After making my version of a Scandinavian bench I realised that it would be very easy to make a portable version of the shoulder vice, similar in use to the Moxon vice, where it can be added to a bench for a specific task, ie dovetailing. Rather than clamping it to the bench top it can be simply clamped in your existing vice. The wooden screw was made from one of those freely available kits you can buy and has a 1 1/2" thread with a 6 TPI thread. As it only has a travel of 3" this is easily fast enough.
A few years ago I bought a few lengths of 1 1/2" maple dowel and so no turning was required and the hub is also tapped for the thread and glued in with epoxy resin.
You can make the capacity to suit your needs, mine has a 10" jaw and here it's being used to clamp a 12" board .
The construction is from solid 4" beech with the jaw section being 6" to provide a means of clamping in a vice. Below you can see both sides of the jaw were lined in suede leather for a good grip.
I cut a hole in the leather on the jaw plate to allow for the screw to be adjusted if ever necessary.
You can also see the slot which keeps the jaw plate from spinning round as it's used.
Below you can see how it sits on the edge of the bench.
I rounded the corners to make it friendly to handle. I will be bringing it to the Tool Chest course for the New English Workshop in the summer, I'm sure it will get plenty of use!