It looks like the motor and quill are suspended by the cast iron top. Not the best design but more common now than using a base heavy enough to support the internals. If the top is the support, it still needs a base designed not to rack or twist when the spindle is turning with a cutter attached. It looks like the top and bottom have welded supports for that purpose. It would take a stout cabinet ( probably not mdf ) to ensure no vibration when shaping. Dave