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Thread: Dip in ukulele top will interfere with fret board mounting

  1. #1
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    Default Dip in ukulele top will interfere with fret board mounting

    Everything was going along pretty well with my StewMac Tenor Ukulele until I noticed that the top has a 3/32 inch dip that's going to interfere with mounting the fretboard. The fretboard at the sound hole is too high to lie flat and will need to be forced down (producing a curve at the at the highest frets) or I could insert a small wedge from underneath to keep the finger board flat. I have two questions: 1. How would you address this problem and 2. Why did the top develop a dip in the center? The flat along the neck aligns with both ends of the top... it's the center of the top that dips slightly. These photos should give you a visual of the problem:

    stewmactop3.jpgstewmactop2.jpgstewmactop1.jpg

  2. #2
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    Without actually looking at the uke, I would guess that the sides of the uke were not flat on the top surface before the top plate was glued on. If you took the uke and laid it on a flat surface, like sheet of glass or a table saw bed, you would have probably seen the gap then. That would have been the time to correct this problem. You can remove the top now and sand the sides so then rest evenly on a flat surface, but that probably is not what you want to do. That is what most luthiers would do if this happened. I suppose also that the top braces could have a reverse bend to them causing the top plate to sink once it was glued on, but that is unlikely. A slight dome is preferred these days by most luthiers but you probably didn't check this out before gluing. This is how you learn. You can do a dry run by calculating how high the bridge will need to be by laying a straight edge on the fretboard and measuring the distance from the straight edge to the top plate where the bridge will be. If it measures more than 1/2", you need to do something different. The bridge is going to be way too thick to try to compensate for the added height. Do not do that, that will be making the problem worse. One way to bring the fingerboard flat to the top plate surface as it is now, is to reset the neck angle so the fingerboard lays flat to the top. If the neck is already glued on, that won't work either. I would remove the neck and do it over.

    Is the neck already glued on?

  3. #3
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    Quote Originally Posted by BlackBearUkes View Post
    Is the neck already glued on?
    Yes, it's glued with Titebond II and I used a bolt as well. I sanded both the top and bottom on a large 12" steel sanding disc laid flat on the workbench as well as on a piece of glass with sandpaper attached to the surface. I didn't notice any problem prior to glue-up. Both sides appeared to lay very flat on a flat surface after sanding. A straight edge laid across the top – touches at the neck joint and at the bottom edge of the top, meaning there is a slight inward dip with deepest part being 3/32" at the sound hole. The flat of the neck (minus the fret board) is inline with both the top and bottom edge of the top plate... the neck is not misaligned, the top has a slight concave dip.... and speaking of dips, I feel like one.
    Last edited by Hobo; 11-13-2011 at 11:02 AM.

  4. #4
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    Here is a builder (ie non-luthier answer). I've produced this problem, a dip around the soundhole. Probably caused by the waist at the back being wider than the waist at the top.

    First, with the fretboard lying on the neck as if glued there, check the bridge height. Place a straight edge with its end at the place where the nut/zero fret will be, put a spacer at the 12th fret which is the action you want (something around 2.5-3mm - drill bits are good). Measure from the straight edge to the top at the bridge position. If your top dips around the soundhole but rises again toward the tail, this may be about right.

    If the spacing is too high for the bridge, then you probably need to remove the neck and reset the angle.

    If it's about right you can proceed to disguise the problem.

    Clamp the fretboard to the neck (at around 1st and 12th fret). If it's already glued on, no clamping is required. Using finger and thumb, try to clamp the fretboard extension to the top. Will they meet? If so, you can simply glue the extension to the top with appropriate clamping. This will raise the top slightly at that point, but you already have a non-flat top so who cares? It will also bend down the fretboard a little, but again why worry? The notes will be playable, though the action there will be a fraction higher than it should be, but these are your least used frets.

    I can tell you from experience that no-one other than a luthier will notice unless you point it out to them.

    If my diagosis of the reason is correct, which you can check by measuring across the waist top and back, the other cure is to remove the back, pinch in the waistat the back until the top lies flat, then glue the back on again and trim off the overhang. On the assumption that this is the first of many I'd reject this option, leaving the dished top as a reminder for future builds.

  5. #5
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    Quote Originally Posted by ProfChris View Post
    Here is a builder (ie non-luthier answer). I've produced this problem, a dip around the soundhole. Probably caused by the waist at the back being wider than the waist at the top.

    First, with the fretboard lying on the neck as if glued there, check the bridge height. Place a straight edge with its end at the place where the nut/zero fret will be, put a spacer at the 12th fret which is the action you want (something around 2.5-3mm - drill bits are good). Measure from the straight edge to the top at the bridge position. If your top dips around the soundhole but rises again toward the tail, this may be about right.

    If the spacing is too high for the bridge, then you probably need to remove the neck and reset the angle.

    If it's about right you can proceed to disguise the problem.

    Clamp the fretboard to the neck (at around 1st and 12th fret). If it's already glued on, no clamping is required. Using finger and thumb, try to clamp the fretboard extension to the top. Will they meet? If so, you can simply glue the extension to the top with appropriate clamping. This will raise the top slightly at that point, but you already have a non-flat top so who cares? It will also bend down the fretboard a little, but again why worry? The notes will be playable, though the action there will be a fraction higher than it should be, but these are your least used frets.

    I can tell you from experience that no-one other than a luthier will notice unless you point it out to them.

    If my diagosis of the reason is correct, which you can check by measuring across the waist top and back, the other cure is to remove the back, pinch in the waistat the back until the top lies flat, then glue the back on again and trim off the overhang. On the assumption that this is the first of many I'd reject this option, leaving the dished top as a reminder for future builds.
    YUP! you've explained that well Prof..I think!..I've given away a few ukes like that..What you need is a good accurate mould to build em' in..another thing that causes a similar problem is clamping radiused edged sides down onto a flat surface...thats why all my tops are now flat
    with a slight rise in the centre of the lower bout only...guess who I got that from?

  6. #6
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    If you're not likely to play that far down the fret board (be honest...), then just cut it shorter, live and learn .

  7. #7
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    Problem #2 is Titebond II...a glue that is unsuitable for instrument making. Too rubbery...too much cold creep. If you have to use Titbond, use the original formula.

  8. #8
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    True flat tops (ie. not domed) always seem to go concave, made worse by humidity issues. They never seem to fully recover even after pushing the humidity up.
    I guess that's why makers started doming the soundboards.
    That dip seems excessive though. Somethings amiss.

  9. #9
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    Just fill with glue and clamp hard together... the top will come up a bit and the tail extension will go down a bit..It won't effect playing at all..and it will look ok to every one but you

  10. #10
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    Quote Originally Posted by ProfChris View Post
    I've produced this problem, a dip around the soundhole. Probably caused by the waist at the back being wider than the waist at the top.
    Thanks to you and the other who have commented. The width across the waist at top and bottom are identical. Apparently, there's another reason for the dip. The kit instructions called for a slightly domed back and provided braces that were shaped to produce the shape. After assembly, I see no dome on the bottom, but rather a slight dip on the front at the soundhole. Anyway, the fret board will bend down to meet the top with no problem... I was wondering if shimming from underneath the fretboard would allow it to remain flat and still allow gluing it to the top. Thanks again!

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