Why sparingly? Why only the first 1/8" of the fitting.
That seems reasonable. I simply let solder melt in until it starts coming out the other side. While maybe a little wasteful and homely with the resulting globs; it ought to be adequate. No?
That is contrary to everything I have ever heard, ie, that the pipe should not be directly heated; only the fitting should be heated.
Do you keept the torch on the fitting until you are done?
You simply don't need more. As to the first 1/8", it minimizes interior contamination, if it doesn't matter on your job smear away :-)
Danger here is excess solder getting inside pipe. I have seen enough solder build up inside joints to severely restrict flow, and globs of solder breaking loose latter and fouling valves. A quick wipe with a damp cloth will take care of that exterior glob and give you a pro style joint. I have seen claims that a wiped joint is stronger than a drippy one but have no personal knowledge.
That pipe inside must be up to temp, both to activate the flux and allow the solder to amalgamate with the copper. That lack of amalgamation is the cause of those good looking joints that leak. Preheating the pipe first is the only way you can be sure that the interior will be up to temp.
No, it's a balancing act. Enough heat that all the solder will melt and not so much that it gets pumped in to the interior of the pipe.
Dave
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