Official Luthiers Forum!

Show us a photo of the bridge bottom and its footprint on the top after the failure.

With HHG a failure could be one or more of:

- poor fit of surfaces
- contaminated surfaces (old glue, finish)
- joint not clamped quickly enough
- joint not clamped effectively (eg bad cauls not providing pressure in the right spot)
- glue temp jssue

Bob’s on the money, a photo of the area will provide useful info to find the cause.

On the temperature question - make sure you measure the temperature of the glue, not the water bath it sits in. In my glue pot, the glue will be 140f when the water bath is closer to 175f. When the water bath is at 140f, the glue is barely 120f …

Thanks, those are good inputs. Will be a little while, but I'll post the requested pix pretty soon. (Have a little surgery to recover from first.) As far as the temp, I was using an IR gun and measuring the outside top of the little metal glue bottle. Next time I'll use an in glue analog thermometer. Plus, I'm gonna practice some routing on another guitar body that's for experimentation. I think that's a likely issue, and I'm always nervous to rout something I haven't done before.
Cauls..I was just using the maple bridge backing piece. If that's not good enough, I may need to make a caul, the one I have seems to fit a little further toward the lower bout than these clamps require.

Appreciate the helpful feedback. Roy

Yes, you need a substantial inside caul to clamp against for successful result - this is also true if you were gluing the bridge with Titebond.

If you try to clamp a relatively rigid bridge against a thin maple bridgeplate glued to a thin soundboard the whole assembly will flex under the clamps, causing many areas of poor contact and probably just a couple of areas of good contact, immediately under the clamp feet.

Can you also tell us what ratio of dry HHG to water you are using?

As to ratios, No, I just made sure I had enough water to cover the 'crystals' didn't know there was a ratio I should be using for the HHG. Pls advise. OK, will start working on a caul that covers the right region. Could be the one I have fits better than I originally thought. Three white spots are from the Marine JB weld filling in divots.


I need to learn to do this properly, and this guitar is good for learning better processes; played well, looked only fair.
I just used heat gun w aluminum covered cardboard blanket protection. Would it have come off cleaner if I'd sprung for a dedicated bridge heat blanket?

Thanks, guys for helping me understand the errors... Roy

Ratio is usually somewhere in the ballpark of 1:1.8 or 1:2 glue to water although different glues do vary so check with your supplier.

Scoring the bottom of the bridge is a no-no with hot hide glue or aliphatic glue.

Where you had wood transfer, you had a good glue joint. Where you didn’t, it looks like the bridge barely touched the top, if at all. Either the bridge wasn’t fit well to the top, or it was insufficiently clamped, or both. As Barry said, don’t score it. Hide glue doesn’t fill gaps. The fit has to be perfect. When you think you have everything right, clamp it up dry and use a .001” or .002” (or a piece of copy paper—about .003”) feeler gauge to probe from all of the edges to make sure you don’t have any gaps.

I warm my bridges with a heat gun before gluing to give me more time to put everything in place. I use a little iron, some water, thin spatulas and a lot of patience to take off bridges. A heat blanket would probably be at least as good. The finish doesn’t forgive heat gun mishaps. I wish I didn’t know that.

Hide glue forgives slight variations in mix ratios. It doesn’t forgive overheating (aka “cooking”). I use a 135F water bath with my HHG bottle in it. It liquifies in the 100-120F range. Being closer to 135-140 gives you a bit more working time, but heating the bridge does that, too. As long as you clamp it before it gels, you’re good.

OK, those are all helpful, I'll think a bit and come up with a couple more questions pretty soon, like fer instance:
Whether I have other options for treating the bridge bottom besides just sanding it, like a layer of epoxy first to fill the crosshatching?
Assume I should try to refill the wood divots back into the cedar as best I can? And if I still have some variations, is it ok to fill them like I tried before to make it all flat?
And the HHG itself, expect I should mix up a new batch, if I get the ratio and temp right, should the viscosity feel more like other glues, this stuff seemed quite thin to me. I will use a caul (duh).
And then do I have to get rid of all the residual HHG so both surfaces are clean? I guess I'm looking for the best rework process.
Thanks again. Roy

Do not use epoxy or JB Weld, or any other type of glue to fill gaps in your top or bridge. Only use matching pieces of wood (spruce for the top, ebony/rosewood for the bridge). Hot hide glue sticks best to wood. Not so much to other glues.

For HHG, the claim is (when you have it right) that it will run off the glue brush in a little rivulet as you lift the brush out of the reservoir. You might like it a little thicker where it will easily drip but not run. If it’s thicker so it won’t drip at all, it’s probably too thick. I mostly use the 192g from LMI. The instructions have varied over the years 1.8 to 1.9 ratios water to glue by weight. When I do a bridge, I use 315g at a 1.8 ratio. It doesn’t run quite as easily. 192g will work in this application, and, if you need to rework it yet again, will be a bit easier than the 315g.

