Continued: Stock 3 point bridge replacement on 2009/12 Epiphone bird, with Babicz aftermarket replacement bridge.
I put the strings on, and noticed that the bridge may not be making 100% full contact. It's snug where the bolts clamp the bridge down, but there is a small gap in the distance between the bolts.
It' s more noticeable on the "front" side nearest the neck. It didn't seem like a big deal at first, but the more I looked at it the more I thought, "that's not optimum". I took a piece of paper and it was easy to slide it right under the bridge. So I took the strings back off, took the bridge off, put it back on and bolted it back down. I ended up with the same results. I put the strings on again to see if that would have any effect. It didn't. It was late so I left it. I adjusted string height and played around with the new bridge. I adjusted the truss rod a bit. It plays well. I'm gonna have to go back and figure out how to get the bridge more flush with the body.
Any tips or suggestions are welcome.
The gap at the rear of the bridge wouldn't bother me but that front gap would. Keep in mind the original three point bridge was never supposed to be in contact with the body so there wasn't necessarily a strong need for the bass builder to create a dead flat body surface to rest the bridge on. Since you're using the same three bolts I suspect you've got a good enough mount to make the bass function as intended. That said, the fit in the front would drive my OCD nutz.
Some random thoughts...
you mentioned that the three stud inserts aren't perpendicular. I suspect the bridge body is too thick and robust to let a little misalignment bend the base but just to make sure, take the strings off, completely unscrew the bolts and just set the bridge in place on the body. When you do that can you rock the bridge, or do you still see the gaps?
If not, then the misaligned inserts are messing with your bridge and the best fix will be to pull the inserts, glue dowel rods in the holes and drill new holes using a drill press vs a hand drill, then reinstall the inserts and you should be good to go.
However, if it's not the inserts and you see the gaps, or the bridge rocks when you just set it in place on the body, it's you're bridge bottom that isn't parallel to the bass top.
To test the bridge bottom for flatness set the bridge on a known flat surface (kitchen countertop will work). Does the bridge rock on that surface or do you see the same gaps? If yes, then your bridge isn't flat across the bottom. However, if there's no gap or rocking then it's your bass top that isn't flat. I wouldn't mess with the bass top, so that means you'll need to mess with the underside of the bridge to either make it flat or to compensate for how unflat your bass top is.
If you need to create a flat bottom on your bridge just run it in a circular motion over some 200 grit sandpaper that's on a solid flat surface until it sits flat on the kitchen counter and your bass.
If you need to compensate for a non flat bass top you'll need to mark the portions of the bridge bottom that are contacting the bass and sand them down until the bass sits flush on the body with no gap or rocking.
Alternatively - you could just keep everything as is and use the front bridge gap as a pic holder.
