Official Luthiers Forum!

scalloping is done for tone enhancement and manipulating where the top plate moves .
The engineers at Martin had done a number of studies and actually look at this more as a drum. Interesting .

_________________
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

@ John,
Thank you for your considerate response. I do get the point you are making about the top working with the braces and the bridge/bridge plate. The one point I didn't think about was cold creep and I know that wood will also conform to stress.

I am however still of the mindset that the lowest point of the scalloping at the bridge plate is not as big of an issue as other aspects, i.e thickness of the braces above and below the bridge plate, thickness of the top as well as the type of glue that is used. I have repaired a lot of old guitars made with HHG and have yet to see a HHG joint creep. I have seen other types of glue creep but then I also think anyone that uses anything but HHG on braces/bridges/bridge plates is only asking for issues (but that is for another topic).

I have been looking at the cad drawing I made and have been thinking about your post but I am still not seeing how the thinner brace will allow the top to fail as you have said it will. Not that I don't believe you because you have much more experience than I do. What I am seeing in my drawing is essentially the bridge plate tied into the low spots in the braces with 2 triangles (the high points on the scallop) trying to keep the rotation from happening. Since the bridge plate is essentially integrated into the structure of the braces by being glued to to them and both glued to the top. That system makes up a triangle (looking from the top) radiating out from the center of the X bracing. As you probably know a triangle is one of the strongest structures you can make so the fact there are triangle shapes formed in the scalloping of the braces (side strength) and the triangle of the X braces with the bridge/bridge plate tying the system together.

I am not trying to convince you or anyone of my ideas I am only pointing them out because this is how I think. I am sure I will start to understand more as I build more guitars but I am staring to think that what I need to do is build some test models and put them under stress myself so I can actually see what is happening.

Taking your point of view for a minute... What I am finding odd is the fact that braces are scalloped at that point. Why wouldn't the peak of the scallop start at the center of the bridge plate and taper out from there. That would allow the belly to form but resist the rotation. I do know that it is important to have a belly form since I also think as you posted about Martin thinking of the top of a guitar much like a drum head. It will not make very good sound if it is loose and sloppy.

Anyway, Thanks for your explanation in helping me understand why my thinking may be misguided. I think it will take some experimenting on my part to fully understand.

Cheers,
Bob

The conversation is moving out of my depth (which was shallow to begin with) but I have thought that the wood it self will creep toward the stress basically permanently deforming. If that is the case the glue used is not really the issue.

_________________
http://www.Harvestmoonguitars.com

I frankly am not convinced Titebond is as prone to cold creep as people think, aside from a few anecdotal stories. The only woodworkers I hear talking about that are luthiers. I'm also not convinced that hide glue never creeps either.
Hide glue is composed of collagen which is a thermoplastic protein polymer. It certainly is less resistant to impacts and shatters easier than Titebond, but being thermoplastic, it would certainly be prone to some level of creep just like any other thermoplastic polymer residue.
I'm more prone to think that the elastic properties of wood are more responsible for creep deformations than the glues used.

_________________
Old growth, shmold growth!

The point that you may be misunderstanding , is that yes the bridge and plate are pretty rigid but they are attached to the top. The top is held by the braces. Proper scalloping is indeed below the bridge. Your print out is a stress plot and what happens is the bridge will rotate and push the top down in front and raise in the back. The braces help the top to hold the bridge from doing this. I have seen way too many tops fail and will try and take some pics of the tops that failed.
The stress of the top on the rotation will couple with the compressive load of the strings. As for cold creep it happens and as far as creep with tite bond that is a fact. That isn't to say it is a horrible glue but it does move. Hot Hide glue is not prone to cold creep. The glue fracture is why it is popular with luthiers, it makes repair much easier. Guitars are indeed built with the idea of future repair.
As for your triangle that is strong when you apply a load that is in plane , your are flexing this and that is a different load application. Think of this , the whole top wants to deform in the line with the bridge. The braces help the top fight this.
the one point that you may be missing also is the scalloping is not so much about the load bearing as the tonal influences. Any top that is underbuilt will fail.
A triangle is a strong structure when force is appled in plane . but when the force is applied laterally, the load is on the beams, they will still flex.

