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Old 10th Dec 2017, 6:59 pm   #1
Al (astral highway)
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Default Cutting and soldering Teflon covered wire

Hi folks,

Any tips for a really professional finish here? I note that Teflon covered wire doesn't cut very neatly and also that the insulation retreats/burns easily when soldered. The joints can look very neat indeed - that isn't the problem.

I've seen some cracking good finishes on other projects and would like to emulate the same. Any tips, please. I may simply be using the wrong tool for stripping, for example...

This may seem minor but it's important to me.

Thank you, from a snowy East London!
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Old 10th Dec 2017, 7:16 pm   #2
TonyDuell
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Default Re: Cutting and soldering Teflon covered wire

Are you sure it's Teflon? Teflon is PTFE, which shouldn't melt or burn in a short time atnormal soft soldering temperatures. It's what the tips of solder suckers are made from, for example.
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Old 10th Dec 2017, 7:26 pm   #3
Al (astral highway)
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Default Re: Cutting and soldering Teflon covered wire

Tony, it was described as Teflon, so that's what I'm assuming it is.

Not that the tips of desoldering tools are very heat resistant, I note! They quickly melt and discolour, but I don't want to go OT.

This material sure is tough to cut, very hard. I suppose I could go round it with a knife, but that isn't easy to do with 22SWG.
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Old 10th Dec 2017, 7:59 pm   #4
kalee20
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Default Re: Cutting and soldering Teflon covered wire

Teflon - PTFE - insulation doesn't burn - you can wrap the wire around the barrel of a soldering iron, unwind it, and not even know later that it has happened!

Get PTFE really hot (400 degrees C or more) and it decomposes with some rather toxic fumes. But we're not up there so no worries.

It's fairly soft, though not as soft as silicone. It does tend to tear, unlike PVC, when stripping, which makes it a bit of a pain. However, as the characteristics of the stuff you're describing are not those of PTFE, we first need to identify the insulation before pooling knowledge!

Last edited by kalee20; 10th Dec 2017 at 8:00 pm. Reason: Clarification
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Old 10th Dec 2017, 8:40 pm   #5
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Default Re: Cutting and soldering Teflon covered wire

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Originally Posted by kalee20 View Post
Get PTFE really hot (400 degrees C or more) and it decomposes with some rather toxic fumes. But we're not up there so no worries.
I think that concerns about PTFE decomposition could start below 400°C. Our safety guy refused to let me use it on pipe fittings at 325C. In our workshops, there was a lathe with a special fume extraction system for machining PTFE. The use limit is a grey area but exposure to the fumes can result in "Teflon Flu" at the mild end to "life-changing" effects at the high end. And yes, I do have a solder sucker and my iron is always higher than 325C .

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Old 10th Dec 2017, 10:29 pm   #6
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Default Re: Cutting and soldering Teflon covered wire

A really sharp scalpel blade or old-style safety razor blade was the only thing I found would work for stripping PTFE wire cleanly. Run the blade round the wire carefully, exerting sufficient pressure to cut the insulation but not damage the conductors and pull off the end. I don't know what our production line used, but I never had any joy with the wire strippers we had in the lab.

I have had the insulation of PTFE-insulated wire pull back when soldering when a wire stripper has been used to strip the end. Pulling the stripped end off stretched the unstripped insulation partly over what should have been the stripped conductor, and the heat of the soldering iron made the insulation recover and shrink back to where it had been prior to stripping.
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Old 10th Dec 2017, 10:33 pm   #7
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Default Re: Cutting and soldering Teflon covered wire

Are you sure this is actually PTFE covered wire? I've encountered a fair amount of it and it always seems to have a very glossy, slippery (non-stick!) feel to the insulation, and it's almost impossible to burn with a soldering iron. Yes, it does tend to stretch instead of stripping with wire strippers, but with sharp tools that's not a problem. The only oddity I noticed was that yellow PTFE insulation tended to turn orange when it got hot, and then turn back to yellow again when it cooled. Curious.

