Coil Base and Primary


The coil base is composed of two circular pieces of .75" plywood. The bottom deck has 4 wheels mounted on it for easy movement of the coil. The top deck has 8 primary supports, each consisting of a wooden piece with a routed groove that matches an HDPE strip, with notches to hold the primary tubing. The HDPE pieces were made from cutting boards (Wal-Mart). I cut these with a table saw, routed the notches, filed the rough edges and then used a heat gun to melt down the fine ragged pieces that were left.

Mostly for appearance, I added an acrylic cover for the primary. I drilled one small mounting hole into the center of the square acrylic sheet. A second hole, large enough to accept the cutting bit for a Dremel MotoTool, was drilled at the correct radius. Then the sheet was mounted onto a piece of 1x2 (clamped onto my work table) into which I had mounted a MotoTool attachment and cutting bit. By slowly turning the sheet, a perfect circle was cut. The edges were pretty ragged (quite a bit of melted acrylic), but some work with a file trimmed it up pretty well. I had two cuts to make. The second one, for the inner hole through which the secondary passes, is shown being cut in the pictures below.


Shown next is the assembled base. There is sufficient room on the bottom deck for the MMC and triggered spark gap. The secondary support is made from a variety of PVC pieces, constructed to provide adjustment of the secondary 3 inches above and below the plane of the primary.

Here is a closer look at the secondary support assembly. The basic construction is an interleaved combination of three major parts. On the bottom deck, a single firmly mounted piece of PVC projects upward. It is the innermost part of the three interleaved parts. In the picture, it is the piece at the very bottom with the holes drilled through it and the wooden dowel in place to select a height. The middle piece attaches to the secondary. It slides over the piece that projects from the bottom deck. The middle part consists of two reducing couplers and a short piece of PVC. The bottom (smaller) reducing coupler had to be ground out a bit so that it provided a snug fit over the bottom deck PVC piece. That coupler is sitting on top of the wooden adjustment dowel. The other coupler is the larger one that holds the secondary. It can be seen at the very top, amid the primary supports. The third major part is a second large reducing coupler and drain flange mounted to the top deck with bolts through four small pieces of PVC. This coupler also was ground out so that is would provide a snug fit for the middle part. The long tube of the middle piece (that has the coupler on top that holds the secondary) slides through the bottom of the coupler that is mounted to the top deck and then over the PVC tube projecting up from the bottom deck. The entire assembly provides a very solid and adjustable support for the secondary.


The primary is constructed from .25" copper tubing, with .25" edge-to-edge spacing between turns. The notches on the HDPE supports were routed to be .25" but the use of the heat gun to finish those pieces resulted in notches that were a bit smaller than .25". That worked well because the primary coil could then be mounted snugly. It wound onto the supports quite easily with just a little bit of adjustment after the coil was mounted to even out a few areas.


Here is the finished base and primary, with the acrylic cover mounted (nylon screws tapped into the HDPE primary supports) and a strike rail added (.25" copper tubing, mounted on HDPE supports, above and outside of the last primary turn).