Official Luthiers Forum!

I've done two. Both with 192gm HHG. One held, one didn't. Same process I always use, scrape the top, scrape the bridge bottom, apply HHG to both sides then clamp overnight.

This one released from the torrefied red spruce and pretty much all of the glue is on the BRW bridge. This bridge was put on about 6 weeks ago.





I'd be interested to know what others are doing and have experienced before I put this one back on.

_________________
Steve Smith
"Music is what feelings sound like"

Wow! I don't have any experience to offer but it looks to me like the glue up was done very well, the glue just didn't stick to the spruce at all. I'm following this with interest.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Interesting!

Sent from my SM-N960U1 using Tapatalk

_________________
Pat

How long did you wait between scraping the top and gluing? The process changes the chemistry of the wood, such that it has naturally lower 'surface energy' than non-Torrefied wood. Even with normal wood you get a stronger glue bond when the surface is worked within 15 minutes of gluing, and I'd expect this to be even more the case with Torrefied stock. Also, the margin of finish you're leaving around the edge doesn't help, particularly if, as it seems from the photo, you're not making a bit of a rabbet on the edge of the bridge to get the wood surfaces into close contact. What you lose with Torrefied wood is some of the already low peeling resistance of the glue line, and adding in a stress riser along the back edge of the bridge doesn't help.

Time from scraping the top to gluing was no more than 30 min but probably less. I scrape the top and bridge, get the clamps in final position then glue it.

Not sure what you mean about margin of finish? The dark line around the edge of the bridge is the rabbit which is about 50 thou. I index the bridge in place with two 3/16" stainless pins and mask with frisket so that the finish extends under the bridge about 30 thou. I may not have scraped enough since this was a new top with frisket mask and not a repair.

_________________
Steve Smith
"Music is what feelings sound like"

I was able to speak with John Hall about this and besides some of the other steps we've discussed, he emphasized that for torrefied tops the bridge needs to be clamped for at least 24 hours. I think I took this one out of the clamps in about 12 hours as I was in a hurry to get it finished.

_________________
Steve Smith
"Music is what feelings sound like"

I see something here
A LIGHTLY CHAMFER THE EDGES SO YOU ARE SURE YOU ARE WOOD TO WOOD
b SAND THE AREA BEFORE GLUING 80 GRIT
c APPLY GLUE TO BOTH SURFACES
d WORK FAST
e CLAMP FOR 24 HRS

The finish is working like a shim and you are relying on the glue only you want to be sure you have wood to wood contact . DO NOT OVERTIGHTEN the clamp

_________________
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

I have been using LMI white for bridges on T-Top guitars. I use fish glue for the bracing as I have heard from respected luthiers. I have my own working hypothesis on why that works well and of course I am going to state it

Fish glue has a long open work time, pot life. T-Wood is very hydrophobic. So the long open and long cure time of Fish glue, and to some extent AR glues especially TB extend, so it has plenty of time to wet both surfaces and stay wet long enough to get into the T-wood fibers and then chemically bond. HHG gels really fast.

That's my working hypothesis and I'm stickin' to it

All the bracing and bridges get clamped for 24 hours.

John, Thanks for jumping in here. I already do a, c and d so it looks like b and e are what I need to add to my process. I scrape but have never sanded, especially with 80 grit, but I'll give it a try. And I usually clamp overnight so about 12 hours, I'll give it a full 24+.

_________________
Steve Smith
"Music is what feelings sound like"

Wow the forensics here look excellent Steve, great use of the vast majority of the foot print, complete glue spread and a goodly amount of glue too. I'll show this to Dave and see what he thinks. It does raise questions about gluing to these tops for sure.

See my comments in the 'Torrifying Tone Wood' thread linked below re: issues with bridge retention on highly torrified tops.

viewtopic.php?f=10101&t=53918&p=708865&hilit=torrified+tone+wood#p708865

In summary, we were able to keep bridges on the Martin D-35 Anniversary Models with VTS European spruce tops without issue during a time when the factory and many of their repair people were not able to do so. After what was reported to us as 'numerous bridge joint failures' of both production and repaired guitars, Martin opted to re-top warranty bridge repairs on those guitars with a Level 1 top (lowest level of torrification from supplier) and stopped using highly torrified tops on any of their instruments.

