Sometimes while working on a project there comes a point where a specialized tool is needed. That necessary tool may or may not even exist. While [Fabien] was working on his DNA Lamp project he needed to bend a copper wire into a helical shape. Every one of us has wrapped a wire around a pencil and made a little springy thing at some point. While the diameter may have been constant, the turn spacing certainly was not. [Fabien] came up with a simple gizmo to solve that problem.
The tool utilizes an 8mm rod that will ensure the ID of the helix is indeed 8mm. We’ve already discussed that was the easy part. To make certain the turn spacing is not only consistent but also of the correct amount, a wooden frame is used. The frame has holes in it to allow the 8mm rod to pass through. Adjacent to those rod holes are much smaller holes just a bit larger than the copper wire that will become the helix. These holes are drilled at an angle to produce the correct turn spacing. [Fabien] figured out the correct angle by taking the desired turn spacing distance, helix diameter and wire diameter and plopping it in this formula:
asin(8+1.5/24+1.5) = 21.87°….. 22° is close enough…
At this point the rod is inserted into the wooded frame and the wire is passed through the 22° hole. The wire is then held to the rod and when the wooded frame is twisted, a perfectly spaced helix is left in the wake. The measured variation of the 24mm spaced helix was only 0.2mm. [Fabien] is not done with his lamp yet but he expects it to be completed in a couple weeks. We are looking forward to it.