Introduction: Swiss Army Chair
The Swiss Army knife was designed for optimal utility and convenience. This pocket knife consists of an assortment of tools that can fold into a compact configuration that safely and comfortably fits into a pocket without compromising the functionality of the tools when unfolded.
The goal of this project was to modify the Swiss Army knife design to build functioning full scale objects not typically associated with being portable. As a proof of concept, I chose to design a pocket chair with the cheapest materials I could find.
In the end, the bounding box of the unfolded chair was 67 cm x 36 cm x 28 cm. The bounding box of the folded chair was 16 cm x 7 cm x 3 cm, equal to 1/200 the volume of the unfolded chair's bounding box.
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Step 1: Materials and Tools
The chair is made of the following components:
(A) 6" tongue depressors (Amazon)
(B) Snap fastener posts for leather (Line 24, 5/8" cap diameter)
(C) Snap fastener studs
(D) Snap fastener sockets
(E) Upholstery fabric (strong fabrics such as nylon, polyester, etc.)
Epoxy adhesive/Krazy glue
- Laser cutter
- Line 24 snap setting tool
I chose to use tongue depressors, but a 1/16" sheet of plywood (or any other suitable laser cutting material) would work, too.
Most snap fasteners come in a set of 4 components. A full snap fastener kit can be found here including all components and the snap setting tool. Some leather and sewing shops sell replacement parts of individual components such as this one. Alternatively, the design can be altered to accommodate the use of grommets.
Step 2: Lasercut Tongue Depressors
Cut out the 30 tongue depressors based on the attached DXF file. In the red and blue image, the blue lines are the outline of the tongue depressor and the red line are the cutting lines.
The laser cutting components are:
(a) Regular Beam x16
(b) Slot Beam x2
(c) Long Beam x2
(d) Flat Beam x4
(e) Short Beam x4
(f) Short Slot x2
(g) Straight Connector x16
(h) Angled Connector x4
Step 3: Glue Connectors to Beams
Connectors are used for hard stops to limit the rotation of beams. There are two types of connectors: straight and angled. The procedure for gluing connectors to beams is shown in the first image.
The second beam shows all the beams and connectors that need to be glued. The orientation is important. Note that for the straight connector to slot beam connection, it is inverted compared to the other connections.
After gluing, wait for the bond to develop full strength (one day for epoxy).
Step 4: Making Hinges - Joining Procedure
The snap fasteners act as a hinge between beams. Most hinge connections join two beams together. The image shows the procedure for making a simple hinge between two beams.
There are three types of hinges in the design. This connection is used for the majority of the hinges and the other two hinges will be shown in the next two steps.
Step 5: Making Hinges - Triple Joint
In two of the hinges in the design, there are triple joints that connect three beams. The procedure for the triple hinge is shown in the image. The beams need to be stacked in the right order and orientation. From bottom to top, the order is short beam, flat beam (connector end), and regular beam (mating end). The snap post is about the same length of the three stacked beams, which requires more care when hammering the post.
Step 6: Making Hinges - Socket and Stud Joint
These snap fasteners are traditionally used for leather as seen in this tutorial. In this design, the leather is swapped with the beams.
After making two triple joints and joining the double joint between the short beams, lay out the beams into an H configuration (top left). Get two regular beams, 2 snap posts, 1 snap socket, and 1 snap stud. In the top left figure, the numbers are ordered so that number 1 is closest to the ground and 4 is furthest. In the end, you want to make these hinges so that the socket mates with the stud when the beams are cross-oriented.
Step 7: Making Hinges - Beam and Hinge Map
Here is the overall layout of how the beams are connected for one half of the chair. The other half of the chair is the exact same layout. Arrows denote hinge locations. The bottom two connections are triple pivots and the middle connection is the stud/socket hinge.
After making a duplicate of this layout, the rigid components of the chair are finished. The next step is the chair seat. This is made up of two sets of two joined beams, which will be explained further in the next step.
Step 8: Fabric for the Chair Seat and Backrest
The chair design requires two pieces of fabric: one for the seat and for the backrest.
For the seat, cutout a 26 cm x 45 cm piece of fabric (see first image). Place the two set of beams for the seat parallel to the short edge of the fabric. Draw two lines parallel to the short edge that are 35 cm apart. Add super glue (or other adhesives for fabric) along these two lines and fold the outer edges of the fabric. Wrap around the beams to create a loop on the edges and pull out the beam.
For the backrest, cutout a 13 cm x 36 cm piece of fabric and repeat the same steps as the seat. The two seams for gluing should be 26 cm apart.
Instead of gluing, sewing works as well.
Step 9: Chair Unfolding
Step 10: Chair Folding
Step 11: Summary
Unfortunately (and probably expected), this chair is not functional and can support about 20 pounds. The chair buckles and collapses under heavy load. Future iterations of the design will be aimed to accommodate a larger load through material choice and geometric refinement.