Indespensible tool

[knary]

Greetings:

I am new to the forum and have found a wealth of information here in preparation for my build. I plan to build a 42" Pompeii. In scanning the forum, I have found several posts regarding the "indespensible tool" and its variations. Several people have stated that they would either pass their tool along to the "community" or build one for those interested. I do not know how to weld and would love to get one of these tools prior to building the dome. Can anyone help me out? Thanks

[fxpose]

Re: Indespensible tool

Several variations of this tool require no welding at all to build. In fact, I believe the majority of the I-tool users here didn't have to weld any part of their tool, including the one I used.

[DaveW]

Re: Indespensible tool

A friend welded one up for me but if you are building a half-sphere dome all you need is a stick. Attach it to the center with a hinge and mark your dome diameter on the stick. Then all you have to do is make sure your bricks line up with the mark and that the stick rests flat on the top of each brick as you build the dome. I would send you mine but i pitched it.

dave

[knary]

Re: Indespensible tool

Obviously this whole oven building experience is new to me, so please bear with me. I did see some variations that do not require welding and will pursue building my own indispensable tool. For a 42" oven, I assume the tool should be 21". That would create a dome height of approximately 21 1/2" when factoring in the width of the plywood base. That is 3" higher than recommended. Does it matter? Is there a technique to create a lower dome height? Thanks again.

[gdest]

Re: Indespensible tool

Take some advise here from the slowest oven builder known to man. Your playwood base can be made from 1/8" luan. Now you will also find out that once you draw your radius (21") and set your first course, your indenspensable tool will be a little shy depending upon how high your shoulder course is. Now that is all said and done, don't worry about the small stuff.

Gary

[DaveW]

Re: Indespensible tool

Does it matter? Is there a technique to create a lower dome height? Thanks again.

If you use a hinge to attach the indispensable tool so that the hinge pin is an inch or two from the center pivot you will achieve a slightly lower dome.

We built a 38 inch oven. You can see the indispensable tool is hinged only about one inch from the center. Therefore the tool is 18inches long rather than 19. If I used the tool for all of the bricks I would have achieved an 18inch dome with a small flat center two inches in diameter. But the tool is just a starting point not an exact science.

Happy Building!

Dave

[dmun]

Re: Indespensible tool

You can also make the length adjustable, so the upper courses are closer to the pivot point.

Remember: The strongest dome is an inverted catenary shape. That is very high, too high for a practical oven. The hemisphere shape, what you get with a plain pivot arm, is nearly as strong, but lacks the resemblance to the domes they make in Naples. The flatter the dome, the more side thrust, and the more engineering challenges. Very flat domes, particularly with high soldier courses, need side buttressing or reinforcing to succeed.

[fxpose]

Re: Indespensible tool

Here's a crude, but effective off axis I-tool I used which required no welding at all.

You will find that no matter how well you design your I-tool it will require slight adjustments as you go and you'll quickly adapt to it.

[terrihoward]

Re: Indespensible tool

Hello.....

I just finished my oven and have a tool you can borrow. I am in Leavenworth Washington. I will try and e-mail you directly.

[knary]

Re: Indespensible tool

Thanks Terri, but I built a version that I think will work for my build.

[Faith In Virginia]

Re: Indespensible tool

You can also make the length adjustable, so the upper courses are closer to the pivot point.

Remember: The strongest dome is an inverted catenary shape.

Hay dmun,

That is a great page on "cantenary" I hope the link was not overlooked it has a wealth of information. Thanks for the link and that fills my "lernt something today" quota.

Thanks Faith

[dmun]

Re: Indespensible tool

That's one of my long-time frequent links. It pays to read it, as it explains a lot about the forces acting on arches and domes.