I've done searches but cannot find an answer to the following question:

When undercutting a masonry fireplace with a Crane 812, how do you cut the last couple of inches near the wall without cutting into the sill plate and the wall stud if one happens to be right next to the fireplace?

I use a carbide scoring tool like is used to score CBU and then carefully chisel it out. That said, its not going to hurt anything if you cut into the sill plate some.

Additionally, If you are using a dry diamond blade. The cut masonry well but are worthless when cutting wood. Actually I don't even think you could. It will burn faster through the 2x4 than it would cut it. Not an issue.

I have shoved my diamond blade into a sill plate or baseboard a time or two, to get as far into the corner as possible.

I do it most every time.......... go as far as it will reach. Cutting the smoke alarm off is a good idea too.

I ended getting all but the last inch cut using the saw. A $3 masonry bit on my drill and chisel cleaned out the rest.