Originally Posted by
Bill Kapaun
To set the lower limit, have the chain on a larger ring and screw it in enough that the chain WON'T drop to the smallest ring.
Push the cage over a bit and back the screw out a bit.
Repeat until the shift to the smallest ring occurs reliably.
trailflow1 is correct about this. I've never set a limit screw in the manner that you are suggesting.
Park Tools doesn't suggest your method. Nor does Shimano, for example. They suggest adjusting the inner limit screw with the cable with the least amount of tension on it. Adjustments to the limit screws
should be done so seldom that worries about damaging the aluminum shouldn't a concern.
The limit screws
should only need adjustment
once...upon installation. If the derailer is moved from bike to bike, it may need another adjustment but the amount of adjustment required should
never be enough to wear out the aluminum. Frankly, I'm not even sure that most derailers have the limit screws through threaded aluminum anymore anyway. Shimano's derailers look like they use some kind of insert.