Sticky?: Sanding / (re)finishing fretless bass neck - tips and links

[goonieman]

Hi All,

If you find you are not getting even 'mwah' or buzzes, or just general weirdness, on your fretless bass neck, then this thread is designed to start you off in the right direction.

Having recently re-finished a fretless bass neck with very good results, I thought I would post some lessons in case anyone wants to learn, critique, or do this themselves. Note that I am not a trained luthier - just someone who likes to work on their own instruments.

The first thing I learnt is that doing a fretless neck is NOT easier than doing a fret job on a fretted bass or guitar. If you want top-notch results, with ability to go to lowest action physically possible (or near enough) then this job has substantially greater margins for error. The give away being the 'mwah' factor: at low action, differences in the resonant characteristics of the mwah are very easy to hear on a fretless bass. If you want a decent consistent shape, timbre and decay of the 'mwah' across the neck at low action (say... measuring 3/64ths on low E, 2/64ths on G, at '12th fret' - without the any strings depressed, relief at around 0.001 - 0.002 inches, measured with the bass IN PLAYING position, not laying flat - because the strings pull down due to gravity... ) then you have your work cut out for you!

If you are not feeling confident, then take your fretless bass to a pro technician... but beware: all techs were not made equal. I humbly suggest you show them this thread to ensure that they are familiar with the range of challenges one might encounter on a fretless bass job.

Here goes...

1. Do your homework

You gotta get familiar with the ideal shape of the final product. The final shape should not be an even radius across the board, nor should it be a compound radius. It should be...are you ready for this... an '[color=#141414][font=verdana, geneva, lucida,]offset hyperbolic paraboloid' ! Yes, that's right. [/font][/color][color=#141414][font=verdana, geneva, lucida,]Before you start, read this whole thread from start to finish: [/font][/color][url="http://www.talkbass.com/threads/even-fretless-fingerboard-levelling-tips.905673/page-2"]http://www.talkbass....s.905673/page-2[/url]

Note the CAD images in the above thread. It is important you get your head around this idea.

Read this on the 'Mwah Interference Zone' as well: [url="http://fretlessbass.com/viewtopic.php?t=177&view=next&sid=6a66e2fd6c717dd2b029988aeaf53106"]http://fretlessbass....029988aeaf53106[/url]

2. Decide whether you want to:

a) use a neck jig, shape the neck with strings on, or c) shape with strings off. The last is the easiest, but less likely to give optimal results. The first is far more expensive... and finding a tech who does this is not likely to be easy. Option ( can be tricky, but not impossible if you use a long thin stew mac straight edge and if you shim the nut and the boost the saddles temporarily.

Why use a jig or shape with strings on? Because a rod under tension (truss in this case) behaves in WEIRD ways, and actually makes an odd 's-shape' in practice. This is called 'buckling' and research on this was made famous by Euler in studies of columns. see here: [url="http://www.fyldeguitars.com/blog/eulers.html"]http://www.fyldeguit...log/eulers.html[/url]

So if you level or sand the neck with no strings and truss tensions, then you are already off to a bad start. However, it is possible to do it - it just takes more problem shooting in the final stages. Read on near the end for that...

3. Get started:

Anyway you cut it, you'll ideally want a full length radius sanding beam to start, or a precision straight edge with 400 or 50 micron grit sandpaper stuck on. The 3M sticky plastic paper is the best quality in my experience. Hard to find though....

You'll want to level the neck with it as straight as possible to begin with. I will bet money that your bass has some odd shapes to it even when it looks generally straight. 'Straight enough' is not good enough! Use a straight edge to get the best compromise of the pre-existing errors.

If you've used a radiused beam, you can skip this step, but if you've used a flat beam, i'd suggest you gently radius the fretboard now.

Next, as per the link above, you want to level the frets IN THE LINE OF THE STRINGS. This gives the 'paraboloid' shape required.

I strongly suggest using the strings you are likely to use for a long time - this is because the balance of the gauge is likely to effect the shape of the neck. I use a balanced tension set of flatwounds.

4. Tailoring, and the 'dark arts'...

Ok, see here is where things get quantum. My view is that the higher guage strings need a touch more room to vibrate. I personally built-in a touch more sanding the lower I go across the string alignments. A true professional may disagree with me on this.

My view is that you should be aiming for a difference of 0.001-0.002 inches (use feeler guages under a precision edge) from the E to the G string.

Now finish the board with gradually lower micron sandpaper. As far as 15u or 9u (1000 grit).


5. testing time, and more 'dark arts'...

Tune the bass to concert pitch and do a full setup (documented elsewhere) - but note that nut height is critical and should be much closer to the board than most people think.

My relief preference on the G string is that it should basically be dead flat on the board - or ridiculously close to it. Less then 0.001 inch anyway. E string at around 0.001 to 0.002 inches.

Now do some slides down the each of the strings from high to low. Do this with treble pickup on max because resonance is easier to hear at this end of the spectrum. What you want to hear is a consistent timbre and shape of the 'attack' or resonance. You might get a drift to a more resonant 'mwah' the closer you get to the nut. The point of this is that it should be GRADUAL... with no 'squarks' or peaks or sharp drifts in resonance.

If you hear any inconsistencies, then what it will be at this stage is height errors that are within the 'Mwah Interference Zone- MIZ'. These errors might even be bits of wood dust, but are very likely to be 'bumps' of as little as 0.001 or 0.0005 inches that are within 1 -2 inches up the fretboard from where the string is depressed.

Different materials (such as the juncture of a filled-in fret marker or a fret marker made of different material) can also affect the shape of the note bloom in the MIZ, so be wary of this.

Get out your precision straight edge and feeler gauges and sand accordingly. Take it slow! You can take wood away... you can't put it back! This process will be more familiar to those who sanded their neck without string tension or without a jig!!!

6. Finish line!

When you have a nice steady change or consistent resonance dragging down each of the strings at your desired setup, then you are home free.

Remove the strings, and sand the neck with 00000 or super-fine paper and then oil the board, and polish with just a fine cloth.

7. Stop chasing the dragon! AKA the REAL finish line...

My end product is close to perfect - but not quite. The are one or tiny inconsistencies in the neck where the mwah blooms a touch more or less easily than others. Nevertheless, I have decided to stop chasing the dragon.

It easy to reach out for the sandpaper again and try to fix things... but if you're setting-up the bass to within very low tolerances, then you'll likely just make more work for yourself. Ask yourself, 'Am I listening to hard for errors', or 'will this "error" jump out in recordings or live?"

If you can answer honestly with 'yes' and 'no' respectively, then you'll be done. good luck!

Edited July 29, 2015 by goonieman

[gary mac]

Hats off to your thoroughness and willingness to share but it has made my head hurt

A revisit will be required.

[Roland Rock]

Nice one. Thanks