Soundboard gluing failure

[Richardl]

Hi All

I've just inlayed my rosette and cut out a soundhole, picked up the board and the upper bout glueline cracked

I've re-glued that and guess that is braced a good deal with the neck block etc so maybe it isnt a huge issue (and the glue line is covered) but I'm now worried that the rest of the soudboard glueline is probably not very strong - not sure why - I've never had titebond let go before. The glueline of the circle removed from the soundhole also failed very easily when bent. If I hadn't cut the soundhole and done the rosette, obviously I'd just re-do the joint. Unfortunately, its a bit late for that. What would folk recommend? How strong does that glue line need to be given the amount of bracing - I guess it is a likely failure point with expansion and contraction. Should I try carefully cracking it and re-gluing from the back without damaging the rosette (which may result in an ugly glueline)? Anyone else had that problem?

Thanks

Richard

[kiwigeo]

If you're worried about the centre seam glue joint over the lower bout then just stick a few reinforcement diamonds over the underside of the seam.....I often stick then in on my conventionally braced builds as a routine precaution.

[Richardl]

That was quick! Thanks. I also just had a thought that I could rout a 2 mm deep x 10 mm wide channel in the back centre of the soundboard - maybe just in areas there is less bracking and inlay a strip of spruce (either long or cross grain). Maybe that is overkill if the diamonds work just as well. But is there any harm in trying that?

Cheers
Richard

[jeffhigh]

Routing and inlaying like that will leave a vulnerable area at each edge of the channel.
Best to just add reinforcement on the surface.

[Richardl]

OK, thanks, I'll do that. I re-glued the cut out sound hole to test it and it has glued so well the wood failed not the glue line, so the titebond is fine. I didn't get much squeeze out so I must have just starved the joint. I was shocked how easily it broke though.

Cheers
Richard

[kiwigeo]

Richard you could whack in a soundhole patch to help reinforce the seam forward and aft of the hole.

[Richardl]

Is a soundhole patch just reinforcement under the rosette?

Cheers
Richard

[kiwigeo]

Is a soundhole patch just reinforcement under the rosette?

Cheers
Richard

I put in a plate that reinforces the entire area around the soundhole.....as detailed in Trevor and Gerard's books. I install the patch before cutting the soundhole. You'd have to retrofit and then cut a hole in the patch and carefully finish the opening out to match the hole you've already cut in the top. Whacking in a couple of small diamond patches along the centre seam immediately aft and forward of the soundhole might be the easier option.

[Richardl]

Right, well I bent the board a bit and heard a crack so the whole glue line failed with little effort and I have re-glued it from the back, forcing glue in the best I can without completely separating the halves (and not wiping the glue off with a damp cloth) ... and hopefully without wrecking the inlay...guess I'll find out tomorrow. Hope that takes and I'll add some diamond reinforcement patches if it looks OK after clean-up. Not a good start to a new build but I'm hopeful it'll be ok - it would certainly have failed as it was! I did re-glue the spruce removed from the sound hole and that formed a very good bond.

Thanks for your help.

Richard

[Steve.Toscano]

Personally i'd scrap it, OR cut down the join and reglue. May have to install a new rosette.
You are not too far into the build, so wouldnt take too much to redo it.

[Richardl]

Seems a shame to scrap it as its not easy to get the wood here in NZ. I'm not sure how to re-do the sound hole /rosette on the existing board as the dimensions will have changed after sawing it. Do you think the glue won't take to a previously glued surface? It actually looks fine now. When I bandsaw out the soundboard shape, I'll test the joints of the off-cuts. If they fail easily, I'll have to re-think what can be done.

Cheers
Richard

[Dave M]

I am absolutely with Steve on this. The surfaces with titebond on them will not reglue properly. You are at an early stage with this soundboard.

Cut down the line with the finest kerf saw/bandsaw you can find and just maybe the rosette can be fudged a little to look OK.

It is my experience as an amateur that mistakes (and as an amateur there are plenty) small, or in your case large, simply must not be ignored. Each process has to be done as well as possible before moving to the next stage or it will be regretted later.

[Richardl]

Unfortunately, it a patterned rosette, not just plain rings, so if its cut and re-joined it will look terrible. If the soundboard is cut, planed and re-glued, I'll end up with an elliptical hole and rosette anyway. I can router the hole circular OK, but will have to router out the rosette and find something to replace it with. Before doing that, is there a way to test the existing glue joint? As mentioned, I did re-glue the wood removed from the sound hole which re-glued so well the wood failed before the re-glued glue line. I take your point though that there is no certainty that the joint will be sound and better to find out now than later!

Cheers
Richard

[Richardl]

Right, here is a plan. I can cut the board, plane and glue not worrying about the size and shape of the soundhole. Re-router out the centre hole to 104 mm and router out a 15 mm trench for this rosette so the rosette comes to the edge of the soundhole...

http://www.lmii.com/products/mostly-woo ... ge-noimage


This will cover the existing inlay.

Then add a maple strip to the inside of the sound hole to bring it to 100 mm diameter if that is necessary...does it matter if the sound hole is slightly bigger? I'm reluctant the chuck away the spruce as its a nice piece to waste - not to mention the cost of getting another.

Does that sound like it might be successful?

Cheers
Richard

[lamanoditrento]

Andrew Armstrong recently had a bit of success at re-jointing a soundboard that already had the rosette inlaid;

https://www.facebook.com/permalink.php? ... 1526954780

[Richardl]

Thanks for that. Hadn't thought about using a scalpel rather than a saw! Should only loose a mm or so that way.

Cheers
Richard

[Richardl]

Got home and tried an experiment.

Cut off the top and bottom waste of the soundboard and bent the strips. The wood broke next to the join, not the glue line. The glue line is almost invisible but seems quite sound and a great deal stronger than the previous one that failed. Ive pushed and pummelled the soundboard with no signs of any cracking to a point where I'm afraid the wood will crack. I'm wondering now if this is an aqequate indication that it is a good joint? While recognising that a second glue with titebond is not ideal I doubt I could get a much better join repeating it and run the risk of stuffing it up completely.

Am I missing something?

Cheers
Richard

[Fisherman]

For my two cents i’d redo the join. Cut it down the centre, replane everything and join again. Then flip it over and rout and install a new rosette on the other side. Depending on the size of the boards you may also be able to join the current outside edges, if you dont mind the wider grain to the centre...

[Richardl]

Well, there seems to be a consensus to re-do it so that is what I have done. Actually, I've manged to cut and plane it with the loss of about 1 mm in width so the rosette looks fairly intentional and I can't tell it isn't a perfect circle by eye. I used a lot of glue and ensured plenty of squeeze-out. So, if that doesn't work I'm doing something wrong (I'm using the Kinkead approach for joining the boards, which might not be the best approach but has worked for me before)!

The technique suggested of using a scalpel woked very well, for the record. Thanks for all the tips and suggestions.

Hopefully that is my last major stuff-up for a bit.

Cheers
Richard

[Richardl]

For the record, I contacted Titebond for info on the loss of strength likely when re-gluing. They very promptly replied with the following:

"Testing being performed here shows when regluing joints, you could lose up to 15% of the strength, which is still very strong. When you have a glue in the 3500 to 4000 psi range, 15% is not very much."

So everyone is correct there is some loss of strength, but if the re-glued joint is still stronger than the wood itself, the 15% or so loss might not be that significant. I thought the figure might be significantly more than 15%.

Cheers
Richard