it helps a LOT to use plumbers sandcloth to clean the copper down to where it is not oxidized also. weld has to be done quickly or like solder the material will start to transfer/run down the pipe and get lumpy and a mess to fix later. practice makes perfect and turbotorches work OK for regular fittings but take too long and will cook/damage a service valve. depends on the skill of the tech but not recommended for fine work.
"Cut it twice and it is still too short".