The wet tile saw will occasionally kick back/out a brick if it is not sitting perfectly flat or if it catches on something. Not for the faint of heart to cut all these brick, but can be done if you are methodical and careful.
I'll post a picture of the angled jig when it stops raining.