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DPO
07-30-2017, 03:46 PM
So I sold the Vita Uke prototype to a buyer in New York. The uke is kept in a case with a humidifier and the soundboard joint has opened up. I have never had a joint fail in my over fifty years involvemnt in woodwork. Any ideas as to why this has happened? I have made other ukes in the same wood (Tasmanian Blackwood), my own uke hanging in the workshop is five years old and shows no sign of anything going wrong with it. Is this a climatic issue? could the humidifier introduce excess moisture, or is it just one of those things. I have no knowledge of using humidifiers, so others more experienced may wish to chip in here.
Have other builders had issues like this?. Maybe this will be the last uke I export, just sell them locally and stick to selling my banjo ukes overseas, which in over forty instruments I have had zero issues with. Anybody?
I have offered a full refund.

southcoastukes
07-30-2017, 04:57 PM
Hey Dennis,

Lot of variables, but I'd start by doubting the excess moisture idea. It appears to have shrunk, not expanded (thoough from that angle difficult to say for sure).

One of those variables, of course, is you trusting the word of your customer when it comes to case storage. In most instances, it's right to do so. Then again, if you're searching for an explanation to avoid a reoccurence; well you weren't sitting with it in New York were you?

-------------------

Edit: And then again, I just remebered an instance where the joint edges weren't perfectly matched. It might pop open in that instance just from playing.

P.S: Do you have any sort of bracing other than around the soundhole?

tobinsuke
07-30-2017, 05:03 PM
I have never touched Tasmanian Blackwood and also never had this problem so I can only offer my sincere condolences. However, maybe I can ask some questions that may prompt some more informed replies...
Did the uke arrive unscathed? How long had the buyer been storing it with the humidifier? Not sure if you want to go down the "which glue" trail?
Good on you with the full refund, by the way (and of course). I hope you get some solid replies ASAP, and I'm sure everyone feels for you and the buyer. Wish I could give you more.

DPO
07-30-2017, 07:22 PM
I have never touched Tasmanian Blackwood and also never had this problem so I can only offer my sincere condolences. However, maybe I can ask some questions that may prompt some more informed replies...
Did the uke arrive unscathed? How long had the buyer been storing it with the humidifier? Not sure if you want to go down the "which glue" trail?
Good on you with the full refund, by the way (and of course). I hope you get some solid replies ASAP, and I'm sure everyone feels for you and the buyer. Wish I could give you more.
Hi Tobin,
The buyer has only had the uke about three weeks, it did arrive with a finish issue which is a totally separate problem am has been dealt with. Titebond glue, as I say this is the first joint failure I have had so a little perplexing. Thanks for your thoughts .

DPO
07-30-2017, 07:24 PM
Hey Dennis,

Lot of variables, but I'd start by doubting the excess moisture idea. It appears to have shrunk, not expanded (thoough from that angle difficult to say for sure).

One of those variables, of course, is you trusting the word of your customer when it comes to case storage. In most instances, it's right to do so. Then again, if you're searching for an explanation to avoid a reoccurence; well you weren't sitting with it in New York were you?

-------------------

Edit: And then again, I just remebered an instance where the joint edges weren't perfectly matched. It might pop open in that instance just from playing.

P.S: Do you have any sort of bracing other than around the soundhole?

Yes two braces and a bridge patch.

sequoia
07-30-2017, 07:59 PM
Wow. I feel your pain and it is things like this that cause me to wake up screaming in the night... A few things to think about: What does it look like inside? Get a mirror in there and see if the braces separated too.Was this a bracing failure or a top plate joint failure? .... Anyway, you have my sincere sympathy.

southcoastukes
07-30-2017, 08:03 PM
Yes two braces and a bridge patch.

So the two braces are in addition to the soundhole braces? Where do they run? Two small fans or something else?

DPO
07-30-2017, 08:15 PM
So the two braces are in addition to the soundhole braces? Where do they run? Two small fans or something else?

Two fans.
Regards Dennis

Kekani
07-31-2017, 04:05 AM
Without knowing anything else about the build conditions or how it was kept, for future builds, I'd stay away from using flatsawn wood, or wood with potential runout for the top. If you do, I'd keep that section for under the fretboard, instead of under or behind the bridge.

