On Friday, July 17, 2020 at 11:32:08 AM UTC-5, wrote:
I'm looking to cut 3 pass-through mortises (2"x6" long) on each of eight large pressure-treated square timbers (8"×8" wide x 8 feet long) for a small post & rail fencing project.
I've cut mortises on smaller thickness using just hand tools (drill, chise, wood file). I can't justify buying a plunger router or drill press just for this project and hardware companies near me don't rent them out. My plan is to purchase a longer drill bit, drill numerous holes along the inside edges, chisel out an opening on each side, use a sawsall tool to cut around the perimeter, and use an oscillating tool to clean up the edges. This will take some time since I have 24 mortises to cut. Not needing a tight fit since the rails will be loosely placed inside the mortises. Any other suggestions on how to do this easily with hand power tools?

How is this project coming along? Do you have pictures?