Coil winding advice

[kernowcam]

I am trying to sort an old dwell meter with a bad coil on the 6" moving coil meter.
I have removed the windings and worked out I have a 10mm square former, brass, 337 turns of .04mm copper wire. On the former it gives 40mm per turn. Total 13.5m.
This gives me the original ohms of coil

Any advice on winding this coil neatly?
I can make a ten mm carrier for the former.
I have an old manual sewing machine with a bobbin winder with a four mm shaft. Also a lathe available.
I have sourced the wire.

[TrevorG3VLF]

Please supply a picture of the coil. Is it to provide a magnetic field?
A brass former would indicate that it is not to provide inductance.
If it is to provide resistance, then the wire diameter and number of turns would be critical and also, constantan would be preferable to copper.

I have a coil winder but need a couple of half nuts, 0.5inch diameter, 40 tpi, left hand buttress thread! I will try to mould them with epoxy. I could then have a play.

[kalee20]

Definitely make yourself a de-reeler, a wooden frame to hold the reel horizontal, a rod going through the centre of the reel of wire, and a couple of ball-bearings so it goes round without friction. 0.04mm wire breaks easily!

And as the former is square, the wire tension will pulse four times per revolution of the former, as it goes round the corners. So you'll need to make a fishing-rod like guide out of thin springy piano wire, to absorb the jerks. Otherwise you'll need to wind super-slowly so that the inertia of the reel doesn't keep snapping the wire at each jerk.

Use a temperature-controlled iron to solder this wire, set as low as you can, and practise soldering it! Wire this fine dissolves fairly readily in hot solder, you will be surprised!

[David G4EBT]

As your sewing machine is a manual one, using the bobbin winder with a 4mm shaft might be a bit more 'tactile' than other methods. Turning the bobbin with one hand, and feeding and guiding the wire onto the former between the fingers of the other hand, lightly tensioning the wire as you go. 337 turns isn't very many and doing it slowly by hand overcomes the problem of jerkiness which will arise if winding at a faster speed. 0.0.4mm is 48 SWG so quite fine.

As you have a lathe, alternatively, you could mount the former on a 4mm shaft held in the headstock and rotate the headstock by hand using your left hand, while guiding the wire with your right hand. If your lathe can be run at a slow enough speed, (50 RPM for example), you could of course do that rather than turning the headstock by hand, but it's so few turns that in my view, hand winding gives a better chance of success.

If it's modern wire that you're using, it will most likely be self-cleaning/fluxing, which makes soldering much simpler.

Good luck with it, whatever you do.

Wire for coil winding should be taken off the reel on it's axis i.e. over one of the end cheeks. That is why a proper reel of wire has smooth ones.

[Boater Sam]

Originally Posted by merlinmaxwell

Wire for coil winding should be taken off the reel on it's axis i.e. over one of the end cheeks. That is why a proper reel of wire has smooth ones.

Agree fully, unwinding off an horizontal spindle is fraught with problems.
I have a 4" nail sticking up in the floor and the reel goes on this with the winder on the bench.

[kalee20]

It solves a lot of problems I agree. (A whisker disc is helpful to stop it unwrapping at random).

But have you ever tried winding with square-section (or rectangular) enamelled wire? I have. And a rotating reel is the only way, unless you want the square all twisted!

[kernowcam]

Goodness your frightening me! So remove wire over end of spool. I assumed I should mount on a horizontal shaft.

[David G4EBT]

Originally Posted by kernowcam

Goodness your frightening me! So remove wire over end of spool. I assumed I should mount on a horizontal shaft.

There are countless youtube videos of winding guitar pick-ups, using both professional and amateur coil winders. The invariably place the feed spool on the floor, run the wire through their fingers and typically wind on 5,000 - 6,000 turns at fast speed, traversing the wire back and forth across the former by hand.

See comments about placing the wire spool on the floor at 3.25 in this video by a pro pick-up winder:

https://www.youtube.com/watch?v=uhke5_KFF90

[M0FYA Andy]

The Avo Solenoid and Wave-winding machines all take the wire off a horizontal spindle...……..

[Diabolical Artificer]

"Wire for coil winding should be taken off the reel on it's axis" Why? AFAIK the wire was put on the reel horizontally, if the reel turns as the wire is taken off this is that process in reverse. Taking it off the end of the reel will put twists in it, albeit minor ones, which may or may not make a small difference.

