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Did not do what I have Done

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Project by amagineer posted 07-03-2011 01:33 AM 1567 views 1 time favorited 8 comments Add to Favorites Watch

I posted my nordic harp over two months ago (see picture). I took the harp to a craft show to show of my instuments. Being tone deaf I could never adjust the strings properly. At the fair a music teacher tuned it form me, it sounded beautiful. As the day progressed the sun was beating down in the pins, all of a sudden the wood that I had adhered with two part epoxy came springing by my face. I have since learned not to put string instruments in extreme hot or cold situations so as not to have this happen. I just purchased a high strength two part epoxy with a 5000lb strength value, and will be regluing it. If anyone has any other suggestions I would be appreciated.

-- Flaws are only in the eye of the artisan!





8 comments so far

View ajosephg's profile

ajosephg

1860 posts in 2315 days


#1 posted 07-03-2011 01:56 AM

Why epoxy? With the amount of surface area to be glued, I think Titebond III would be stronger than epoxy.

-- Joe

View fussy's profile

fussy

980 posts in 1804 days


#2 posted 07-03-2011 02:00 AM

That’s a real shame. Epoxy will work, but so will ordinary pva glue. Just get it clean and keep it out of the sun. I’ve glued bridges back on dozens of 12 string guitars and never had a failure; but I told them to de-tune them when transporting them in a car or when not being played in hot weather. Sun is a killer as you found out. At least it’s repairable. And really, I would stay with pva. The glue failed because it got too hot. Shouldn’t be an issue, normally.

Steve

-- Steve in KY. 44 years so far with my lovely bride. Think I'll keep her.

View BobTheFish's profile

BobTheFish

361 posts in 1305 days


#3 posted 07-03-2011 04:10 AM

What about pegs.

forget about the glue for a moment.

What’s happening is that the strings hold a lot of tension and are putting a sliding tension between the lamination. Whatever “part” of the lamination is weakened, be it the top pieces loseing from the epoxy, or the bottom piece ungluing, it’s not the sort of force that the epoxy itself is tested for. If you peg the boards to each other as well as glue, you have some sort of struts holding the lamination in place.

At least that’s my reasoning. Feel free to point out why it might be wrong.

View Derek1980's profile

Derek1980

31 posts in 1661 days


#4 posted 07-03-2011 04:15 AM

My experience is that with a good wood glue joint the wood will usually be what fail before the glue. However, if the surfaces of the broken harp are now saturated with the original epoxy Im not sure how it will affect PVA glue. You may need to carefully sand or scrap down to a good fresh surface, witch seams like it will be hard to do with out disturbing the finish of the instrument or you could just try the stronger epoxy and use PVA on next one you make.
good luck

-- Derek

View David Kirtley's profile

David Kirtley

1285 posts in 1751 days


#5 posted 07-03-2011 04:15 AM

Don’t switch glues unless you plan on sanding both sides to bare wood. The other glues won’ stick to epoxy that well.

Any of the modern glues will bond stronger than the wood itself so it really boils down to what you like to work with. That type of instrument probably would not benefit from glues that you can remove so I wouldn’t go with hide glue.

-- Woodworking shouldn't cost a fortune: http://lowbudgetwoodworker.blogspot.com/

View shipwright's profile

shipwright

5318 posts in 1551 days


#6 posted 07-03-2011 07:32 AM

I have a lot of experience with epoxies and trust me, it wasn’t because the glue wasn’t as strong as the wood, unless it was a five minute variety which I doubt it was.
What will make epoxy fail is exactly what makes pva work….......... pressure. If you have a perfect fit and apply a lot of pressure, you drive the epoxy out of the joint. It’s the nature of the beast that it needs to have a film of glue between the pieces.
When laminating sharp curves with epoxy it is common to put a thin glass cloth or the like between the pieces to prevent complete squeeze out of the glue.
Don’t blame the epoxy. Just don’t clamp it so tight.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fiberglass trees. http://prmdesigns.com/

View amagineer's profile

amagineer

1392 posts in 1351 days


#7 posted 07-03-2011 02:24 PM

Thanks all for the advise. I will have another go at gluing it back together.

-- Flaws are only in the eye of the artisan!

View Bluepine38's profile

Bluepine38

2954 posts in 1839 days


#8 posted 07-03-2011 05:32 PM

I would also go with Bob the fish, some nice contrasting pegs/dowels put in at a slight angle, would definitely
help give strength as well as add a nice touch of color.

-- As ever, Gus-the 76 yr young apprentice carpenter

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