Sorry, doesn't explain what's happening in front of the bridge.

For conversation, I had an 8-string on my bench with similar top grain. The bridge popped off. I did the repair, but told the owner because of the way the bridge popped, it'll probably happen again, so either string it as a 4, or get another instrument. The original glue joint was great, the wood from the top failed.

RPA_Ukuleles
07-31-2017, 05:09 AM
I would agree on not using flat sawn plates for tops and backs. Perhaps some may be stable after 50 years, but seems an easy thing to avoid in a new build. As I look at that crack, it seems jagged so it appears the glue joint did not fail, rather the wood did. If it was the glue it might look as smooth as when you assembled the two halves. Of course we're only looking at a low res pic, but it does look jagged to me.

Best practices are your best friend in this business. Well selected, well quartered, well seasoned, well... every bit of conventional wisdom in your build will help you avoid these kinds of issues - that cause frustration and discouragement.

Many folk are successful ignoring the best practices, but i'm not willing to take those chances anymore.

southcoastukes
07-31-2017, 12:44 PM
Looks like the last two answers are the best (I had looked right past the obvious). But here's something you might also consider for future builds.

Cuatro builders traditionally didn't use any top bracing at all. Tops were thin and so deflection was pretty common. As time went on, the instruments kept growing in size, so the situation kept getting worse. Today a lot of the really big ones have traditional guitar-style fan bracing but a sort of intermediate arrangement was used as well.

Use a bridge plate (as you have done) but in addition to (or even instead of) your two fans, glue a strip of top material under the seam of your two top plates. Maybe just a bit thicker than your bridge plate and around 1/2" wide. Start under your soundhole brace, run it to the top of your bridge plate, then start it up again on the other side and run it down to the bottom. The combination of these two allows you to keep the thickness down on your top without deflection, and your seam joint is reinforced at the same time.

When the sufrace area is as thin as the edge of an Ukulele top you just don't have a lot of glue area to begin with.

Rodney, my guess is that the jagged edge might mean that as it pulled apart at the joint the glue did indeed hold, but only in spots.

DPO
07-31-2017, 01:23 PM
Looks like the last two answers are the best (I had looked right past the obvious). But here's something you might also consider for future builds.

Cuatro builders traditionally didn't use any bracing at all. Tops were thin and so deflection was pretty common. As time went on, the instruments kept growing in size, so the situation kept getting worse. Today a lot of the really big ones have traditional guitar-style fan bracing but a sort of intermediate arrangement was used as well.

Use a bridge plate (as you have done) but in addition to (or even instead of) your two fans, glue a strip of top material under the seam of your two top plates. Maybe just a bit thicker than your bridge plate and around 1/2" wide. Start under your soundhole brace, run it to the top of your bridge plate, then start it up again on the other side and run it down to the bottom. The combination of these two allows you to keep the thickness down on your top without deflection, and your seam joint is reinforced at the same time.

When the sufrace area is as thin as the edge of an Ukulele top you just don't have a lot of glue area to begin with.

Rodney, my guess is that the jagged edge might mean that as it pulled apart at the joint the glue did indeed hold, but only in spots.

Thanks for the great advice, much appreciated.

ProfChris
08-01-2017, 03:55 AM
It looks to me like the wood has failed at the joint, rather than just a glue failure. It also seems pretty clear that the top has shrunk laterally, which must mean that it spent time at a lower humidity than when it was glued up.

Two likely causes:

- flat sawn wood shrinks much more across the grain than does vertical grain wood - maybe 3 x as much. If I were building using flat-sawn wood, I'd put a substantial dome in the top to allow somewhere to take the shrinkage without pulling the top apart.

- building in higher humidity than the uke ends up living in. I'm in the UK and don't export ukes, so I simply take care to glue up when the humidity is "reasonably low". That's good enough for UK conditions, and my guess is NZ might be similar. If I were making a uke to go to the US, whose buildings are heated far warmer than here, and whose air conditioning produces much drier air than here, then I'd be trying to glue up in low (around 40%) humidity to give the instrument a chance.

My guess is a combination of these two is what gave you the problem.

Timbuck
08-01-2017, 06:34 AM
A few years ago, I had a one piece top split down the grain ..It turned out the wood was not seasoned long enough.