Secondary base finished

Just got in from the garage.  Spent a couple of hours drilling and tapping the holes in the secondary coil and the bottom disc.

The eight holes around the perimeter are tapped to accept 20mm M4 bolts which will pass through corresponding 4mm holes in the secondary coil. The other eight holes started as 7mm plain holes and were then tapped to M8. They will be used to bolt the secondary coil down to the base.

The holes were drilled with the disc in situ inside the secondary coil. The drill size required is 3.3mm. After drilling the components were separated and the disc tapped to M4. The 3.3mm holes in the secondary were opened up to 4mm.

Here you can see the base disc bolted inside the secondary coil. Think it looks great and, as usual, completely over engineered.

I have used nylon bolts, not sure if it would be OK to use metal so opted for nylon.

Second Thoughts

After deciding to upgrade to a 6" secondary coil I got on the phone to Trent Plastics to order the relevant pieces of perspex. These consisted of a 810mm length of 150mm diameter clear acrylic with a 3mm thick wall and two 144mm diameter 15mm thick clear acrylic discs which will be inserted inside the ends of large tube and form the top and base of the secondary coil. I normally deal with a guy called Levi who is always on the ball, I was a little concerned that the discs would not be a good fit inside the 150mm tube due to variations in wall thickness that occurs in extruded acrylic tube so I asked Levi to check the fit of these discs inside the large tube. Three days later and a long cardboard covered tube turned up. I checked the fit of the discs and they were a perfect close push fit inside the large tube.

The above pic shows the 150mm diameter tube, it still has the protective plastic film and I have added masking tape so I can mark the position of the 8 4mm holes that will accept the M4 nylon bolts to locate the top and bottom perspex end caps.

Here are the 2 end caps. They are sitting on a 12mm thick 500mm clear acylic disc which will be the base for the primary coil. The disc on the left is for the bottom of the secondary coil and will be secured to the primary coil base by 8 M8 40mm Nylon bolts. You can see I have already marked the disc for drilling.

The holes need to be drilled to 6.8mm and then tapped for the M8 bolts. This means the bolts will be captive in the secondary coil base which is needed as there will be no access to the bolt heads once the secondary coil is assembled.

Assembled so you get the idea.

The base disc will attach to the secondary coil tube by 8 X 20mm M4 nylon bolts which will be located equidistant around the circumference at a height of 7.5mm.

Starting to get worryingly large!!

Power Feeds from the Variac

The Tesla coil will need 2 power sources. One variable AC from 0 to 110V for the neon transformer and one fixed 240V AC in to supply the synchronous motor for the spark gap. Both power sources will come from my variac module, obviously the fixed 240V is just taped from the mains feed inside the variac case. The synchronous motor runs at a 110V so the 240V fixed supply runs through a stepdown transformer inside the Tesla coil case. I decided to use 2 IEC female panel connectors to get both power supplies into the Tesla case. They are positioned vertically aligned in one of the perspex sidewalls.

The lower IEC socket connects through a retro looking ceramic terminal block to the EFI/RFI filter and then to the neon transformer.

The hole required for each IEC socket was rectangular with rounded corners and was achieved by drilling four 8mm holes in a rectangle and then using a coping saw to saw from one hole to the next.

Have yet to wire up the top socket which will supply 240V to the stepdown transformer for the synchronous motor.

Ordered Bigger Toroid

I am now ready to start on the primary and secondary coil construction. So I started to look around for a toroid. Checked out a few sites but in some cases I was being quoted more for p+p than for the toroid itself. The plans I am working too (component wise) show the completed Tesla coil with a 12" toroid and an upgraded version with an 18" toroid. The later looked so much better, so I decided it would have to be an 18" diameter toroid. I emailed Alan from Teslastuff.com and he told me than he no longer stocked the larger toroids but would check to see if he could get one. A few days later, he emailed to say he could get me one and quoted me a very reasonable price with delivery from the US.

The above pic shows an 18" X 4.5" fitted to a 4" secondary coil. These toroids are constructed from 2 spun pieces of aluminium welded together then de-seamed. I checked with Alan to make sure that this upgrade would not need an increase to the dimensions of the secondary coil. He informed me that if I were still going to build a 4" diameter secondary then the dimensions would be as quoted in the original plans and no change was needed for the larger 18" toroid. However, if I wanted to upgrade to a 6" secondary the windings would have to be longer. Here we go!

Guess what? Yes. Have decided to upgrade to a 6" diameter secondary.......

Secondary Coil Winding Jig

After reading lots of tesla build diaries and after visiting many HV websites I have realised the only way to create a nice secondary coil is by winding it on some kind of jig. One of the favourite ways is to use a lathe and if the lathe is not long enough to create an "extended" tailstock. Unfortunately my lathe is nowhere near big enough as the chuck is only around 80cm and there's just not enough clearance to spin a length of 110mm (4") pipe. So I have decided to build a jig, but to keep it simple, it will be human powered (son Damien to be exact) and will be big enough to wind up to 6" diameter coils, just in case I want to upgrade from 4" in the future.

   One visit to B+Q later. I have

Pack of 2 lengths of 1800mm by 144mm by 20.5mm planed pine.
1 metre length of 10mm threaded bar.
1 metre length of 12mm OD 10mm ID steel tube.
Small bag of 40mm wood screws.
4 10mm plain nuts.
Wood glue.

While at B+Q I got the wood cut to the lengths needed for construction. The cutting service was free and meant all cuts where perfectly square.

The above pic shows the finished article. The base and the backboard are both 900mm long and are glued and screwed along the adjoining edge. The end plates are made by gluing and screwing 2 pieces of 144mm by 144mm by 20.5mm together. The end plates can then be stacked together and drilled at the same time. The hole needs to be 12mm. I then cut 2 40mm lengths of 12mm tube and hammered one into each hole in the end plates. This creates a neat metal bush in each of the wooden end plates. The two end plates were then screwed to the back and base board. I didn't glue them so they can be repositioned if needed.

Here's a closer view of one of the end plates. Doubling up and using 2 pieces of wood provides a bigger bearing for the shaft and also adds extra strength. The 12mm holes are offset to front and top of the end plates. This provides clearance from the base and back board to accomodate a 6" diameter pipe.

Not easy to see, but there is a neat little bush in there which should stop the threads chomping away at the hole.

First layer plastic surgery

Spent a couple of hours in the garage drilling the various mounting holes in the base. 4 X 6mm holes for the neon transformer and 16 X 4mm holes for the Terry filter, the emf filter and the mains connector module.

Another 12 X 4mm holes were needed to mount the 10x10mm perspex square rod that runs around the perimeter of the base.

These 10x10mm perspex rods provide a means to screw the side panels onto the base.