_________________
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

As someone who has only built a few (less than 10) classicals, does seem like tapering braces as one moves further away from the bridge area might be just as good as scalloping. If nothing else, Trevor's comment made me check out radial bracing, and for my 10th classical I'm now tempted to follow a radial bracing pattern similar to one I saw used by an English builder (Adrian Lucas) which has a long median brace running across the width of the lower bout in the bridge area; this brace apprears tapered towards the sides and there is no bridge patch used. Anyway, this is an interesting thread.

I guess my earlier comment about tapering not scalloping has a lot to do with the OP's original statement. Students, probably first timers, should start with the most basic approaches in my opinion.

bluescreek wrote-

scalloping is done for tone enhancement and manipulating where the top plate moves .
The engineers at Martin had done a number of studies and actually look at this more as a drum. Interesting .

I'm not going to debate this but the percentage of good sounding Martin's built in the last 40 years that I have heard is pretty poor once again IMO. I think they are concerned more with things other than tone. Like gluing the bridge in the right place, sorry I couldn't resist. Now if you want to study some of the good sounding Martin clones I would say any of the builders who are selling Schoenbergs' clones would be a good place to start. Both Bruce Sexauer and Laurent Brondel scallop pretty deeply but I believe there is far more to their superior tone than the bracing.

whisperer wrote_

I frankly am not convinced Titebond is as prone to cold creep as people think, aside from a few anecdotal stories. The only woodworkers I hear talking about that are luthiers. I'm also not convinced that hide glue never creeps either.
Hide glue is composed of collagen which is a thermoplastic protein polymer. It certainly is less resistant to impacts and shatters easier than Titebond, but being thermoplastic, it would certainly be prone to some level of creep just like any other thermoplastic polymer residue.

I'm more prone to think that the elastic properties of wood are more responsible for creep deformations than the glues used.

I Have tested glues extensively for the past 10 years and can't get a quality joint to creep using Elmer's Carpenter's glue, Titebond original, Titebond II, LMI white or hide glue. On poor quality joints, where gaps exceed .002" all glues I have tested both creep and fail under load. The biggest failing of hide glue is cold joints that are gelling during assembly, these joints will fail quickly. Hide glue will also soften, recrystalize and weaken on exposure to much smaller swings in temperature and humidity than generally believed, hence the tens of thousands of loose jointed antique furniture. The merit of repairability is very valid and for that reason hide glue is a great glue for guitar building, just be sure your regimen is a rigorous one.

Happy building, Tim

I don't think this point has been brought up but the main thing I would be interested in is if this student guitar will be the ONE AND ONLY guitar this student builds or just one of many many future guitars.

If it's the one and only then your advice should be taken with the gravitas your experience lends such things, leaving the decision up to the student.

If it's one of many then I would suggest you still leave the decision up the student so he/she can learn the consequences of brace design - both bad and good. What better tool than a guitar that fails - or plays great and lasts a lifetime!!

And of course no one here, or even there first hand, can tell if the scalloping is too low until the guitar has been played and strung up for 6 - 8 months.

_________________
Thank You and Best To All

Have you tested Fish Glue? If so I'd love to hear your opinion of it. After 20 years I've only just started using it and for me it's like a miracle glue. So easy to work with and seems quite strong.

I have not tested any fish glues but would be more than happy to. Let me know if there is a particular brand you prefer. I have a relatively simple and repeatable system and would enjoy starting a thread so the integrity of my testing can be verified, judged, etc. Just need some time as our shop is under 4 pretty large deadlines until June.

Tim

Yep John P is correct -- its getting deep all right but not in a good way.

Funny how these threads will sometimes morph into different discussions. Not that I can't learn about different glues but I was wondering if the scalloping is too deep?

_________________
Thank You and Best To All

education is information shared.
I base what I learned from experience and as an engineer ,the ability to reproduce the result. To test creep would not be a thing that happens all to quickly. I agree that creep in many cases may also have a poor glue technique or contaminants involved. I have seen martins that were over 15 years old that do show creep you can see it where the finish is plowed up.
Still that is no reason that it cannot be used , as without knowing the true history, one has to wonder if the glue was ever exposed a hot auto .

