MIMF

The bridge on one of my ukes has just popped off, taking a single splinter of the yew top with it. I'd glued it using HHG, and the glue adhered well to the yew but I can see that it only stuck to the rosewood in a few places. It was originally glued up about 6 months ago with freshly-made glue. I'm sure I had good, level, mating surfaces.

My home-made bridge clamp is not ideal, but I'm about to modify it to the Mark II version (New and Improved) which might help a bit.

I think I have two options:

1. Reglue as is using fresh glue to reactivate the joint and relying on improved clamping.

2. Shave off the yew splinter, glue it in place. scrape the top to a level surface, scrape or sand the base of the bridge, and then glue up.

Are there other options? If not, which is the best way to go? I've read that rosewood is tricky, and generally I use something else (so far, mahogany, walnut, yew and laburnum). I've only had one other bridge pop off, and that was rosewood on a yew top also - maybe I should take the hint!

got a pic?

The only thought I might have is to ask if the bottom of the bridge was freshly scraped right before gluing the first time? Also, did you pre-heat the bridge to make sure the glue didn't gel before gluing.

Your number 2 choice is my recommendation.

I occasionally have a bridge come off after 3 or four years.

It is easy to say that it was not glued well, or prepped bad, or a bad batch of glue.

If that were the case, then why did it stay in place under tension and use for the first few months or years?

It just happens, glue it back on and make sure you use good technique.

One bridge popped twice on me. I believe I didn't clamp it well enough and possibly the bottom was not quite flat enough. It was a very pretty madagascar rosewood. I replaced it with IR and no problem. Nevertheless I'll think twice about Madagascar R and will probably stick with IR for a while.

Thanks all.

I think I'll go for option 2, and take the opportunity to refinish the top at the same time. This wasmy first attempt at a shellac finish and it's along way from what I can achieve a few builds later.

If the bridge goes again, then it's bye-bye rosewood for this one.

Here's a picture of the uke (pic of the faiure won't help as I noticed it was lifting just before I headed off to a uke festival so flooded hide glue underneath and clamped to keep it together for that weekend, thus hiding much of the evidence).

No reason to abandon any rosewood for bridges; it's been used millions of times, mostly in EIR and BRW, successfully.

It's easy to blame the material or the glue, when 99.99% of the time, it's simply operator error(in other words, -we- messed up), either from a not-ideal surface, not ideal fit, glue too cold, worked too slowly(allowing the glue to cool) or not enough/too much clamping pressure. Sometimes, a combination of the above.

I had a couple pop off with HHG and other glues.
I think I was not quite getting a good enough fit. No pop offs in the last several guitars with HHG.
I use automotive feeler gauges all around the bridge until the .004 won't slip under the bridge with a little pressure.
Seems to work.
Also, an In-law of mine who is a well known luthier for many years gave me a tip. He uses a utility knife blade and bends it like a scraper and puts a very slight cove in the bridge so the outside edges contact a little before the middle. Swears by it. Haven't heard that one from anyone else.
I have moved to southern Arizona so the Hot that goes into HHG is a lot easier in the warmer months here. I Had to do a lot of tricks to delay gelling up in Spokane, Wa.

Mike Ryan wrote:Also, an In-law of mine who is a well known luthier for many years gave me a tip. He uses a utility knife blade and bends it like a scraper and puts a very slight cove in the bridge so the outside edges contact a little before the middle. Swears by it. Haven't heard that one from anyone else.

I thought that was quite a well known trick. Helps stop the bridge base going convex with water-based glues. Same idea as leaving a wisp of daylight in the middle when joining panels, which then expand to straight rather than convex when you apply the glue.

Thanks for the well-known trick (which I hadn't yet come across). I'll use a single-sided razor blade as the bridge width is less than 1 inch.

As for Mario's list of sins, I probably committed them all. Will try harder next time.

I know one problem that I have had with fingerboards, but I don't know if it possibly extends to bridges glued with HHG - I glue fingerboards with epoxy and I have had a few just come loose in a fairly short amount of time because they were over-clamped. The fingerboard surface in the region that came loose just looked glue-starved. Could the same thing happen with HHG? I'm becoming a fan of fairly lightly clamped fingerboards, and can see the attraction of the mythical rubbed joint for bridges too.

Hi Jim,
I've done the rubbed joint for some bridges using HHG and have had good luck with it. I think the glue consistency is important when doing this. I like it to be like fresh honey - thick enough to have glue under there when the water leaves, but thin enough to allow it to squeeze out around the edges.

Jim, with epoxy, you need to "tooth" both surfaces. Epoxy bonds mechanically, and is the only adhesive that requires toothing. You can then clamp it tightly, and know that you're still getting good wood to wood contact, maximum strength and minimal creep. If you simply clamp lightly with smooth surfaces and epoxy, you'll have a relatively thick layer of epoxy separating each surface...

Rub joints only work if we have two perfectly mated surfaces.

Mario Proulx wrote:Jim, with epoxy, you need to "tooth" both surfaces. Epoxy bonds mechanically, and is the only adhesive that requires toothing. You can then clamp it tightly, and know that you're still getting good wood to wood contact, maximum strength and minimal creep. If you simply clamp lightly with smooth surfaces and epoxy, you'll have a relatively thick layer of epoxy separating each surface...

Rub joints only work if we have two perfectly mated surfaces.

Mario,

Thanks for that reply - I wasn't paying attention. I'll give the toothing a try on the next one. I don't think my clamping is too overly light, as I don't get a sense that there is a visible glue line between the fretboard and neck (lloks clean to me), but you know this business a thousand times better than i do.

Mario, How much tooth are you talking about. In other words, are you doing this with coarse sandpaper or actually using a toothed plane?

West Systems recommends 80 grit surface prep.

I ground the end of a single-cut file so that the teeth are exposed on the end, and use that. It's a bit more "tooth" than with 80 grit, but doesn't produce dust(and gluing dust to dust can't be good...). It's worked perfectly for me....

Can take photos if it isn't clear?

The following advice is for epoxy-glued fretboards, NOT for bridges.

Here we go. I simply ground the end of the file flush, to expose the teeth. In use, I have to hold it at the angle of the teeth(more or less), and drag it lengthwise while applying downward pressure. How much pressure will depend on the wood and on how sharp your file is. I only make one "pass", then move it over, make another "pass", until I've toothed the entire width. I don't try for a cross hatch pattern. I'll tooth the neck surface exactly the same manner and direction, and will do this right before gluing, after the epoxy is actually mixed.

In the final photo, hopefully we can see the amount of "tooth" I cut into this ebony fretboard, and note how it produces clean shavings and little dust.

OK. Thanks.

Do you tooth the neck blank as well?

Nice photos Mario.
I suspect that West Systems recommend 80 grit sandpaper as it's a common easily available consumable for most users of their product and is the finest grit which will give acceptable results, where as a toothing blade or file would be considered a "specialty" item.
The reason for toothing epoxy surfaces is that unlike other glues, it is primarily a cohesive (meaning it sticks to itself), as opposed to an adhesive (meaning it sticks to other materials). Most glues are adhesive and only work properly applied in small films between two surfaces, and rapidly loose strength if any gap filling is attempted. Epoxy is only a very marginal adhesive, but due to its cohesive strength, it can be used to mehanically lock two toothed surfaces together. Imagine tiny little dovetail joints <g>