Clamp on strike rail earth connector

Today I fabricated a mock up clamp to earth the strike rail. I started with one of the copper electrical lugs that I bought from Teslastuff.com.

You will not find these listed anywhere on the website or on the Teslastuff eBay shop you will have to email the owner Alan and ask for a price. They are far better quality than anything I have found available in the UK. If you know different drop me an email. I used a length of aluminium 1/2" square rod to make the pieces that form the clamp.

These pieces started off as one block which I drilled with a 12mm bit to form the internal curve and a 6mm bit to form the bolt hole. I used a file to produce the curve on the other end. The block was then cut down the middle using a slotting saw on the milling machine. The two pieces were then clamped back together in a vice on the milling machine and then a 4mm hole drilled exactly on the interface of the two pieces. Using a perfectly flat surface and a piece of fine glass paper I worked the adjoining surfaces this makes the 4mm hole slightly smaller so it clamps tight on the 4mm strike rail. 

Here are the assembled pieces. Straight away I spotted an improvement that could be made when fabricating the actual unit, if I put threads on the bolt hole on the top aluminium clamp plate I can dispense with the nut and use a shorter bolt. Also the actual unit will have copper clamping plates to reduce resistance (aluminium 2.7, copper 1.7ohm.m).

I will mount the finished clamp the other way up than shown above. There will be no need to move this clamp once it is in position on the strike rail. But, obviously, access to the grub screw will be needed to clamp the grounding wire.

With the improvements mentioned I think this clamp will do very nicely. Off to eBay to get some copper square rod.

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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