So what you are saying is that a mech mod with crappy rough, tarnished threads and contact, that is made out of metal that is essentially one step above "pot metal" will conduct electricity just as well as one with smooth, polished, clean threads and contacts, made from metallurgically superior metals?
And I'm the one who doesn't understand how a mech works?
You don't understand how electricity works.
At 4V / 0.2 ohm, you're trying to push 20A through the circuit. To safely pass a constant current of 20A - and then some - you need a conductor with a cross-sectional area of 4 mm2 or more. Vaping isn't a constant current, so in reality, you don't need that much, but let's assume the most stringent requirement for the sake of argument - i.e. let's assume that you absolutely NEED 4 mm2 to vape safely with a 0.2 ohm coil.
Now, what are the cross-sectional areas of the various conductive bits in a mod?
- The outside of a 510 connector - assuming a badly worn out thread - makes contact over 2.6 mm2 per turn (area of thread in contact between each turn of the male thread and each corresponding turn in the female thread). Assuming you only screw your topper 2 turns, that's still 5.2 mm2 of electrical contact - way more than needed, even if it's not made of magic metal.
- The inside of the 510 connector: mine here has a 3 mm diameter. That's a 7 mm2 contact area - way more than needed, even if it's not made of magic metal.
- The mod's body: suppose it's a 20 mm tube with a 0.5 mm wall thickness. That's a cross-sectional area of 30.6 mm2. WAAAY more than needed, even if it was made of a metal with a really bad conductivity.
- The battery's terminals: suppose it's a button top terminal with a 5 mm diameter. That's a 19.6 mm2 contact. WAAY more than needed. But for the sake of argument, let's say it's rounded and it only makes contact over half the diamter. That's a 2.5 mm diameter contact patch. Still more than enough at 4.9 mm2... As for the battery's minus terminal, it's wider, but it's in contact with the spring. Which brings us to...
- The spring: say it's 1 mm spring steel wire. The cross-sectional area of this wire is only 0.8 mm2. Now that is not enough. So let's work out the resistance it adds. Say it's a simple straight coil spring with a 15 mm diameter and 4 turns (oversimplifying here, but it's good enough): that works out roughly at 188 mm of spring steel wire. Assuming a resistivity of 6E-7 ohm/m, that's a 0.14 ohm resistance. Surprise surprise, it's not too far from 0.2 ohm eh? See why springs melt in mechs with shorted atties? See why sub-ohming with ordinary vaping hardware is completely dumb? But I digress...
- The button: resistance unknown in the OP's particular mod, but it's made in China and it's probably not designed to handle 20A. But more importantly, it's probably not designed to be arcing repeatedly each time it's used. How do I know? Because the OP says it gets really hot.
- The wiring, going from the battery's plus terminal to the button, and from the button to the 510 connector's center post: gauge unknown in the OP's particular mod. But what I can tell you is this: in my own Firebox mod that I've opened, I was shocked to find a really thin wire going to the 510 connector, considering the current going through it. Good thing it has time to cool off between vapes, because it must get quite hot. And *I* don't do sub-ohm. I wouldn't be surprised to find the same sort of thin wire in the OP's mod. The Chinese... they'll use anything as long as it's cheap.
So, you're free to buy mods made of super-duper magic metal, and you're free to polish and scrub them squeaky clean if that's what you like, but you should know that what you advise is more OCD rituals than engineering.
