Primary coil assembly

With all the combs finished and the primary coil approximately shaped to the correct spiral I decided to thread the primary copper tubing into the combs. It was slow going as you have to move the combs along the tubing one at a time working around the spiral.

It took about an hour to get all the combs into the right position. Next I drilled out the mounting holes in the anti-strike disc to 4mm and placed it over the top of the comb assembly. I noticed that the holes in the combs were not going to line up with the holes in the anti-strike disc. The combs were to far out from the centre by about 5mm. After my initial panic I realised all I needed to do is tighten up the spiral to bring the combs closer to the centre. This done, I fitted the 24 10mm M4 nylon bolts through the anti-strike disc into the support combs.

Here you can see the 3 nylon bolts that fasten each comb to the anti-strike disc.

The disc underneath the primary coil is still covered in masking tape as I have yet to make some electrical connections so may need to do some more marking up and drilling.

At the moment the primary coil assembly just sits on top of the perspex disc underneath. I will add some system that will allow the primary to be located into position, perhaps locating pegs or guide blocks.

Primary coil support combs finished!

Tonight I finished off the 8 primary coil support combs. Each required 3 mounting holes drilling and then threading to take M4 bolts. The position of the holes were transposed from the mount holes already in the anti-strike disc. This was done by carefully positioning all the support combs underneath the anti-strike disc and simply sticking a pencil through the holes to mark the drill points onto the combs. The holes were drilled to 3.2mm diameter and to a depth of 9mm then each hole tapped to take M4 bolts.

Here's all the combs after removing protective tape. You can see that the sets of holes are staggered to accept the spiral of the primary coil.

I engraved a reference number on the end of each comb to help during assembly.

The bolts to secure the combs are 10mm M4 nylon. I don't want to use anything conductive on the anti-strike disc except the strike rail of course.

I still need to open up the mounting holes in the anti-strike disc to 4mm, but I threw the assembly back together for a quick pic of the combs in place.

This is what Santa brought me this Christmas, it has a basic function generator built in so will be very useful when tuning the coil.

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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Finishing the toroid mount

Spent a little time tonight soldering a small piece of copper tube onto the end of the winding wire at the top of the secondary coil. Although my final design for mounting the toroid means I will not have to keep disconnecting this wire, it's still good practice and makes a very secure attachment. I didn't take any close up pics of the wire at the top of the secondary but heres a pic of the bottom connection showing the little piece of strengthening copper tube soldered onto the end of the magnet wire. Don't forget to remove the varnish from the wire before you solder.

Completion of this job meant I could do a final assembly on the toroid mount. I had already removed the top cap from the secondary so I could insert the brass bush made to convert the hole from 10mm to 8mm. Next a copper lug was placed onto the copper mounting pin and the pin inserted up through the brass bush. One of the perspex spacing disc was placed over the pin and then a stainless washer and finally the M8 stainless nut. As the pin was now captive the top cap could be secured in place, remembering to make the electrical connection by placing the soldered tube into the copper lug.

After securing the top cap back onto the secondary with the 8 nylon bolts the next spacer was fitted to the top cap.

This perspex spacer is the one with a 25mm circular cut-out in the centre and allows the securing bolt to be counter sunk into the assembly so the toroid rests on the large face of the perspex disc rather than the top of the nut. I was going to bond this disc to the one underneath but on second thoughts I dont think it needs to be, plus, if I leave it separate, it will be easier to modify.

With that done I remounted the secondary coil assembly back onto the base assembly and placed the toroid over the mounting pin and secured in place with the M8 knob.

Here's a shot from underneath. Should be reasonably simple to adjust the height of the toroid by adding or removing perspex spacers.

The toroid can be easily removed and fitted by a quick spin of the knob with no additional need to make and break an electrical connection. Pretty neat and totally over engineered as usual.


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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.

