Below is the drawing from the Tesla Patent

United States Patent Number 512,340 – COIL FOR ELECTROMAGNETS – Nikola Tesla. Details can be viewed under Patens

Winding a Bifilar coil on a form is not an easy task. I have been asked many times how to do it and decided to give you an example which works well for me.

 

What do I need?

1. A flat form. Example: Wood, Glass or Acrylic

2. Double sided carpet adhesive tape. Chose the one for a rough surface.

3. Magnet wire. Any gauge and element you require. Best is Copper enameled.

 

1. Prepare the Form

In order to wind the coil we need to have a centre drilling done into the form to mount it on a turn table. I use 12 mm because I have bearings for 12 mml which I mounted on a support.

 

2. Mount on the support

I use a 12mm steel rod and fix with collars on the base. Two reels with enough length of wire to wind the coil to feed the winding. In my picture you see 4 KG reels. My support is fixed on an adjustable table in front of my winding rig.

3. Add the double sided tape on the form

Use a very strong tape to keep the magnet wire in place. I used cheap tape in the beginning. A night mare. The windings don’t stay at the form. It took my 3 days to finish one layer. With a good tape that is done in 20 minutes. Take one wire from each reel and insert into the middle hole. Add a little edge inside the hole for the wire to move without friction around the steel rod and fix with a tape at the back. Use enough length of the wire for the connection later. Rule of thumb twice the length to the size of the form.

 

4. Cut out the middle of tape protection in order for the winding to clue on.

Add the collar to keep the form in position. One collar is below the form. I use a washer as spacer where I start the winding. Which way you wind is up to you. I use clockwise in this example. Turn the from counter clockwise for clockwise winding fixing.

 

5. The first couple of windings on the form

Use a plastic stick or any other small pointy form to keep the windings in position while you turn the from. I used at the beginning my finger nail. I had sore fingers for a week.

6. Finished coil

The diameter of the form and the magnet wire gauge will determine the winding number. Make sure you wind as tight as possible. Remove the rest of the double tape. Fix the wire with stripes of masking tape and varnish. Be careful. To much varnish dilute the clue and the coil comes off the form. It happened to me. The only solution is to throw it away and start again.

Acrylic form completed and mounted with 2 layers, not fixed

 

Acrylic form completed and mounted with 2 layers and fixed