Depending on context the job can be as simple as boring a plain hole into a lensboard.

At the other end of the spectrum it can involve the complex work of determining and/or "optimizing" a set of orphaned lens cells to fit them to a shutter. Also see about Packard shutters and front mounting of barrel lenses.

      The sections here explain what's needed, including the prices to have a lens useable for photography. From getting the hole in the right place thru to the right shutter or any other configuration we can do the work from start to finish.