Always use the manufacturers instructions and information, lightly mark out the door (I do mean lightly or you may never rub it off).
Then hold the lock up against the marks to check and re-check. Make sure it’s the right way up. This is especially important if you are working with a handed lock. Now cut the slot, I use the reciprocating saw, but I have also used the Souber fitting jig with a cutter kept for such a purpose, this does make a ferocious mess but was a clean and accurate way to get there and you do stay within the pencil lines. Jigsaws are great reckons Paul from Locksmith Liverpool.
Clean the cut, remove the piece and place it somewhere safely as it may be hot and it will definitely be sharp. Clean up the slot with a power file, be aware they cut fast and will not do corners. Don’t try to clean up to the line, then try the lock body, do not hold the lock body outside the door and use the face to try the cut clot. Important point says Tim of Locksmith Liverpool.
This is because I have seen more than one lock go neatly into the hold then slide from view, now file the corners by hand file and test. Look carefully for the high spots and take off a little.
Eventually it will fit without a big whack. See how neat you can make the slot by finishing if off by hand. Now cut the cylinder holes, these are slightly bigger than the 32mm saw blade and it needs to be sharp. Job done says Craig of Locksmith Liverpool.