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 Post subject: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 2:49 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1460
Location: Santa Rosa, CA
I've been making home brew coil forms for my current project.
Hammarlund Comet Pro. Simply using old tube bases and turning
down PVC tubing to fit in the base. But I'm having a heck of a time winding coils
that stay put and have consistent spacing. I'm using 20 gauge
enamel wire, so its fairly stiff and the windings have quite a bit
of space between them. It'd be a lot easier if the windings were
adjacent but won't work for this project.

In the past I've used candle wax to hold windings in place but
maybe someone else out there has a better and more consistent
method. TIA
Steve

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 2:55 pm 
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Hi Steve,

You can put additional lengths of wire between the actual winding turns, to space them as desired. The exact dimension is seldom critical. Then remove the extra wire after the winding is finished.

You put the start and end of the winding through holes in the form, and fold back to hold the winding in place. Then you can apply adhesive to hold everything down.

- Leigh

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 3:15 pm 
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I have been using zip ties at the start and finish to hold the wire ends. This is easy and removeable if I want to make changes later. Then I slip some heat shrink over the whole form right where the wire coil is located and heat it with a heat gun. I did a lot of gluing before I started down this path and now have a bag of forms, wire, and dried glue representing a useless waste. Since wire, zip ties, and heat shrink are cheap and forms are gold, why waste a form? I now can make a coil, try it and when everything works right, I know exactly what the number of turns will be for a permanent coil.

Leigh has a good suggestion about using another piece of wire, or really, anything cord-like, as a spacer between turns. Once the coil is wound and secured, the spacer is removed.

Norm

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 6:30 pm 
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On spacing the wire turns, it's been found that the highest Q is obtained when the turns are spaced one wire diameter apart, all other things such as form diameter being equal. If this is desirable for your application, the easiest way to achieve this is to wind two wires of the same gauge together and remove one of the wires when done. Note that the number of turns required for a given inductance will change compared to a close-wound coil. I use this calculator using iteration to figure the number of turns: http://electronbunker.ca/eb/InductanceCalc.html.
John

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 8:27 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 1460
Location: Santa Rosa, CA
Thanks guys, great ideas! Leigh, I think you solved a very frustrating
problem concerning spacing. These coils are 6, 12 and 18 turns
per inch. Your comments about max Q (and
reasonable interwinding capacitance) is a good one John and
hadn't considered that.

Will run some experiments and comparisons.

Something else I've been considering is cutting grooves in the PVC
with my screw lathe but setup is very time consuming.
Steve

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 8:31 pm 
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I've found that using wide clear packing tape over the windings will keep them in place until I've finished the coil, then remove and glue as necessary.

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 9:27 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
If you are using a poly type of coil (something rigid), and you know someone with a thread cutting lathe, you can cut small grooves in the OD of the form and wind the wire in the grooves. I've done this quite successfully for crystal sets.


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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Sun 19, 2019 10:02 pm 
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Location: Annapolis, MD
Not much to add, but maybe a few crumbs....

By the time you get to ~#20, the wire starts being pretty disobedient. I like the groove the best, but using a "spacer winding" is also good. With the right material, you can leave it in place when applying the final wax.
Speaking of the right material, not all insulators are good for coils--especially RF. One standard is 3M #56 which is Mylar (polyester)--I think this is good over a broad range of conditions

If the coil is going to have open space to get the right Q, I don't think there is anything to be gained by having it neat---a wire that is "off-center" a bit adds C on one side and subtracts it on the other. I think things tend to balance out.

All other things aside, tension is your friend. If a winding is tight to the form (or another winding below), then it is easier to nudge each turn into the right position.

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Mon 20, 2019 2:05 am 
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I have used Q-Dope in the past to "glue" windings.

https://www.alliedelec.com/product/gc-e ... /70159780/


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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Mon 20, 2019 3:51 am 
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Get it really tight by tying one end of wire to fence, the other to your coil, get it taut, keep it taut while walking toward the fence, turning the coil as you go. So fast and easy fourth graders did a beautiful job.

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Mon 20, 2019 4:41 pm 
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Location: WA 98407
What Macrohenry said. It's a skill that takes practice. I clamp one end of the wire in my bench vise, and roll the coil form toward the vise, keeping tension on the wire the whole time. I gave up using #20 and now use nothing heavier than #22. I typically use #26 for tickler coils.

Tom

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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Tue 21, 2019 5:35 am 
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 Post subject: Re: Trick to winding tight coils?
PostPosted: May Tue 21, 2019 7:11 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1773
I use an old lathe. Space winding is done as threading. I made a device with a brake to hold the spool of wire in the tool holder.

Use the lathe to cut grooves in plastic pipe. Wind the wire int he grooves.

Make a hand crank coil winder. They work just as well as the lathe. To make a space wound coil feed fishing line and wire at the same time.

Use double sided scotch tape to hold the wire in place on the form. I keep pre-torn pieces of masking tape handy to tack it down at the end.

For air core coils make a wood cylinder form in two pieces with a diagonal cut from end to end. Use screws to hold it together when winding. Put parchemnt or wax paper between the form and the wire, then the double stick tape. CD cases can be cut up to make strips to support the coil. Duco cement is decent q-dope. You can make you own Q-dope by melting polystyrene in acetone. Take the screws out of the form and extract the coil.

Hope some of these ideas help.


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