First build - split in back due to humidity :-(

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mhunte12
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First build - split in back due to humidity :-(

Post by mhunte12 » Tue May 20, 2014 1:25 pm

Hi

After a few less ambitious projects, I found myself thinking "how hard could it be to build a guitar" sometime ago, and decided to find out. It's been a really rewarding experience, and I'm very happy with the results so far (and the lessons learned from a smorgasbord of mistakes along the way), but am a bit stumped as to how to work my way through the current predicament.

The rear of my GA cutaway is made from bookmatched Tasmanian Sassafras. I'd noticed that it seems to be more sensitive than most to changes in humidity, but hadn't really thought much of it until we had a run of 40deg+ days in the summer. By the end of the few days, what had looked like this:

Image

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...now looks like this:

Image

The split is only between the sassafras panels, the internal reinforcing strip along the seam has held everything together really well, so there's no rattles or loose wood inside. However, I'm a bit stumped as to how to repair this flaw. Some tentative pressure with a clamp across the read bout has shown that it's highly unlikely that I can squeeze this gap closed without causing major damage elsewhere.

Ideas that I've had so far are:

1) Pick a good day where the split swells to (nearly) closed, then wick CA glue into the gap and hope for the best
2) Mix up some 2 pack epoxy with fine sanding dust to create an almost wood coloured filler with great bonding strength and squeege into crack, then scrape flush

I'm really cross with myself for not seeing the potential for disaster and mitigating it properly, but what is done is done. I wondered if anyone has come across this sort of problem before, and had any wisdom they could share to help me get this project back on track?

Thanks very much in advance for anything you're willing to share,

Mark

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kiwigeo
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Re: First build - split in back due to humidity :-(

Post by kiwigeo » Tue May 20, 2014 2:35 pm

Perfect place for a centre seam inlay :D
Martin

mhunte12
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Re: First build - split in back due to humidity :-(

Post by mhunte12 » Tue May 20, 2014 2:54 pm

In hindsight, you're spot on. Given the fact that the back is compound curved, I can't believe that I didn't view the back seam as an obviousl weak spot (with a ~2.5mm butt joint) and adequately reinforce.

I'm not sure about the practicalities of routing the channel now - I guess I could reclamp the body in the mould, apply some (flexible) straight edges across the length of the body and rout a ~1mm depth channel for a seam.

My palms are sweating just thinking about it....!

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kiwigeo
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Re: First build - split in back due to humidity :-(

Post by kiwigeo » Tue May 20, 2014 3:28 pm

I've done it on a classical back. I used BWB purfs each side of the inlay (same as youve used on your binding purfs). That way any gaps between the outside of the purf and the channel side could be infilled with ebony dust/epoxy filler
Martin

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Re: First build - split in back due to humidity :-(

Post by Jeremy D » Tue May 20, 2014 3:36 pm

Kind of looks like the join wasn't quite tight enough, you can see a bit of a glue line towards the tail of the guitar. I would be interested to see what the fix would be (sorry I am not experienced enough to have a solution).
Jeremy D

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Allen
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Re: First build - split in back due to humidity :-(

Post by Allen » Tue May 20, 2014 5:07 pm

Simple enough fix. Inlay as Martin suggests.

Careful placing of a fence to run the laminate trimmer along. On that much of a curve back you will need something that will have a bit of flex in it to conform to the back.

Lot's of checks to make sure you are hitting the seam on it's entire length. And then route away. Inlay appropriate size strip or purfling. How fancy you want to get with that is up to you. Another binding strip and some purfs along each side with mitre joins in the corners would really tie it all together, but maybe too difficult on your first go at a fix like this.
Allen R. McFarlen
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kiwigeo
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Re: First build - split in back due to humidity :-(

Post by kiwigeo » Tue May 20, 2014 5:13 pm

Further to my earlier comments...use epoxy glue mixed with ebony dust to actually glue in the inlay. This will reduce risk of purfs swelling and also take care of any gaps.
Martin

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56nortondomy
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Re: First build - split in back due to humidity :-(

Post by 56nortondomy » Tue May 20, 2014 6:58 pm

What about a decorative inlay just over the split? A tree branch or something ala Jeff Jong. Wayne

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Trevor Gore
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Re: First build - split in back due to humidity :-(

Post by Trevor Gore » Tue May 20, 2014 7:24 pm

I put the back strip in this guitar after the box was closed. Flexible straight edge, good double stick tape, a laminate trimmer with an adjustable fence and a steady hand. Start with a cut (bit size) narrower than the intended inlay, because if any cut wanders, it will be the first. So use, say a 3mm bit and work to, say, an 8-9mm slot, at ~1.5mm deep. The centre should match the binding (rosewood, by the look of it) and then the BWB either side, mitred into the back purfling. Once you have a good parallel channel for the inlay, size the rosewood so that it is a tight fit in the channel with the purfling. You can try to match the channel to the centre strip width, but that means you need really good control of your routing (difficult with the compound curves). You should finish up something like this:
Back strip.jpg
Back strip.jpg (66.85 KiB) Viewed 22487 times
...which was likely done after the box was closed, too.

simso
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Re: First build - split in back due to humidity :-(

Post by simso » Tue May 20, 2014 7:52 pm

Nice back

Go the inlay option
Steve
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Re: First build - split in back due to humidity :-(

Post by mhunte12 » Mon Jun 02, 2014 4:22 pm

The wisdom of crowds...