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Old 10th Dec 2017, 10:58 pm   #8
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Default Re: Cutting and soldering Teflon covered wire

Al's wire is probably the stuff I sent him recently. The label doesn't explicitly say it is PTFE, but it certainly looks and feels like the PTFE wire I was using in the 1970's. The drum has a safety warning label (scan attached) that refers to PTFE, FEP, TEFZEL, PDF and PFA. I don't know what the other insulation types look and feel like, as PTFE is the only type I have used of those mentioned.
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Old 10th Dec 2017, 11:16 pm   #9
ronbryan
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Default Re: Cutting and soldering Teflon covered wire

All of the ptfe wire that I have used in industry is silver plated and solders easily. I assumed that it had to be silver plated to be compatible with the insulation, but I may be wrong there. The wire strips well with Stripmaster automatic wire strippers, provided the correct gauge is selected.

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Old 11th Dec 2017, 12:29 am   #10
jamesperrett
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Default Re: Cutting and soldering Teflon covered wire

I remember a colleague telling me to use a special version of the Stripmaster wire strippers for PTFE wire. I seem to remember that the cutting angle on the blades was much shallower than the standard blades. Most of the time I've used the standard blades but I often find that they leave a whisker of insulation that has to be cut off.
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Old 11th Dec 2017, 1:18 am   #11
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Default Re: Cutting and soldering Teflon covered wire

I have found a home made tool useful for stripping this kind of wire.

Take two similar small blocks of wood or MDF, place between these a sharp blade such as a Stanley knife blade or razor blade, secure the two blocks to each other with a bolt and a wing nut.
Adjust such that most of the blade is concealed, but that about 1mm or 2mm along the length of the blade protrudes.

To use, place the wire to be striped on a firm smooth surface, apply the blade to the wire and roll the wire along whilst trapped between the blade and the surface.
This will give a neat cut of the desired depth, around the circumference of the wire.

Any bladed tool should be used with care, but this is safer than most because much of the blade is concealed, it can not inflict any serious injury.
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Old 11th Dec 2017, 1:35 am   #12
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Default Re: Cutting and soldering Teflon covered wire

I use a number 11 scalpel blade on a handle being careful not to push it too deeply into the insulation and damage the strands, just enough to put a sharp score into the insulation surface so it gives a clean break. The wire and blade are rotated in reverse directions, with the blade on the insulation to get the full 360 degrees. I'm used to working with small sharp blades so it seems easy to do without cutting myself, but perhaps this method will not suit everyone.

Then remove the insulation end with a gentle grip distal to the cut with side cutter jaws. After a while you'll get used to the wire you are working with and won't damage the strands.

If its real teflon it won't shrink back with soldering (unless as pointed out the insulation was pulled by a stripper tool). Heating it though produces some interesting thermochromic effects, for example red wire can turn brown, but it returns to its initial color when it cools.

All of my homebuilt radios I use multi colored stranded teflon wire which was an ex submarine product. I also use teflon wire wrap wire for wiring up logic pcb's. I built a hand wired Pong pcb with over 900 connections, each one had hand stripped small diameter teflon solid core wire and then soldered. With this wire its best to create a 90 deg bend before stripping the end, as sometimes the solid core can slip in the length of the insulation for a short length of wire.

Practice makes perfect.
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Old 11th Dec 2017, 4:27 am   #13
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Default Re: Cutting and soldering Teflon covered wire

The roll on a sharp blade works for me. Sounds like its not the PTFE that I know. Is it really TEFLON insulation? I have never seen that.
As an aside, PTFE sucker tips don't last like they used to, I put a Helaman sleeve on mine, easy to replace, aids the suck, saves the sucker tip.
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Old 11th Dec 2017, 9:57 am   #14
Craig Sawyers
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Default Re: Cutting and soldering Teflon covered wire

All the wiring on spacecraft is PTFE insulated. It does not outgas, it is radiation hard, and has very predictable characteristics. And you can't use the good old scalpel blade trick, because with hundreds of thousands of wire joints in a spacecraft, you need a 100% reliable way of stripping the insulation without nicking a single strand of wire. Transparent heatshrink is specified so that joints can be 100% inspected.

