This stool resulted from an effort to utilize manual metalworking tools to realize an elegant and functionally designed stool. Using just a bending brake, a metal shear, a drill and rivet gun, you can construct a stable and functional metal stool out of a single sheet of 18 gauge aluminum.
With the simple methods of fabrication, the design embraces an geometrically modular aesthetic, and can be expanded upon in a modular fashion. Other, larger versions of this modular object could be a display rack, a frame for planting or storage, a larger seating area, etc.
Step 1: Design Stool, Catalog Members.
This project can take any number of permutations based on the angle of your vertical supports, desired seat shape, etc. This instructable will be outlining the steps required to make a 3-step stool with a hexagonal footprint and parallelogram steps.
Once the design was finalized, I cataloged down the members I would need. I set the step heights at 14", 28", and 42", so I needed four 2" strips at each height. In addition, for lateral bracing, I would need to form some angle straps. I identified 15 distinct areas at which horizontal angles could be used to stabilize the stool. These bracing members are 18", the length of one side of the equilateral triangle on which the footprint is based. Lastly, we will need the steps. I had considered a mixed media approach and using wood steps, but ultimately decided to leave it all aluminum. These platforms are a essentially a parallelogram formed by combining two of our 18" equilateral triangles.
Step 2: Acquire Materials
Once you've determined the quantity and type of members your design will require, lay them out on a sheet to determine the size of sheet metal you will need to get. Try to get a sheet about 25% larger than you think is necessary, to account for errors or extra members you may need. A 4'x4' sheet of 18 gauge aluminum was more than sufficient for this project. You will want to check to see the thickest gauge your tools can handle, and shoot close to that maximum to ensure greatest rigidity. In general it is not recommended to drop below 24 gauge.
Step 3: Cut Members From Sheet
You have already cataloged your members so this step will be relatively simple. You will be using the sheet metal shear to cut your vertical members, horizontal members, and platforms. As previously stated, the linear members on this stool were cut at 2" thickness to allow for 1" on each face once it is bent to an angle.
Step 4: Form Angles on the Bending Brake
Now you will be adding rigidity to your supports by bending them to angles. For this hexagonal design, the vertical supports needed to be angled at 60 degrees or 120 degrees, based where they are providing support. The horizontal members must be 90 degrees to provide two planes of shear rigidity. Determine the quantity of each angle at each length, set your bending brake to the appropriate angle, and bend away!
Step 5: Drill Holes
In order to rivet the members together, you will first need to drill holes in the aluminum. Determine what size rivets you will be using and choose a bit in accordance. Make sure your drills and bits are appropriate for drilling through aluminum. Drill your holes at every pin connection, which means the ends and sometimes middle segments of the vertical members. Set a standard, for example 1/2" from the edge. Accuracy in this step is essential towards having an well-fit final product. You will want to have several rivets along the perimeter of your steps, so set a standard for this as well and match these holes with the horizontal joist members which will be supporting the step.
Step 6: Fix the Connections
You will mostly be using rivets but if you would like to disassemble you can choose certain connections to use nuts and bolts. Try to assemble the step modules separately and then join them together at the end. You may have to do some re-drilling at this point if your original holes don't line up. Make sure not to forget your horizontal angle braces, these are essential to the stability of the stool.
Step 7: Final Touches and Testing
Once all your holes have been riveted and all your bracing has been fixed, give it a test run! If you aren't happy with the stability think about where you could potentially add more angle braces to provide rigidity in whatever direction the movement is taking place. Add any finishes - anodizing, painting, or powder coating.