Indispensable tool issue - i'm flummoxed!

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

I now know what you guys were talking about re arch and dome transition. I've used the IT to figure out arch position.

Glad I did. I was probably 2-3 inches out from where it should be.

Might look into tapering some of the bricks for the arch... Seems to transition better in the pics I've seen?

[Greenman]

Re: Indispensable tool issue - i'm flummoxed!

The beauty of the castor is that there is no engineering required, just drill the appropriate size hole in the castor wheel and screw the threaded rod into that. Dead easy and cheap as chips.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

Haha fair enough. Last time i build a barrel so I guess I'm keen as to use the IT just for something different...and want to get it right but i'm only faffing around because I won't be laying the first course for a few more days yet so all I can do is muck around with that. Gives me time to think!

[wotavidone]

Re: Indispensable tool issue - i'm flummoxed!

We were far too tight-arsed to buy castors for pivot points.
But the castors do appear to work well, so why not?

To me the idea is to ensure the whole thickness of the dome meets the arch. I just like the comfort of knowing we have full thickness mortart joints, etc.

Anyway, in the build thread for the oven my mate and I built early January,
take a look at post #22.
I still managed to build in a little bit of "teardrop" , that we had to cutom cut a couple of bricks at the top of the arch, to take out the tear drop in the next course.
It'll all work mate.
You are close neough to start laying bricks.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

Yea i can appreciate that it is easier to demonstrate!

I get what you are saying. The idea is you don't want any brick hanging below the eyeline of the arch...so it isn't necessarily a structural issue but an aesthetic one?

Most people seem to say build the arch first so that is what i'll do. i'll lay the first course and the arch...

I am happy with my IT but i should have said that was just a mock up. I want to have something a little more sturdy than a screw into a bit of timber as my pivot point. I'm off to bunnings this morning so going to grab a couple small things. I have some threaded rod at home already so will get a few bits and get the welder out.

from what i have read, casters are good pivot points...?

[wotavidone]

Re: Indispensable tool issue - i'm flummoxed!

G'day
You now appear to have to IT in place and operational.
Next brain teaser is make a mock up of entrance (cardboard cut out will do) and use you IT to find out where your dome meets the entrance.
A 42 in high dome nominal entrance is 12 1/2 in high 20 in wide.
I'm not bringing this up to tease you. You may as well be prepared now.
These guys are better than me at this point, they're your brains trust and will get you through the dreaded transition.
Regards Dave

Dave raises a very good point. Referring again to the picture of my last build, that IT was indeed used to check that the brick would meet the arch at the top.
I put the swivel point at the centre spot I had decided on (arch was already built) and put a half brick in the IT and made sure that the brick sat on the bevel/chamfer without the bottom edge hanging below the cut edge of the arch bricks.
The brick hung down just a tad, so I moved the centre point forward about a half inch, so the brick was in the right place. Then the IT was used from that position to start the bottom course of the brick in the right place.
It's all about looking at the oven in plan view and ensuring the arch is set back far enough in the circle that everything mates up.
I'd drawn it out on paper to scale with a compass and a square, but it doesn't hurt to check.


Edit:
However, if you want to build the arch as you go, that will work too. If you look at the chamfer I put on the arch bricks in that oven, you'll see they are all the same, I just measured 50mm from the corners and cut a triangle off.
They don't have to be. If you are building along and realise that the dome bricks are going to hang off a bit, the back of the arch chould be a bit lower, just measure say, 35 mm from the corners and cut the chamfer a bit bigger as you go, so you have a full flat surface to meet with your dome bricks.

I wish I was there, it's a lot easier to demonstrate than it is to describe in words.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

was thinking about that earlier too...

ive got a 20 inch wide and 12 1/2 inch opening planned...that is 12 1/2 inch at the top of an arch.

ive marked out where the opening will be, and where the offset will be for the door jam. to be honest i was going to build up two courses to the opening bricks, build the arch, and then keep going. If i have the opening in the right spot in relation to the dome shape, it should just build around and fit nicely?

