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Fretboard extension shim or taper?

Posted: Thu Oct 12, 2017 11:21 pm
by Stray Feathers
I have my two first builds strung finally. One is okay, saddle a little on the high side but it plays okay and sounds pretty darn good even without final compensation. On the other guitar, somehow the neck angle came out wrong. A line across the top of the frets ends up 1/8" above the top of the bridge, which is 3/8". I have put a classical saddle in (12 mm high) and some of the strings are clanging on the frets. It looks obvious to me that it needs a reset. It's a bolt-on neck and there are lots of how-tos out there. My concern is, what happens about the presently very nice alignment of fretboard over the upper bout? I've read about people accepting the neck-body joint "dip", or alternatively using a tapered shim. In my case, rather than raise the fretboard at the body joint (and shim it), I would gain more by lowering the fretboard extension at the soundhole end. (I figure about 3/64"?) That means tapering the underside of the fretboard extension (and adjusting the neck heel). The fretboard is a little heavy, 1/4" thick along the edge, so there seems to be enough wood to do that. But I have not come across any discussion about doing this, or how to do it. I wondered about the Safe -T -Planer from Stew Mac? I have a belt/disc sander but sanding always seems to be imprecise to me. Any help appreciated.

Re: Fretboard extension shim or taper?

Posted: Fri Oct 13, 2017 4:52 am
by MaineGeezer
I shim mine, as does the luthier who taught me. According to his analysis of neck geometry and top radius, you should have to shim it, so don't assume you did something wrong -- maybe you did it right! Tapering the fretboard is an interesting alternative. I don't see why that wouldn't work, although as you note it might be difficult to cut, and 50 years from now when the guitar needs another neck reset the required taper might be different. A tapered wedge may be the most flexible option .

Re: Fretboard extension shim or taper?

Posted: Fri Oct 13, 2017 9:56 am
by tippie53
I don't shim on a new guitar
here is my method
https://www.youtube.com/watch?v=TXfyVb3L3G0&t=2570s

Re: Fretboard extension shim or taper?

Posted: Sat Oct 14, 2017 5:55 am
by Diane Kauffmds
An 1/8" is pretty high. I did the same thing on my first build. O)Have you thought of pulling the neck and trying again? I would pull the neck and add wood under the heel to get the proper angle.

Re: Fretboard extension shim or taper?

Posted: Sat Oct 14, 2017 10:23 pm
by Stray Feathers
Thanks for comments on this . . . um . . . mistake. Diane, I am just about resigned to pulling the neck and redoing it. But I am wondering, since the fingerboard is fairly thick anyway, whether anyone tapers the extension thinner towards the soundhole, rather than shimming the extension higher at the body/neck joint. Seems to me that with the fingerboard raised that way, that the peghead end has to be even higher to produce the right alignment. I guess the angle is the same; the difference is the extra height of the thickest part of the shim. It also means (I am guessing) 2 - 3/16" more sides showing below the heel which might cause problems. I hope to visit my luthier instructor/mentor in the next couple of days so will take these thoughts to him.

Re: Fretboard extension shim or taper?

Posted: Sun Oct 15, 2017 7:24 am
by tippie53
good point about fretboard thickness
I sand mine down to about .200 thick
this lightens the guitar
we don't need a thick fretboard.
The key is that you want the fretboard plane as true as you can make
it. I then sand in a slight fall off. I want the extension to be
just a tad under so if the top rises you won't get buzzing

Re: Fretboard extension shim or taper?

Posted: Sun Oct 15, 2017 7:53 am
by Kbore
Stray Feathers wrote:A line across the top of the frets ends up 1/8" above the top of the bridge, which is 3/8".... and some of the strings are clanging on the frets.
After re-reading your original post, I want to ask, if the neck is set so the string is high at the bridge, strings clanging on the frets wouldn’t be caused by the neck angle would they?

Re: Fretboard extension shim or taper?

Posted: Sun Oct 15, 2017 9:57 am
by tippie53
I suspect you have one of 2 issues

A did you prep your fretboard and make sure it is leveled and radiused? Also are you sure you have no loose frets

B did you true your frets before you strung it up?


If you have frets buzzing then you have geometery or the frets messed up

can you post a few pics

also if you don't have the proper neck relief that can also cause you some of these issues,

When you think about this no matter how careful you are you will always have one fret that is higher than another. If you have too low neck relief that high fret will always find the string. If that happens you may have the action too low , relief maladjusted or bad frets.

No matter what I like to check my frets close and now do all my fretting on the guitar. If you can at least level the fret board before gluing that is better than thinking the fretboard is ok and never prepped it properly.

Ebony especially can be funny. When you add water from the glue it can do funny things so I re-level after it is glued on the guitar to get the best possible fret plane I can. Then before stringing I will level my frets.

Re: Fretboard extension shim or taper?

Posted: Sun Oct 15, 2017 9:58 am
by tippie53

Re: Fretboard extension shim or taper?

Posted: Sun Oct 15, 2017 11:32 am
by Stray Feathers
I should have been a little more clear in my description, and I will post an image later, but for the moment, the bridge is 3/8" high at the centre, the saddle is almost 1/4" above the bridge, so at the centre of the bridge the strings are about 5/8" off the soundboard, yet the strings are too close to the frets. I have done nothing to radius the top of the saddle blank which is about 12 mm tall, and is seated an appropriate depth in the bridge. It's a little odd that it is the treble strings that are hitting frets the most, when there should be more clearance there because of the fretboard radius (16"). The high E is almost okay open, but buzzes at every fret up the board. I made two guitars at the same time, checking geometry dozens of times along the way, but must have slipped on this one. The other is a little high at the bridge but it plays well so I am okay with that for now - might consider a reset after it settles in. Picture to follow.

Bruce