Coil former made of cast acrylic sheet

This article describes a coil former made from 3mm cast acrylic, cut on a CNC router, part designed in Freecad. The project is really an exploration of manufacture of one on my CNC router.

Above is a 3D view of the part design.

The small holes are for the coil of hard drawn copper wire, formed into a helix on a mandrel then wound into the holes. A small python script was used to layout the wire holes. The tab is designed to be folded so that the left hand end forms a mounting foot.

Above is for made part. This is black acrylic which I would not normally use because of the risk that it is a lossier dielectric than clear acrylic. On test, this does not warm in the microwave like I have seen grey PVC, so it is likely that it does not contain carbon black, or other very lossy pigment.

The glass transition point of acrylic (PMMA) is around 105°, somewhat higher than the styrene often used for coil formers.

The inductance of the 6t helix of 2mm copper with 3mm pitch should be about 470nH which happens to be the inductor used at A common scheme for narrow band match of an end fed high Z antenna.