At Martin's request, we documented our process and passed it to them, but I never did see any feedback as to whether the repair people or production line altered anything with regards to their VTS system process for bridge glue-up beyond what was already mentioned above.

The method used at Greenridge was a variant of our standard bridge reglue: meticulous surface prep, a light scrape of the spruce patch at the last possible moment before glue-up, fresh standard mix 315g HHG, heating the bridge to 150 deg F (entire bridge - not just a blast of heat on the glue surface), glue applied to both surfaces, then a third, heavy coat on the patch just as the bridge went on. By the time the clamps were on, the bridge dumped heat into the glue patch and the usual five-clamps went on for a 6-8 hour clamp. As mentioned before, the major difference with 192g and 315g bridge glue-up is the ability to load the joint in as little as 3-4 hours with the higher gram strength glue.

I am headed back to Greenridge over my next three-day weekend to continue helping with the post-COVID dig-out... four neck resets and an early 2000's stump-wood Beardsall with 90 running inches of cracks on the back - all showed up in the past week and more on the way, plus what was already in work before Hurricane 'Rona swept through the shop. Also a couple of bridge reglues and one restoration/conversion of a pretty little 1927 O-18K that I most likely will take measurements on once the neck and bridge are off.

I'll get an update on the information above reference torrified top/bridge joints and post if anything has changed.

_________________
For the times they are a changin'

- Bob Dylan

Thanks Woodie, I had gone back and reread that thread but was wanting to explore the current state of affairs on the subject.

I’ll look forward to any updates you can provide. I do like the torrefied tops and would like to use more of them as long as I can come up with a reliable build process.

_________________
Steve Smith
"Music is what feelings sound like"

Hey JF, meant to ask earlier - have you done very many with the LMI white? And what's your process??

I've used fish glue in the past and had no issues. I tossed the last bottle I had this past summer because it was wayyyy out of date.

_________________
Steve Smith
"Music is what feelings sound like"

When the Forest Product Lab did the research on glue lines back in the '40s they found that working the surface within 15 minutes resulted in a measurably stronger joint in wooden aircraft structures. In another similar project at about that same time they found that sanded surfaces produced weaker joints than ones that were machined to thickness in layups for wood propellers. I give things a quick scrape just before applying the glue. This worked well on a mammoth ivory bridge I used a few years back. The supplier of the bridge blank suggested Titebond, but I prefer HHG, so I made sure everything fit properly, had the all the clamps in place and ready, and warmed things up well. I gave a quick scrape with a hard scraper, applied glue to both surfaces, and had the clamps on within a minute or less. No problems.

Thanks Woodie this is one of the very rare occasions when we read something here that actually helps us with our work. Thank You and the Greenridge Crew too! Going to show this to Dave Collins he will be fascinated as am I.

So far so good anyway. It's been 3 years since I have built my first with T-Top wood and it's still holding. I have learned from Alan's posting in the past that scraping or sanding the wood fresh before gluing makes a better joint so I always do that now. I make sure to scrape the foot print and sand the bottom of the bridge just lightly to 'energize it' then wipe away the dust with a dry cloth and glue up right away. Clamps stay on for 24 hours.

It seems most luthiers suggest you don't use fish glue on bridges and so I don't anymore. Though I have in the past and have not had issues with it. If I was building a T-top guitar for myself I would use fish just to experiment.

---

This may be a whole other thread but, I believe it was John Hall that I spoke to when buying stuff from him a couple years back that the gram strength of HHG has nothing to do with how strong the joint is rather how long the open time is. IOW 300 gels faster than 190 but in the end the joints are just as strong. I certainly could be mistaken and I wonder if anyone else here has hearrd this same thing.

