"Wire-Wrap" construction - can normal magnet wire be used? - Page 1
Forum section: electronics / projects

author: wobbly
author_rank: Regular Contributor
timestamp: January 28, 2025, 04:48:45 pm
content: I inherited a wire-wrapping tool (the manual type that you spin with your fingers) and I want to use it to make a circuit, for fun mostly and because I like the look of the results.I was wondering about using regular magnet wire for this as I have a few reels of enamelled wire with an outer diameter of 0.35mm including enamel coating.So I tried it 10 times and I was able to get a 0-Ohm connection every time which is encouraging. But what I don't know is how resilient this connection might be over time (vibration / temperature etc). I've been using normal gold- or nickel- plated square post 0.1" pin headers as the pins to wrap onto. They are a bit short and limit the number of wires that can be wrapped, but the connections seem to be sound at first attempt.I don't think I'd use this method for power rail connections but rather for low-current signals such as logic.Does anyone have any experience of this old wire wrapping technique and have any tips on what kind of wire / pin combination is best to use (if they are even still available in 2025!)?

author: TimFox
author_rank: Super Contributor
timestamp: January 28, 2025, 05:39:59 pm
content: In my memory, the wire specified for Wire-Wrap should be OFHC copper, usually plated, to get the proper cold weld on the sharp edges of the hard posts (often Be-Cu).Magnet wire is usually normal ETP copper under the enamel.A tutorial:https://www.nutsvolts.com/magazine/article/wire_wrap_is_alive_and_wellThe mechanical properties of OFHC differ from ETP: OFHC is softer and resists work-hardening.

author: incf
author_rank: Frequent Contributor
timestamp: January 28, 2025, 11:53:47 pm
content: Quote from: wobbly on January 28, 2025, 04:48:45 pmI really like wire wrap compared to soldering. Much more forgiving.Magnet wire might work if you are just playing around.However, if you want whatever you make to be reliable, I would like to encourage you to try to buy proper wire for the best chance of success.Something like thishttps://www.mouser.com/ProductDetail/TE-Connectivity-Raychem/55A9002-30-5?qs=BM0LbQdndF08ybIp%252BhH6%2FQ%3D%3D(but it's out of stock)Silver plated, ~30AWG, jacketed insulation, and specifically made for wire wrapThis is in stock, close enough,https://www.digikey.com/en/products/detail/alpha-wire/5952-BK001/6003202

author: wobbly
author_rank: Regular Contributor
timestamp: February 07, 2025, 05:48:31 pm
content: Gave up on the magnet wire idea. Dug out some old kynar reels from the junk box instead...I made a cute little electronic "Die Roller" with configurable modes, pictures below.I do like the wire wrapping method for circuit construction. It is quite satisfying to methodically place each wire, but there are some problematic downsides, such as being awkward to re-work a mis-placed connection. This is especially difficult when you need to remove the first wire on a 4-wire stack! Urgh.Good fun though, I'd recommend anyone interested to have a play around with this method.

author: incf
author_rank: Frequent Contributor
timestamp: February 07, 2025, 06:33:18 pm
content: Was it ever common to parallel up wire wrap posts/terminals to facilitate rework?For example, having a strip of 8 posts either soldered or wired in parallel at the bottom level just for power distribution.

author: wobbly
author_rank: Regular Contributor
timestamp: February 07, 2025, 07:44:22 pm
content: Quote from: incf on February 07, 2025, 06:33:18 pmVery good questions. The limited amount of information I've found on this arcane topic suggests that wire wrap was only really intended for mature designs put into small-scale production perhaps into a few thousand units. I think it wasn't supposed to be used for prototyping so much (although you can do that of course).One thing that I did find very interesting was just how much of a problem discrete components such as caps, diodes and resistors are when trying to use wire wrap construction. I mean, you can't easily wire-wrap onto a resistor leg because they tend to be circular in cross-section. Wire-wrap only really works well on square cross-section posts.Take my design for instance, it has 14 LEDs which each need a current dropper resistor - I had to solder them down as one would do in a "normal" design. In fact only 1 terminal of the 2x7-segment display was wire wrapped because of poor planning on my part.I don't think that wire-wrap would be used for power distribution in the normal sense. I reckon bus-bars would have been used.One machine that made use of wire-wrap was the Bendix G15. Usagi Electric has heap of extremely detailed videos on this machine...https://youtu.be/-HibkocVn1UAlthough I think that system uses much larger wire-gauge than the 30AWG stuff I'm using.

