How far to scrape top wood underneath the bridge?

[Alexis Magni]

Hey Guys!

First post here in this community. First I´d like to say I´m a fan of Frank Ford and his ways to tackling issues on guitars. Real clever stuff.

I´m a beginner Luthier, learning from my own mistakes, as I have unfortunately no other way of learning.

I decided to practice on my own cheap Acoustic Bridge Removal, so I did. The finish pulled up, but that´s a question for another day.

The main question is, some wood stayed glued on the Bridg. So the top is missing some grain. How should I approach this? I know the Wood has to be flat before I reglue the bridge, but should I scrape the wood around until it´s all level, lowering the overall thickness of wood on the area, or should I fill the gaps some other way?

I hope you guys can help me on this one

Thank you!

Alexis

[Roger Häggström]

Using hot hide glue (in my opinion the very best glue for a bridge), missing wood can be filled in with Hot Hide Glue mixed with saw dust. Plenty of wood "paste" to be leveled with some scraping and sanding when dry, the "paste" will shrink a lot when drying. HHG don't glue plastic like super glue with saw dust or other types of modern fillers. The top and bridge must be clean from any modern glue, HHG needs clean wood to wood with a tight fit to work.

On a newish cheap guitar the old glue is probably something else than HHG and the top is probably a plywood. In that case slow setting epoxy glue is the easy way out. That glue will fill any voids under the bridge, so there is no need to fill in the voids.

[Alexis Magni]

Thak you for your response!

I have no experience with either Hot Hide Glue or Epoxy. I Feel that Hide Glue is a Glue I want to get experience on, since it´s so well regarded. But I Fear Epoxy, I don´t think I will get near that thing until I have a lot of experience, and I also don´t like the idea of a glue that if something goes wrong, it´s almost impossible to remove. I need this safety since I do so many screw ups :)

About the Plywood top, I should have mentioned that I have also tried on a Cedar Top Classical Acoustic from a friend, which I just removed the bridge. The Bridge had collapsed, and he had it left to gather dust. He will find someone to make him a new one, since I don´t have the proper equipment for that job.

You can see by the picture that some Grain stayed on the bridge. I tried but it´s impossible to remove it without damaging. How you you approach this job?

[Roger Häggström]

Epoxy is a last resort for dirt cheap guitars not worthy of hot hide glue. Go for the hide glue and learn how to use it. It's not difficult. Looks like some kind of modern glue on that bridge. Probably aliphatic glue like Titebond, but it can be something else.

The standard procedure is to add heat to the bridge, either with a small iron or a heat lamp with some aluminum foil to cover the top around the bridge. When heated, I then use two spatulas to pry the bridge off. I do one pass around the rim just getting the tip of the spatula under the bridge to get a start and minimize the risk of getting a splinter on the top outside the perimeter of the bridge. I press the first spatula into the glue seam using a rocking movement side to side, and then the other spatula on top of the first a bit deeper the same way. Having two spatulas protects the top when working with the spatula on top and gives a bit more leverage to lift the bridge. This I do over again to the middle of the bridge from one side and to the middle of the bridge from the other side.

Doing it this way following the glue line and protecting the top with the other spatula it is possible to get the bridge loose without cutting into the top. But sometimes the top have a severe run-out and it's very hard to get it loose without getting splinters under the bridge. When this happens, attack the bridge only from the other side to the run out on one side of the top and do it the other way on the other side of the top. The top is bookmatched with the same wood run-out but in different directions in the two half's of the top.

You can dip spatulas in water now and again to soften the glue if it react to water, but I usually do this job with only heat and force. Water may damage the lacquer.

[Roger Häggström]

If ithe cavity under the bridge is deep and/or big, a small cleat can be cut in the same wood and grain direction to fill the void and glued in with HHG.

[jbbancroft]

You don’t want to thin the wood anymore on the top. If you can remove the splinters off the bridge and reglue them to the top, is best, or fill in the missing wood with wood. Superglue and a caul will work good to glue missing wood. 

Then you can level the area and reglue bridge with hot hide glue.

Jim

[Russell Vance]

Hi Alexis,

Fortunately you do have other ways of learning: to understand how glues work and which ones are best for what job you might like to check out the comprehensive test and evaluation contained here:

https://www.popularwoodworking.com/woodworking-blogs/the-great-glue...

