Indian Rosewood Bridges coming off Cedar and Pine tops

[NotTheMama]

I'm a novice luthier of only two ukeleles. A cedar top and a bunya pine top. Both have indian rosewood bridges. The PVA glue on both bridges has failed after a short time. One of them twice. Inspection of the failed joint shows that there was no glue on the rosewood.

I am thinking about using two part epoxy next but I have never heard of that being used in this application and even traditional relatively weak glues should really be strong enough. I used an unknown brand of PVA, so dud glue is a possibility, but it this glue has not failed in other applications to date.

Do members have any suggestions before I commit to epoxy? Is epoxy even the right choice?

[ozziebluesman]

Welcome to our forum.

Indian Rosewood is a self oiling wood. In other words, if you sand the bottom of the bridge and leave it a few days the joint will most probably fail due to the oil the rosewood secrets. So what I do is sand the bottom of the bridge and then glue up straight away. I did just that method with a rosewood bridge last week and it gave me a great glue joint. I usually leave the glue joint at least a day to dry even 24 hours before removing the clamps.

The yellow glues are a better glue for guitar building. Titebond Original is what I use and many others here on the forum. Epoxy is a great glue but not for the bridge. If you ever want to remove the bridge, it will be a difficult job.

Good luck with your building

Cheers

Alan

[kiwigeo]

If you're using straight PVA in your workshop......grab every bottle of the stuff and chuck it in the bin. For luthiery use modified PVA such as Titebond...Titebond I for joints where moisture in the joint isn't an issue. For bindings and other applications where the glue joint will get exposed to higher temps..use Titebond III. For joints where a non water based glue is required (eg fretboard/neck join, headstock veneers) use epoxy.

For bridges hide glue is probably the best choice..it has a higher shear strength than modified PVA and clean up is also a lot easier.

As Alan the oils in Rosewoods can interfere with a good glue joint. I always wipe the underside of my bridges with acetone to leach out some of the oil before gluing onto the soundboard.

[NotTheMama]

Yeah,

Thank you for the suggestions. I suspect that the PVA I'm using is not up to the job... I did clean up the rosewood with acetone the second time around, but it failed again.

All right. I will try Titebond, roughening up the bridge AND wiping with acetone. If I can get hide glue somewhere I will try that.

Thanks again

[Allen]

I have glued several hundred of bridges on instruments using both HHG and PVA. Not once have I wiped the surface of the bridge with acetone. This very well could be your problem as acetone will pull the oils to the surface and most unlikey that you will ever get them all off.

The only time epoxy is right for this job is when I had to repair a guitar that had an aluminium bridge and was the only option.

[NotTheMama]

I have glued several hundred of bridges on instruments using both HHG and PVA. Not once have I wiped the surface of the bridge with acetone. This very well could be your problem as acetone will pull the oils to the surface and most unlikey that you will ever get them all off.

The only time epoxy is right for this job is when I had to repair a guitar that had an aluminium bridge and was the only option.

So now I'm confused I did not wipe with acetone on the first time I glued them and wiped the one that I re-glued. Maybe its just the glue.

[kiwigeo]

I have glued several hundred of bridges on instruments using both HHG and PVA. Not once have I wiped the surface of the bridge with acetone. This very well could be your problem as acetone will pull the oils to the surface and most unlikey that you will ever get them all off.

The only time epoxy is right for this job is when I had to repair a guitar that had an aluminium bridge and was the only option.

You'll find that if you do a couple of wipe sessions on a rosewood bridge the the amount of oil leaching out of the wood reduces markedly as you go through a wipe session. I've left a few wiped bridges for a couple of days a day and then given them another wipe with acetone with very little oil getting onto the cloth.

[lamanoditrento]

I also always wipe down rosewood or other oily wood with acetone. I will keep wiping them down until no more colour leaches out.

The glue may be your issue but other issues to check will be a good mating service between the bridge a soundboard (especially if you build with a radius to your plates) and also your clamping system.

Do you have any pictures of the underside of the bridge and soundboard of the glue failures?

[NotTheMama]

Do you have any pictures of the underside of the bridge and soundboard of the glue failures?

No pictures. Scraped and sanded clean long ago, and put aside the job procrastinating ever since. But there was no glue on the rosewood and lots of well adhered glue on the soundboard that I've actually had to scrape off and then sand - So I'm sure that its the glue/rosewood interface that's the problem. What's more, I've had no problem gluing any other component of the ukuleles, which used a mix of Ash, Black Wood, bunya pine and cedar.

