First build - split in back due to humidity :-(
First build - split in back due to humidity :-(
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:
...now looks like this:
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
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:
...now looks like this:
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
Re: First build - split in back due to humidity :-(
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....!
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....!
Re: First build - split in back due to humidity :-(
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
Re: First build - split in back due to humidity :-(
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
Re: First build - split in back due to humidity :-(
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.
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.
Re: First build - split in back due to humidity :-(
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
- 56nortondomy
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Re: First build - split in back due to humidity :-(
What about a decorative inlay just over the split? A tree branch or something ala Jeff Jong. Wayne
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Re: First build - split in back due to humidity :-(
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:
...which was likely done after the box was closed, too.
...which was likely done after the box was closed, too.
Fine classical and steel string guitars
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
Re: First build - split in back due to humidity :-(
Nice back
Go the inlay option
Go the inlay option
Re: First build - split in back due to humidity :-(
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.
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!!
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.
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!!
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Re: First build - split in back due to humidity :-(
Good fix. Wayne
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Re: First build - split in back due to humidity :-(
That's a pretty tidy save!
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.
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
To be stupid is like to be dead. Oneself will not be aware of it.
It's only the others who suffer.
To be stupid is like to be dead. Oneself will not be aware of it.
It's only the others who suffer.
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Re: First build - split in back due to humidity :-(
What repair??demonx wrote:Good repair!
Nice work, Mark.
Fine classical and steel string guitars
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.
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Re: First build - split in back due to humidity :-(
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?
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 :-(
Nice joinery! Great repair.
Re: First build - split in back due to humidity :-(
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....!
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 :-(
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
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
Re: First build - split in back due to humidity :-(
Just to round this topic out completely...
The back is still holding together, despite the challenges of another surf coast winter:
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!
The back is still holding together, despite the challenges of another surf coast winter:
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!
- 56nortondomy
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Re: First build - split in back due to humidity :-(
Well done Mark, that was a nice fix and the guitar looks great.
Wayne
Wayne
Re: First build - split in back due to humidity :-(
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?
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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Re: First build - split in back due to humidity :-(
I never noticed that, I think rounding them off is a nice touch and always do mine.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?
Wayne
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