Make a wooden adjustment knob

I want to make a jig that will include a flat suface of wood about 18” long and 4” wide on top of some kind of box/frame of same size (yet to be designed and made). I want to be able to raise and lower the box very simularly to the raising and lowering of a palm router bit with the adjustment knob.

I would like to find if I can purchase such an adjustment knob or make one.

Any suggestions will be appreciated.

Phil

-- Phil