If you have limited surface space on you work bench or do not want to drill 4 holes for a permanent bench vise installation- here is what you can do- make a Clamp On adapter for your bench vise: Here is all that we need to get started making a clamp on adapter in my case it was USA made Craftsman 51865 from 1973 that has 4.5″ jaws but similar process will be carried out to make adapter for another type of vise. Parts: we need pair of C clamps, 4 bolts/studs with nuts and washers, 1/4″ steel plate…as of tools we will be using MIG welder, another bench vise, drill, and angle grinder. Below i am posting comments that i made to this video slide show to make it easier for you to follow the steps:
0) Make a base plate out of 1/4″ or thicker steel.
1) In my case I had to cut 4 bolts to make studs for the base plate. Once cut – grind the edge at 45 deg to make welding work easier and stronger.
2) Now it is time to map holes for the studs and plan where we will be attaching a pair of C clamps. Once done place vise over to make sure studs easily go into 4 mounting hole on the base of the vise
3) Weld studs to the back and the front of the base plate
Grind excessive welds on the back of the base plate as it will be facing the surface of your work bench later on
4) Here is a side view how vise should be seating on the base plate with no gap between vise swivel base and a base plate as we do not want it rock on top of the welds of 4 studs. If needed grind welds a little.
5) Now it is time to position C clamps. Do not forget to put a disposable spacer between the base plate and your work bench as we will be welding C clamps to the base plate and do not want to burn the work bench.
6) Start welding after aligning both C clamps in such a way so that they take min space against the edge of the bench vise and as far as possible from the vise to make sure we minimize the interference with items that will be clamped in a vise between the vise jaws once we start using it.
7) Continue welding C-clamps and make sure as with all other welds we have good penetration without overheating/burning the steel.
8) Final check- mount your bench vise and see if everything works the way it should, if not fix it.
9) Now it is time to this Clamp On bench vise adapter a good steel brush cleaning and a fresh coat of your favorite paint.
Note- i am using enlarged plate grips on C clamps for more positive holding power and non slip grip without potential to dent the back side of the work bench.
10) Works like a champ – i really needed it as have limited space on a work bench that i did not want permanently take by mounting a vise as well as wanted to avoid drilling 4 holes as well 
11) The vise was 27lb alone now with 7lb clamp on base we have a one heck of clamp on vise that has a total weight of 34lb!
The happy end- we have a med size USA made bench vise that can be clamped on and off to our your work bench or carried to a job site where it can be clamped on as well and quickly removed upon departure at the end of the day.
Post time: Apr-09-2017