Fwiw, out of maybe 30ish torrefied tops, I’ve def had a few do what yours looks like, with hide glue. I was using the lower strength hhg.

I switched to using titebond and haven’t had further problems. I scrape the finish all the way to the edges.

meddlingfool wrote:
"I switched to using titebond and haven’t had further problems. I scrape the finish all the way to the edges."

IMO clearing the whole footprint is probably more of a factor than the glue used.

My experience is that fish glue is actually harder to get loose than hot hide glue. It's possible that the fish glue is stronger, but it also seems tougher. Since I find a properly done HHG joint to be more than strong enough, and would want to be able to remove the bridge without damaging the top, I don't use fish glue.

I always understood the higher the bloom strength, the stronger the joint?
The very high bloom strengths were/are actually used to chip the surface of glass to give it a textured appearance.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

John told me the same thing on the phone the other day.

_________________
Steve Smith
"Music is what feelings sound like"

I braced the top with titebond and they seem to be just fine. Of course, not as much stress as the bridge.

_________________
Steve Smith
"Music is what feelings sound like"

I appreciate the thoughtful opinions from people I've learned to listen to over the years. Not sure which way I'm going to go at the moment but when I get to the shop tomorrow I'll pick one and get it done. I'll let you know what I do then I'll try to come back in six months or so and update this thread (assuming it lasts this time - ha).

_________________
Steve Smith
"Music is what feelings sound like"

Every time I hear stories about torrified wood being difficult to glue, I think of that episode of Gillian’s Island where they discover this incredible tree-sap glue that sticks to everything; but it only holds for a few days. They fix the SS Minnow with it before they understand the glue’s fatal flaw, then the Minnow sinks back into the lagoon when boards on the hull start SPROINGING off a few days later.

Oddly enough, it’s not as funny when bridges SPROING off my guitars.

From the L.D. Davis site:

"The higher the gram strength, the stronger the cohesive forces in the glue. Cohesive forces are the attractive forces between the molecules in the glue, so as the gram strength gets higher, the glue will stick to itself better. The bond will also become more rigid as the gram strength increases."

Gram strength:

- Is an artifact of a specific test method and standard
- Is determined by how much force must be applied to a steel ball of specific diameter to penetrate a given distance into a standard gelatin sample (yes...it should be dyne strength in cgs, but no one expects measurement systems to be entirely rational)
- Does relate to how resistant to failure the glue line will be under load, as well as how rigid and resistant to deformation (but we have two other types of joint-related failures to worry about as well, so not the whole picture)

I would say that higher gram strength HHG is more resistant to wood movement-related glue line failures, dries faster, and is more resistant to failure due to high heat. Does that equate to higher strength? The glue manufacturers claim as discussed above - stiffer and internally stronger glue line - but like that 'stronger than the wood' business, other factors likely dominate ultimate strength of a joint, and seldom really matter for the joints we make in any case if the joint is a) durable, b) does not move, and c) can be made in conditions found in small craft shops.

What we saw at Greenridge:

- Zero failures of bridge properly made with 315g HHG
- Hundreds of failures of bridge joints glued with 192g HHG, fish, Titebond, and other AR/PVA (including both factory and custom instruments)...sometimes as a result of the joint design or workmanship, but too often just the joint giving way for no apparent reason
- Higher gel temps with increasing gram strength, with about 95 deg F for 192 g HHG and closer to 125-130 deg F for 315g HHG.
- Somewhat more difficult removal of bridges glued with 315g versus 192g HHG
- Reduced clamping time with 315g HHG - we loaded several bridges on quick turn-around repairs or test joints after just 3-4 hours with zero issues.
- Like other animal glues, no cold creep issues as seen with Titebond/thermoplastic glues and no hot releases on the unfortunate few guitars we've seen come back after automotive bake-offs.

That 315g HHG keeps the bridges on highly torrified tops is just icing on on the cake... Greenridge has been using 315g for all bridge joints since what appears to be 2009.

_________________
For the times they are a changin'

- Bob Dylan

Woodie where can we get some 315g at so we can give it a try? Thanks.