Sketching in metal

I’ve been busy lately preparing a production model of the Sparrowscope. A production model not only functions in the same way as the final product, but it’s made in the same (or close to the same) way as the final version will be as mass-produced, from the same materials. I have several components being machined, laser-cut, bent, welded, and 3D printed, all of which will make it to this blog soon.

Getting to this stage has taken a lot of testing, in approximate calculations, simulations and physical models. It’s possible today to—without leaving a computer—design a part, specify the forces acting on that part, and measure the stresses and deformations. But only a part of the academic engineering world thinks that physical prototyping is history. I think Boeing even changed their mind about this one. There are all sorts of things you find out when you put all of the components together in real life, which you may have missed on a computer. Sure, there are some simple products where our ‘virtual prototyping’ capabilities are sufficient, but I’ve certainly learned lessons and made improvements to the Sparrowscope by going to the shop and making things.

I had to pick a gauge of aluminum for main structural components in the Sparrowscope. Running a few simulations was a painless way to get a sense of an acceptable range, given a multiple (that’s the safety margin) of real-world forces. I knew these forces not from simulations, but from actual measurements in experimental tests. But rather than try to simulate all of the possibilities of loading the part, I took a high-strain area and roughly manufactured it in a few different metal gauges. That gave me a real sense of how stiff this part feels. I didn’t need perfect test pieces, I scribed a segment of the design onto each sheet of aluminum by tracing a pattern, cut them out with tin snips, and took then to a sheet metal brake to make the test parts.

scribing cutting bending

Now of course, to anyone who has dealt with sheet metal, you know there’s a bit of a trick here. You can’t make these three bends together on the sheet metal brake I’ve shown; the two bends in one direction would put metal ‘in the way’ for doing the outward bend. The last bend of the tapered segment was done by hand in a vice. Like I said, it didn’t need to be perfect, rough edges were fine. I just needed approximate versions of these shapes to play around with. It’s like a sketch, but made from sheet metal.

Leg segment sketch in sheet metal

The last picture shows the orientation of this segment in the actual design, but I realize that writing this doesn’t explain how the part works… soon I’ll have pictures to show yo how the whole Sparrowscope comes together! I’ll also talk a little bit more about prototyping in a future post.