Using acetone just prior to gluing makes sense to me. The first time one of the bridges came off and experienced luthier advised that it was most likely due to contamination and to clean, sand, and try again. Acetone is a good solvent that dries quickly without residue and so I figured a good way to clean the surface resin and any impurities.

But now I've had three bridge failures and that's why I thought that I should try epoxy next. There is not much evidence for Titebond being better than white PVAs such as Aquadere and anyone who says there is is probably just expressing preference or quoting anecdote. I hear that Titebond has a higher viscosity and that may explain the perceived difference.

Thank you very much for all the comments everyone: I think that I'll try again with a fresh bottle of brand name PVA (maybe Titebond ) on a clean and roughened up bridge - keep the two surfaces clamped a good long while.

[kiwigeo]

There is not much evidence for Titebond being better than white PVAs such as Aquadere and anyone who says there is is probably just expressing preference or quoting anecdote. I hear that Titebond has a higher viscosity and that may explain the perceived difference.

While eventual strength is similar once set Aliphatic Resin glues do have a few advantages over PVA glues. AR has a higher instant tack (less tendancy to slide under clamping), a better resistance to heat and water (try bending bindings glued with PVA) and once set is a lot harder than PVA (much easier to sand). As far as Aquadhere goes....I have issues with the quality of Selley's products....they used to make decent stuff but over the last few years Ive noticed quality of same go down.

[Mark McLean]

Trent mentioned a really important cause of failed bridge glue-ups - imperfect contact of the two surfaces. This is common if there is a slight arch to the top of the instrument, but the bridge is flat. Are you confident the shapes correspond well? Many people use the technique of placing sandpaper on the top of the instrument and sanding the bottom of the bridge directly on that surface to get an identical shape. Put pencil marks on the face that you are sanding and keep going until they are all removed. Apologies if you have already done it this way - but it is a common issue leading to bridge failures. Then there is the issue of how you are clamping it. And I will join the chorus recommending Titebond Original. Cedar is known to shed bridges more often than spruce tops do, but it usually involves splintering of the wood rather than a clean separation.

[NotTheMama]

Are you confident the shapes correspond well? .... And I will join the chorus recommending Titebond Original. Cedar is known to shed bridges more often than spruce tops do, but it usually involves splintering of the wood rather than a clean separation.

Thank you Mark - all suggestions welcome. If I take the attitude that I am confident about any of this groups' suggestions being wrong, then I will not learn anything and my bridges will keep failing.

Both the bridge and the top on both these ukuleles are flat, or at least they are meant to be. But I did not use a bridge clamp (I don't have one) - I used a strong elastic band and stand off on top of the bridge to hold the bridge down onto the top while the glue cured. Its possible that the top buckled a little under the pressure, as there was nothing to support the top from the underside.

The observation remains that there was NO glue on the bridge and plenty of well cured glue on the tops so that must have something to do with it. I cannot be certain about the quality of the glue or that it is not as good as it may have been when it left the factory. But it has never failed in other applications in the past, including other parts of these ukuleles.

I don't have the luxury of experimenting with different glues, timbers, acetone, roughening, etc. So I might take ALL of the suggestions on board: clamping, ensuring mating surfaces match, roughening, solvent cleaning and yes Titebond... I don't want to try one thing at a time and risk the bridges failing again otherwise they may one day fail beyond repair.

My first tasks is to build a bridge clamp or three... I am not sure that I will build many more instruments and that's why I don't have that sort of gear in the first place.

Thank you all for being so generous with your replies.

[kiwigeo]

Both the bridge and the top on both these ukuleles are flat, or at least they are meant to be. But I did not use a bridge clamp (I don't have one) - I used a strong elastic band and stand off on top of the bridge to hold the bridge down onto the top while the glue cured. Its possible that the top buckled a little under the pressure, as there was nothing to support the top from the underside.

By applying pressure down on the top you're basically creating a situation where you're trying to glue a flat object onto a concave surface.....probability of a good glue joint is very low.

[Mark McLean]

Of all the variables that you have identified, I think the clamping is perhaps the most pertinent. Bridge clamps are an important tool. Most common clamps are unsuitable for this particular job and the ones specifically made for this purpose are the best solution. Vacuum clamping is also great - but all of these solutions cost money. Where are you located? Someone might be able to help you get this done.

