Saturday, August 13, 2011

Tesla coil progress

Due to lack of employment and therefore money (and other reasons I won't get into) the various projects I had been actively working on have ground to a halt, so I turned back to what I'd been pushing before I got distracted by the Mad Scientist Light Switch, Fast Compact Marx Generator, and the Field-Distortion-Triggered Spark Gap Switch: my "Last Tesla Coil".

It was tabled because I lacked the copper strip (about 10 pounds worth) for the primary and the money to buy same.  I got lucky and scored (more or less) what I wanted while working on the aforementioned stuff so with that in hand, and certain other difficulties being somewhat ameliorated, I can resume work on it.

So, this post is about the primary coil, its support structure or "deck" as I call it, a grounded "strike rail" mounted above and to the outside of the primary winding, and the various bits and bobs to make it all work.

I'm building this thing with several goals in mind which I don't often see implemented in other Tesla coils, even those built professionally for museums.  I want it to have a classic, slightly ornamental, but thoroughly old-world hand-made. I want the build quality to be top notch.  I'd like to see it last at least as long as the Griffith Park Observatory coil lasted before some future coiler has to rebuild it.  I'd like to see it find its way into a museum or educational facility, so it needs to be well made and sturdy.  Unfortunately, I also want it to be portable, so it can't be as sturdy as it would be if it was never to be  moved.  I want it to have the highest possible performance while retaining spark gap operation.  Honest to goodness, for long term reliability and simple lifetime I believe an old-fashioned spark gap coil will last longer than a more efficient and higher-performing solid state coil.

So, for ease of use, the primary will be accessible (for tap connections, using a special connector I've designed) from below the primary deck through any one of eight radial slots.  These slots would significantly weaken the deck structurally if it were not for the primary supports which stiffen the deck radially and a glue-lam reinforcing rib around the circumference of the deck.

Here's the glue-lam rib being glued and screwed to the underside of the deck:
 The sanded areas on the bottom will be finished with urethane stain/varnish just like the top, after everything that needs gluing is done.  Holes for the ends of the radial slots have been drilled, but the slots have not yet been cut out. The black objects are ABS sockets for the uprights which support the primary deck above the base.  This "post and two decks" implementation is a very common construction style for amateur-built Tesla coils.  It's not as nice looking as a full box or base (of any shape) but it's a lot lighter, it knocks down, and is therefore MUCH more portable.  That ring was finished two years ago, and the deck was ready before that.  Because of how this thing goes together, it is necessary that construction of the primary deck go in a specific order of steps.  I couldn't glue this on until various other things happened, culminating in the need for the copper.  Once I obtained the necessary copper, I was able to answer various questions letting me finally finish this bit.

The next bits necessary for this thing are the primary supports, which were last seen looking like THIS.

This week, I finished all of the brass "P-clips" which will fasten the strike rail to the strike rail insulators which are those white cylinders with the button-head cap screws in the ends.  Now they look like this:

The clips are all done.  Each was individually hand made from brass strip because I couldn't find what I wanted off the shelf.

The supports (which by the way are maple and are going to be f_cking gorgeous when they are stained and finished) have been marked with pencil for the saw cuts which will hold the primary windings. Each support has its cuts offset from those of its neighbors by 1/8 of the distance between two cuts, so that the spiral of the primary will be as smooth and step-free as possible.  That is solely an issue of aesthetics, it will not affect performance.  The long piece is a special feed-through for the ground connection to the strike rail on support #1.  This connection passes entirely through the primary support and deck, is insulated to prevent primary voltage from reaching it (and setting its primary support on fire) and connected to the secondary's bottom ground connection through a brass strap attached to the bottom of the primary deck.

Now comes the "fun" part, and by "fun" I of course mean painful, torturous labor:

 Each of the eight primary supports must receive fifteen carefully spaced saw cuts, for a total of 120.  Maple is HARD even among hardwoods.  As you can see, I have already damaged the tops in a few places.  That's what happens when you're exhausted, with aching, twitchy muscles, and you decide to press onward anyway. *sigh*
I have arthritis and other musculoskeletal maladies, so this part is going to go very slowly, but just like those thrice-damned brass clips, if I do a little each day, in a week I'll be done. This is all being done by hand, as I do not own much in the way of wood working power tools, and in any case, this would require a very special (thin) power saw blade indeed, of a sort I've never seen.  I am using a "back saw" (normally used in a miter box) to make cuts roughly the same width of the copper's thickness, so I shouldn't need anything fancy to keep the windings from shifting in their supports.

More as it happens, stay tuned.

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