The leveling tool called an "indispensable tool" (IT) or dome gauge is used to help builders of igloo-shaped traditional wood fired ovens maintain the correct brick placement and angle when laying the bricks. For cob constructed ovens the cob is generally placed upon a foundation of sand where the level of the walls is not critically important. With brick ovens it is important to maintain the level and angle of the bricks to make construction easier and ensure the completed dome is aesthetically pleasing.
There are a number of ways to build a dome of bricks including with or without a temporary supporting frame. For an experienced builder, this may be performed freehand without a leveling tool or supporting frame. As most DIY builders are not particularly experienced, constructing by freehand may not be the best option and thus the indispensable tool becomes useful. The tool is usually placed in the middle of the dome during construction, similar to a compass, and is slowly rotated to keep the spherical shape of the dome consistent.
A lot of designs for making a leveling tool exist. The form chosen is highly dependent on the preferred usage, the tooling material available, and the structure of the oven you are trying to build. Some builders use bar clamps or spreaders while others use a piece of wood with a small block attached to the end where it will support the brick. There are a lot of DIY builders who have been very crafty in making up unique ideas in building this tool. A cheaply built tool may be constructed out of scrap wood pieces. Bolts, clamps and metal rod may alternatively be used to construct a more reliable and longer lasting tool.
The following are some examples which give an indication of how to make the tool and which type of materials are usable:
One of the famous tool builds was Hendo's Dome Gauge which was innovated by Paul Henderson, nicknamed Hendo, from a popular DIY forum. Unfornately, we was not able to perfect the tool before his demise which led to a lot of other forum members to use his work as a foundation and then, modify it in some way that is compatible with their plans on building their domes.
There a number of factors you have to consider in making a leveling tool. Some of which are:
Also, using a round board (for wooden builds) could be helpful when stacking up the bricks as this serves as the guide to where the indispensable tool will be attached and how the bricks will follow the curves. Although the IT needs to be attached to the center of the dome, it still needs to be adjustable to complete the dome accurately.
The center of the IT should hit at half the thickness of the brick or else the angle of the tilt on the dome is off center. It then becomes cumulative on each course.
When building an indispensable tool, it should definitely be adjustable to suit the movements it will undergo in accurately completing the dome. Regardless of the primary material (metal or woood), a turnbuckle could be helpful especially when dealing with tight spots to avoid bump newly set bricks.
Making a wooden leveling tool is relatively easy. You just need a measuring tape, hammer and a set of nails to attach everything together. For proper structuring, the L-bracket or metal clamp goes on the top of the leveling tool. This will hold the bricks in place in making the dome. The length of the lumber will depend on the diameter of the dome. Usually, it is the same length as the radius. You need adjustments, however, to make it easier for you to pivot the tool around the middle of the dome.
Before starting to weld your leveling tool or indispensable tool together, you must cut the metal pieces for your clamp slide to fit in your clamp. Next, weld the slide to the end of the clamp. After welding is complete, attached the welded parts to the wing nut, the screw bar, internal tooth lock washer rod coupling nut and hollow steel together. Use the recess to accommodate both the washer and post. Place one washer beneath the recess and another flat washer at the base of the hinge. Secure the pivot post by welding it to the hinge.