> According to the formula a coil 5" diameter, 10" long, and 35uH would have
> to have 26 turns. This would be a coil with ±1/4" spacing between the
> turns.
Using 1/4" tubing with 1/4" spacing a second coil could be wound at the same
time, or you can hold a 1/4" thick piece of wood or plastic between the
winding being laid down and the previous winding. It takes a little practice
but let the tubing run between the thumb and forefinger and under the heel
of the hand. The tubing is pressed down with the end of the thumb while the
forefinger holds the spacer between the previous winding and the tube. It
helps if the form can be mounted in a manner that will allow it to be
rotated.
Except for the actual winding of the coil try not to let the tubing bend.
Any bending quickly causes work hardening in Copper and that makes it
difficult to keep it from springing away from the form after, or even while
winding. Take any irregularaties out at the point where the tube is laid
down on the form rather than prior to that point.
Good Luck
73
Roger (K8RI)
>
> Bob W6TR
>
> ----- Original Message -----
> From: "Roger" <sub1@rogerhalstead.com>
> To: <Amps@contesting.com>; "Dennis Ashworth" <K7FL@arrl.net>
> Sent: Tuesday, November 20, 2007 5:59 PM
> Subject: Re: [Amps] Winding large inductors
>
>
>>
>>
>>
>>>I need to construct a 35uH air inductor using .250 copper tubing. D
>>> is around 5"; L = 10 inches. I can play with the dia & L a bit and
>>> still be in the Q ballpark I desire.
>>>
>>> Does anyone have a jig or technique they use to make such a coil
>>> while maintaining the turn spacing and not kinking the tubing? It
>>> needs to be "pretty" because of where it will be located :-)
>>
>> Much depends on the tubing you'll be working with. IE, "temper" which
>> depends on manufacture and it changes with age, heat, and how much the
>> tubing has been "worked".
>>
>> New, "dead soft" 1/4" Copper tubing "should" be capable of being bent to
>> a
>> diameter of 5" with little problem of flattening. The problem comes from
>> what diameter you will have to use for a form to get 5". If the copper
>> is
>> dead soft you can wind it on a 5" tube and expect to see it still grip
>> the
>> tube. The higher the temper (age, how much it's been worked) the smaller
>> the
>> form required. Much smaller than 5" and flattening will become a problem.
>> As
>> has already been suggested sand (or salt) used to fill the tube works
>> well
>> when needed. I've wound 1/2" diameter Copper tubing to 5 and 6 inch
>> diameter
>> although that was over 20 years ago.
>>
>> Without digging out the books (I don't remember the formula and the
>> handbook
>> is in the shop) what is the number of turns required in 10"? If space
>> wound
>> I wind two coils at once. So they serve as spacers for each other. It
>> sounds
>> easy but you have to "unscrew" one from the other when finished and they
>> often don't want to come apart. Wire of various sizes can also serve as
>> a
>> spacer being wound with the tubing other than the smaller stuff will just
>> go
>> under the turns so wire and cord probably won't work for close spacing. A
>> 5"
>> diameter coil 10" long may want to sag a little even when mounted
>> vertically, so it may take a bit of playing to get the turn spacing to
>> remain equal along the full length.
>>
>> When I was working in industry I always had lots of pipe scrap from PVC
>> to
>> Stainless to use for forms and a lathe to cut a shallow grove for a
>> guide.
>> Probably a piece of rigid 5" plastic drain pipe will work. It might be a
>> tad
>> large, but you said the dimensions were not critical. You might find some
>> PVC couplings of the right OD that could be glued together to make a long
>> enough form. Lowe's and the local Ace Hardware store are getting used to
>> me
>> asking for "something" that will be of a given size and it doesn't matter
>> what it's original purpose was. <:-))
>>
>> Sounds like the beginnings of a tesla coil (as it has to look good) or
>> one
>> whale of an antenna tuner.
>>
>> Good Luck,
>>
>> Roger (K8RI)
>>>
>>> Thanks
>>> Dennis, K7FL
>>>
>>>
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>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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>
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