Nice clean installation. Congratulations. I've never seen an undercut saw before. I have dozens of different types of saws, but now I now what my next one is going to be!!!!
What do you use it on other then cutting flashing into barns?
It's really intended for flooring install, to undercut door jambs, doors, baseboard trim, etc... Basically, it's a lot faster/easier than how I'd normally under cut a jamb with a hand saw or vibrating saw. It can get down flush if needed, or be adjusted to cut up to about 1" off the floor. Also has a depth gauge to limit depth of cut, so you won't saw into framing (I removed it for the flashing cuts, since I wanted to go clear through the battens and siding boards).
They make a masonry blade for these saws that can be used to undercut brick/etc -- say if you were installing flooring up to a hearth/chimney and wanted to tuck it under. I have only ever used them on wood though, so I can't say how well they work on masonry.
I rented this one for $25/day. Most rental places have them, including Home Depot rental. I think they are around $150-250 to buy new. If you do a lot of flooring installs, it might be worth it.
Me, I was happy that a tool exists that could easily be adapted for this non-traditional flashing job. I always seem to be in a pinch where I can envision the perfect tool, or material, or product, but can never find it. In this case, everything came together perfectly. For me that's like 1 out of 1000 where the magical tool exists....
My other option would have been to use a skill saw, with blade set to an angle, to make the cut before the roof went up. Could have been done from the inside or outside, but it would have taken perfect calculations and super good luck to know that the cut I made beforehand would line up in the right place above the roof shingles. Making the cut after the roof framing and sheathing was up eliminated all of that uncertainty.