One of the nice things about HHG is that it reactivates and sticks to itself, so you don’t have to remove it all.

If you are both lucky and good, with a chisel you will remove the wood that stuck to the bridge and, using HHG, glue it back into the divots on the guitar top. Where you can’t fill with the wood you have on the bridge bottom, you’ll chisel some cedar splinters from a scrap piece of cedar and glue them piece by piece into the gaps on the guitar top. After all of the divots are filled and the glue dry, you’ll put some stickit sandpaper on a small sanding block and make the bridge footprint on the top smooth and regular.

At this point, when I do it, I take a piece of stickit sandpaper cut to the bridge footprint shape and stick it to the footprint. Using whatever I can manage to hold the bridge, like something that fits the saddle slot to use as a handle, I sand the bridge bottom against the bridge footprint with very small strokes (to keep the action very local) until all of the pencil marks I put on the bridge bottom (and those extra grooves) are sanded off. Then, I mark it again and sand it clean again just to make sure. I remove the sandpaper and test my fit with the feeler gauges. Perfect is good enough. Dry clamp it and test your fit again. Keep working it until you get it right.

If the channels on the bridge bottom are deep enough that sanding the bridge to fit will make it too short, then make another bridge.

If you touch it with anymore epoxy, I won’t respect you in the morning. Think of the epoxy as a contaminant that will be in your way if you have to work on it again. Note that there doesn’t appear to be any adhesion to the epoxy fill that you used before.

This will take a lot longer than you want to spend, but each time you do it, it gets easier and takes less time. Enjoy the process.

Or, we could both get lucky and someone will suggest a much easier way to do it.

I was seeing cedar—if the top is spruce, use spruce for the fill pieces.

Re: viscosity of warm hide glue, sometimes there is a temptation to dilute it a little in the hope of more open time, and even some books that recommend this, but I think thicker glue actually seems to retain heat better/cool to gel point slower. I’ve not done any testing to verify this, it’s just a casual observation.

I want to first say sorry you're having to go through all this- this seems to be the dues we pay for excellence.

What method of work are you using to prepare the gluing surface of the underside of the bridge (and all of your glued surfaces)? Could surface finish/ preperation be a possible a contributor to the adhesion problems?

I don't think you would want to remove any wood from the top to accommodate the reglue of the saddle. Carefully sand and chisel the old glue away. I use shop-made small, hard sanding blocks from scrap hardwood that make level sanding more joyous (if there is such a thing).

EDIT: I just read the new posts from after I started this reply.
Rough surface to provide "tooth" for yellow wood glue is a myth and was proven in the wooden airplane construction era. Freshly scraped (with a wood scraper) is the absolute best while fine smooth sanding will suffice. Perhaps we have found the cause and solution to your delams?

_________________
Measure Twice,

Karl Borum

Beau Hannam has an excellent video showing you what the proper viscosity of HHG looks like:
https://youtu.be/VfCI95jEBpQ?feature=shared

_________________
Measure Twice,

Karl Borum

Being neither lucky nor particularly good in the skills department, I tried peeling the cedar off the back of the bridge. Got nothing usable. After thinking awhile I decided to do this:

I'll look at the fit a little harder tomorrow, but it seems pretty darn good to me today. I had to go around 0060" deep to get past the deepest divot I had filled with epoxy. Did a little pencil shading to see the flatness of the depression, which seems good. The beveled edges are not all perfect, as my usual but it "snaps" into place quite nicely.
Thought I'd see what opinions I get for this approach. Between the modified caul for more complete coverage, eliminating the crosshatching and the complete removal of all divots with a new piece of cedar, I'm cautiously optimistic. I appreciate the inputs on HHG viscosity. I'll toss what I had originally used and make a new batch.
In case anyone is wondering I have a 25' radius on the top, and a couple of sanding cauls to get the bridge to sit flush with no rocking from either end. I'll check with feeler gauges after matching the patch to it's surroundings. The patch is a bit proud now, which is what I wanted. Roy

I really thought this would work...


It pulled loose shortly after tuning it. I left the clamp setup for 2 days this time....Also ordered some different hide glue from LMI.ld be here before I try again. I bought this HG from Lee Valley, and it didn't come with the 1.92 spec, (or any other number that I found) and still seemed thin to me, so I may be mixing it wrong. Temp was just under 140F.

i'll pull it off and show the failure pix as soon as I calm down enough to want to share another view of misery. I'm quite nervous about the same process on #4 now. Almost feel like fish glue worked better for me the one time I tried it, especially if I couple it with the HHG clamping setup using the three screw clamps. Roy

Hang in there! Did you make an interior caul? These failures happening so rapidly after initial stringing suggest either poor contact between surfaces or clamping after the glue has already gelled.


Sent from my iPhone using Tapatalk

You can slightly warm your top, and even your caul, as well to increase the HHG open time a bit.

