Scored a nice set of Ridgid pipe threading vises, dies, and ratchet off of Craigslist for $200.00. No cracks in the die bodies and the cutting teeth look rather unused.
The bench vises are nice but permanently mounting them to a bench is rather poor planning with limited shop work surface real estate.
No worries, a dive into the steel on-hand supply turns up the necessary components. An I-beam with a 4" flange will work as the pipe vise mounting base. Although, the pipe vise will have to be angled out of phase with the mechanic's vise for the mounting bolt holes to fit within the confines of the I-beam flange.
The I-beam was cut and coupons of metal made to act as end caps to stiffen up the assembly. 1" wide strips of 0.25" metal will go on the bottom of the I-beam webbing so the setup can't slip out of the vise accidentally during use.
Once everything was welded up, a 1/2" transfer punch was used to mark the holes to be drilled in the fabricated mounting box. The drill press put the holes exactly where indicated by the punch. There was no need to file, ream, or die grind any slop in the holes. They lined up perfectly with the pipe vise allowing everything to bolt up with 1.5" and 2.5" long, 1/2" diameter bolts.
The cast iron of the pipe vise will crack long before this mounting box fails.
The #23 pipe vise is a bit bigger than this #21 example. I'll do the same thing but use the receiver hitch of the pickup truck as the "base" platform. Attempting to thread the bigger pipes of a #23 vise would just cause this mechanic's vise to torque over on its side.
Tomorrow, I'll sand blast the mounting box and shoot it with some rattle can paint.
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Notice the photo of the mechanic's vise? I bought the vise and stand off a co-worker when his father died. The father was a woodworker with no metal experience. All that angle iron is assembled with nuts and bolts... I can only imagine the amount of time and effort it took to build that thing.