Soundboard crack

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Pat.Hawkins
Myrtle
Posts: 76
Joined: Thu Mar 13, 2014 1:30 pm
Location: Lower Barrington

Soundboard crack

Post by Pat.Hawkins » Wed Jan 17, 2018 12:24 pm

Hi Folks,
my son is slowly building his first tenor ukelele and I'm still in single figures.
We've had a bit of a soundboard disaster (as the image shows).

I think we'll try some cross-grain cleats underneath pulled up with some fine wire and a home made winch using a tuner - but we're open to suggestions.

I have three main questions....
the crack seems a bit reluctant to close back up. Should we dampen/swell the joint along with side clamping to "make' it close up?
or fill the joint with a slither of spruce?

If we use a slither, any advice on getting it right would be appreciated. eg how to make them, one section or several (As there's a slight kink in the top half.
also,
what's the best method to hide the holes left over by the wires?
the top is still raw timber so I guess that's an advantage.

Thirdly, this is in Tassie. Is it likely that humidity was the cause?
I didn't think is was a concern down here.

(I've ordered one of those endoscope cameras to help out).

PS... thanks heaps for the earlier advice on rescuing the neck pocket on this body... it work a treat.
Soundboard crack.jpg
Cheers

simso
Blackwood
Posts: 1768
Joined: Mon Apr 25, 2011 10:36 pm
Location: Perth WA

Re: Soundboard crack

Post by simso » Fri Jan 19, 2018 11:06 am

Pat.Hawkins wrote:
Wed Jan 17, 2018 12:24 pm
Should we dampen/swell the joint along with side clamping to "make' it close up?
or fill the joint with a slither of spruce?

If we use a slither, any advice on getting it right would be appreciated. eg how to make them, one section or several (As there's a slight kink in the top half.
http://www.mirwa.com.au/HTS_Splint_repair.html

Steve
Steve
Master of nothing,

Do your own repairs - http://www.mirwa.com.au/How_to_Series.html

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Mark McLean
Blackwood
Posts: 1084
Joined: Thu Apr 10, 2008 2:03 pm
Location: Sydney

Re: Soundboard crack

Post by Mark McLean » Mon Jan 29, 2018 7:15 am

Steve's tutorial above is a really nice walk-through of a splint repair. If you are going to do this there is an additional trick that can be used to get a tight fit. I have only done this once (it worked for me) - so more experienced people might advise. You cut the sliver a little thicker than the width of your crack and then squash it flat by lying it flat on a hard surface (something like a ceramic tile) and rolling the shaft of a screwdriver over it. You are compressing the fibres of the wood to make the sliver thinner. Then coat it with a heat-soluble glue - hide glue is ideal as it dries clear and doesn't discolour the spruce. Titebond original will also work (and is what I used). Then let the glue dry on the surface of the pancaked sliver (you haven't inserted it in the crack yet). You can squish it again if the moisture in the glue made it swell a bit. The trick of this is that when you place the sliver in the crack you then reactivate the glue with steam (put a wet cloth over it and use a clothes iron). It is like the trick to steam out dents - if you know that one. The heat and steam swells the crushed fibres of the spruce so the splint expands to tightly fill the gap. At the same time the glue becomes activated - so it gets glued it in place. Of course you want to do this with a piece of spruce which is thicker than your top, so it ends up a bit proud of the top and you can then scrape and sand it down for a flush finish.

If you think that you are immune from humidity issues where you are - think again. This looks like a classic case of a top which was glued to the rims at a time when it was relatively swelled by high RH (did you close the box on a rainy day?). It has subsequently dried out and shrunk across the grain. RH is an issue for all of us I am afraid. Most (including myself) have learned this lesson the hard way! Pay special attention to the humidity when you are bracing the plates, and when you are closing the box. The instrument is really vulnerable at those specific point in the process because you are essentially "locking in" the dimensions of the timber as it is on that day. I have sometimes had to wait a couple of weeks to do those critical parts of the build because the weather isn't right. It can be frustrating! The good news is that rest of the build process is relatively unaffected by humidity issues. So once the box is closed up you don't need to worry too much.

Pat.Hawkins
Myrtle
Posts: 76
Joined: Thu Mar 13, 2014 1:30 pm
Location: Lower Barrington

Re: Soundboard crack

Post by Pat.Hawkins » Wed Jan 31, 2018 6:27 pm

This is such a great forum! The support is really appreciated.

Thank you for the replies, it's given us real confidence in making a good repair.

As it's a tenor we can't get a hand down the sound hole.
Just waiting for that camera now - hopefully a repair image later :)


Just as an aside.....I must throw out that white matting in the photo above. (I think I got a long roll of it from the supermarket).

I left a pretty figured box wrapped in some of it on a hot day and by the next day it had left its pattern behind on the box!

Cheers

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Mark McLean
Blackwood
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Joined: Thu Apr 10, 2008 2:03 pm
Location: Sydney

Re: Soundboard crack

Post by Mark McLean » Thu Feb 01, 2018 5:49 am

Yes - good point about those plastic mats. They not only leave impressions on wood as you have observed, but they also leave silicone residue which can bugger up your subsequent finishing. The best bench padding is carpet offcuts or old towels and bathmats. Where do you get old towels? Well, you just have to suggest to your wife that you would love to go shopping with her for new towels and mats for your bathroom - and instantly you will have some old ones that can go to the shed. Everyone is a winner.

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