Ever heard of Zipshape? It's a technique developed by Schindler Salmeron which lets you to draw a free-form profile curve for (say) a piece of furniture, and then cut a series of teeth into two sheets of thick material like MDF. Those custom-cut teeth are very specifically shaped and matched to each other such that they can "zip" together, but only when the sheets are bent into the curve that you drew at the beginning. The result is amazing: free-form bent furniture parts that you can glue up without molds of any kind. Draw a curve, cut the teeth, slather glue, stick it in a vacuum bag, and let it set.
Here's the rub: each tooth needs to be cut at a very slightly different angle in order to "zip" together properly. Thought you could rig your shopbot to do this for you? Nope, sorry. This process needs a full-fledged 5-axis CNC, or a 5+ axis industrial robot arm, or some crazy experimentation with an open saw blade. Not your usual fabber's tools. Here's how Schindler Salmeron illustrate it:
This instructable is the first in a planned series, the ultimate goal of which will be to make zipshape accessible for all with a regular 2-1/2 axis CNC (Ie, using only profile and stepped fixed-depth cuts). I will be developing browser-based online tools to handle the geometry of it, and I'll be inventing a new form of zipshape which makes it possible to cut it using only straight orthogonal cuts. Follow my series! By the end, you'll be able to draw a curve, download a DXF file, cut it on your shopbot, and glue it up into a beautiful piece of furniture. No molds required! Here's a rough table of contents for the series:
Part 1: Introduction to zipshape, my own experience with zipshape, prior work that's been done in the area, the problem to be solved, the proposed solution, tests proving the concept.
Part 2: Refinement of the tooth geometry, a more in-depth look at the geometry and math that make zipshape work. The building blocks of the future web-app to bring the process out of Rhino and into Chrome.
Part 3: To the CNC! Prior tests will have been lasercut in 2 dimensions; In part 3 we'll be moving to the CNC and fixing any bugs that come up with the shift to more furniture-like parts.
Part 4: Design of a finished piece, and Introduction of the web-based tool. Since it will be built on fundamentally different platforms, further 2D tests will be done to verify that the geometry is true to the original method. A final piece of furniture will be proposed, but for all those following along, this is the point where you can design your own.
Part 5: Construction of the new & improved 2-1/2 axis zipshape furniture (type to be determined in part 4).