Project: Fretless bass guitar

In the late summer of 2016, after a very long layoff from music, I decided to purchase an inexpensive bass guitar. I found someone selling an Ibanez GIO on Craigslist for around $50. I thought that was a reasonable point of entry, so I bought the guitar and also picked up a small Fender amp from Guitar Center.

The Problem

I got the bass-bug, and ended up purchasing two more cheap bass guitars off eBay, with the intention of modifying them at some point. What I initially envisioned was a setup like Mark Sandman‘s bass: Two strings, custom tuned, and played with a slide. I may still end up doing that at some point, however, what I ended up doing first was converting one bass to fretless.

As an aside: If you’re unfamiliar with the band Morphine, I highly recommend looking into them. They are one of my favorite bands of the 1990s due to their unique noir sound.

The Planning

I had made a couple tweaks to this particular bass already. I changed out both the potentiometers from the original 500K Ohm to 250K Ohm ones. Additionally, when I added the tone capacitor, I opted to install a socket so I could experiment with different capacitors. I’ve played with the capacitor values, but haven’t found one that makes a significant difference in treble cutoff.

Attached to the back of the right potentiometer is the socket with a small capacitor installed.

I read up on fretless conversions, scouring the bass player forums for posts by people who had done it. Mostly what I learned was people can’t agree to anything online. So I took the ideas that made the most sense to me and ran with them. In particular, once the frets are removed the fingerboard, there’s a significant loss in structural integrity. (In addition to being rough surface.) So what do you fill the slots with? Putty? Epoxy? Sawdust and carpenter’s glue? Maybe even superglue? Eventually I found the idea I liked best: use slips of polystyrene and superglue them into the fret slots. With this plan in mind I set to work.

The Project

I called the local hobby store to make sure they had 0.020″ polystyrene sheets available (they did) and picked those up. I’d already pried the frets out, so, all that i needed to do was glue the styrene in place, sand and finish the neck, then bolt her back together.
I used a Japanese style pull saw to clean out the fret grooves before gluing the styrene in.

Frets removed, and slots cleaned out. Fingerboard radius gauges on the right.

The process I used to the styrene inserts was to cut strips that were slightly wider than the neck, and about 1/4″ thick. I had WAY more styrene than needed, so conservation of materials didn’t come into play.

Gluing the styrene strips into the grooves.

The whole neck filled with styrene slips. On the 19th and 21st frets, you can see where I filled voids with sawdust and superglue.

Once the glue had set, it was a matter of trimming the styrene down and fairing the fingerboard.

The styrene trimmed down to a sandable level.

To maintain the curvature of the fingerboard, I used a radiused sanding block which matches the fingerboard’s convex shape. After knocking down the rough bits and ensuring the entire length of the board was being sanded, I moved through several grits of sandpaper. Starting with 80 grit, and working my way up to 220.

I believe this was somewhere in the 150 grit range. Starting to feel pretty smooth.

Once the fingerboard was sufficiently smoothed out, I applied three or four coats of wipe-on polyurethane, letting each coat thoroughly cure before sanding with 220 grit paper, and applying another coat. After making a huge dusty mess in my office, I was finally ready to bolt the neck back on, and try it out!

All done, and looking alright.

My completed custom fretless bass.

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