author: incf
author_rank: Frequent Contributor
timestamp: February 07, 2025, 09:07:56 pm
content: My impression was that resistors and capacitors were typically installed in sockets or soldered to strips of square pins (ie. wrap the resistor lead around a tall square pin that extends both above and below the board, then solder the resistor above, and wire wrap below)Years ago I built a LED sign using a FPGA breakout board and LED driver shift registers at ~100MHz if I recall correctly. Even using 30AWG wire wrap wire, power distribution to the logic ICs (>>100mA over ~2 feet) was not a problem so long a I had decoupling capacitors.

author: wobbly
author_rank: Regular Contributor
timestamp: February 07, 2025, 09:29:39 pm
content: Quote from: incf on February 07, 2025, 09:07:56 pmI have tried to "wrap" a resistor leg (using the proper tool) onto a proper square wrapping post - it doesnotwork well. Perhaps resistors of the past were designed to be "wrapped" but I don't know.I think it is unlikely that both wrapping and soldering would be used on the same connection. They are competing methods. You'd do either one or the other, but not both. Again I'm presuming a mature design and in a production environment.Also, I think that this was a time of experimentation in the industry and I reckon that an attitude of "whatever works - wins!" was prevalent. History does not give me the details easily.Having to reserve board area for sockets for simple passives is MASSIVELY wasteful in terms of 3-dimensional space if you consider the length of the wrapping pins below and/or above the board substrate.The very simple device I made is vastly volumetrically thicker than a "normal" build where no wire-wrap is used. In fact I can't easily find an electronic enclosure that would fit it nicely. No matter how fun it is to build this way, it's a pain in the ass and totally impractical.Not that it'll stop me making more stuff like this

author: incf
author_rank: Frequent Contributor
timestamp: February 07, 2025, 09:40:33 pm
content: Yup, the thickness is a pain. But the flexibility is a gain.Typical example of resistors and transistors on wire wrap sockets. Multi-terminal junctions (eg. power and clock distribution) could easily be done by soldering a wire on the top terminals of one of these sockets.The space usage isn't too bad if one is clever about packing as many components as possible onto a single socket.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 07, 2025, 09:46:01 pm
content: The wrapping must be around a pin with a square section, or else it won't work. The square shape is essential to make good contact between the wire and the pin. If the shape is square, the elasticity of the winded wire makes each corner into a contact point. If the pin is round, then the elasticity of the wire will just enlarge the coil like a spring, with no contact points.Take a round pencil and wrap some turns around it, then leave the wire free, to see what I mean.Try the same experiment with a square-shaped rod with sharp edges.

author: wobbly
author_rank: Regular Contributor
timestamp: February 07, 2025, 09:50:48 pm
content: Those pins underneath look far too short to be wire-wrap posts, but yes, I get your point.Sad thing for me is that my Grandpa would have known all about this kind of thing. Can't ask him now

author: incf
author_rank: Frequent Contributor
timestamp: February 07, 2025, 09:57:52 pm
content: Same here, mine worked for bell telephone, was into ham radio. But, cancer got 'em nearly as soon has he retired. (exposure during military service, tobacco, etc.)It's entirely possible to wrap short pins with conventional tools (at least, mine worked on standard length 0.1" pins). It just limits construction to one connection per post - which is very reworkable, and makes the construction very "thin" in comparison to normal wire wrap.

author: TimFox
author_rank: Super Contributor
timestamp: February 07, 2025, 10:06:56 pm
content: Quote from: incf on February 07, 2025, 09:40:33 pmThose are "headers" that allow soldering of discrete components onto a male plug that can mate with a DIP socket (either solder-tail or wirewrap).

