CNC milling of ribs

Last time we wrote about how verly light AIREX® panels can be produced. Now it’s time to use that panels. Obviously one can use a simple saw and cut ribs off the panels. However, the ribs are large and need to be somehow transferred. A piece can be drawn in a CAD program and printed on several pieces of paper or tranferred by mere measuring and painting on the panel. Both approaches are tedious and precision is an issue. We are lucky to know somebody nearby with a self built CNC machine. With a good drawing and some experience it works like a charme. Thanks again for the help, Marcel!

Everything starts with making a good drawing a the piece:

rippe

I use a simple but good 2D-CAD program (QCad for Linux). If you look carefully at the drawing, you’ll see a chamfer at the left edge, which makes the piece more complicated (3D instead of only 2D). This drawing was imported in SolidWorks—a great but expensive 3D-CAD program—and converted via a STL file into G-Code by another tool. G-Code is what the milling machine understands. So much for the theoretical part…

Theory ends and practice starts after having a milling program. The panels have face sheets of carbon and flax fabrics. Carbon creates very stiff but brittle laminates. Flax keeps the carbon together and substantially increases robustness—similar to aramid. The AIREX® core is light but also soft. This mixture is difficult to mill properly, when the wrong router is used. Probably milling aluminum is easier than these panels. Anyway, the first time we used a router for metal. The result was pretty good, but the edges were quite fluffy. Nothing that cannot be corrected with some 400 grit sand paper. For the following pieces we bought a composite router (Karnasch 29.1783). It was not cheap, but the result was great.

Here’s a video of the machining:

I think the video speaks for itself!

We started to fix the ribs on the upper sandwich of the center section. Soon we’ll be able to „marry“ the to halves.

 

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