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Coil Wrapping Jigs

Here are four takes on coil wrapping jigs:

These all work by the way and there is absolutely nothing wrong with them. They all reflect the needs of the brilliant minds that designed and built them and all have followers that also really like them. Probably the most flexible and usable is the aluminum one on the right hand side. It seems to be the smallest. 

The advantage of these coils is that the wire is held in place and the drill bit is more secure. You still have to wrap by hand and videos showing how to use these jigs all use pre-heat to anneal the wire before wrapping and heat with tweezers to aid in compression. One video showed a perfectly formed coil (that was the one tutorial featuring the aluminum jig).

In my past, I used to wrap wire around 0.5 mm posts on circuit boards. As i looked at these jigs, it occured to me that old technology could be applied here. I designed such a jig. It features a base similar to the ones above, but straight across (no step). I also designed a mandrel to twist the wire around the drill bit. 

You can see the base at the right. Lying across the base is the first coil I wrapped with this and the mandrel (the mandrel is not shown at this point, it's still in the proof of concept stage). 

The coil turned out to be absolutely perfect. it's a 28 AWG and required no pre-heating before wrapping or heat/tweezers after wrapping. Once wrapped with the mandrel, there is no "spring" to the wire.

Let me describe what you see.

This is for proof-of-concept. It's made of hardwood (a scrap of red oak I had lying around) that is 5/8" thick by 1 5/8" high and 3 1/2" wide. Once I finalize the design, I will make the "production" version from aluminum flat bar, and likely about 2.5 inches wide. The height should remain about the same, the thickness might be 1/2":.

At the top is the 5/64" drill bit. It is inserted in the oak with the twists down. All that is sticking out is the smooth portion of the bit. I plan on putting one other hole beside that for a 1/16" to give flexibility in coil building. I also plan a second "row" of holes (one 5/16" and one 1/16") to allow for parallel and serial coil building.

At the right of the base is a hex head 1/4 x 20NC threaded bolt in a brass knife insert nut. It is covering a hole that is about three-quarters the length of the unit and is used for storing bits. The storage can hold about six bits. In the production version, the 1/4 x 20NC bolt will be replaced with a 1/4 X 20 knurled head screw. The storage area is the reason why this hardwood version is 3 1/2 inches. The area below the drill bit has to be solid, then there is the length of the bit to consider, the length of the brass knife insert, and the length of the screw. When I use aluminum, there will be no brass knife insert and the drill bit will be closer to the edge (I should be able to reduce the width by about one inch).

At this point, there is nothing else on the base. I am keeping the wire "level" to the base with a slot that is near the bit. I plan on adding two more features to the base. One will be a 510 connector so that an atty can be mounted on the base to assist with mounting the coil and wicking. The second will be a 1/4 x 20 knurled head screw to attach one of the coil legs. At the moment, I am holding the wire down with a finger or thumb. Holding the wire down manually it not practical though, the finger (or thumb) gets in the way of the loose leg and the mandrel. Note that the wire has to be below the surface of the block of wood. That's the only way any mandrel system can work. 

This base is my second version. Nothing wrong with the first one, I just hadn't cut the wood straight and when I added the brass knife insert, I cracked the wood. When I switch to aluminum, I expect that both the width and height will be much smaller.

I have not discussed the mandrel publicly yet. The reason for this is that the mandrel is what makes this whole system work. It's the way that the coils gets compressed and is tight against the drill bit. It conforms to the drill bit extremely well. I had expected that the coil would be a bit difficult to remove from the bit (being wound really tightly), but that is not the case. Once the coil is built, it just glides off the battery quite nicely. I really am thrilled with this.

If you do research on "circuit board wire wrapping tool", you will get a sense of what I am doing. These tools are great for small posts on circuit board, up to about 0.5 mm. For use with the jig I designed though, I had to make some major modifications to the mandrel design. In terms of technology, though, the concept is quite similar. When you turn the mandrel, the coil itself pushes the mandrel up. With a tiny bit of pressure downwards, you are effectively compressing the coil so that it remains tight. With each subsequent wrap, the previous wraps all "lock" into place. 

As with all mandrels, you need one for each size of post/wire guage. My design will accommodate more than one pairing. Mine is already working with 32 AWG and 28 AWG (it should also work with twisted 32 AWG). That is because the thickness of each of these guages work within the tolerances of the mandrel design. Thicker guage wire will each require their own mandrel. The good aspect of this is that the donor tool i am working with only costs about $2.75. (I paid $2.60). 

Check back again for more details.

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