The Twine Lock Method of Toroid Winding

Credit to Jack Purdum (W8TEE) for introducing me to this ingenious method of winding toroidal inductors.

Materials Required

• Toroid core
• Magnet wire
• Twine

Tools Required

• Bench Vise
• Crochet hook (use a size appropriate for the wire)
• Inductance meter (optional)

Process

Cover the jaws of your vise with masking tape or another soft tape. Without this protective layer it’s easy to scratch enamel of the magnet wire as you pull turns through the core.

Cut an appropriate length of magnet wire for the inductor you are winding, a little long is always better than a little short. Straighten out the wire by hand to ensure there are no kinks.

If you find that the wire kinks up while winding you may want to further straighten out the wire. Grasp each end with a pair of pliers and gently pull to remove the coil memory from the wire. I did not find this necessary when winding my inductors.

Pass a short length of twine through the center of your toroid core and secure it tightly in your vise.

Feed about 1″ (3cm) of wire through the core. Wrap the rest of the wire around the back of the core and pull both ends snug. This is the first turn.

Pass the hook through the center of the core and hook onto the wire. Pull the wire through.

For the first few turns you will need to hold onto the opposite end of the wire to prevent the hook from pulling out your earlier turns. After a few turns friction against the core should keep the turns in place.

Pass the wire over the coil and around to the back side, pass the hook through the center of the core, hook onto the wire, and pull through for the next turn. Keep turns tight to the core and keep the spacing as even as possible.

Pass the wire over the coil and around to the back side, pass the hook through the center of the core, hook onto the wire, and pull through for the next turn. Keep turns tight to the core and keep the spacing as even as possible.

If your inductor requires so many turns that the twine gets in the way simply release the vice, adjust the twine over earlier turns, and secure the core again with the empty space now exposed.

Once the inductor is complete double check your turn count before removing the inductor from the vise. Each pass through the center of the core counts as one turn. If you have difficulty seeing the individual turns use a jeweler’s loupe or take a picture with a digital camera so that you can zoom in closely. A macro lens is great for this if you happen to have one.

Trim the leads on the now complete inductor to about 3/4″ (2cm) and strip them with a bit of medium-grit sandpaper or a sharp knife (be sure not to nick the wire). Finer wire may be stripped by applying a blob of solder and holding the iron on the wire for ten seconds or so. Heavier gauges and high temperature tolerant enamel requires mechanical stripping.

Use an inductance meter to confirm the finished device achieves the required value. For very small inductor values this may not be practical and remember that most inductors created this way can be tuned +/- 10% or so by adjusting the spacing between turns.

After winding inductors the hard way for so many years (since my very first radio!) this method is a delight. Try it out and let me know what you think.

73, AI6YM