Maybe a "pre-flight" checklist would be helpful?

You've got this.

_________________
Measure Twice,

Karl Borum

Just looked in here for the first time in a while and now it's about bridge reglues? Might want to start a separate (new) thread so that the contributions of others can be found via the search function.

Also some quick thoughts from me.

1). Never leave masking tape on any guitar finish for more than a day and even that is long. Some adhesives and tape will react with the finish and then you are in deep doo doo..... We hate the blue tape for this reason and instead use quality 3M masking tape but we only leave it on for a few hours if that.

2). Don't use HHG unless you have done enough dry runs to be capable having everything where you want it, all clamps in place in 15 seconds or less. It will bite you sure as shootin if you do not observe the short open time.

3). Clear bridge patch to close to the perimeter.

4). Scrape bridge gluing surface within 15 minutes of gluing.

5). Bridge should fit top well with wings completely down everywhere with only light finger pressure.

6). I preheat my bridges in a 600 watt microwave for 12 seconds or so until they are hot to handle and I have to juggle it a bit carrying it back to my bench.

7). Have done dry runs with the clamps and have the clamps prepositioned so that you only need to crank them down and can have it all clamped up in 15 seconds.

Seriously though if during dry runs you can't observe the 15 second things use Titebond original. Lots of bridges have been glued on with Titebond. It's not perfect and it does cold creep but HHG will come right off if you do not observe its requirements.

_________________
Ann Arbor Guitars

Ok, pretty clear what happened...

Open to inputs, but what I see is that my HHG attachment of the plug was crap, and although I felt good about the surface match, the left side in the pix shows little to no attachment until the end.

Barring inputs that dissuade me, I'm inclined to use a "high temp" epoxy for the next plug, but not totally clear about how to mate the two more exactly. I have a 25' radius on the top and a sanding caul to match for the bridge. That felt very good to me w no rocking in any direction. So I need to follow Bob's advice more completely with feeler gauges, but correcting what that tells me is a new skill I need to develop.
.
And as for a better titled post, I'm not against it at all, just my computer skills on this forum aren't the best.

The clamping technique worked great, my attach time (no stop watch, just nerves) was well below 15 seconds, I'd guess mebbe 5-10 max.
Still not comfy with the HHG viscosity I'm getting. Will not try again til I get the shipment of 1.92 stuff from LMI. I used three different thermo measuring devices, tossed the original one as too inaccurate. Remaining 2 are sorta close to each other, and I stopped when the immersion temp read about 140.
Again, I really appreciate the inputs. Roy

Hesh,
Not sure I understand #3, are you saying make the next patch wider all the way to the front part of the bridge?

How about fish glue for the patch?

For heating I was just using a heat gun and an IR thermometer, I did scrape, but only the bridge. Since you say scraping the soundboard can be done before the clamps are totally in place, I can do that next time.
I'd like to stick w HHG for the actual bridge attachment, primarily because I have another guitar out coming out of lacquer cure and I want to learn on this one. If what I learn is that my skill set works best with fish glue, I'll use that instead. I tried it once, and although my attachment process wasn't the best it held pretty darn well till I got sick of looking at it and took it off; (on this poor guitar) so now I'm at four removals.

And yes, I had a caul I'd made and forgot about. I used it this time.

Not the quickest learner,, although I was the 3rd grade spelling champ. Roy

Tried to start a new thread titled HHG Bridge Attachment for future searches. Got some error message that my IP has been blacklisted.

Roy

Most of your bridge adhered pretty well. So, it’s likely a question of getting the fit better where it didn’t. I can’t tell about the patch—I hope you glued that first and then fit the bridge and top together with the patch installed. Don’t use any epoxy. If your repair fails with the epoxy, then you have to get the epoxy out to repair again. With HHG, you can keep doing it until you get it right.

The stickit sandpaper in the bridge footprint is the easiest way I know to fit the bridge to the top. Chalk fit is better, but harder to do. Practice patience. It gets easier with experience.

Now, about that patch: When you first posted that, I couldn’t think of a positive reply. I’m going to try now. You have cut a significant part of the long grains that give your top strength and hold the bridge down against the string tension trying to rotate the bridge up. Where you need the most strength along the grain, you now have an endgrain joint for a good part of your top thickness. You should keep working on this bridge project to get the experience of fitting and gluing the bridge. But, your bridge will rotate and the joint will eventually fail here even after you get it fit properly. In the long run, you will probably elect to retop this guitar.

Note that cedar is relatively weak across its surface and will sometimes delaminate within itself so that a bridge will come off with no glue failure and cedar transferred all across the footprint. Redwood can be like that, too. So, even when you get it perfectly fit, cedar can disappoint you on a steel string guitar. Extra light gauge or silk and steel strings can be your friend with cedar tops.

Do you use any silicone in your shop?

_________________
Jim Watts
http://jameswattsguitars.com