Fitting the Primary Coil strike rail

With all the strike rail mounts finished and the strike rail formed into the approximate correct shape it was time to fit it all to the anti-strike disc. It was possible to loosely fit all the strike rail mounts and then thread the strike rail through each one.

I have used 15mm X M4 nylon bolts to secure the mounts may substitute these for stainless steel, still not decided.

Made a quick video just to give you a bit better view of the complete strike rail.

The rail is not a complete loop, it has a gap which is located inside one of the mounts. It needs this break to prevent induced eddy currents when the coil is running.

Here's a festive shot of the top of the tesla coil. Well it is Christmas!

Finishing the strike rail mounts

Finished for the xmas break today and thought I would get the strike rail mounts finished off. I had already drilled a 3.3mm vertical hole in each one which would be tapped to accept a 4mm bolt to fasten to the anti-strike disc. Before tapping I needed to drill a horizontal hole through each mount through which the strike rail will pass. The strike rail is 4mm in diameter and as the rail is a large loop the holes in the mounts need to be slightly over 4mm to allow for the curve. I opted for 4.4mm and set up the milling machine for drilling.

 I marked up the vice with masking tape so I could position each mount in the exact same place so I could lock the bed once the first mount is lined up for drilling.

All I needed to do is line up each mount with the masking tape as above and my holes will be in the same position on each one.

It was nice to be able to see the progress of the drill through the top of the mount. When approaching breaking through I greatly reduced pressure on the drill to prevent chipping the edges of the exit hole. This technique worked well, on inspection the exit holes were very neat. With the first mount drilled I checked that the 4.4mm hole would accept the curved 4mm strike rail. Bingo, 4.4mm is perfect.
  After another 15 mounts the drilling was done. Now to tap the mount holes.

It's about now that I'm regretting the choice of using 16 mounts for the strike rail, 8 would have been plenty, keep telling myself it will look really good.

9 done, only another 7 to do. Didn't take quite as long as I thought as there's only about 10mm threads to cut in each one.

Here are the 16 mounts done and de-masked. They look fantastic.

Primary coil strike rail

I have also decided to fit a strike rail to the primary coil assembly. This, in conjunction with the anti-strike disc, should help prevent stray streamers hitting the primary coil. The strike rail is made from a length of 4mm diameter micro-bore copper tubing. It will be mounted around the perimeter of the anti-strike disc and will form an 86cm diameter ring, hence I bought 3m length of tubing from a seller on eBay (86 X 3.141=270cm). The strike rail will be fitted on the underside of the anti-strike disc and will be supported by 16 mounts evenly spaced. Each mount is a cut from a 20mm diameter clear perspex rod, each one 20mm long. The tops and bottoms of each were polished to a glass like finish. These mounts were made and supplied by the excellent Trent Plastics, a company I highly recommend for all your plastic needs. The finish quality was amazing and the price for 16 of these little beauties was very fair.

Here's one of the mounts, I have already drilled this one ready to accept M4 threads. It will also require a horizontal 5mm hole drilling that will accept the 4mm copper tubing.

The mounts are masked up again for the next drill hole and tapping.

Here's the mounting blocks almost in situ. They will actually be bolted to the underside of the anti-strike disc by M4 12mm bolts, probably nylon but possibly stainless as insulation is not an issue here. There are 16 mounts, 8 of which line up with the 8 primary coil support combs, the other 8 are evenly spaced between these. 8 would have been enough to support the strike rail but 16 looks better.

The 3m length of 4mm micro-bore tubing arrived tightly coiled in an A4 size jiffy bag. It took a little work to slowly open the coils up to the approximate correct diameter.


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Marking out and drilling mounts for the primary

Today I spent a few hours progressing with the primary coil. I needed to mark out the positioning of the 8 primary support combs. These will be attached to the underside of the large anti-strike disc by 3 nylon bolts per each comb. I had already masked up the anti-strike disc to protect it and to allow marking out, I marked up 8 "spokes" onto the disc by taping the disc down to our glass dining table and taping a 360° protractor into the centre cut-out.

The position of the 8 spokes could then be easily marked out using a long metal rule placed over the relevant degree markings and lined up with the dead centre.

Also mounted to the underside of the anti-strike disc will be 16 evenly space strike rail holders around the perimeter so I marked on another 8 spokes at 45° intervals between the primary coil combs. With all the spokes marked up I could decide on the nylon bolt positions and mark them out for later drilling. 

Next job was to mark out the primary support combs. I don't want to "notch out" the combs as is the usual way to support the copper pipe of the primary. This method means you have to either glue or zip tie the tubing down, neither of which appealed to me. I plan to drill "full" holes into the combs and thread them onto the copper coil.

If you look at the coil plan above (or into my eyes, not around my eyes) you can see that the positions for the holes in each comb will be different. For my coil there is 8mm space between each rotation of the coil and the diameter of the copper tubing is 6.5mm so the holes in the combs need to be 14.5mm apart (centre to centre). This measurement is the same for each comb. As you move around to the next comb the spiral moves out by 14.5mm divided by 8 (1.8125) so there is an offset of 1.8125mm as you move around from comb to comb. You can avoid this complication by just moving the combs outwards by the same value when fixing them in place but I wanted all the combs to be the same distance from the secondary coil.

All the combs were masked up in the usual manner and then through carefully measuring my full scale primary plan I determined the position for the hole for the innermost coil on comb number 1. It was the easy to mark the position for the 1st hole in comb number 2 by adding 1.8125mm. And so on up to comb number 8. I didn't bother marking any subsequent holes onto the combs as I decided to fire up the digital vernier scales on my milling machine and locate them by just adding 14.5mm each time.

Not the best video but its really hard trying to film while drilling. Think I might invest ia a small tripod for my little Sony Bloggie.

I set up the milling machine so each perspex comb could be clamped in the the same place with an 10mm piece of pine stripwood underneath to prevent the drillbit chipping the back of the perspex as it breaks through. I positioned the bed so the drill bit was directly over the datum mark for the first hole. The hole was drilled and then the bed was moved 14.5mm to the left and the next hole drilled and so on.

I jotted down all the datum points as I drilled the first comb so I could use the info for the rest of the combs. And about 140 holes later......

Here's the drilled combs underneath the anti-strike disc. I have drilled all the necessary pilot holes in the strike disc, this will make it very easy to mark up the 3 bolt holes onto each comb by simply sticking a pencil through the pilot holes in the anti-strike disc.