EMRFD Message Archive 1051

Message Date From Subject
1051 2007-09-25 13:37:45 bkopski Binocular Core Winding
Hi All,

For what it's worth ...

I've recently wound several BN-43-202 cores and in the process found
that very often I was scraping the wire insulation - no matter the wire
type and the care I used - it seemed. Perhaps these cores are
expecially rough inside but in any case I was uncomfortable with the
prospect of scraped insulation.

I had several pieces of "3/16" OD thin wall heat shrink tubing on hand
and found that some would fit very nicely inside the core passages but
some would not quite fit. It seems that all "3/16" tubing is not
created equal - and a caliper confirmed about +/- 0.002" variation
among samples. This was just enough so some would not go through

For the latter, by experiment, I found that a simple stretching an end
by hand - thereby necking it down a bit - permitted this reduced-
size "leader" part to be pulled through the core with the undisturbed
remainder snugly following behind. Presto!

In either tubing case, the subsequent winding process went very
smoothly - much better indeed - and even snugging the turns got much
easier. Upon unwinding several there was no evidence of scraped
insulation. I'm posting a photo illustrating all the above.

Cordially and 73,
1052 2007-09-25 14:01:14 Graham Re: Binocular Core Winding

Having had the same experience winding the BN-43-202 or -302
cores, and getting the insulation scraped off of enamel wire, I found
that there appears to be a sharp edged mold parting line at the
entrance to the holes. Rather than line the cores as you did, I found
that putting the point of a knife into the opening of each hole at
each end, and turning or rotating the knife would round off the
parting line, and round the entrance to the holes. After doing
this, I found the scraping problem to have almost totally
gone away.

1053 2007-09-25 18:12:45 Allison Parent Re: Binocular Core Winding
1054 2007-09-26 05:35:08 jr_dakota Re: Binocular Core Winding
I take a drill bit about twice the diameter of the whole and use it
(by hand) to ream out the edge of the hole but the last couple of
batches I got didn't need it

I have had the same problem occasionally with ferrite toroids,
1055 2007-09-26 21:03:06 Dan Reynolds Re: Binocular Core Winding

I used a small piece of Teflon thread sealing tape and just ran it through a couple of times and snugged it up.


Worked pretty good and Teflon tape is incredibly thin but strong.



1058 2007-09-27 04:27:29 Kenneth Stringham Re: Binocular Core Winding
I agree with the use of the drill bit and the needle
file. I've been doing using the same technique myself
for as long as I can remember.

Ken - AE1X

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1064 2007-09-27 20:23:33 jr_dakota Re: Binocular Core Winding
I do that with ferrite toroids but it'd be pretty tough with some the
bino-cores I use

It's usually a good idea to use the teflon tape on ferrite cores as
some, such as the 75 or 'J' mix, are actually semiconductors so any
nick in the enamel coating could cause a short to the core so your
wideband transformer isn't wideband anymore (your impedance