This copper loop jig should help me create a perfect circle for my magnetic loop antenna.

So, how do you transform a small coil of copper from Canadian Tire into a large five foot diameter loop antenna? One way is to un-twist the 18” coil by hand and slowly form a larger loop. This will work, but probably look a bit distorted. Another way is to buy a professional copper bending tool for doing the job. Plumbers use these. But I would prefer not to spend that much money for a one-off experiment.

My compromise is to build a copper loop jig with my CNC. The diameter of the flexible copper tube is 1/2”. Using a CAD program, I designed an arc with a 2.5 foot diameter and placed it onto an 18” long solid form. I widened this arc to form a 1/2” channel in the material.

Shown above is my MPCNC carving out a contour into an 18” length of hardwood. The piece of wood is 3/4” thick and 3” wide, so there is just enough room for the curve to fit.

If all goes well, I should be able to unwrap the small copper coil, and use the copper loop jig to slowly form the larger loop eighteen inches at a time. Stay tuned.

Copper Loop Jig Learnings

While making this jig, I learned a few things.

• Probably use softwood instead. Hardwood is, well, hard. Milling a contour requires slower feeds and shallower cuts, and takes a long time.
• Check to ensure that you are making the channel wide enough. I needed to waste timing filing the width to get the pipe to fit.
• Check your calculations. The first time I tried this, I mistakenly used the diameter of the loop rather than the radius when designing the arc. This resulted in a copper loop jig designed for a much larger circle than I needed.