Work on the Secondary Coil End Caps

I was hoping to finish off the top and bottom coil end caps today but this didn't work out. I needed to bond an acrylic plug into the central hole in the bottom cap. This is to close up the hole needed to mount the coil in the winding jig.

I also trial fitted the eight nylon bolts that will hold the coil down onto the Tesla body.

Here's a close-up of the plug in place. I also planned to bond the toroid mounting assembly to the top cap of the coil. This would, again, close up the hole needed for the winding jig.

Bonding was going to be achieved by using Tensol acrylic cement which a had purchased a while back from Trent Plastics. When I dug out the bottle the liquid was thicker than I had anticipated. From videos I had seen, bonding sheet acrylic was done using a water-like solvent that used capillary action to penetrate between two close fitting acrylic sheets. The liquid I had was like syrup and there was no way this would seep into a fine gap. I assumed all Tensol was the same and you know what they say about assumption. After a bit of investigating I think I have Tensol 12 which can be used for bonding gaps between rougher cut acrylic pieces. Tensol 70 is the version more suited for close fitting sheet acrylic but it was averaging out at £40 and minimum qty 500ml. Too much and too much. More homework was needed.

Here's what I found out. These water-like acrylic cements don't actually "glue" things together. It's more like a weld. The solvent dissolves the surfaces of the two pieces and the molecules merge from either side. The solvent evaporates and the two pieces become one. The solvent in these cements is Methylene Chloride also known as Dichloromethane. It's pretty nasty stuff but apparently it's all you need to bond close fitting acrylic and you can get it from eBay or Amazon. I paid £4.79 for 250ml, delivery was almost £8.00 because of it's hazardous nature. It should turn up tomorrow so will try it and let you know.

Anyway, crack on. I bought some shorter (12mm) cheese head slotted M4 nylon screws to fix the top and bottom caps in place. The 20mm bolts are a bit excessive!

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Secondary Coil Ground Terminal

I have just finished the lower electric connection to the secondary coil. As explained in previous posts this connection is made up of a 70mm x 23mm copper plate on the side of the secondary coil. The plate will be glued in place using 2 part epoxy. After deciding the final position of the copper plate I surrounded the area with masking tape, not really to offer any protection to the surrounding area, just as a guide. The inside of the area was deeply scored with sharp craft knife to produce a good key for the epoxy.

The copper plate was tinned (to aid soldering) and then the lower lose tail of the windings stripped of varnish and soldered to the copper plate. I used my new Dremel VersaTip to do the tinning and soldering. I bought it really to use as a small blow torch for tinning and delicate metal work, however I was very impressed with its soldering capabilities.

Here's a shot of the tail end of the windings attached to the copper terminal. The back of the plate was cleaned up with a brass wire wheel on the Dremel 8200 then cleaned with meths to remove all soldering residues. I removed the masking tape from around the scored hatchings on the coil, this would allow me to position the plate better by eye.
I mixed up a blob of 2 part 5 minute epoxy glue and applied it to the back of the copper terninal plate. Forgot to mention I had cross-hatched the back of the plate to aid bonding.

I positioned the plate onto the coil and lined it up parallel with the windings and made sure the lose tail was positioned nicely around the coil and taught. I held in position for about 5 mins while the epoxy hardened.

The plate got warm as the epoxy went off,  so easy to judge when it was safe to release pressure. I neatly positioned the tailing winding wire so it made a nice spiral from the end of the windings to the copper terminal.

Then I used a small brush to cover the tailing wire with insulating varnish which will protect and hold the wire in place on the form. I gave the tail wire 3 coats.

Here's the finished terminal. Think it looks pretty good.

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Winding the Secondary Coil for the second time.

The new secondary coil form has been sat in my homemade coil winder for long enough. It's time to start winding.

In my last post I gave the new stats for the replacement coil. The only change I have made is to start the windings 4.5cm from the base of the coil rather than 4.0cm. This change is just to allow a little extra room at the base of the coil to accomodate the copper plate that will act as the lower electrical connection. This will mean with the same number of turns (1050) the windings will finish 0.5cm higher, 8.3cm from the top of the coil.
 Before starting the winding I thoroughly cleaned the outside of the coil with meths to remove all traces of grease. I ran a line of masking tape around the coil with the top edge of the tape exactly 4.5cm from the base of the form. This would ensure that the windings would start exactly level with the base of the form. I measured 67.2cm (total height of windings required) from the top edge of the tape and marked this point on the form with a small pen dot. I would coil tightly up to this point then loose coil to the top of the form.
Well almost ready to start. Not quite. This time there's no help available..... and believe me, its better to have an extra pair of hands when winding a coil especially if you are relying on human resources to tension the feed wire and direct the winding wire onto the coil. Manual winding requires both hands, one to feed the wire (left in my case) and the other hand to push the coils together either with a non scratch implement or the back of your finger nail. This means you have no free hands if you need to stop (or start) the winding motor. My winding motor is powered by a variable power supply on the bench the winding jig, not exactly "to hand". I would need some way to switch it on/off remotely.
Bingo. Idea.

I plugged the power supply into one off those remote control mains switches. This one is a cheap as chips version from Maplin similar to the one linked.

Here's the little controller. I can either have it close to hand or even put it on the floor and press the off button with a press of a toe.

The winding wire end was clamped under the head of one of the white plastic bolts that holds the base coil end in place. You need to have a plan in place to clamp the wire end tight when you finish the windings, I decided to clamp it with the same method as the start, using one of the bolts that holds the top coil end in place.

Time to turn.

Well it took about an hour and went pretty well. Stopped just once when I realised I had left the door open. Two kittens and turning a tesla secondary coil are not compatible. Here's a quick vid of the finished coil. I have put on a couple of coats of insulating varnish. Still needs another couple of coats.

I am really happy with the finish. The varnish has a better finish than on my first coil. Next up is a few more coats and then fitting the copper plate electrical connection at the base of the coil.

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