[cobblerdave]

Re: Indispensable tool issue - i'm flummoxed!

G'day
You now appear to have to IT in place and operational.
Next brain teaser is make a mock up of entrance (cardboard cut out will do) and use you IT to find out where your dome meets the entrance.
A 42 in high dome nominal entrance is 12 1/2 in high 20 in wide.
I'm not bringing this up to tease you. You may as well be prepared now.
These guys are better than me at this point, they're your brains trust and will get you through the dreaded transition.
Regards Dave

[Greenman]

Re: Indispensable tool issue - i'm flummoxed!

I used my IT fixed and that is how my dome was built. A hemisphere it is and it works fine. My only suggestion is that the part of the tool that addresses the top of the brick is long enough to ensure that the angle is right.

I think you are on the way. Enjoy the ride.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

im still not 100% sure i follow.... all good though. i'll figure it out. if i line up each course with my template then fix the IT it will be fine..

[wotavidone]

Re: Indispensable tool issue - i'm flummoxed!

Yours is going to work, no need to stress, but here is what I used last time.

Edit: no need to post the link, you've already found the tool I used for the last oven I built.

See how the bottom edge of the L bracket is above the plane of the hinge point, so as you lift the IT up the L bracket pulls away from the brick?
Also, the hinge point is away from the central swivel point, just a smidgeon, enough to allow for the thickness of the wood it was mounted on. The further away from the central point that hinge point is, the shorter the stick can be and still reach the ring of bricks. And the lower the dome ceiling will be when the stick is standing vertical.
Imagine a T hinge instead of a butt hinge, and you can have the hinge point a couple of inches away from the central swivel. Then you will build a dome a couple inches lower than the radius of the circle.
Unfortunately that oven is not the best example of use of the IT, it's actually deliberately built fairly high, with a biggish door, so as to accommodate turkeys and other large roasting jobs.
He's started using it without finishing the chimney and outer arch, and it currently has no way at all of excluding the horrible afternoon winds we get.
It makes very good pizzas just the same.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

mine looks very much like this one...

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

the only reason ive made it adjustable is to account for the thickness of the board it is sitting on...but i suppose if you start at the right distance at the first course then it would continue up...

not sure i am getting what you mean about the l bracket...well i do but i can't picture it... be great to see a pic of yours or to get sketchup working!

otherwise might be settling for what ive got or a timber form...

I should add, that when i mocked up a couple of chains of bricks, 3 high, the angle was perfect to the shims I had already measured...so i figured it was correct.

[wotavidone]

Re: Indispensable tool issue - i'm flummoxed!

I'm struggling to put this into simple sentences but here goes.

1) A properly constructed IT does not move the just-laid brick when you lift it off. The bottom edge of the L bracket must not fall below the plane of the hinge. If this is done correctly the L bracket is pulled away from the brick as the IT is lifted.
2) If the IT is properly constructed so that the hinge point is level with the middle of the face of the first course of brick, it does not have to be adjustable.
3) What make sit difficult is that when the first course of bricks are laid on top of the floor, the centre of the bricks is not the bit that would touch the hemisphere. So the top edge is further out from the arc of the hemisphere than it should be.
4) if the hearth bricks are laid inside the dome, the first course of bricks can be cut so the bit rising above the hearth floor is exactly half a face brick, then using the IT to do a hemisphere works properly.

I wish I could get sketch-up to work so I could illustrate what I mean. A fixed IT has worked twice for me, so i'm kinda convinced I'm right.

[alexi82]

Re: Indispensable tool issue - i'm flummoxed!

Nice. I actually have just been outside thinking about it and have figured it out. This is what i made. Off set the angle iron, bent it a bit. I have got a couple of wing nuts and a groove in the timber so i can move it up and down and tighten it easily. so I can place it against my semi circle timber form, measure it, then adjust and reattach. works a treat!

thanks for the help guys