Andy.

I missed the word “thin” when describing the reel off method.

[M0FYA Andy]

I wonder if the reel on the floor is simply a production method for fast winding of transformers, rather than having any properties which make it 'better' in all cases?
A pal of mine winds transformers, and his background was in a commercial transformer company, where of course 'time is money'. When he said you need a big coil of wire I realised it was because his technique had the coil on the floor with the wire coming off the end.
From our viewpoint as restorers, time is not money so we can do the winding slowly. As I said above, the Avo winders are designed to have a relatively small feed coil mounted horizontally.

Andy

[Station X]

The problem is that a large coil full of wire needs power to rotate it and that power is transmitted by the wire. If the wire is very thin then the tension in it is so great that the wire may break, especially at start up when the inertia of the coil has to be overcome.

I have some very large coils of thin enamelled copper wire and it is obvious that the cheeks have been rounded to facilitate feeding the wire off the ends. When feeding off the end the tension in the wire only has to be enough to permit close winding on the former.

[David G4EBT]

In the 'MFJ' (made from junk) coil winder I designed using a sewing machine motor and foot controller, the feed spool was only 0.5KG so I mounted it horizontally and designed an adjustable tensioning drive to keep the wire taut as the coil was wound, and to stop the feed spool from 'free-wheeling' and loosing tension if I slowed or stopped the motor. I mounted the feed spool at the rear of the winder to lessen the angle of the wire at the front pulleys as they traversed back and forth to guide the wire onto the inboard coil former.

But that was for winding a field coil with 20,000 turns (2.2km) of fine wire from a small spool. Had it been a large spool it couldn't possibly have been mounted in that way or the kinetic energy required to turn the spool would have been too great and would I think have snapped the wire. Likewise, the stored kinetic energy in a large spool rotating at any speed would have caused it to 'run on' when the motor was slowed down or stopped. Hence, the feed reel would have had to be on the floor, end-on for the wire to have been spooled off the end cheek.

Hope that's of interest, but it's a bit off topic really, because the coil that's the subject of this thread consists of only 337 turns, and only 13.5 Metres of wire, for which either the manual sewing machine bobbin winder or lathe will be fine and most likely only a small spool of wire is involved.

[Uncle Bulgaria]

What a wonderful machine, David! I'm always impressed by what people come up with to solve a mechanical problem. Perhaps it's my lack of experience with such systems, but I could never come up with such an elegant and well-made solution. It looks like you bothered to varnish the box, too.

I've been musing on rotation recently as I'd like to have a go at winding my own transformer, and have just joined a forum for people who cut their own records - a fascinating process!

[kernowcam]

Very nice work there David.

[emeritus]

When I needed to rewind the solenoid coil of mum's spin dryer, I used the take-up arm of my cine projector, improvising a mount for the coil former from an old 50' plastic spool. The gentle slipping clutch of the projector allowed me to feed the wire by hand, adjusting tension by how hard I pressed my fingers together. The number of turns was not critical for that application, I just wound wire of the same gauge as the original until the former was full.

[retailer]

A decent de-spooler for .04mm wire is a must - I recently wound an output transformer for an audio compressor project and had a few problems with 0.1mm wire breaking. My despooler consists of a ball race mounted shaft that has a static brake to provide tension and an overrun brake to stop the wire spool from spinning and unwinding, just the drag from the bearing grease was enough to brake the wire. Sitting the wire spool on the floor does work I've done this many times but only with spools that are cone shaped - not sure if the shape has any bearing on this.

In the case of my transformer I ended up making a small depooler using a old VHS video head bearing set - they have very low friction bearings, the despooler mounts on the traverse arm, it is possible to do this as just about all fine magnet wire is wound on small spools. I saw the idea on the Jogis Röhrenbude web site - buried some where in his web site is an article on rebuilding an American valve tester, he goes to the trouble of rewinding the coil in the meter movement and uses an old video head for the despooler bearing. I think most forum members would have spent a bit of time looking around his site he has a lot of interesting stuff.

[Diabolical Artificer]

Ahh, so the the wire off the ends of the spool method is only really needed when winding with thin wire with no power assisted wire spool, thanks all.

Andy.