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| What could cause back braces to come loose??? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=43600 |
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| Author: | Tai Fu [ Fri Jun 06, 2014 2:14 am ] |
| Post subject: | What could cause back braces to come loose??? |
I've had it with ukelele builds... it's just nothing but trouble. First it's binding issue, then it's unintended damage, and now I discovered that ALL of the back braces are loose at the edge. What could possibly cause that? Bad glue? I used HHG. The body is too small so it's really hard for me to reach in and glue it back together, so I'm about done with them and it's going to make a really good bonfire... |
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| Author: | warmong [ Fri Jun 06, 2014 3:50 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
did you preheat the back before glueing the braces? I always place a hot metal piece on the spot where the brace will come, just before applying glue to the brace. do you have a good caul for clamping the braces? For back braces I have laser-cut cauls of the same radius as the brace, so there is full contact between the back and the brace during clamping. oh yeah, and I always use a lot of go-bars per brace. so they are spaced approximately 4-5cm apart. and I always make sure to have 2 go-bars at the very edge of the brace. |
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| Author: | Arnt Rian [ Fri Jun 06, 2014 4:04 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
It could be the glue, it could be the technique, wood preparation (or lack thereof), temperature, lots of things. Time to analyze your whole process to make sure you have everything under control. Isn't that just lovely, another learning opportunity! 
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| Author: | Tai Fu [ Fri Jun 06, 2014 4:18 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I only had this problem making ukes, not guitars. It's weird that I could get everything right, everything looks and feels right and right as soon as I close the box, I hear knocking and only to discover a long time later that back braces are loose. Worst thing about them is that they're hard to visually inspect because the cracks almost require an electron microscope to see! I worked on another luthier's guitar and could not find what's wrong at all, only for someone else to find the loose back brace. There must be an exact science to finding loose brace because I can poke and prod all day long with a palette knife and find nothing, but there is something wrong. |
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| Author: | DennisK [ Fri Jun 06, 2014 4:25 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Two things I know of that could pop all of them at once: low humidity making the back want to turn inside out, or something set on top of the instrument, pressing the domed back against a flat surface. Either way, the force is focused toward the brace ends. Best prevention is to notch the brace ends into the linings, so they're mechanically held down. It's a pain, but after having a couple come loose myself, I've decided it's worth the trouble. The first brace is the most structurally important, so glue that through the soundhole if you can. But at the low string tension of ukulele, it might be fine without any back braces at all. Just more delicate. Let the others flop, or try to peel them out entirely. |
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| Author: | DennisK [ Fri Jun 06, 2014 4:29 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Tai Fu wrote: There must be an exact science to finding loose brace because I can poke and prod all day long with a palette knife and find nothing, but there is something wrong. Press over the brace on the outside with your thumb, and you can hear crunchy noises, and see the end pop up inside. |
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| Author: | ernie [ Fri Jun 06, 2014 8:14 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
It could be the way the clamping pressure (type of clamp) is distributing pressure on the brace and the quantity/quality of HHG ,it should be done vy quickly before it cools. I had some gaps on a spruce inside backstrip or marriage strip when glueing yesterday aft. After removing the clamps I noticed small 1/16in gaps along the edge of one side. I quickly applied hhg using a small spatula all along the edge of one strip by feeding small amts of hhg as needed .Naturally there was some spillover which was cleaned with a tissue and hot water, or as the HHG cools and gels, a scraper can be used and then hot water . Closed the gaps. I/m using moose cam clamps so that could be my problem .I/ve had that occur on gtr /uke radiused bracing as well using hhg.Just went back and redid it till I got it right. |
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| Author: | Tai Fu [ Fri Jun 06, 2014 8:47 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Hard to redo them with the box closed and bound. Redoing them means opening the box back up, rip out whatever bindings used, redo the braces, close it back up (which takes a while because of alignment issues), redo the binding and any grain filling/finish that goes with it. Much easier to just start from scratch. |
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| Author: | ernie [ Fri Jun 06, 2014 10:29 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Your right Tai , what a PITA! I see your point. I now double check and test all my glueing operations because murphy has been chasing me as well..I/ve redone several tops and backs because of glue line failure on braces using hhg .in the past .Personally I might switch over to doing braces to titebond or LV 202gf glue which I used to use a lot in cabinetmaking in vancouver bc , but it takes 1 week to get here from NY state. I/ve closed the box and had problems down the road as well .I think it/s the wide fluctuations in temp and humidity here in KC. Where temps swing wildly from 10 f and 20%humidity in winter to 90deg F and 60% humidity in summer ouch. What I need to do is test bracing samples in all kinds of weather using all the different glues I use in constructing and leave them outside for awhile.I did this once with glueing pearwood to pearwood using fish in vy wet weather to see if the joint failed.Will do it with the 2 types of HHG as well as titebond and maybe the 202 gf in the fall. gud luck ,hope you find the culprit. |
