Trouble with setback on brick courses. Need advice.

[Xene]

I'm on my fourth course above soldier and I've got a problem with setback of the brick courses measuring as much as 1/4 of an inch in some places. The setback isn't exactly the same all the way around (its a little less in some spots) but I can no longer get the angle correct with the indispensable tool and have the lower edge of the brick line up with the upper edge of the last course. Is this normal? I'm having a hard time searching the forum and finding the correct search words to use to find my answer.

Here is my picture to illustrate the issue:

What do I have going wrong? Is the tool meant to be adjustable? I could cut the bricks in half at an angle to compensate for the difference, but I'm not feeling confident that is the best idea.

What to do? I'm a bit stuck as to how to proceed. Thanks for your help!!

[Laku]

Re: Trouble with setback on brick courses. Need advice.

If the indispensable tool is in the middle of the oven floor, and its position has not changed in any way (up,down or sideways) since you have started the build, then this should not happen. The angle should stay consistent throughout the whole build.

What's that thin bit of wood between your IT and the brick? It looks just the thickness of what your IT is off.

[deejayoh]

Re: Trouble with setback on brick courses. Need advice.

Xene -
If your IT is set in the center of the dome and you are working on a constant radius - then the angle the IT indicates for the brick is actually the halfway point between the angle of the chain you are setting and angle of the next chain.

So if you lined the top of the brick in the last chain with the IT - then you're going to be a bit ahead on your radius. I suspect that's what is causing the problem.

[Xene]

Re: Trouble with setback on brick courses. Need advice.

Ah ha, my IT is mounted to cardboard, which got wet and can now shift on the floor a bit. I was going to start with remounting it to a more solid foundation.

That thin bit of wood has been there from the start, as I had the husband make the tool for me and he didn't grasp the concept, so he had to add it in there for me.

You are right, if I remove that little piece, I can probably get it back into alignment. Would I be correct to assume that I probably wouldn't notice the adjustment if I took out that 1/4 inch?

[Laku]

Re: Trouble with setback on brick courses. Need advice.

Well, depends if the IT can still move after you remove it, and if it's at the correct distance on every side of the dome.

I'd mount it on a proper solid foundation and then check how much it would need adjustment. It needs to be exactly in the middle.

The angle discrepancy comes from what deejayoh described above.

[Xene]

Re: Trouble with setback on brick courses. Need advice.

Xene -
If your IT is set in the center of the dome and you are working on a constant radius - then the angle the IT indicates for the brick is actually the halfway point between the angle of the chain you are setting and angle of the next chain.

So if you lined the top of the brick in the last chain with the IT - then you're going to be a bit ahead on your radius. I suspect that's what is causing the problem.

I see, yes I'm lining each course with the top...and I could see I was getting further out of alignment with each level. Okay, I'm feeling better about how to proceed.

I think I will chip out that extra wood and work from there...get a more solid base for my IT to swivel on, and then make my alignments on center of brick instead of edge. Does that sound about right?

[Laku]

Re: Trouble with setback on brick courses. Need advice.

and then make my alignments on center of brick instead of edge. Does that sound about right?

Or you could just add little more thickness between the swivel arm and the bit that goes on top of the brick so that the swivel arms end is at about the centre of the brick. From the looks of it about one piece of same thickness wood that it's made of.

[deejayoh]

Re: Trouble with setback on brick courses. Need advice.

Yes. That should work fine. Just make sure that the next course has the right amount of "free angle" above it when you set it - e.g., if you are tilting each brick 6 degrees, make sure you've got 3 degrees between the top of the brick and the IT. That may mean that your don't tilt the bricks at all on that course in order to correct your radius. Your dome will be slightly lower but that shouldn't be an issue.

[GianniFocaccia]

Re: Trouble with setback on brick courses. Need advice.

You may have to shave the face of each brick slightly to re-set the proper angle for subsequent courses. If you have to do this, don't worry: No one's (except for Les' maybe) oven is perfectly round throughout, and once your oven is completed you will never notice.

As Dennis knows, as successive courses become slightly out of round, a little face shave here and there goes a long way to getting back to round.

John

[texman]

Re: Trouble with setback on brick courses. Need advice.

Or, you can start over like me. (just kidding!!!)
Tracy

[deejayoh]

Re: Trouble with setback on brick courses. Need advice.

Yes, I know how important it is to shave face

Sorry, I just couldn't resist

[Laku]

Re: Trouble with setback on brick courses. Need advice.

Yes, I know how important it is to shave face

Sorry, I just couldn't resist

Interestingly I do it every day!

[Xene]

Re: Trouble with setback on brick courses. Need advice.

Thanks for all the help today! I did as I promised, reset the base that my IT was attached to, making it more substantial, knocked it back 1/4-inch, and set the next course with an eye toward the middle of the brick instead of the top edge. It laid in there nicely. I'm happy with it so far, and I'm honestly not concerned with an exact half circle (maybe I should be, but I don't plan on letting my friends stick their heads in there to check it out - and they wouldn't know any better that it wasn't as I intended anyway!)

I'm dealing with the cuts that frame the arch into the dome tomorrow. You just might be hearing from me again. Thanks again for your great response.

[Amac]

Re: Trouble with setback on brick courses. Need advice.

Hi - a little late to this discussion but maybe i can help a little to throw some light on this.
The problem I believe is due to the design of the IT. The design which you are using must cause the exact problem you describe. Think of it like this:

- Your IT is a straight piece of wood from the centre of the dome.
- The brick is at right angles to it.
- Imagine then a straight line between the bottom of the brick and the dome centre.

What I have just described is a right angle triangle and the imaginary line is the hypoteneuse - and therefore longer than the IT to the top of the brick.

You can use pythagoras theorem to work out exactly what your "setback" should be. For example a 20" IT with 3" brick will give a hypoteneuse of 20.22" and .22 is just under a 1/4 of an inch.

The solution to the problem is to make the IT exactly as jcg31s design which is quite brilliant but more difficult and points the shaft of the IT at the centre of each brick. That way you effectively have two right angle triangles with a common middle and two equal hypoteneuses - centre to top of brick = centre to bottom of brick.

Look at post 1 and 3 here - I ( and many others) copied this - it should be a sticky
http://www.fornobravo.com/forum/f28/...heme-2985.html

[Xene]

Re: Trouble with setback on brick courses. Need advice.

I love how technically you all get about building these ovens, but I'm the first to admit I'm way more artist than engineer. I'm hoping to pull this off with my stick.