There are many other practical and scientific glue tests available which helps ovecome old fashioned prejudice and folk lore advice which permeates all aspects of working with wood and similar organic materials.   For instance, Hot hide glue is particularly unsuitable for gap filling compared to a job specific gap filling epoxy.    In this case the condition of the repair dictates which glue to use - many glues will do a fine job on a clean mated joint whereas the same glues may fail miserably when use on a rough tear-out joint.   Other examples are Titebond Original works for bridges as does HHG, however, Titebond 2 and 3 has less creep resistance and will fail in the same bridge application.   Go study the tests and application freely available on the web as they contain much of the information you will need in your future luthiery.

Good luck on your journey.

Rusty   

[Roger Häggström]

So it's that old glue war again? I will only state that hot hide glue is not folklore or old fashioned prejudice, it's simply the best wood-to-wood glue to use for musical instruments in so many ways. Also the easiest glue to use when you get the hang of it and the learning curve is steep.

[Russell Vance]

Roger, 

No its not "that old glue war again" otherwize I wouldn't have wasted my time directing a new forum member to adopt an educative rather than opinion based approach.  To adopt the position that there is only one dead animal glue solution to the myriad problems facing the modern luthier is not helpful.   

As I said,  overcoming prejudice and  folk lore is a key aspect of progress and hopefully science and practical testing and evaluation may be helpful here, especially for new guys and easily influenced amateurs.   Simply regurgitating an opinion is no substitute for real life testing at a professional level.

Furthmore, the solution to this particular problem is either epoxy or a medium/thick density superglue (and apropos my previous, there are many different types of superglues - Fastcap 2P-10 is our choice for woodworking application).    The reference to Titebond was specifically used as an example of how understanding glue technology is often critical to outcomes.

I'm also keen to remain in business as a professional luthier, artisan level guitar builder and national repair and refurbishment center so I will agree to disagree with JB and ignore his advice to not bother learning technical data and learn by having repairs and processes fail.

My input to this post ceases now. 

Regards,

Rusty

vancecustomguitars.com   

 

[jbbancroft]

Rusty, 

with all due respect l take you don’t do much work on acoustic guitars?

maybe on a really cheap guitar and you never expect to have to remove the bridge in the future, you could use epoxy or superglue. But Never use it on a quality instrument.

concerning reading technical data, that is ok too, as long as it doesn’t get you too confused.

nothing better than actual hands on experience with glues. 

There is a lot of information that hot hide is still a superior glue to most more modern glues, especially in musical instrument repairs.

Jim

[jbbancroft]

Another fact. If epoxy or superglue is a better glue for gluing on bridges why don’t instrument manufacturing companies use it instead Of aliphatic wood glue or hot hide glue?

Jim

[Russell Vance]

i said  i wasn't going to continue engaging with this fuitile post but enough is enough.  We are a contracted repairer to the largest acoustic instrument maker in Australia and if you noticed the recent post on replacing the bridge for a $40,000 Martin which we were tasked with you wouldn't question my credentials. 

Also, the reason that major manufacturers don't use epoxy or superglue  is that they are not repairing a tearout bridge situation  - which goes to my point of using a glue that is appropriate to the situation.  Which also goes to understanding what it is we are looking at.

Similarly the OP said he was doing a cheap repair on a cheap learner,   The Epoxy or Superglue suggestion took into account his learner status and the cheap guitars.  

I'm definitely done here.

Rusty

[jbbancroft]

On this instrument and a bridge re-glue, hot hide glue wood be my glue of choice, not Titebond.

the thing is you want all the gaps (missing wood on the top) repaired before glueing the bridge on with whatever glue you decide to use. You want to glue the bridge to a flat, clean, no gaps top.

personally I would gluing the missing wood splinters to the top with a superglue or epoxy, as the glue would be less likely to release if heated for future bridge removal.

some added advise. To remove a bridge cleanly you need the bridge hot enough, water, and a thin spatula. Once the bridge is hot enough, or you think hot enough, dip spatula in hot water and work around the bridge perimeter. If it doesn’t want to penetrate the joint, you may need more heat. Also watch for top run out during removal. You will generally get some fine wood fibers from the top still glued, these can be scraped off.

Now if someone glued the bridge on with epoxy, in the past, you may as well set up a router to grind it off.

 You also don’t need to read all the technical data about glues.  Just get some glue and start using it, you’ll learn a lot by using it.

Jim