The example you give of polishing inside the rungs of a “ladder” is
relatively easy for someone practised in burnishing with a polished
flat graver (#40, 42, etc). Once you’ve got the hang of this you can
polish a surface in a single stroke. In your case two strokes as you
would have to start the graver in each corner, apply downward force
carefully so it is distributed across entire surface to be polished,
and then pull the tool towards the center of the surface - ie.
towards the opposite corner.
Exterior flat surfaces can be sanded on a flat surface and then
lapped on a flat wheel.
You may have to go to a trade shop rather than a contract finishing
company to get these processes done to the degree of precision you
want as they are time consuming and cannot be achieved past a certain
point with mass finishing techniques.
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