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Path: utzoo!linus!philabs!cmcl2!seismo!hao!hull
From: hull@hao.UUCP (Howard Hull)
Newsgroups: net.micro
Subject: Re: Re: How to fab One-Of-A-Kind systems?
Message-ID: <1577@hao.UUCP>
Date: Mon, 3-Jun-85 20:07:02 EDT
Article-I.D.: hao.1577
Posted: Mon Jun  3 20:07:02 1985
Date-Received: Tue, 4-Jun-85 08:17:31 EDT
References: <202@ganehd.UUCP> <1690@sunybcs.UUCP>
Distribution: net
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 50


In the cited article by Ken Smith, almost all of the technicalities with
respect to wire wrap have been expressed better than I could say them.
I would like to add, though, that use of a 110v powered hand wire-wrap gun
takes a little practice.  I have found that there are two major disasters
that can happen:
	1. If you press the gun too firmly down around the base of the post,
	   the wire will not feed properly, and (if you are lucky) the wire
	   will be broken after only one and a half turns.  Given that (you
	   were unlucky) the wire was nicked, and that you didn't notice it,
	   it will fail later at it's own convenience, not yours.  Be prepared
	   to do the wrap over, but keep in mind that the wire wrap system
	   depends on the posts remaining *square*, and that each attempt
	   puts little dents in the post that may compromise subsequent
	   attempts.  Above all, WORK CAREFULLY.  You may want to warm up
	   on a "junk" board before you start for real.  For the bottom
	   wrap, press the gun all the way to the bottom of the post, and
	   then lift it about a millimeter off the board.  Apply just enough
	   upward force to support the weight of the gun minus ~ .00001 oz
	   at that height while the trigger is pulled, allowing the gun to
	   rise slightly as the wrap proceeds (a major fraction of a second).
	   Whatever ya do, don't flinch.  Inspect the wrap when you are done
	   to see that all the wire went on the post, and that the wrap is
	   even.  This is a necessary, but not sufficient condition, so see
	   number 2., below.
	2. If you suffered from linear withdrawal symptoms while doing the
	   wrap, and you thus lifted the gun slightly while wrapping, you will
	   have an even wrap, but nonetheless a *stretched* wrap.  Since a
	   stretched wrap can be compressed (and thus result in a slightly
	   shorter wrap with an *expanded radius*) by pushing down on the
	   gun, if you want to have any hope of spotting a stretched wrap
	   you might have made, DO NOT press down on the gun as you are done
	   with a wrap!  The result of pressing down is a floating wrap
	   (we call them "Weber Junctions" in honor of a certain technician
	   that did several hundred of them for us in a bit-slice micro we
	   put together some time ago).  They are *very hard to detect* by
	   physical inspection, and may even pass electrical inspection until
	   the wire oxidizes.  After that, kiss your sanity goodbye.
	3. Always strip wire_wrap wire with a "gauged" stripping tool.  Just
	   pulling the wire from the reel until it breaks, or use of a pair
	   of long-nosed pliers may stretch the wire, resulting in a tapered
	   gauge along the wrapped length.  I don't know that this causes so
	   much trouble in the actual finished wrap as it does in the handling
	   of the wire by the tool while the wrap is being completed.  It does,
	   however, contribute to failures as outlined in (1.) above.

						Regards,     Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
                   ...Then only the deranged will discuss yet unproven concepts]
        {ucbvax!hplabs | allegra!nbires | harpo!seismo } !hao!hull