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I have a small, sensitive pressure transducer with extremely thin wires. I frequently install and uninstall this transducer and route the wires through various small holes.

The overall length of the wires is about 2ft.

How can I bundle the transducer wires and keep the overall bundle as small dia as possible?

I want to bundle them for convenience and added durability. A bundling technique that can be removed without cutting the wires would be beneficial. For reference, I am a mechanical engineer.

enter image description here

nwsteg
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    That's what, AWG28 or so? That's not "extremely thin". Just twist them together tighter - I don't really see the problem. – Lundin Nov 03 '23 at 14:02
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    @nwsteg Seriously: that's not thin. – Mark Morgan Lloyd Nov 04 '23 at 07:29
  • Continuing my earlier comment, and writing as somebody with clock and watch experience. I think the OP, as an ME, would agree that something like the precision bearing and hairspring at https://www.petervis.com/avo-meters/avometer-repair/avometer-meter-movement-repair/avometer-phosphor-bronze-hair-spring-and-needle-counter-weight.gif is "fine work". EEs would similarly agree that the 50 SWG (25 micron) wire shown winding the bobbin is "fine". – Mark Morgan Lloyd Nov 08 '23 at 21:06
  • @MarkMorganLloyd I submit to your adjectival expertise – nwsteg Nov 08 '23 at 23:45

6 Answers6

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Use expandable cable sleeving. It is a synthetic fabric tube that expands when you push the ends together, so you can slide it over any small connectors. When you pull it longer it narrows back down. Reusable and easy to remove, though if you want it to stay in place securely you may need to secure the end with some tape or heatshrink.

Digikey link to the product category.

jpa
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    Otherwise known as braid. I think this is the best solution, everything else would make the bundle stiff. – Mark Morgan Lloyd Nov 03 '23 at 17:27
  • other benefits of this method: cable sleeving provides more shrink ratio than heatshrink (so you can often put this over things that a heatshrink cant), more resistant to friction wear than heatshrink, easier to remove if necessary (and/or to add extra cables since its easy to expand) – Wesley Lee Nov 03 '23 at 19:27
  • Does get mucky as the braid is slightly open and not a smooth surface. – D Duck Nov 04 '23 at 14:56
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Kapton tape is probably the thinnest material, it is available in various thicknesses, it is not super great if your wire is going to be bending.

If it's going to bend, get heat shrink, you can get some available with wall thicknesses down to 8mil.

Voltage Spike
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A solution we often use is to twist together the wires that have to be bundled. In comparison to the heat shrink, this has the added plus that there is no extra diameter. Depending on the type of wire you have to be careful about the extra stress that the twisting will introduce, but you can twist some solid wire together with the thin and sensible ones to introduce some support.

To twist them I usually use an electric drill at the lowest rotation speed and attach the wires I want to twist together on the drill, straighten them as much as possible, and then create my wire bundle.

villanif
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    That's not how to make a lasting twist. The wires need to be individually twisted, then the overall bundle will twist itself. Check the kind of tools rope makers use for inspiration. Without the individual twist, the bundle will unwrap itself rather promptly. – user107063 Nov 03 '23 at 14:43
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    @user107063 it works very well for single strand, and OK for fairly stiff stranded wires. But you're right here, the OP's wire won't be stiff enough to hold a nice twist. – Chris H Nov 03 '23 at 14:50
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    @user107063 Would braiding work better? (It shouldn't take too long to braid 60 cm of wires by hand.) – Andrew Morton Nov 03 '23 at 20:31
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    @AndrewMorton In my experience, braiding takes considerably more space, and bends then cause single wires to stick out. Twisting two wires together is easy as long as only one side is soldered in: you just twist both free wire ends independently in the same direction, and a strand will form by itself. While this would also work with more wires, few people have more than two hands. – user107063 Nov 03 '23 at 20:38
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As an alternative to Kapton or heatshrink, you could also wrap the bundle in PTFE tape - the same stuff plumbers use to wrap around pipe threads.

If you can wrap it around the wire tightly enough with significant overlap, it should hold itself together. Could be a rather fiddly task for a small wire bundle, but has the advantage of being very thin yet quite strong, and also lubricating as you pass the bundle through the various holes.

You could also just get some very thin walled flexible plastic tube, that is sized such that the internal volume is at most 60% filled (to make it easy to slide the wires bundle in).

This doesn't have to be heat-shrink tubing - in fact leaving the wires free to float in the tube may minimise risk of damage as you are bending it around because all the strain is taken up by the tubing not the wires.

We have some pressure transducer catheters at work that use this exact technique - three very thin metre long enamelled wires inside a 2mm OD flexible tubing (I think PVC, but could be any number of things).

Tom Carpenter
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    Silicone tubing is available in many sizes, which might have a better usable temperature range than rubber or PVC. – Andrew Morton Nov 03 '23 at 10:15
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    If you want to PTFE coat it, there's PTFE heatshrink. It's not very nice to work with because it insists on sliding along the wires, and getting full shrinkage means you're likely to melt any solder joints inside it, but it's useful stuff. It's more flexible than regular heatshrink in the same sizes. I've been using it for wires that will experience 200°C - also PTFE-insulated of course. – Chris H Nov 03 '23 at 14:53
  • @ChrisH Off topic, but how did you manage to shrink the PTFE heatshrink you use? I tried to use it once and even using an open flame it was near impossible to get it to shrink. – Hearth Nov 04 '23 at 20:06
  • @Hearth a heat gun, but a pretty big one on high, like you'd use for paint stripping. I believe it's 550C in that mode, and powerful enough to solder small pipework. – Chris H Nov 04 '23 at 20:34
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If thinness is your priority, you could just pain them in an adhesive. Liquid electrical tape for example, but I imagine any rubbery adhesives would work too. Perhaps even a varnish.

DKNguyen
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A thin-walled PTFE tube used as an individual wire insulator will work for a bundle of wires this thin. Use vacuum to pull them through the tube. PTFE is very slippery and will easily pass through small holes.

Kuba hasn't forgotten Monica
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