I can't recall offhand what strippers are used, but I do remember them being an order of magnitude or more than any sane private person would think of paying.

Oh and BSG210 (which is on the reel photo) is indeed PTFE insulation http://www.klaceycables.co.uk/defaul...3G210-y09a.pdf

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Old 11th Dec 2017, 12:36 pm   #15
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Default Re: Cutting and soldering Teflon covered wire

Thanks for identifying the cable and confirming that it is PTFE: it was one of many drums of cable of various types I salvaged (with permission) a couple of decades ago from the abandoned stores of the Marconi site I was based at when it was being closed down, so I didn't know its provenance. That particular drum was unopened.

Last edited by emeritus; 11th Dec 2017 at 12:42 pm.
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Old 11th Dec 2017, 1:30 pm   #16
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Default Re: Cutting and soldering Teflon covered wire

Quote:
Originally Posted by Craig Sawyers View Post
A And you can't use the good old scalpel blade trick, because with hundreds of thousands of wire joints in a spacecraft, you need a 100% reliable way of stripping the insulation without nicking a single strand of wire.
That is because they cannot control the different people with different skills & abilities and short or long fuses that might be working on the wiring, so they needed an idiot proof tool. However, if you do it yourself and perfect the art, it is easy to check under magnification if the strands get damaged, and with practice you can learn yourself, to do it as perfectly as any tool, with the scalpel. But with all things good, it requires patience and effort.
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Old 11th Dec 2017, 1:36 pm   #17
Craig Sawyers
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Default Re: Cutting and soldering Teflon covered wire

It'll come as no surprise that I too use a scalpel
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Old 11th Dec 2017, 1:56 pm   #18
Al (astral highway)
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Default Re: Cutting and soldering Teflon covered wire

Good to have so many replies, thank you.
Emeritus, it is indeed your wire. It is beautiful material and I would like to work it to the standard it deserves.

Argus25, the scalpel blade is a good idea. Any form of pulling the insulation to stress it as part of the cutting is messy and doesn’t work (as it would for pvc in devices that both hold and cut) I wild like uniform, perfectly circular cuts.

Peter, the insulation does soften a little at above 400 C centigrade. I use this temp for hard wiring to assemblies like main switches and to a ground plane when there are several thick wires... arguably better than a longer contact time at 285 C which cooks things that way.
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Old 11th Dec 2017, 2:02 pm   #19
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Default Re: Cutting and soldering Teflon covered wire

Quote:
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Then remove the insulation end with a gentle grip distal to the cut with. With this wire its best to create a 90 deg bend before stripping the end, as sometimes the solid core can slip in the length of the insulation for a short length of wire.

Practice makes perfect.
Good tip, Hugo. I had noticed the slipping problem and this solution of yours sounds very effective. Thank you

I will grip the distal end by taping it temporarily to a work surface and then start on the proximal end with a suitable scalpel before applying the 90 degree bend. If find this very pleasing material to work with.
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Old 11th Dec 2017, 2:15 pm   #20
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Default Re: Cutting and soldering Teflon covered wire

Working with very fine teflon wire can be fun.

I've attached images of the teflon wire prototype Pong PCB I made.

I used this prototype to iron out the 6 bugs in the original design before I had my formal pcb made. There are over 900 connections.

One problem was how to keep the many wires orderly. Though you will find with many hand wired projects, this is always an issue to consider. So I ran the wires in an orderly manner along the long axis of the IC's and laced them into looms with some surgical silk thread.

In the looms there are as many as 10 to 12 wires in places, but it doesn't look like it in the photo. As noted each wire was sized, the end was stripped, pre tinned before soldering to a pad. I have not had a single connection failure, but it was a very large amount of work, but not actually as much as it took me to design the pcb that replaced it. So as a "one off" it was quicker.
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