John,

The busted vises are an interesting topic, as you can see by the number of
responses.  Repairing things is very galootish!

Does the school also have metalworking and welding programs?

Broken castings can be brazed.  I used a brazed-up face vise for about a decade.
It had been brazed where one of the guide bars met the front jaw. The front jaw
was no longer true and square to the back; this was addressed by making a
softwood jaw of irregular thickness.

Broken mechanism parts which can’t be brazed can be re-created by weldments or
by “hogging out” of solid.  This would be a great exercise in a CNC machining
program!

Definitely braze any broken castings. There are electric welding processes for
cast iron which involve nickel rods, but these are very tricky. The weld often
cracks as it cools, or later.

Then again, if they were not made well in the first place, the effort to save
them might not be a good use of your time!

John Ruth