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Well yeah, it's the bolting to a bench part I struggle with. I have some kitchen cupboard doors I can bolt one to and then maybe clamp to the dining table and see what happens.
hippy-
I think the problem with the type of vice at the start of this discussion is the position of the clamp - it's unlikely to stand 50Nm around the axis of the clamp unless you tighten it so much it will damage the table, especially with the clamp being relatively close to the edge.
Fixing a vice to a board, and using a pair of G clamps should get round this - clamping off axis will be better, the larger area will avoid marking the table top, and suitable packing pieces underneath should prevent the clamps from damaging the underside of the table.
Can you cut up one of the kitchen cupboard doors? Glue and screw together to make something thick enough to recess the heads of bolts, and use offcuts to protect the underside of the dining table. Possibly use plain bolts and washers rather than coach bolts - this will make it easier to take apart for storage.
This is starting to sound like a project in it's own right - if it's for a one off job then offering beer money to someone who owns a vice will probably be quicker and cheaper. You can use mine, but I'm in darkest Shropshire...
MrE
I've used and abused one like this for 10 years or so without problems (admittedly bolted to a bench) - if you go much bigger then a couple of G clamps probably won't be enough.
https://www.machinemart.co.uk/p/cl-cv75b-bench-vice/
It's also possible to spend silly money on a Record...