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.

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.

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.

Starting on the Primary Coil

Spent the last few weeks decorating the lounge, those of you who have followed my blog may have spotted the rather flowery decor in some of the pics, for this I apologize but can now confirm that the decor is a little more up to date. Now onto the primary. As per the original plans from Tesslastuff.com I acquired a fifty foot length of 1/4' copper tubing. This can be sourced from many places, I picked a well priced listing on ebay from a seller with a healthy feedback score.

I have spent a long time deciding on the final design of the primary coil, the plans from Tesslastuff.com give you the basic idea and all the correct measurements but, as usual, I wanted to enhance the design with my over engineering. After reading several blogs and coil build diaries there seemed to be two ways to help prevent primary coil strikes (streamers hitting the primary coil- not good). Firstly to fit a ground rail around the primary and secondly to completely cover the primary with a non-conductor. So I decided to do both.

Above is my solution to covering the primary coil. It's a 5mm thick perspex disc with an external diameter of 900mm and an internal diameter of 170mm. The cut-out allows the secondary coil to pass through and as this disc is prominent I want it to be aesthetically pleasing so paid extra for the inside and outside edges to be polished. Here's another pic to give you an idea of the disc size next to the tesla base (room still with old decor).

I would also need some way of supporting the copper tube spiral of the primary. Most people used strips of plastic with evenly spaced cut-outs with accepted the coils of the primary. The coils were secured with glue or by zip ties. I didn't like the idea of glue cos of it's general messiness which doesn't go well when combined with lovely clear perspex. The other option of zip ties just didn't look that good. The best looking install I saw was to use nothing to hold the coils in place. The coil passes through holes drilled in the supports, very neat but a lot harder to achieve. I ordered the material needed for the supports.

These were 8 pieces of 250mm X 30mm X 10mm clear perspex with the top and bottom edges polished.

Primary thoughts

As the secondary coil is pretty much finished I have already been thinking about construction of the primary coil. Both coils will sit on a perspex 50cm 12mm thick disc which is supported above the second layer of the main module on 8 30mm diameter 20cm long perspex pillars.

The second level contains the MMC module, the spark gap module and a step down transformer module for the spark gap motor. All modules are mounted on ceramic standoffs.

I have yet to finish off wiring and the support disc is not yet fitted. As you can see I have coated it in masking tape ready for marking up the holes for drilling.

The pillars are drilled out to 5mm and then threaded to take M6 bolts. If you want some advice for drilling and tapping perspex takes a look at my Drilling and Tapping Perspex page.

The primary and secondary coil will sit on the top perspex disc (covered in masking tape above). At this point I have decided to upgrade the design from the original plans (yet again). I thought it would be a good idea to mount the primary coil underneath a perspex disc which should help prevent strikes to the primary coil. Also I heard if you do this any strikes that hit the perspex create an interesting effect as they spread out over the perspex. I will install a more traditional strike rail around the edge of this protection disc. The disc diameter was decided at 90cm and it would need a 170mm diameter central cut-out to allow the 150mm diameter secondary coil to pass through.

And here it is. Ordered from Trent Plastics, it turned up at work this morning. Took me about 10 minutes to remove the 3 layers of cardboard packaging.

The thickness is 5mm and I paid extra to have the inside and outside edges polished. It's a big piece of plastic and does flex a little, but there will be 8 radial combs from the centre outwards to support the primary coil and these will add extra stiffness.