DCA: Fabracation 5 — How to Almost Scientificaly make a spiral

Making the brass spirals was a fun challenge. I could have freehand cut them with a plasma cutter but I’m not really steady enough to have them come out with nice even edges.

I could have drawing one on the computer and transfered it wood and used it as a jig/guide but not only would that take allot of work it would also be difficult to do for such a small tight spiral.

I really wanted to be able to geometrically construct and scribe a nice spiral on the brass and cut it with snips. However, geometrically constructing a spiral is even harder then drawing one free hand.

I also wanted to do this quickly — So I cheated.

I knew I wanted a 6.5″ diameter circle with a 0.75″ spiral strip. So I laid out a center mark, an abscissa and a ordinate. I then put another punch mark at + and – 0.1875″ (0.75/4) along both axes. I then placed one point of the compass at (-0.1875,0) and opened it up to 6.5″ from the origin. I then scribed a 90°, clockwise arc. I then moved the compass to (0, -0.1875) and closed it till it touched the end of the previous arc. I then scribed another 90°, clockwise arc. I then continued this pattern.

Of course, this is not a spiral. An Archimedean spiral, which I was trying to make, has a radius proportional to it’s angle, here the radius was fixed until it abruptly changed at each quadrant. In the photo below you can see this clearly and you can also see how this approximates a spiral very well on the exterior but breaks down severely on the interior.

However, the fact this breaks down at the center is not really a problem for me because this is where it will attach to the hub and so I won’t be cutting it all the way down. In the next image you can again clearly see how this approximation breaks down.

Deep scribe marks helped with the cutting quite a bit as they tended to guide the snips.

When ever I cut an arc I have a wonderfully experience where there is a sustained connection between my abstract, mathematical understanding of an arc as a line where no two successive points are linear and the concrete experience of slowly and continuously rotating the piece I’m cutting in my hand. I try to inhabit the curve — or “be” the curve in a kung-fu kind of way — is very meditative and zen. I think it is what I love about fabrication specifically, and creation generally — moving form the abstract representations in your mind to the concrete representations in the world. Science, to me has always been the same process but in reverse — taking something concrete in the world and abstracting.

Here you can see one spiral completely cut and raw. I’ve not cut it all the way down because this is where it will attach to the hub.

Here you can see the final two spirals. One is clockwise, the other counter clockwise. Now they are all filed down smooth and have a hole in them so they can slip down the copper rod and onto the hub.

I’ll be damed if any one ever notices that this is not a real spiral.