To pin mortise-and-tenon joints in a table frame, lay out the mortise location on a piece of 3/4-in. scrap the width of the table leg. Then drill two holes using the drill press at the desired pin locations. Now position this jig on the table leg flush with the top, and clamp and drill the pin holes into the leg with a portable drill. Flip the jig for the other side of the leg. All holes will be in the correct location, drilled straight with no tearout or wandering.

See the jig in action in this companion video.

Drawing by Jim Richey.

From Fine Woodworking #107

Drawing by Jim Richey.