We have all seen the YouTube video where the guy retracts the frets via a lever, unfortunately the mechanism doesn't work in practice. We have also seen that bass that is fretted from 1-12 positions and fretless 13+. There is also this Nexus guitar from Poland: And let's not forget this oddball Rob Allen creation: I was contemplating purchasing say a used Conklin 7 string off ebay and attempting to make it half fretless. Now I could go the route of simply removing the frets and putting in shorter frets, so say it would end up 4 strings fretted and 3 fretless. Or another idea is to remove the frets and build up the height of the fretless side by adhering an piece of wood to bring that side up to the same height as the frets will result in. Another idea, but probably not doable is to simply fill between the frets with wood filler and apply a veneer over the radiused base to give a consistant playing surface that is within thousandths of an inch of the fret height. What makes the most sense?