Time for a fresh update,
I think I have lost some photos somewhere because last year I managed to lay the firebrick floor, this was somewhat difficult to get level and into a nice herringbone pattern due to the bricks being reclaimed.
Also I was incapable of working out the oven size and where it would extend to, in keeping with my cheapskate build I use using the local Guardian paper stuck together to make a large 2m square. I had got some string and two pens and tried to tie them togehter. I think went about making circles for 26" all the way to 36".
Using this and the centre point of my slab I was working out what I could fit on there, I have had to make it arround the area prescribed by my good wife anddue to shoddy ground work is not perfectly square or even with 90 degree corners
I settled for my estimated 30" oven but I do not have much space for my enterance, I have not decided what I will do here yet. Not only is it only 1 brick ling but due to the edges any side walls will have to follow the angle of the wall. this is difficult in as much as I am not sure I can cut the bricks to my anal level of perfection (lol) for that as the cut will be exposed.
anyhow on to where we stand today
this weekend I had my brother down to assist again, after offering his services for the Sat he managed to arrive at arround 3....
so whilst waiting I did another ring of bricks and tried to prepare for the dreaded enterance arch. Given the knock on problems I have had with my cheap ness I decided I would bite the bullet and spend some £ to make life easy.
Terry used some celotex insulation board for a form, and a trip to Wicks and a whole £5 spent I had a board.
With my extravagance spent it was back to the bodgeing designs, my dome being 30" or so I thought untill I measured it and found it closer to 31", a quick bit of maths and ther 63% rule says my enterance should be 19.5" high.
My enternace is 16" wide so need to make another 3.5", a brick is 2.5" so decided it was easier to make a perfect(sic) semi circular form and be slightly low than risk it all on a hand crafted form or try to get too fancy.
its here and now I look back and realise i make a complete balls up, given I was using Diameter and not Radius that whould have yielded hight. Luckily I was wrong consitently so its not so bad.
The arch is 10.5" high so nearly 68% of the final dome hight, scary as I initially thought it was a little low. But without the extra brick layer it would have been low 50% on the ratio.
This is what happens when you are rushed and also trying to do other things at the same time.
I could have lowered my form, or even raised it as I was thinking and thankfully I was just consistently bad with measureing.
there is a lesson here somewhere about measuring twice and cutting once but I forgot in then and will probably forget next time I am in a rush
anyhow back to more detail on arch construction.
I used some cardboard to make a compass, I measured out my 8" and placed a hole at each end. Then from the end of the celotex cut two 8" rectangles off. With each of these I put a nail in one end of my compass and a pen in the other, I make a perfect semi circle on each piece of celotex. I then cut with an old kitchen knife I save for these sorts of DIY, and taped the two together with some underlay tape of all things I had laying to hand.
The ease of cutting, thickness and strength of this stuff does make it very useful for these forms. It is really quite easy to work with and when doubled up is almost exactly brick length
I lined up my half bricks and saw I was using 10 bricks so had 9 angle joints, for 180 degree arch thats 20 degrees each. I got a real protractor out and measured 20 degrees on and end of celotex, and then continued to draw 20 degree triangles and cut them out for measurement wedges.
On the ground this all looked good, I offered it up and decided that full half bricks was too much and cut them down by half. When offereing this up I must have rotated them 90 degrees as they did not fit, so cut another couple to fill in and that was almost perfect except the top two where very tight and sat verticle so would fail as keystones.
removed them and counted my bricks again and decided that I needed a real keystone and it should have 20 degrees on either side, this is the first time using a hybrid franken mitre saw has paid off. It was easy to set to 20 degrees and with some slight measurement I managed to knock out what I hope will be a very secure keystone.
I will at this point tip my hat to the FB boys, as tapering one brick was enough for me, I think I would be hung by half the street if I was to be doing that level of detail cutting to each brick.
also I measured the bricks I was going to use, and length on they where a nightmare to work with, so took the decision to halve them all, everything lined up nice on the ground so went to fit it, and then realised that for some reason there was a much smaller gap at the top and the two bricks would be laid effectivly flat making them useless as a keystone and the arch would fail.
so there is the arch in all its gory glory. The homebrew seems to take a while to set so it still feels a little squidgy but will pop the form out when I get home I think.
and to finnish an internal shot which also shows the back of the form, and my home made indespencible tool.
You can also see in my haste to finnish it I forget to cut an angle off the back of the bricks, so joining the ring course to it is going to be a pita :/ oh well.