[lamanoditrento]

If you have an air compressor, a vacuum clamp is not too hard too make and venturi value is pretty affordable at about $30.

[NotTheMama]

Mark, Trent,

I live in Canberra - I reached out to the local woodworkers guild but I have yet to meet a luthier here.

A Chinese mail order company is asking $100 for a guitar sized bridge clamp (just a deep throated C clamp) that would need modification to spread the pressure across the bridge. I saw some cam clamps for a lot less, but they are all for guitars not ukuleles.

I am sure that I can build a few ukulele sized cam clamps with bridge adapters to spread the pressure evenly quite cheaply and it may be a fun job - Don't know why I didn't do it before - just lazy I guess. In my defense, I am not yet retired and the ukuleles have taken me years to build because there is a 1,000,000 jigs and tools and templates that are needed, and they all take time to make or source.

Never heard of a vacuum clamp - will look that up.

Certainly making these items should be no harder than the PID controlled electric bending iron that I made to bend the sides - I am quite proud of that one... I might post that one day... (now I'm just bragging ) -

Again thank you for all suggestions

Jorge

PS: Incidentally the ukulele in my profile picture is one of the two ukuleles that I built - photo taken when the bridge came off.

[kiwigeo]

.

A Chinese mail order company is asking $100 for a guitar sized bridge clamp (just a deep throated C clamp) that would need modification to spread the pressure across the bridge. I saw some cam clamps for a lot less, but they are all for guitars not ukuleles.

$100 for a bridge clamp???!!!!

I use Stewmac's bridge clamps. Not the cheapest but they're reliable. Ive used them on a uke build. https://www.stewmac.com/luthier-tools-a ... le-clamps/

[Mark McLean]

I have a few different types, including the aluminium Fox brand one, which is OK and pretty cheap.
https://www.amazon.com.au/Shop-Fox-D280 ... 0000DD1TC/
If you got two of those you would be in business.

If you are in Canberra and making ukes you might want to look up our esteemed colleague Graham McDonald. Among other things, Graham has written a great book on uke construction.
https://www.mcdonaldstrings.com/ukulelebook.html

[kiwigeo]

The Stewmac clamps come in three sizes....I usually manage to cram around 10 clamps into the sound hole of one of my acoustics. From memory I managed to get 4-5 into the sound hole of the tenor uke I made a few years ago.

The longer versions of these clamps have handy little level adjusters......you can get the clamp set up and just touching the top of the bridge before you wind up the main screw.

[Mark McLean]

I usually manage to cram around 10 clamps into the sound hole of one of my acoustics. From memory I managed to get 4-5 into the sound hole of the tenor uke I made a few years ago.

But Martin is known to sometimes tend towards overkill.............

[kiwigeo]

But Martin is known to sometimes tend towards overkill.............

You're one of those guys who puts up photos of a freshly clamped up top...with gaps between the clamps big enough to drive a car through!!! If you can see what's being clamped up then you don't have enough clamps!!!

[lamanoditrento]

But Martin is known to sometimes tend towards overkill.............

You're one of those guys who puts up photos of a freshly clamped up top...with gaps between the clamps big enough to drive a car through!!! If you can see what's being clamped up then you don't have enough clamps!!!

I only worry its too many clamps when you start to get a bit of clamps on clamp action.

[56nortondomy]

There's no reason not to make some clamps that will fit, I made some for a baritone uke, I have plenty of stewmac bridge clamps but the but the bigger ones were too big hence the reason for custom size clamps. I use EIRW bridges on all my instruments and have never had a problem, I always use titebond and always use clamps.
Wayne

[NotTheMama]

[/quote]

$100 for a bridge clamp???!!!!

[/quote]

https://www.ebay.com.au/itm/23460503873 ... BMzMnY4sRg

Rough as guts too! . But I've also seen better less expensive ones - I might just make some though. Why not?

[NotTheMama]

There's no reason not to make some clamps that will fit, I made some for a baritone uke, I have plenty of stewmac bridge clamps but the but the bigger ones were too big hence the reason for custom size clamps. I use EIRW bridges on all my instruments and have never had a problem, I always use titebond and always use clamps.
Wayne

Yep some like these - could even make some wide pads to spread the pressure across the bridge and straddle over the fan brace under.