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| Author: | Tai Fu [ Fri Jun 06, 2014 10:57 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I'm wondering about gluing braces with epoxy. I don't mean cheap HW store epoxy but good epoxies that cures rock hard. The reasoning being that braces isn't really something that needs to come off sometime in the future, and if something breaks epoxy will stick to itself. One benefit of epoxy is not introducing moisture into the wood causing problems, and it's heat resistant. I can now see why manufacturers use titebond, it doesn't fail as much as HHG, or at least it's more forgiving in processing. I've had HHG fail on so many occasion even though the process has been more or less the same. One time on a customer's guitar I restored... really sucks to reset the neck for free. I've read somewhere that hide glue is known to become brittle with age and simply crack off. I don't trust fish glue so much either. I mean it's a great product but someone has reported that it does not tolerate high humidity at all, and will come apart at the seams. Obviously this is going to be a problem with customer's guitar because they might live somewhere with constant high humidity and they might be surprised to find joints coming apart. By the way has anyone tried LMI's new yellow glue? They said it's better than titebond but what are the tests so far? The florescent dye really helps with finding invisible glue residue for sure! |
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| Author: | DennisK [ Fri Jun 06, 2014 1:11 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Epoxy would indeed be good, if you don't mind working with it. Probably the best glue there is for braces, from a finished product standpoint. Plus then you could try carbon fiber falcate bracing  I'd use it if it wasn't such a pain to mix up and keep from getting all over the place. And the nasty fumes ![[xx(]](./images/smilies/smiley11.gif "Dead")
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| Author: | ernie [ Fri Jun 06, 2014 2:43 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
Tai, I hear your pain abt the hhg and fish. I would take the( high humidity post with fish glue) as one persons negative experience .The same person who posted that thread ran the same thread on delcamp forum about the woes of using fish glue. So I ran my own tests. By leaving a sample outside in rainy damp. hot an cold weather for 1 month including dunking the sample outside in a bowl of water freezing cold. The sample held together with no seperation.It could also be because I joined 2 pieces of a vy tight grained wood like our local bradford ornamental pear. Anyhow , FYI Dennis I have used fish glue to do my falcate bracing , by laminating thin englemann spruce with fish and the carbon fiber , even though I have some system 3 epoxy. which gives me 1/2hr set up time .The fish tacks in 1 minute but also allows for aligning the thin falcate/ CF bracing to be glued without hurrying. |
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| Author: | jfmckenna [ Fri Jun 06, 2014 3:12 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I think it's odd that it only happens on your uke's. Are you tucking the ends into the linings on the guitars? I really didn't think that was so important but maybe it is. I know some people don't tuck the X-Braces but maybe the backs get bumped around more. |
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| Author: | RusRob [ Fri Jun 06, 2014 3:38 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
That is strange Tai, HHG has been used for hundreds of years on guitars, piano's and violins and you can find examples of those instruments and they are not falling apart. I have repaired 50 and 60 year old guitars that have been made with it and it seems to hold quite well. I do know that extreme heat will soften HHG which will allow the glue to get air bubbles in it which will cause a joint to fail but HHG is one of the best glues for instruments ever made. My guess is you are either clamping it too tight and staving the joint or you are moving it before the glue sets up. Either one will cause a joint to fail prematurely. Just my 2c but I think it is more your technique than the glue. Bob |
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| Author: | profchris [ Fri Jun 06, 2014 3:45 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I only make ukes, and am a mere hobby builder whose work is far from perfect, but I've not had back brace problems yet. Sometimes I tuck the brace (only one on a soprano), sometimes not. If not, I taper the ends to nothing. If I'm relying on the brace to form the arch of the back then I always tuck the ends. Might that be what's going wrong? It might be relevant that I don't form the arch before gluing the back on - instead I glue the brace to the linings, then the back is glued to linings and brace in a single operation. If I curve the back heel to tail only then the brace is flat, and then I leave it untucked and glue it to the back before the back goes on. |
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| Author: | Greg B [ Fri Jun 06, 2014 5:34 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
If I had to guess, I'd say heat and humidity -- mostly humidity -- combined with some wood that wants to wiggle. There are numerous ways for technical problems to arise. The first few that come to mind are: glue gels before it is clamped, glue too thin, poorly fitted joints, and dirty or glazed gluing surfaces. HHG has some good properties, but there's a reason the rest of the world left it behind. I've never had a failure, but I have repaired plenty of old instruments and furniture that had failed hide glue joints. If I lived in Taiwan I'd probably just use a PVA: Titebond, LMI, Lepage/Henkel, whatever. Epoxy is a toxic PITA, and it often has high damping, depending on the formulation. I glued a bridge once with epoxy, thought the instrument sounded a little lifeless, and reglued it with titebond. It instantly came to life. The difference was so night and day it surprised me. |
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| Author: | Jim Kirby [ Fri Jun 06, 2014 8:27 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I think that the likely fish glue story in question was a really extreme example. All my guitars are done completely with fish glue, except for the fretboards, and spend their summers in the humidity in locations from home (Delaware, the northernmost) down the coast to Florida and around to Houston. If any were going to disintegrate in humidity under normal operating conditions, they'd be component parts by now. |
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| Author: | bluescreek [ Fri Jun 06, 2014 9:07 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
post a pic of the braces if you didn't fade the braces to the back the edge develops a stress risor and they can fail if the end can'g flex |
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| Author: | Lonnie J Barber [ Sun Jun 08, 2014 7:34 pm ] |
| Post subject: | Re: What could cause back braces to come loose??? |
I've never used HHG. I have an unopened container that I've had for 25 years. But Titebond 2 works great and never had a joint to fail. Sent from my iPhone using Tapatalk |
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| Author: | Tai Fu [ Mon Jun 09, 2014 2:13 am ] |
| Post subject: | Re: What could cause back braces to come loose??? |
So how well did Titebond II do as far as cold creep goes? I keep hearing luthiers say to avoid TB II but it's the only TB apart from III that's available in Taiwan so I'd like to know. It is much cheaper for me to get TB II in Taiwan than ship a bottle of heavy liquids by air. |
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