Building a Tesla coil is hard and takes time. Despite this it is not too difficult. I managed it! If you have any experience with any kind of construction it will be of great benefit. Model airplanes, tables and chairs, homebuilt computers, even Lego will help u when it comes to building a Tesla coil. Most of the parts are readily available, although a few may be harder to find.
The power source for a Tesla coil is potentially the hardest bit in the construction. This is because depending on where you live you may find it very hard to get hold of a high voltage transformer. The easiest kind to get is a Neon Sign Transformer (from now on NST). If you live near a neon sign shop you can often just walk in and ask if they have any old NST's. They may give you them for free. This is because the old units must be thrown away otherwise. New ones can cost up to £100 so shop around. The higher the power of the NST the better. Mine each give 7500 volts at 30mA, or 225 watts each (power = voltage x current). I combine them for 450 watts at 60mA and 7500 volts by wiring the outputs in series. If you live in the UK it may be much harder for you to find a neon sign shop. There are alternatives. Oil burning Ignition Transformers (OBIT's) can be used but are generally not as good as they operate at a lower power output. Microwave Oven Transformers (MOT's) can also be used, but you need to get hold of two like units and build voltage doublers for each which can be difficult. The good news is once you have an NST or equivalent there is not much you have to do with it to make it work (unless you have two MOT's)
My Neon Sign TransformerThe secondary coil is the second hardest bit as it is easier to get hold of the stuff to make it, but much harder to make. In order to build one you need a length of non-conductive tubing, some thin magnet wire of 22-28swg, and a lot of varnish. The tube is the former for the coil and is used to wrap the wire around. The wire is wrapped around the coil. The varnish is to seal the wire to protect it and to add insulation. For this reason it is very important to use either a clear polyurethane varnish or an enamel varnish which must be solvent based, not water based. Tubing can be bought from almost any DIY shop, and better from specialist plumbing shops. The wider the better. The exact dimensions depend on the power source you are planning to use, the greater the power, the bigger the coil. With my 450 watts supply (which is quite small for a Tesla coil) I used a 68mm wide by 50cm long section of pipe. I prepared this by cleaning it with white spirit, sanding it smooth, then letting it dry and finally varnishing it thinly to seal it from moisture. Moisture is bad because it makes the pipe more conductive. The wire I ordered from Maplins web site , and I used a 28swg gauge. For bigger more powerful coils sizes 22-24swg are used. Thinner than 28swg is not recommended as it becomes fiddly and prone to snapping when being wound.
I made a little winding jig for winding the wire onto the secondary. This was very quick and easy to make and saved me hours and hours of winding by hand. I would strongly recommend the building of a winding jig to anyone winding a secondary. All I did was get some scrap pieces of wood, mount them vertically on a base board with hot glue gun glue and drill holes in the vertical wood. I then got two Pepsi bottles, as they just happened to fit inside the 68mm pipe I used, and drilled hole through the bottoms and tops of these. I placed each Pepsi bottle inside either end of the black pipe. I then put wooden dowel through the vertical wooden support, through each Pepsi bottle in turn, through the other wooden dowel, so that the pipe rotated freely about its centre, supported by the Pepsi bottles which were supported by the dowel which rotated in the holes of the vertical wooden supports. The wire I bought came on a spindle. I mounted this spindle on another wooden dowel, as the spindle had a hole through its middle, and supported this dowel parallel and below the 68mm pipe. I found the end of wire and pulled 3m spare. I glued the wire at 3 meters to the 68mm pipe with a tiny amount of hot glue gun glue. I then wound the 68mm pipe about its spindle with one hand whilst putting tension on the wire and keeping it in place with the other. Once this was finished I varnished the coil repeatedly over a period of several weeks until none of the ridges of the windings could be felt through the varnish. The below diagram shows the design of the winding jig. The Pepsi bottles are not visible as they are inside the 68mm pipe.
It is very hard, although not impossible, to buy commercial high voltage capacitors. Fortunately, making your own high voltage capacitors is very cheap and easy. All you need are some wine or beer bottles of any colour (although clear is best), some tinfoil, and some glue (spray on carpet glue is best). Soak the bottles in warm soapy water to soften the labels and then remove the labels with a blunt knife. Dry the outside of the bottles. Spray the glue onto the outside of the bottles then wrap them smoothly in tinfoil. Try to get the tinfoil on as smoothly as possible and smooth it with your finger once it is in place. Fill the bottle with saturated salty water. The inside of the bottle is one side of the capacitor and the outside tinfoil covering the other. If you have also covered the bottom of the capacitor with tinfoil it is possible to stand them on a conductive plate and thus connect all the capacitors together on one side. Place lengths of stiff wire into the inside of the capacitors, and connect the wires together for the other contact.
One of my capacitors