Six Pearls Designs

On Datum and Tolerances

2013 August 01

I have a home gym and recently began working out with friends of very varied heights --my tallest workout buddy stands 6'5" and the shortest at 5'4". Pull ups are an important upper body exercise, so I thought it would be great to build and install a pull up station with an adjustable height bar hanging from rafters.

Exposed rafters in my garage

The goal was just to suspend two 2x4's from the rafters with multiple holes drilled to fit a 1" pipe. Initially, getting the right measurements to cut my 2x4's and drill the holes seemed like it would be a headache due to the geometry of the rafter trusses and roof. Fortunately, I realized I could reference the "bottom chord" (the dark brown horizontal span) and the two light brown 2x4s running perpindicular as referencing surfaces to simplify my measurements. Using these references, I only needed a few easy measurements and some geometry to line everything up:

  • Pull-up bar second position
  • Pull-up bar bottom position

I'm pleased with how well all 4 positions line up, especially given that I only used a 1-3/8" spade bit which was not very over-sized. It was fun explaining to one of the kids I had helping me that 2x4's measure 1.5" x 3.5" and a 1" pipe has a 1.32" OD.