Half-fretless banjo with brass plate up to the sixth fret. I used an old Saga open-back. From October 2011.
Here are the steps I went through to make an old Saga open-back banjo into a semi-fretless (this is not a howto, it worked for me but it might not work for you! Also, I WOULDN’T DO THIS TO AN EXPENSIVE BANJO!):
1. Remove strings.
2. Prise the frets off using a combination of a pair of pliers, and a fairly wide chisel slipped under the fret to gently lever them out. I’ve heard that heating with a soldering iron helps, it didn’t much in this case.
3. Gently sand the fingerboard a little.
4. Find a piece of brass exactly the same height as the frets. My frets were 1.2mm high. In my local DIY store I could only find a piece of brass 1mm high, and about 20*10cm in area. I decided to risk it, it worked fine. If the brass is much lower, there would be fret buzz, and if it’s much higher, you’d probably have to raise the nut somehow.
5. Cut a piece of cardboard the same size as the area to be covered by the brass plate. After much deliberation, I decided to put the plate on up to and including the sixth fret so the seventh would still be usable. Also, I made a cutaway in the brass for the fifth string as I often fret the fifth string and it seemed the simplest way to get around issues regarding the fifth string pip position and intonation.
6. Tape the cardboard template to the brass, draw around it and cut out. (I used a hacksaw. It wasn’t the ideal tool for the job, but I only wanted to do this once and it didn’t seem worth buying anything more expensive). Gently file the edges of the brass, all except the straight edge which meets the nut.
7. Stick the brass plate to the fingerboard. I’ve heard that carpet tape works well to attach the brass to the fingerboard, but I didn’t want to buy a whole roll for the sake of a few centimeters. There can (apparently) be problems if the glue used is too strong, i.e. with the wood shrinking and the metal staying the same size. I used simple double-sided sticky tape from a stationary shop, it held remarkably well. I reasoned that if the plate came off, I could just stick it on again…
8. Finally, I had a couple of spare frets left over from an old guitar, so I cut mini-frets for the 5th and 6th positions on the fifth string, and squeezed them into the holes. They work fine.
9. If you get bored with your half-fretless banjo, as I did, it’s easy to pop the brass sheet off (although it was stuck surprisingly well) and push the frets back in (I had saved them from earlier). The fretboard was a little discoloured from the tape etc., but it’s fine.