Advice needed regarding truss rods and refretting

chris_john

I have an old guitar that needs a refret. I have pulled the old frets out and checked the neck. With the truss completely relaxed, the neck has a forward concave bow. Is this normal? Should the fretboard be level when the truss rod is relaxed? Or does the fretboard need some sanding?

BillDL

Yes, that's quite common, BUT before you start attacking the fretboard with a radius sanding block what you would generally do is tighten the truss rod and use a long and accurate straight edge to get the fretboard as straight as you possibly can while looking for gaps of light under it.  At that stage you should have a good idea whether the fretboard has any undulations that might need to be sanded level.  If it does turn out to be level after you have straightened it with the truss rod it might only need a cleanup with fine sandpaper before you insert the new frets.  Any VERY minor irregularities can be addressed by levelling the frets afterwards.

As long as the truss rod was previously able to compensate properly against the tension of the strings while tuned to pitch and you were able to have the neck set with a slight concave (relief) you should have no problems.

There is one small but important thing to mention here though.  You will obviously have to scrape out any glue residue or gunk from the fret slots without widening them or chipping out fretboard wood.  This is more difficult on a bound fretboard where the slot ends are closed off, and you need a fine hook-ended scraper tool or similar, whereas on a neck with no fretboard binding you can use a very fine saw or scraper to clean the slots out.

IF you have had to sand any wood off the fretboard to get rid of undulations or deep dents you will need to deepen the fret slots accurately with a fret saw or the tangs will hit the floor of the slots before the frets are hammered or pressed in fully.  There is also the issue that if you hammer or press frets with thicker tangs than the old frets into the slots, each fret tang is going to try and expand the slot and the combined effect of this from all the frets can sometimes force a backbow into the neck. Luthiers will often use frets with larger tangs than the slot widths to deliberately straighten a neck on a guitar that has forward bow that cannot be corrected with the truss rod or if the guitar is an old one with no truss rod.  The tang width should match the width of the fret slots so that only slight pressure would allow the actual tang to be pushed in, and the barbs on the tang are what hold te frets into the wood after you hammer or press them in.  Depending on the age of the guitar the tangs could be thinner or thicker than modern fretwire, so it would be a good idea to measure with a vernier caliper.

BillDL

Thinking ahead for you.  Do you have a notched straight edge that matches the scale of the guitar?  You should have no shortage of quality tools where you are currently living.

This is an invaluable tool to ensure that the actual fretboard is straight AFTER refretting so that you can level the frets with a sanding beam.  Very occasionally you get the slight effect I mentioned above where the combined pressure of the new fret tangs in all the slots can push the neck into a very slight back bow.  Before you level frets you would then need to relax the truss rod and get the actual fretboard straight again using a notched straight edge.  Some luthiers that use fret pressing jigs or pliers boast about being consistent enough to negate fret levelling.  Normal mortals on normal guitars (not new builds) find fret levelling to be a necessary evil, so you need to plan for this.

chris_john

I have a precision 45cm straight edge, but I don't have a notched edge. Instead, I use some spare tuner bushings of equal height (measured with digital calipers) and attach them to the straight edge to do a similar job. 
I have managed to remove the frets without chipping and have cleaned the slots out. 
Using the truss rod, it is possible to get the neck straight and the board fairly even. However, it requires several turns and the truss rod feels very tight at that point. I am worried that keeping the truss rod at that tension is going to be harmful in the long term.

BillDL

It sounds as though you improvise in similar ways to how I used to, and still often do.  Nothing wrong with improvised tools.

If it's still in a detectable forward bow now with the strings off and you still can't get it straight with the truss rod, there must have been excessive relief while it was strung to pitch.  I would say that any "harm" you might do by leaving the truss rod tight would therefore be a benefit for when you get the fretting done and do get it back to pitch.  I suppose it depends what you mean by "long term" though.  Some guitars have to live their lifetimes with the truss rods fully cranked because that's the only way short of heat-pressing or planing the board to get acceptable relief.  It's really a case of deciding how much money or effort you want to expend and whether the guitar has any monetary value that could be drastically reduced by invasive work.

It can be helpful to put gentle backward pressure on the neck while tightening the truss rod adjustment to see if you can get even one more turn, but if it already feels very tight it is entirely possible that it has reached the end of the adjustment and if you try to wrench it you risk rounding out a hex socket or even stripping threads.  Depending on the type of adjustment and access to the adjuster it is sometimes possible to completely remove the adjuster and insert a spacer like a washer with one side ground flat if it is required to fit the access point.  Sometimes there is only so much you can do though.

It MIGHT be worth considering fretwire with a thicker tang, but there is a risk that you could end up pushing the neck into a permanent back bow.  I've only done this once before and was prepared to scrap the guitar if it failed miserably.  It worked for me but it was a calculated risk.

Compression Fretting and Corrective Refretting:

https://hazeguitars.com/blog/saving-vintage-guitars-with-clever-refret-techniques

What kind of guitar is it?  Electric or acoustic?  Fixed or detachable neck?  Rosewood or maple fingerboard?  Headstock or heel truss rod access?  Dot or block inlays?

A luthier might well choose to level a wooden fingerboard with a long shooting plane set to take off very fine shavings, but you risk snagging fret slots and tearing out chips of wood.  Sanding accurately over the length of the board if you don't have access to a flat sanding belt would require a long and perfectly flat sanding beam of some description.  The best method is to draw cross-hatching in pencil all over the board so you can see what progress you are making, and redraw the lines in between a few passes.  Obviously there's the possibility / probability of sanding the position inlays too thin or completely through, so you would have to consider that possibility.

chris_john

Thank you for the advice. It is a  cheap semi-hollow ES335 copy, and not worth paying someone to refret it. The neck is quite straight with the truss rod tightened, so I think I will just forge ahead as it is.
I have refretted bolt-on necks quite successfully in the past, but the binding on this guitar will definitely be a bit more challenging. Fortunately, I'm in no rush to finish the job..

BillDL

I'm sure it will be worthwhile and rewarding in the end.  One of the hard parts of a hollow body is hammering in the frets on the fingerboard extension past the heel block, but as long as there is a continuous centre block on your semi-hollow it should be OK.  Bound fretboards are much more challenging because you have to find a way to nip off the tang under the body of the fret that sits on top of the binding.  You can buy all kinds of expensive fret tang nippers, but I couldn't justify the cost against the number of refrets I do a year and i have had perfectly satisfactory results sniping out little rectangles under the overhang with some small end cutting pliers and then using a flat needle file to remove the remainder.  It's laborious for sure.

You can buy a set of precut, pre-radiused, and de-tanged frets from various places, but the one set I did buy in the hope of saving some time consuming work were too long for the width of the fretboard and I had to remove more of the tangs anyway.

Good luck with the project.