Careful of sharp bends for coils

[Dave B]

My coil winder is very similar to Dan's with "pins" to form the shape and size of the coil. As with his these pins are nails. I wound 1 coil of new #16 quality magnet wire to fit 1x2x3/4 magnet. I don't know the diameter of the nails used as pins but they are probably 1/8". This made a very nice looking coil with straight legs and even winds but by luck I examined this coil very close. I had planned on slipping heat shrink over the nails to help protect the wire during winding and removal but for this first coil I did not. This would not have helped much with what I found. Seems as if with #16 wire the inner bend at all corners of the coil for the first layer had wrinkled the insulation very slightly. Although I was very careful removing the coil and the form "pins" there was bare wire (nicks and scuffs) showing in spots on the inner bend of the coil. I had to use a jewlers loupe to see it but seeing it with this it obviously could have caused shorting. I will change to using smooth nylon bolts or rod with a larger diameter than the nails for the guides. Might want to take a look at this if you are using a similar winder and nail pins for the coil guide. I also think that a nice winder with a large handle might be part of the issue also being that you can make very tight coils. Something to think about,  Dave B.

[tecker]

I Saw this also and switched to a nylon screw . I'm still concerned about the wire stretching there .The 3/16 nylon is the best compromise as to bending radius and scuffing.I always glue parchment paper to the inside layer(  a dab of glue to the corners). I also like to dip the finished coil in spar urethane.( personal preference)

[Flux]

Some wires are better than others, I suspect you may have some not so good stuff. 1/8" is a tight radius but decent wire shouldn't object. Scratching may occur when you remove the nails and really doesn't matter as nothing will touch the scratched bits.

Too much tension can sometimes lead to crazing of the wire coating but your creasing sounds a bit different from stretching.

It is certainly good practice not to wind directly on metal but as long as the nails are smooth I wouldn't expect any trouble. PTFE sleeving over the nails should prevent any damage and let the nails come out easily.

With winding on a really tight radius I would normally be more worried about stretch cracks on the outer side of the wire but you would never see that unless you looked at the first layer.

Not sure what your wire sources are like, some of the imported stuff here in UK is not as good as it might be compared with the stuff we produced before our industry virtually ceased.

Flux

[Dave B]

Thanks guys for the replies. Looking at it closely again it does appear to be a stretched wire issue probably caused by both a short radius bend and too much tension. This wire was purchased new from a reputable motor service shop locally and they do some serious rebuilds, I am confident of the wire quality. I will be using nylon pins of larger radius and this should take care of things. I think the stretched wire loosened the insulation just enough so even though I was careful removing the pins the friction scuffed it off on certain corners. Learning all the time.  Dave B.