author: tooki
author_rank: Super Contributor
timestamp: February 07, 2025, 11:19:17 pm
content: Quote from: wobbly on January 28, 2025, 04:48:45 pmI have never,everheard of enameled wire being used for wire wrapping.Wire wrap posts and regular square-pin headers arealmostthe same thing, but not quite: wire wrap posts must have sharp corners, so their specifications will specify this, whereas regular header pins might be sharp enough, or might not.I would not expect the consistently reliable results of proper wire wrap wire and posts when using any old wire and any old square headers. Might work, might not, might last, might not.

author: edavid
author_rank: Super Contributor
timestamp: February 08, 2025, 12:50:54 am
content: Quote from: tooki on February 07, 2025, 11:19:17 pmAgreed, but I have had very good results on several projects using the combination of "proper" silver plated wire and "any old" tin plated header pins - 100% reliable connections, still working after 3 years or so. I think it's viable for a personal project that won't be in a vibration environment.P.S. The biggest wire-wrap mistake is daisy chaining - don't do it.

author: shabaz
author_rank: Frequent Contributor
timestamp: February 08, 2025, 01:06:47 am
content: It's possible to get pre-stripped wire which I believe (not 100% sure) is for wire-wrapping.Fry's stores used to sell it. I purchased a few packs but it can oxidize (it's silver-plated wire). No idea if that is acceptable for wire-wrapping or not.There was a slightly odd system called RoadRunner, which used a low-temperature enamel wire, it's not really wire-wrap, it used soldering I believe (i.e. you used a pen shaped tool to lay out the wire, wrapping around component leads, and then soldering them. I never tried it, but recall seeing adverts of it in old electronics magazines.With your manual wire-wrap tool you could lightly sand the end of enameled wire and then wrap it. Not orthodox at all, but if you're just experimenting for a hobby then why not. You could even solder the ends afterwards if you're unsure about it. Again, this is totally against what wire-wrapping is all about, but if there's no-one forcing you to adhere to any assembly standard, then you're free to do as you wish.The attached photo shows a silly example, which used enameled wire lightly sanded on the ends, and then wrapped around pin headers. If you're not careful you end up with tiny inductors on the pin header : ) Anyway, it was just an experiment, worked fine for the short period of my test, I wouldn't rely on it (at least not without then soldering) since it's not true wire-wrap.

author: intabits
author_rank: Frequent Contributor
timestamp: February 08, 2025, 06:46:32 am
content: As I remember it from back in the day:-Wire wrapping involves 7 turns of wire around square posts, thus providing 28 parallel junctions to each wrapped connection.Each junction is wrapped tightly around the corner, causing high pressure between the wire and the post, promoting a strong gas-tight junction.The silver plating on the wire, and the gold plating on the post help to ensure that the contact surfaces are clean and not oxidized or corroded. Furthermore, these two metals somehow tend to fuse together under the pressure of the wrap, creating extremely reliable connections.

author: RoGeorge
author_rank: Super Contributor
timestamp: February 08, 2025, 07:04:39 am
content: The big advantage with wire wrapping was that it was easy to automate. There were CNC machines with wire-wrap header tools that were able to wire very fast a board or a backplane.Other than that, to do it manually it was rather slow, and good wire-wrap sockets were always very expensive, because of the long pins, more metal and more gold was used for them than for a normal soldering socket.Back then breadboards were not yet a thing, so wire-wrap was sometimes used for prototypes, mostly for digital circuits. In telephony the wire-wrap maybe was making more sense, because the work was often done in the field, where soldering was not an option.For electronics, however, I've ended up soldering the wrap wire straight to the protoboard, either directly on the IC pin, or to the pins of a normal PCB socket. For anything bigger than a few IC's, the wire-wrap can get tedious, either wrapped or soldered:https://hackaday.io/project/1411-xor-hobby-a-vintage-z80-computer-prototypeI still use soldered wire wrap sometimes, as a permanent build for smaller one off boards:Though, no matter if you solder or wrap the wrapping-wires, it is rather time consuming when compared to a breadboard, or to soldering the same parts on a proper PCB with all the traces already in place.