Wind round, then mount on bobbin?

[pilotjones]

I was wondering if anyone uses, or any company maybe formerly used, the following method. (Sorry if this has been covered, but I didn't get it with a search.)

What if you were to wind a coil on a round drum, then remove the coil and "stretch" it over a properly shaped core? I would think that, while bringing up a new unique new set of issues, this method might allow a much faster coil winding, since the wire feed rate and tension would be constant instead of the usual near-stop-start, allowing you to work up to a much higher RPM.

Has it been done? What would be the pros and cons?

Thanks
Pete

[Rosewood]

All I can say is I wouldn't try it even at gun point. Have you wrapped any pickups yet? It's hard enough winding on a bobbin and not breaking or shorting a wire.

[soundmasterg]

The old Burns Tri Sonics were an air coil, and they were wound on a removeable former, then wrapped with a sort of string, then the former was removed and the coil was stuffed inside the cover with the magnet and epoxied. These are similar to your idea, but not quite the same. You'll notice that they didn't move the coil at all in any way until it was wrapped. With your example, the coil would fall apart if not wrapped with something to hold it together, and stretching it would break it.

Greg

[Mark Hammer]

What if the round pre-assembly coil was wax-potted prior to removal, then gently warmed to pliability before removal and relocation? Or is that still too risky?

What COULD work (though only in theory) might be a pliable bobbin that could be round to start, then gently warmed to pliability and reshaped. Assuming such a compound a) exists and b) is suitable for bobbin dimensions with the requisite sturdiness and pliability.

[David Schwab]

Originally Posted by pilotjones

What if you were to wind a coil on a round drum, then remove the coil and "stretch" it over a properly shaped core?

I was toying with this idea for a while. My reason was to try and eliminate fabricating a bobbin. I was going to make a round form from UHMW polyethylene, wind my coil on that, and either use bondable magnet wire, or after giving the coil a liberal coating of something like polyurethane, I was going to remove it from the form and flatten it to fit over a blade.

Q-tuner pickups are wound on a form using bondable magnet wire, which is then bonded in an oven, and the coil is removed from the form. They are self standing air coils.

[pilotjones]

Originally Posted by Rosewood

All I can say is I wouldn't try it even at gun point. Have you wrapped any pickups yet? It's hard enough winding on a bobbin and not breaking or shorting a wire.

I'm definitely not some guy from Turkey, trying to tell everyone their business! I've never wound a pickup, but I am involved in manufacturing, and I had an idea that I'd like others' thoughts about.

The goal is conversation, not conversion.


Re your other comment, I was thinking that the even tension during winding would eliminate pressure points at the ends, and the cyclic accel/decel of the wire, maybe helping with both breakage and shorting problems.

[pilotjones]

Originally Posted by soundmasterg

The old Burns Tri Sonics were an air coil, and they were wound on a removeable former, then wrapped with a sort of string, then the former was removed and the coil was stuffed inside the cover with the magnet and epoxied. These are similar to your idea, but not quite the same. You'll notice that they didn't move the coil at all in any way until it was wrapped. With your example, the coil would fall apart if not wrapped with something to hold it together, and stretching it would break it.

Greg

So, they formed to the final shape, but on a former, i.e. shape tool, right? Like you said, similar, but different.

Also, I didn't mean actually stretching it, what I meant was re-shaping it.

[pilotjones]

Mark and David, I was thinking of some ideas similar to yours. Also, another one I had: round drum; put around this a piece of rubber or silicone tubing that has been slit lengthwise, and is properly cut to encircle the drum once; slit facing outwards. There are two rows of clips of some sort, one on each side of the tube, to pry back and hold open the slit. Neglecting details of start and stop termination, you would wind into the rubber groove thus formed, release/remove the clips, and pull off a nicely constrained but still flexible air coil.

Potting material would of course have to be able to penetrate the slit, and it would have to be seen whether the contained air could be made to exit the tube to pot properly.

[Ruel]

There's only one way to find out if it's worth the trouble. Do it and post your results. I'm sure they will be aprreciated.

[David Schwab]

Originally Posted by pilotjones

I was thinking that the even tension during winding would eliminate pressure points at the ends, and the cyclic accel/decel of the wire, maybe helping with both breakage and shorting problems.

I thought the same thing. You would have very even tension when winding on a round form. The jerking of a oblong bobbin gets very noticeable when winding with very thin wire like 45 AWG.

I just remembered another way I was planning on doing it was to make a form with two dowels (for each end) and wind a regular shaped coil, bond it, and remove it from the form.

[David Schwab]

Originally Posted by pilotjones

Also, another one I had: round drum; put around this a piece of rubber or silicone tubing that has been slit lengthwise, and is properly cut to encircle the drum once; slit facing outwards. There are two rows of clips of some sort, one on each side of the tube, to pry back and hold open the slit. Neglecting details of start and stop termination, you would wind into the rubber groove thus formed, release/remove the clips, and pull off a nicely constrained but still flexible air coil.

That's an interesting idea. I think the key is to use bondable magnet wire. You make it solid with either heat or by brushing something like alcohol on it.

These types of things were done all the time on old pickups. You see paper bobbins and stuff like that.

Alembic makes their pickups from PC board material... they just glue two pieces onto a magnet to form the bobbin. On the stacked pickups, there's one more sheet with a plastic core.

making anything that doesn't have "standard" available parts is always a chore. You either have to hand make the parts, or invest in injection mold tooling.

[David King]

Jones I don't see a problem doing it this way. Electric motors are rewound this way and it certainly works for them. I like the idea of a thermoplastic form, perhaps something like poly-form plastic. You can dip it in hot water and reshape it to your hearts content but it goes completely rigid at 110º or something.

Actually come to think of it, transformers are sometimes wound this way too.