Despite being pretty nervous, I cracked on with your suggestion yesterday evening. Made up some straight edges for the router to follow and cut the channel to suit the rosewood / BWB pattern I had decided on.

Image

Image

Image

Used a chisel to extend the trench to the existing binding, then a scalpel to cut the mitre into the existing perimeter BWB. After that, things got a lot easier - just cut the rosewood & BWB to length, mitre accordingly, glue, clamp, scrape and breath massive sigh of relief.

Thanks ever so much for the advice - I'm not sure if I'd have ever got here without some pushing, but I'm really happy with the results. Hopefully it's all downhill from here!!

Image

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kiwigeo
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Re: First build - split in back due to humidity :-(

Post by kiwigeo » Mon Jun 02, 2014 5:17 pm

Nice work....
Martin

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Re: First build - split in back due to humidity :-(

Post by 56nortondomy » Mon Jun 02, 2014 5:26 pm

Good fix. Wayne

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Re: First build - split in back due to humidity :-(

Post by demonx » Mon Jun 02, 2014 5:56 pm

Good repair!

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Re: First build - split in back due to humidity :-(

Post by Crafty Fox » Mon Jun 02, 2014 7:28 pm

Great save!
Ken

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charangohabsburg
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Re: First build - split in back due to humidity :-(

Post by charangohabsburg » Mon Jun 02, 2014 8:23 pm

That's a pretty tidy save! :cl
No one will be able to tell the strip was added to fix a crack or gap.
Know what? Guitars can talk. This one literally screamed for a center back strip. At least in my opinion, guitars without a decorative strip between the back pieces look somewhat strange.
Markus

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It's only the others who suffer.

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Trevor Gore
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Re: First build - split in back due to humidity :-(

Post by Trevor Gore » Mon Jun 02, 2014 9:37 pm

demonx wrote:Good repair!
What repair??

:lol:

Nice work, Mark.

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Mark McLean
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Re: First build - split in back due to humidity :-(

Post by Mark McLean » Mon Jun 02, 2014 10:24 pm

That is a very fine job!

I am noticing the similarities between your lesson in humidification/dehumidification and my own
[/url](viewtopic.php?f=1&t=3749&p=45079#p45079)[url]
I wonder if it is partly due to the susceptibility of the blackheart sassafras that we were both using. Tim Spittle warned me when I got it from him that this was flat sawn, not quartered - so as to see the great figure, but I think that will make it cup some more?

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Re: First build - split in back due to humidity :-(

Post by johnparchem » Tue Jun 03, 2014 1:24 am

Nice joinery! Great repair.

mhunte12
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Re: First build - split in back due to humidity :-(

Post by mhunte12 » Tue Jun 03, 2014 8:28 am

Thanks everyone, you're very kind given that substantially more luck than judgement was involved in the end product.

Mark - I'm building the guitar in my unheated, non humidity controlled garage right on the ocean in Vic. I was aware of the difficulties that this was likely to cause, but didn't have a viable alternative available to me. I was interested to note the different behaviour of the woods that I've used during fluctuations in humidity / water content. The yellowgum was almost totally stable, the Huon pine a little less so, but the Sassefras tried to curl up at a moments notice and required significant efforts to keep it anywhere near flat. Once I'd finished the rear plate it was clamped into my (rather heath-robinson) radiused mould and moved inside. Again, I think more luck than judgement saved me from a concave back like yours, and it seems to have survived without any cracking either.

Does look amazing though....!

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Re: First build - split in back due to humidity :-(

Post by vandenboom » Tue Jun 03, 2014 9:26 pm

I got a split in a back on guitar 2 a few years back because I knew nothing about humidity considerations at that time.
After assembling in a high humidity environment in my shed in a Melb winter, and after putting on lacquer, I thought it would be smart to leave the guitar hanging in a centrally heated room for 2 weeks to cure - one humidity extreme to the other. It was fixable but a good lesson.
Frank

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Re: First build - split in back due to humidity :-(

Post by mhunte12 » Mon Jul 20, 2015 10:58 am

Just to round this topic out completely...

The back is still holding together, despite the challenges of another surf coast winter:

Image

Finally got around to fitting the neck (tapered dovetail, never again), finishing and setting the guitar up, and was finally able to have a play with it this weekend. I was quite surprised how much the tone developed in the first few hours of playing (it's getting better and better), and overall I'm really pleased with this as a project. Overwhelmingly tempted to buy up some more wood and start on #2...

Thanks to everyone who supplied advice during the darkest hours of this build, it was enormously reassuring to have some experienced opinions on the way forward. Thanks!

Image

Image

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56nortondomy
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Re: First build - split in back due to humidity :-(

Post by 56nortondomy » Mon Jul 20, 2015 12:23 pm

Well done Mark, that was a nice fix and the guitar looks great.
Wayne

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kiwigeo
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Re: First build - split in back due to humidity :-(

Post by kiwigeo » Mon Jul 20, 2015 1:13 pm

Nice work Mark. The sas is...sassy!

Just one detail missing and this may just be me being anal.......IMHO rounding off the edges of the soundhole would be the icing on the cake. What do others think?
Martin

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56nortondomy
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Re: First build - split in back due to humidity :-(

Post by 56nortondomy » Mon Jul 20, 2015 2:41 pm

kiwigeo wrote:Nice work Mark. The sas is...sassy!<br abp="725"><br abp="726">Just one detail missing and this may just be me being anal.......IMHO rounding off the edges of the soundhole would be the icing on the cake. What do others think?
I never noticed that, I think rounding them off is a nice touch and always do mine.
Wayne

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