Attaching the Toroid to the Secondary Coil

I have been considering how to attach the toroid to the secondary coil. This involves a physical connection to hold a rather expensive gorgeous hand spun aluminium toroid and an electrical connection between the toroid and the secondary coil. I would like to be able to quickly remove the toroid for transport and access purposes but without risking damage to any electrical connections. I have come to the conclusion that the secondary coil should have a permanent threaded conducting protrusion on its top cap which is electrically connected to the secondary coil. The toroid simply slots over this protrusion and is secured by a threaded knob.

Here's the top of the secondary, the central hole is 10mm and was drilled originally to mount the secondary coil onto the winding jig shaft (a 10mm threaded rod). I thought 10mm was a little excessive as a mount for the toroid so decided to bush the hole down to 8mm with a piece of brass rod.

I turned a flange on one side of the insert. This would sit on the under side of the secondary top cap.

Here's the bush fitted, admittedly the wrong way, just making sure it was a snug fit.

Ok, so I now have the top cap ready to accept some kind of 8mm bolt that will protrude upwards. I need to do 2 more things. Firstly, I want to add a little height to the top of the secondary to lift the toroid,  secondly, I need to make this protruding bolt captive so when I undo the fastening for the toroid this bolt doesnt spin or release and drop down the inside of the secondary. To cover off both these requirements I am going to use two pieces of perspex. The first is a 100mm diameter 15mm thick clear disc ordered from my favourite plastic supplier Trent Plastics.

As you can see I have masked the disc up and drilled a central 8mm hole. This disc will sit on top of the secondary coil top cap. The second piece of perspex required is exactly the same size except it has a 25mm central cut-out.

These two discs will be bonded together as shown in the mock up below.

The larger hole in the top disc will provide clearance for the nut which will make the toroid mounting pin captive. OK, now for the mounting pin.

I cut a length of 16mm diameter copper rod, started off with about 10cm. The shank of the pin needed to be 65mm long and 8mm in diameter.

Turning the copper rod down to 8mm was down using a type 5 parting tool. Probably not the best tool to use but I always have the most success with this type. The material was removed in 0.4mm passes, I didn't want to risk any deeper cuts as it's quite a long shaft to turn and copper is pretty soft. I had an experience in the past where the tool dug in and the work was completely destroyed.

The toroid will be secured in place with an M8 threaded knob so I needed to cut some threads into the pin. There's quite a lot of info on the web about cutting threads onto copper rods, lots of comments about poor results and differing views on cutting methods and lubricants. I used plenty of WD-40 and patience. Don't try to cut too much thread in one go, I found it best to cut 1/8 of a turn each time and reverse the die 1/4 turn back every time. Use plenty of lube and clear swarf from the die when needed.

Here's the assembled mounting pin.

The copper lug will provide electrical connection to the secondary coil. The nylon M8 nut in the top pic will be replaced with a stainless steel version.

Shaping the tubing for the primary coil

Next job is to form the 1/4" copper tubing into the approximate spiral required. I say approximate as it will be the drilled holes in the 8 support combs that will accurately position the primary coil. The tubing I purchased came in a spiral pack as, I presume, most 50 foot (15 metre) packs will come. The biggest tip is to leave it spiralled. Don't try to straighten it. I found that it needed very little work to open up the spiral to the approximate shape required. I used a Mac program called EasyDraw which has a spiral tool so I punched in a few settings and dragged the spiral out to the approximate diameter and the approximate number of turns. The resulting spiral was exported as a pdf and then printed across 6 pages of A4. I carefully taped the sheets together so I had a full scale plan of the spiral.

I had to be careful when placing the sheets together, the HP printer I used will not print right up to the edge of the paper so I had to work out if the sheets needed to be overlapped or placed edge to edge. After measuring I could confirm that the pages did not need to be overlapped.

Above is the end result on the dining table. The coils should be spaced between 1/4" and 3/8", I opted for 7mm which is just over 1/4".

This is the tubing straight from the packet. Remember, don't be tempted to straighten it out.

After about 15 minutes of easing the coils open using the plan as a guide. It will need a little more work before I move on to the next step which is drilling the support combs.


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