Help with sanding a fretless fretboard?

[Duplo42]

Hey hello,
I have a 30" handmade fretless bass (nothing special, it was done by some local luthier as one of his first attempts) - it used to be fretted, but previous owner pulled out frets and inserted lines. All good, but no matter how I set it up (truss rod, bridge, nut), I still have buzzing on first couple of "frets" and around 9th fret on top strings. Which leads me to believe that fretboard needs some sanding to make it perfectly straight. The fretboard is otherwise smooth and all...

The problem that I see is this - how to I know when the neck is straight (via truss rod) so that when I use block with sandpaper, I know that all is aligned properly. Sorry, not sure how to explain it correctly.

I have no tools as such (like that fancy stewmac calipers jig to see straighness of the neck) but very straight 25cm aluminum block that I will attach sandpaper to and professional metal 80cm straight-edge ruler. Fretboard is made of very nice ebony.

Do I just set neck relief by eye and than sand the board and check it with ruler until it sits flush (and of course until there is no buzz with strings on)?

Thanks!

 

[Bruce Johnson]

Yes, that's basically it. You have the right tools. The first thing is to tighten the truss rod somewhat to verify that it is working. Checking with the straightedge (ruler), you should see the neck beginning to flatten out or go into a slight backbow. Just like that, with the truss rod partly tightened, is the condition you want the neck to be in as you make the fingerboard surface flat.

Now, look carefully at the fingerboard surface, with the straightedge, checking right down each of the string paths. It's very important that you check on the string paths, not straight down the neck. Under the straightedge, you will be able to see where the humps and dips are. That's what you need to get rid of; trimming down the humps until they are even with the dips. When the surface is correctly leveled, you should be able to put the straightedge down each of the string paths, and not see any light underneath.

If the humps are high, you can start with a large flat fine tooth file. Ebony is tough wood, and will take a lot of sanding. A file is faster to get it roughed in, but be careful. File only directly on the humps, checking continuously with the straightedge. Then start working it with 180 grit paper on your aluminum beam. For Ebony, I normally sand 180, 220, and 400 on hard blocks. Then I sand 800 on a small rubber block, followed by grey then white Scotchbrite on the rubber block. Then I apply one coat of Fingerboard oil (or any thin hardening varnish) and buff it on a loose cotton buffing wheel.

It takes patience. Don't cheat. The straightedge down each string path will tell you when it's right.

When you put the strings back on and pull it up to tune, then neck should bend forward a small amount, into a small amount of relief. Then you use the truss rod to adjust the relief up or down to where you want it.

 

[Jonny5bass]

you should see the neck beginning to flatten out or go into a slight backbow. Just like that, with the truss rod partly tightened, is the condition you want the neck to be in as you make the fingerboard surface flat.

Apologies for not totally understanding but should the board be flat first or have just a slight backbow before leveling? Thanks for all your help Bruce.

 

[Bruce Johnson]

Apologies for not totally understanding but should the board be flat first or have just a slight backbow before leveling? Thanks for all your help Bruce.

The important thing is that the truss rod is partially tightened and you can see it beginning to move the neck. First adjust the truss rod to be partially tight, and then look and see how straight the fingerboard surface is. If that makes the board nearly flat, great! Less wood needs to be removed and less work. If it's backbowed or forward bowed or just lumpy, you need to cut the surface to flat....while keeping the truss rod partially tight.

The point is don't adjust the truss rod to try to make the neck as flat as possible, just to make the leveling job easier. That's how you can end up with a neck that is flat with a loose truss rod; unstable and no range of adjustment.

 

[rwkeating]

You mention the bass is hand made. It may have a dual action truss rod as those are popular and easy for the builder to install. Do you know if it is a dual action rod? With a dual action truss rod you have a bit more wiggle room in where you set it with strings off vs. how flat the board initially is.

 

[honeydorick]

Hi,I didnt realize how old this post was.Sorry,but the info is good and updated by honeydorick.Take your time and do exacty what Bruce said.Thanks to Bruce and TB.As an amature moder- builder,I now have the confidence for building short scale frettless basses.The string paths are very important.Here is a pic of my latest 28.6 in scale build.It plays beautif'ly. and purposely has no m-wah or fret buzz.I wanted that old shcool sound of an upright.Mission accomplished..LOL

 

[Matt Liebenau]

Hi,I didnt realize how old this post was.Sorry,but the info is good and updated by honeydorick.Take your time and do exacty what Bruce said.Thanks to Bruce and TB.As an amature moder- builder,I now have the confidence for building short scale frettless basses.The string paths are very important.Here is a pic of my latest 28.6 in scale build.It plays beautif'ly. and purposely has no m-wah or fret buzz.I wanted that old shcool sound of an upright.Mission accomplished..LOL

You can get even more excruciating detail here if you want minutia of the mechanics involved.

Thread 'Even fretless fingerboard levelling tips'

Aug 6, 2012

Hello everybody,

I have this nice medium scale (32") Warwick neck which I thought would be very cool as a fretless so I did the big leap and removed the frets. Removing the frets was a tough job as the wenge board is extremely hard. After removing the frets I placed some medium viscosity ca glue around the fret slots to keep chips in place and as a guide as to when I should stop sanding afterwards. The plan was to remove as little wood as possible afterwards and count on the factory levelling for a nice fretless board. After initial hand sanding with something like 400-grit sandpaper if I...

• jesterbass
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