Official Luthiers Forum!

I haven't been building the last year or two. Recently I decided to finish up a project I had going when I stopped. This is kind of an experimental project I had going. It's a variation of the saprano type 12 string guitars that Veilliette and Emerald Guitars are making. I made up the bridge and glued it on early this week. Yesterday I roughed in a saddle and nut to string it up and start setting it up. Just as I was tuning the last set of strings to pitch the back end of the bridge popped up. The break was clean. The pic below was taken just after removing the strings. As you can see I'm using 6 pins, two strings to a pin. Slotting the bridge, notnthe pins, which I would guess is why the bridge only lifted on the back end while the string were on. My gut tells me my glue joint was not good or I didn't leave the clamp in place long enough. I used regular Titebond for the bridge, which I've always used in the past. Any thought before I clean it up and try to glue it back on?

_________________
Kyle

I don't see much glue residue at all.

Is the bridge fitted to the top meaning that with only light finger pressure it's down everywhere with zero gaps? Also did you by chance give both freshly prepared surfaces a scrape with a single edged razor prior to clamping? Was there squeeze out, is the glue less than one year old per the date code?

Is that a bridge rabbit that I see which is a good thing if that's what it is? When you clamped this Taylor style bridge with the long back end is difficult for many bridge clamping cauls to push downward on because the cauls don't hit the back edge. What kind of caul did you use?

Is the top spruce and is that stain that's visible under the bridge? Bare wood under the bridge is always desirable.

Also any calculations of the collective tension on all these strings tuned to pitch and per the various gauges you are using, this one may have a lot of tension?

Cool looking instrument and beautiful lines, modern and cool.

I did fit the bridge to the top by laying a price of 120 grit on the top and running the bridge over it. The fit looked good. I sanded both surfaces prior to gluing but did not run a razor blade over them as you mentioned. I had plenty of squeeze out. Do you think I could have applied too much clamping pressure? I clamped using bolts through the 1st and 6th pin hole and a caul that fit the bridge fairly well, although didn't quite cover the back side of the bridge. I will make that adjustment. The culprit is quite possibly the age of the glue. I honestly don't know when I bought it. Since I've not done any work in a year or so, I'm saying it's at least two years old, if not more.

I don't recall what the string tension was as I calculated it when going through the design stage. I'm sure I have it in my notes somewhere but I do recall the tension not being much higher than a standard 12 string. The heaviest gauge string is .042 and the lightest .0085.

Thanks for the help. I will keep all of your advice in mind when re-gluing.

_________________
Kyle

I'm seeing not enough glue and contaminated glue surface on the top. Notice how the center of the bridge looks dry, the glue pattern and the stain pattern on the top kind of match up. The glue residue on the bridge shows spruce dust, not fibers. Better prep on the top, clean the bridge, fresh glue and I think you'll be golden.

Like Hesh said, cool instrument. I'm a closet zero fret fan, like them but don't use them.

Steve

Notice the only glue patches on the bridge match up to the only spots without stain? The stain is a contaminate in the joint and must be removed.

_________________
Brian

You never know what you are capable of until you actually try.

https://www.howardguitarsdelaware.com/

Given the OP is the finisher, we have the option to ask a few more questions so that we may avoid having to make imperfect or unwarranted assumptions.

For Mr. Barbour:

- Please describe the full finish schedule and materials used. Specifically,

o What dyeing or staining process was used (e.g., water-soluble dyes applied wet-on wet; shellac-carried dye over sealer, etc.)?

o Was it done directly on the raw wood or over a sealer/barrier coat?

- Was a surface energy test done on both the light and dark areas of the bridge patch before gluing?

_________________
For the times they are a changin'

- Bob Dylan

You have gotten all the advice you need but I just want to say, that's one cool looking instrument right there!

I am in total agreement with Howard get down to wood stain or dye will keep the glue from penetrating the wood cell

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for the help from everyone. Most of this I should have known already but I suppose this is the best way to learn something. I will update after I make the necessary changes. After hearing the sound of the first couple strings going on I am very excited to hear the final results.

_________________
Kyle

Again, do a check with distilled water droplets on the patch - if the droplet does not spread immediately/just sits on surface, likely there is still sealer or other contaminant....which is why I asked about whether the wood was sealed before tint application.

_________________
For the times they are a changin'

- Bob Dylan

I've never done a steel string, and only made 1 1/2 scale classical. I did notice right away that the glue didn't stick because of whatever was coloring the wood. That is the question the OP asked.

But I'd like to know why the bridge isn't glued on BEFORE finishing? That's what I did on mine. With a HHG rub joint because I don't have long arch clamps.

But then I don't know anything. But that doesn't ever stop me.

Also how does a bridge with pins going all the way through the top come all the way off? I guess I could see pulling up on the bottom, that's what my 40 year old or more classical did from sitting in a hot closet one summer, even though it sat in there for 30 some years before. It just pulled up some, it didn't snap off. Now it is hard to tell, but I know that it needs to be fixed. Only one of its problems.

_________________
Why be normal?

Experiments at the Forest Product Lab in WW 2 showed that sanded surfaces glue much less well that planed ones. If you look at a sanded surface under magnification it looks like a plowed field, with dust in the scratches. Iirc, #220 paper leaves scratches that are about the same size as the cells in the wood, so going that fine (but no finer) helps. You still have the dust, though, and even blowing it off with compressed air doesn't get it all.

Yes to getting past the stain. Next time I'd mask that area before staining, if only to reduce the effort of cleaning it up and the amount of wood removed.

Ken:
Pins don't hold the bridge down, they just keep it from flying off. I saw a Spanish 10-string cittern yesterday with a tieblock-style bridge to get the break angle over the saddle, and a tailpiece to take up the tension. The bridge had peeled up simply from the torque.

So what is a good practice for getting rid of dust then?

Naptha (mineral spirits) does a good job of picking up dust (at least in my experience). I use it when sanding fretboards to pull the dust from inside the pores of rosewood. I also use it when doing bridge reglues to clean the area before I glue it back on.

Avoid sandpaper so you don't make it in the first place?