Screw two 4-inch steel pipe nipples into two flanges. These and all pipes and fittings should have a three-quarter inch diameter.
Screw an elbow joint onto the other end of each nipple.
Screw the other ends of the elbow joints onto a 3-foot double-threaded pipe, with both flanges pointing the same direction.
Place the finished chinup bar onto the board. Center it and mark the locations of the screw holes with a pencil.
Drill a one-sixteenth inch pilot hole into the board at each pencil mark.
Use a stud finder to locate the wall studs above a doorway.
Place the board onto the wall above the door and mark the stud positions on it.
Drill three one-sixteenth inch pilot holes through the board for each wall stud, evenly spaced. Drill matching pilot holes into the wall studs.
Screw the board to the wall with 4-inch wood screws through the second set of pilot holes.
Screw the chinup bar to the board through the first set of pilot holes with 2-inch wood screws.