Look at my post further up, I mention a longer bar that the work piece was attached to; I did not use vises. I also mention levelling screws.
The workpiece was fastened to what you consider a sub-table, and it was not moved relative to this sub-table. The sub-table was clamped to the machine table for the first cut then slid along and everything aligned from the previously machined surface and reclamped for the second cut. The levelling screws where to help with the re-alignment.
There were six of these to do along with a whole bunch of other parts. The long ways actually had tee slots machined in the sides of a vee groove and hardened and ground stainless strips where pushed into the slots. A carriage ran along these strips on precision balls and a gimbal assembly supporting a large gyrocompass was on the carriage. These went on some icebreakers being built for the Saint Lawrence Seaway.
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