#1
i understand that you heat up the joints instead of the solder when soldering.
but is it ok to heat up the potentiometers in the guitar before applying the solder?
#2
No it's not. Why would you want to do that anyway?
Derp.
#3
^err... You have to heat the pot otherwise you won't get a good joint

TS, soldering to pots is a tricky thing. If your iron is too hot you will overheat the pot and burn it up. If your iron is too cool or the wattage isn't high enough then you will have to keep heat on the pot for too long which will also burn up your pot. So the key it to get it just right.

When soldering to pots it's a good idea to use some 200 grit sandpaper on the back of the pot to rough up the serface and make the solder stick better. Then make sure your soldering iron is clean and tinned. You want to have just a little bit of extra melted solder on the tip of the iron so that it's about the drip off but doesn't. Then touch the iron the the back of the pot for about 5 seconds before you touch the solder to the back of the pot. If the solder doesn't melt right away then move it closer to your iron. Get it as close to the iron as you possibly can without actually touching it to your iron. Once it starts to melt, move the solder away and take away the iron. You don't want to touch the back of your pot with the iron for more than about 20 seconds and even that is pushing it.
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