Field Coils: Must they all have even turns?

[ryanf1023]

I'm finally able to carry on with my field coil rebuild. So far, I've done four of the sixteen, all of which are clockwise wound with the tab up. And, my fear has come true. The coils don't all finish at opportune lengths, some to worse degrees than others.

The top right one to me is ideal with the end to the right of the upward facing tab. My first one (top left) I made the center tab way too long, and are short by about half a turn. The bottom two are close, but they seem too far back to be able to make a splice.

My question is, can I just unwind what I've done back half a turn to an ideal position? This way, some coils may have more turns than others. As long as they alternate CW, CCW, CW, CCW etc., is that really an issue?

Correct me if my science is wrong, but:
-the more winds of the coil, the more lines of force are cut. I could see an issue with two winds vs one wind (a 50% reduction), but if these coils are around the 20-25 winds range, that's only a 4%-5% reduction.

-electricity is additive. Doesn't the magneto produce a voltage due to the "sum" of the coils rather than the "average"? If so, I can't really imagine some coils not wound all the same to make any noticeable difference in operation?

[Peter, Memphis TN]

I've never wound coils for a Model T magneto, but I have built transformers and re-wound motors - so I have some experience, and a thought.

Here's my question -- Can't a finished coil be re-shaped, so the leads come and go where you want them to?

I envision winding a coil on a round mandrel, then after it's done, re-shaping it to fit the mag ring, with the leads where you want them.

Or, taking the ones you've already wound, and just squeezing them into a different configuration.

Either way, a wood mandrel in the correct shape, then tapered down to maybe half size, could be used as a 'shoe horn' to aid the re-shaping procedure.

Could that be an option?

By the way, you could then wind all of them the same way, then turn half of them over and bend the leads out the other side, before re-shaping them. That'd give you half going one way, and half the other.

Just asking.

[Norman Kling]

Every other coil is wound in the opposite direction, so as the magnets pass you get alternating current. If you turn over the top right coil you will get the top connection in the opposite direction. I think within half a turn would be just fine. You want the ends to come out in the direction you want them when you put things together.
Norm

[Joe Bell]

When ever you rewind old copper it will never come out the way it was before, I have done several and shortened them to fit, it is the right way?? I would rather know I have the same amount of turns on every coil and the same output on every coil to make a smoother flow of current. I quit rewinding my own when I saw how well some one else was doing them and the exact turns on every coil every time since it is new copper instead of cleaned up old ones. If you ever get the chance to see his operation in person you will never attempt doing one your self again, unless you are really that bored. Bill sells them to Snyder's and Lang's and you can tell his from the green electrical triangle on top.

[Steve Jelf]

I made this to get my ribbons a straight. Locking pliers on both ends and an all thread screw to pull the ribbon tight. It stretches the ribbons so that when you rewind them you have a little extra sticking out on the end.

[ryanf1023]

Peter, I won't be wrapping them and sealing them until I know they will fit. That will REALLY make that a permanent option. I might consider rewrapping my first ring now that I know how long the lead should be.

However, I start the wrapping process with the desired lead already (other than the first trial one), and it's a matter of whether or not the variance in length affects it to a quarter turn or not.

Joe, I'm considering the professional rebuild route for any future Ts. At the moment, I'm on quite a budget and this is one of the few things I can do pending proper garage space. That, and I believe a thorough understanding of the build is important for any future diagnosis, and overall, and enjoyable thing to do as much work yourself as possible.

Still unsure if I need to count each layer. That would be an okay solution, and would give me plenty of "good" copper for any splices needed for the soldering.

[John kuehn]

I have done 90% of the rebuild work on my 3 T’s and pretty sure I could do a rebuild on a field coil BUT I’m glad there are those in the hobby that specialize in rebuilding them. I think I would be like others who could say I’ve done it but the next I’ll buy one.
For me the same goes for trying to straighten an exhaust manifold. I can say I’ve done it but I bought a new one for my 21Touring and I was happy.

It would be interesting to see how Ford rebuilt them though and the steps that occurred in production. They must have got pretty good in doing it considering how many were made. Practice makes perfect!

[Steve Jelf]

For me the same goes for trying to straighten an exhaust manifold.

After going to the scrap yard and buying a piece of I-beam to make the jig, I might as well keep doing it.

The last time I checked, the only new exhaust manifolds available were 25-27 style. If your older T is a show car, or if you just want it to look "correct", that wont do.