To shim or not to shim -fretboard height tenor uke

I'm really addressing two issue at this point:

1) You may have seen from another thread that I have slotted my ebony fretboard and now find a pretty determined bow in it. I'm hoping that a good glue job will settle that down. (although I have absolutely zero experience from which to make that judgement...)

2) The LMI plan I'm working from shows a bridge thickness of 7 mm. The LMI sanding beam is sitting on two shims I thicknessed to match the dimensions of my fretted fretboard. I estimate it hits the blank about a half mm low of the top. I have some veneers that come in around 0.020" or roughly 1/2 mm. Would you shim the fretboard from nut to soundhole? Why or why not?

Thanks!

Chuck Barnett, the molehill-to-mountain king

1) I too have had some ebony fretboards get bad curl in them. One was so bad that no amount of persuasion would flatten it out and I had to re-fret it. Usually if I have a little curl in a fretboard, I can flatten it out by flipping it over, putting a shim like a matchstick underneath and clamping both ends to a flat surface and adding a little heat and waiting a couple days. What is happening is that the fret tangs are forcing the wood apart and making the thing curl. Since I quit using a fret hammer and went to using a fret caul press I have had almost zero curl. A little curl is okay since it will glue flat.

A picture of the amount of curl would be nice.

As for #2) I can't say anything since I don't really understand what you are showing and asking but I would be hesitant to start shimming fretboards.

Thanks!

The gap is most pronounced in the vicinity of the 12th to 13th fret and is a good 2 mm.

I guess as regards the second question, either I come in lower than 7 mm for the thickness of the bridge or I get a little bit more height for the fretboard. By shimming, I meant putting a piece of veneer between the fretboard and the neck and top. I'm inclined to just make the bridge thinner. My bridge on the first ukulele was closer to 6 than it was to 7 mm. One plus about doing a lamination would be that I could use a light-colored wood for a nice little contrast line.

I usually glue the fretboard to the neck before fretting which saves a lot of hassle. The neck is not glued to the body at this stage.

Another way to hone in on bridge height for you would be to
1- Glue the fingerboard on and,
2- Adjust the "neck angle" by either sanding the end of the fretboard down (to "lower" the neck angle),
or
3- Sand the nut end to "raise" the neck angle.

This isn't an optimal method but it is a method- Just watch the fret slot depth. If you go to far it will be obvious from the FB tapering, but better that then an unplayable instrument.

ChuckBarnett said:

View attachment 128344

Thanks!

The gap is most pronounced in the vicinity of the 12th to 13th fret and is a good 2 mm.

Click to expand...

Oh that is not too bad and you can "suck" that gap out when it gets glued down. Don't worry about it...

sequoia said:

Oh that is not too bad and you can "suck" that gap out when it gets glued down. Don't worry about it...

Click to expand...

Happy to hear that!

Thanks!

That arch is more than likely caused by the frets. You have cut the fret slots all the way through and this cripples the board and allows it to move like that when frets are installed. Taking up just a tiny bit more space than what the slot is. It's very common to see this.

I cut my fret slots on the CNC and they stop 2mm from the edge of the fret board. When I install the frets the board stays dead flat because it hasn't been cut through.

You can glue that board down to the neck / body without any worry. It will flatten out with even a bit of clamp pressure.