I assume that you are talking about distance from the Fence to the router Bit.
This being the case, you could attach a 3/8-16 piece of all-thread to the back of the Router Fence (in the center), pass it thru a nut fixed to a bracket attached to the table.
This would give you 1/16th inch advance for each full turn of the knob that you will need to attach to the piece of All-thread, behind the bracket.
The attachment to the Router Fence would need to be capable of rotating, but with little or no slop.
This being the case, you could attach a 3/8-16 piece of all-thread to the back of the Router Fence (in the center), pass it thru a nut fixed to a bracket attached to the table.
This would give you 1/16th inch advance for each full turn of the knob that you will need to attach to the piece of All-thread, behind the bracket.
The attachment to the Router Fence would need to be capable of rotating, but with little or no slop.
