I see people suggesting specialized tools, or trying it manually with sharp knife or scalpel, why not just burning the rubber for a second or two with a lighter and just pulling it out a more suggested option?
Is there any con to this approach that I am not aware of?
Insulation is rarely made of rubber. It is usually some kind of plastic. There's also teflon insulated wire, which doesn't burn well but melts. Then there's what's called silicone insulated wire, which is especially heat resistant.
There's also varnish insulated wire meant for winding coils. Of all the wire types, you will most often see recommendations to burn the insulation off of varnish insulated wire. Don't.
For normal insulation, use a good tool.
For varnished wire, use (very) fine sand paper on the thicker wires. For the finer stuff, get a blob of hot, melted solder on the tip of your soldering iron and run the tip of the wire through the blob to melt the varnish off.
A good tool is expensive. I've never found one that I liked, that worked well, and that I could afford.
All the cheaper tools end up cutting into the wire. I've given up on ever finding a good, affordable tool.
I learned long ago to use side cutters to strip wire. I can do it without cutting or nicking the wire inside.
I also quite often use the smaller blade of my pocket knife. I keep it just barely sharper than dull. It can score the insulation, but not cut it well. Wire between thumb and knife blade, a half turn to score the insulation, then pull. Works like a charm, and doesn't cut or nick the wire.
I've already described magnet wire.
That leaves teflon insulated wire wrapping wire.
The wire inside is very thin, and any nick will make it break. Can't use any bladed tool on it because they will all nick the wire.
Just push the tip of the wire into contact with a hot soldering iron. I do mean just the tip - the wire almost always protrudes a tiny bit out of the insulation. Heat that tiny wire protrusion. It will get hot and the insulation will melt back maybe a millimeter or two. That's enough to solder with. Looks ugly, but it won't break off like it would if you used a bladed tool on it.
You don't want to use a sharp knife or a scalpel. You will be guaranteed to cut into the wire. (Or as RoyC mentions, your finger.)
Try it as I described. It works, though it takes some practice.
We old farts mainly do it to show off our skills to young whipsnappers. Few things are as satisfactory to see a student or new employee ogle at how, with just some side cutters, you quickly remove the insulation from a dozen wires.
Also you don't want to breathe toxic fumes or have burn residue on your wires.
Because using the correct tool gives you a better result with precise strip lengths without the risk of leaving combustion products all over the wire which will adversely effect solder-ability or conductivity.
Whether it produces good results or not, wire insulation is one of the worse things to set on fire because "modern electric wires commonly use PVC plasticized with linear Phthalates" as insulation1. The National Center for Biotechnology Information states:
With its high content of chlorine, PVC is frequently branded as a major chlorine donor and spitefully leads to substantial formation of dioxins during poorly controlled or uncontrolled combustion and open fires.
Using your lighter certainly qualifies as "uncontrolled", and while the absolute quantities are small they are produced directly under your nose, often in a closed room. In addition to HCl and dioxin due to the relatively high Chlorine content in PVC, uncontrolled combustion produces the usual array of harmful substances like aromatic hydrocarbons and the simple, good ol' CO.
Don't do that.
1 In recent years there are efforts to phase out PVC as electrical insulation and replace it with polymers which do not contain Chlorine. Those burn cleaner, but it may still not be advisable to light them in a closed room.
Well, it can leave burnt debris when you need to solder it afterwards and, even if it does not leave burnt plastic, it can coat the wire(s) with soot from the flame.
It can be an easy solution when dealing with very thin wires that have a varnish type coating though.
As you have seen most people use some type of tool, there are several tools that can be used - a self-stripping "plier" type, cutters with "holes" in the cutting edge to miss the wire but cut the plastic etc.
Addendum, since two more traps have not been mentioned yet:
Soot can be conductive.
Some PU insulation (common solder-through insulation on magnet wire) actually does have warnings in the datasheets encouraging you to work in a well ventilated place, because some of the pyrolysis products are seriously toxic. An open flame is not unlikely to release even more of these.
ADD: HCl when burning PVC was mentioned in another post. HCl is really bad for metallic components around. In structure fires where significant amounts of PVC insulation burned, the metal damage from corrosion by HCL can be quite significant. You probably don't want these fumes near electronics.
In addition to the other problems mentioned, when burning the insulation off, you can also heat the wire and make it brittle. This increases the possibility of failure later. For smaller wire, I like Paladin, such as the Grip P10. If you're stripping a lot of very small and/or delicate wire, you probably want a thermal wire stripper. There are countless wrong ways to do things. What you do depends on your goals, how much the project matters to you and others, budget, etc.
In the case of magnet wire some are designed for thermal stripping by placing the ends into a pot of solder. Enamelled wire not so. All others require mechanical means. Flame stripping i will admit to having used but depending on the insulation used can be a very bad idea especially for stranded wire where they have to be soldered after, emergency measure only. Mechanical stripping is best but really needs tools designed for the diameter of wire in use , this an get expensive for different sizes and types of wire although adjustable strippers are available.
It all depends on your project. If you are in your garage working on a small project I don't think it is a big deal. We have worked on some pretty large projects in the past and hire out to have wire pre-cut and stripped for us. We tried a lot of techniques when we first started.. tools, cutting, burning, etc... and it was just too time consuming. When we used several tools the wire would always get nicks in it and we needed something cleaner.
It's not recommended to have flames in any environment; you could ignite something in the air or on the table. And if you use a cheap wire strip tool, you can strip a lot more cables in the same time.
Not burning it but heating it with an iron on the copper, not on the insulation. The insulation soften and can be pulled back like shirt sleeves. Use only on thin wires (for electronics).
For normal wires use this: https://cdn.manomano.fr/pince-a-denuder-automatique-P-140971-298992_1.jpg
