Author Topic: Surf PI progress - more coil former photos  (Read 821 times)

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Surf PI progress - more coil former photos
« on: July 12, 2016, 08:51 pm »
Hi all,

Thanks for the comments on my coil former. Here are some more photos which I hope will fill in some detail.

The first (called rib, just in case they appear in a different order on the screen) shows the upper surface of the lower plate, two of the ribs glued in place and a third rib (a spare rib!) standing between them. To give an idea of size, the rib is 30mm long and 6mm high, with a 3mm cut-out. The lower left- and right-hand ends drop into slots in the plate and are glued in place so the top edge of the rib stands 3mm above the surface of the lower plate. The underside of the upper plate rests on these ribs, spacing the plates apart 3mm. I chose this spacing based on the estimated diameter of a 20-turn coil of 0.56mm diameter Kynar-insulated wrap wire, plus a little to spare. The left-hand end of the rib has a semi-circular notch where the turns of wire fit during winding. At first I was going to make a flat-bottomed channel for the wires, then a V-shaped channel, then U-shaped, and finally settled on this shape.

In photo 2 (called ribs) I've positioned the spare rib alongside a rib in the lower plate. This is how they are aligned when the plates are fastened together. You can see how they form a circular channel for the wires, with a 1mm wide entry slot with guide slopes on the left. As the final few turns of wire are added to fill the channel, the bundle is forced into an almost circular shape. Then there is hardly any change in shape when the lacing cord (waxed dental floss) is tied around the bundle to hold the wires tight. The right-hand ends of the notches in the upper and lower ribs are vertical, allowing the plates to be pulled apart without snagging the wires once the lacing is complete. The superior kind of lacing knot (I was told it was called the "admiralty knot") doesn't work with dental floss because the friction is too great to allow it to be slid into position before tightening. It does make a very good start-and-finish knot, though.

Photo 3 (hex) shows the only difference between the upper and lower plates. On the underside of the lower plate I've glued discs of plywood with hexagonal holes to stop the bolts turning when I tighten the wingnuts on the upper plate.

I hope these photos are of interest. I'm going to make four or five identical coils of 21 turns, then try different Faraday shield materials, different amounts of spacing (one or two layers of spiral wrap) etc. For guidance I'm using "Making a Fast Pulse Induction Mono Coil - Geotech" which is on the web and contains lots of useful information.

Thanks for looking!