Mandolin bridge and very sharp G strings

Help!!
Hi, Steve. I am your Facebook friend Steve Spradlin and I recently sold a very nice Epiphone MM30 - but bought it back after the buyer reported there was a crack in the bridge that I was not aware of...long story short, I just received the replacement bridge and jig from StewartMac yesterday. I had to use the new top on the old bridge base - but with new strings, the G strings are horribly sharp when playing intermediate notes - even though the harmonic and 12th fret notes are right on. It is a compensated bridge with adjustment wheels (looks just like the original), the present alignment of the bridge angles the base of the G side toward the tailpiece, and I can see that the bottom of the old bridge base is not well-fitted to the surface. I found your article about using the jig to sand the base...do you think that might correct the problem if I go back and try that? I am surprised because I didn't have this problem with the old strings with heavier gage G strings...in fact, it had perfect pitch with the old bridge and placement and old strings before I attempted to improve things with new strings and a new bridge. I may need to bring this in for you to correct matters..but if you have a suggestion for me to try first (like base fit, etc) that might correct the problem with the G strings - then I would be most appreciative. I have a better mandolin too and will likely encounter this problem again someday. Thanks,
Steve!

Steve,
The "action" on your mandolin is governed by the straightness of the neck, the levelness of the fret tops, the roundness of the fret tops, the height and slot angle of the nut and bridge, and, of course, the gauge and condition of your strings. If you change one factor of the function, you usually need to adjust them all. My guess is that your new bridge top is slightly higher than the old one. A small height change can make a big change in the feel. Also, you have switched to lighter strings. Lighter strings change pitch more as you bend them, and, being higher, you have to bend them farther to get them down to the frets. The most common reason for mandolin players to switch to light strings is that they think that they will be easier on their fingers. A mandolin that is rough on your fingers with .011 E strings needs an action set, not .010 E strings. The lighter strings and higher bridge can mandate a new bridge placement, and since your top is not perfectly cylindrical, the feet of the bridge may not fit in the new spot. Doing an action set and new strings might move the bridge back to a place where it fits. Or, maybe that will need to be refit also.

The most common failing of beginning luthiers is to look for evil in the wrong place. Seeing a bulging top when the problem is the neck set. Seeing a rattling truss rod when the problem is bad strings. Raising the nut to cure a buzz at the 7th fret. When you are sure that you have found the cause of your instrument's inadequacy, test your assumptions, flip the guitar over and look at the other side, think outside the (guitar) box. I once worked for two hours trying to get a buzz out of a stand up bass. It turned out that the buzz wasn't in the bass. It was in the tool cabinet that I had the bass aimed at as I worked on it.

Steve Mason