This coil is wound on a 4.25" OD X 22" long thin-wall gray DWV PVC former. The former was prepared by inserting two 1/4" thick acrylic disks inside at approximately 1/3 and 2/3 of the length of the tube. The disks were epoxied in place and the center holes plugged with clear silicone RTV sealant. The former was then placed in the lathe between two plywood disks specially made for this purpose. The lathe was turned on, then the former sanded with 100 grit sandpaper on a hand held block to remove the printing, dirt, etc. and to roughen the surface. A final sanding with 220 grit wet or dry sandpaper completed the preparation. No attempt was made to dry the former as it had been in the attic for several years and would not have had much opportunity to absorb moisture there. It gets pretty hot up there when the sun is shining (rusty tin roof) even in the winter time so I figured drying would be a waste of time.
The next step was to attach one end of the 26 AWG magnet wire to the former with Scotch 27 (3M brand thermosetting fiberglass cloth electrical tape) and start the winding process. Since I was winding on a lathe, I used the power feed set at 40 TPI to carry the spool of magnet wire and a guide made from 1/4" polyethylene tubing to wind the coil. 20" of winding length resulted in 800 turns. The other end of the magnet wire was then attached by Scotch 27 tape.
After the winding was done, I made a drip pan out of aluminum flashing material to keep the epoxy resin off of the lathe, then poured on a coat of Bondo brand marine epoxy resin with the coil turning slowly in the lathe. The lathe is left running until the resin has set up. This method assures a uniform and smooth coating that is both durable and good looking. Usually. On this coil, however, the temperature was very low at the time and it took a long time to cure. I believe some moisture must have condensed on the curing epoxy as it has a cloudy appearance to it.
Once the resin had cured, I proceeded to install the end disks to the former. The bottom disk has a copper strap set into it. The strap runs from the center hole to the edge of the disk. The magnet wire is soldered to the top of the copper strip inside a small cavity milled out for that purpose. A brass nut is soldered to the top of the copper strap over he center hole. This nut is inserted into the larger center hole in the bottom end disk and the strap, nut etc. are epoxied in place. The nut is used for mounting purposes as well as providing the ground connection to the secondary coil. The top end disk has a 1/4" X 2" nylon bolt screwed in from the bottom and epoxied in place. The tail of magnet wire at the top of the coil is soldered into a piece of refrigeration capillary tubing and one complete turn is made around the coil. The capillary tubing is secured in place with Scotch 27 and a saturating coat of epoxy resin then applied to the tape. The capillary tubing has enough sticking out to make a couple of loose turns up to the top-load attachment point.
The primary coil is made of 1/4" O.D. copper refrigeration tubing. The tubing is wound into grooves milled into 3/8" X 3/4" X 6 1/4" support blocks cut from a HDPE cutting board. The grooves are 1/4" deep by 1/4" wide and are 1/4" apart. The five support blocks are mounted by nylon screws to a 20" diameter acrylic disk. The disk has a 6 1/2" diameter center hole to allow for the secondary mounting assembly and has five hand holes to allow tapping the primary from the bottom. The primary support disk, as well as the secondary support disk, is mounted on PVC pipe "towers". Five for the primary disk, and three for the secondary disk. These "towers" are just friction fit pieces of PVC pipe (schedule 40) pushed into PVC couplings with PVC plugs in the other end of the couplings. The plugs are drilled and tapped to accept 1/4" 20 tpi nylon machine screws. These tower supports are attached to the primary and secondary support disks at the top and to an acrylic base plate at the bottom. This makes for a somewhat spidery appearance, but allows a wide range of coupling adjustment that is relatively easy to do by varying the length of the pipe segments.
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