_________________
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

Yes sure the stuff I use is available at Lee Valley and called High Tack Fish Glue.

http://www.leevalley.com/US/wood/page.a ... 65&p=20019

Regards.

jn

Have you tested Fish Glue? If so I'd love to hear your opinion of it. After 20 years I've only just started using it and for me it's like a miracle glue. So easy to work with and seems quite strong.[/quote]

I have not tested any fish glues but would be more than happy to. Let me know if there is a particular brand you prefer. I have a relatively simple and repeatable system and would enjoy starting a thread so the integrity of my testing can be verified, judged, etc. Just need some time as our shop is under 4 pretty large deadlines until June.

Tim[/quote]

Yes sure the stuff I use is available at Lee Valley and called High Tack Fish Glue.

http://www.leevalley.com/US/wood/page.a ... 65&p=20019

Regards.

jn[/quote]

Very cool, I have some Lee Valley items on the wish list and will add this. I will start a thread in late May or so, I looked at some of the test glue-ups I've done and indeed they will be 10 years old this summer and have been under constant stress except for a couple weeks when we moved the shop.

Enough said, I wouldn't want to get too "deep".

Tim

And thanks for sharing all that info John. It is very much appreciated.

Enjoy the Day

glad to help
Norland fish glue is most common in the states. I believe in this so much I also sell it.

_________________
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

John, are there any joints in a guitar that you wouldn't use fish glue for?

I've seen Martins fresh off the PALLET with the finish plowed up and the bridge crept, delivered right from the factory.

I've seen many more Gibsons that had even BIGGER problems.

I'm fairly certain in those cases that temperature had a role to play.

_________________
Old growth, shmold growth!

About cold creep with tite bone , that is documented . I have seen it 1st hand as other builder have. Still it isn't a reason to stop using it if that is what you like to use. Martin used it for years and still do. As for scalloping and tone , when you change the physical strength of the top by adjusting the braces , this indeed will effect tone. It is how the top moves that allows the string energy to be made to do work. Changing the physical relationship of the braces to the top is what we call voicing.
I look at the joints of a guitar as critical to tone. So Braces for sure , bridge , gluing plates on the top and back. Areas that I use what is handy and don't matter as much , Fretboard and kerfing , tail blocks, even neck blocks. You have a large surface area and the joints are not in shear . I also am a dove tail joint guy. Here I will use Fish and HHG. On the fret board extension I don't glue them down like Martin , I do it more like Gibson. Often the cracks at the fretboard extension are from mis matched expansion so I just use a slight about of glue on the edges and a drop in the middle.

_________________
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

Problem is I've seen fretboard extensions peel up from not being glued down... so I don't know, unless the FB extension was very thick to begin with. It might not be a problem but when a customer can stick a sheet of paper under the FB extension they might complain about it (even if it's just cosmetic).

As for titebond glue creeping, I heard Titebond II isn't good but I'd like to know for sure, has anyone done a test? Titebond II, III, and liquid hide is about all Franklin International carries in Taiwan (I do not know why) so for me in order to get Titebond I I have to pay a lot of money to ship it. It would be great if II works as well as I because then I won't have to use expensive glues... I seen luthiers use Titebond II in Taiwan simply because that's all they can get. I mean I'm fine with importing hide glue simply because a 1 pound tub makes a LOT of glue.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

John, can you explain the difference between how Martin glues the tongue down and how Gibson does?

If you're using hide glue for bridges, most of the problem is already solved, IMO. I've also had the experience of a titebond I glued bridge sliding up the soundboard, while remaining stuck. I don't use it for bridges anymore.

RE availability in Taiwan: There might be an equivalent PVA available? For example, Loctite/Henkel wood glue is pretty similar to Titebond I. Titebond I dries harder than Titebond II. I don't know if there is any difference in creep resistance. Titebond II's slightly softer dried state is probably not the end of the world if the joints are good and tight.

Well of course there are PVA available in Taiwan but they are basically the equivalent to white glue, which I am not sure if they are suitable for instrument building. I mean, Titebond I, II, and III are about the same basic chemical, they just have different properties to work in various situations... I found Titebond I to dry the hardest and Titebond II dries kinda rubbery.

I don't always use hide glue because hide glue requires you to clamp things very quickly, it's ok for bridges but not when a joint requires a lot of clamps to clamp properly (such as neck joints, I have to glue the fingerboard and the dovetail at the same time, and that means I can't get it all clamped up in 5 seconds). Fish glue solves a lot of that problem while still having the same advantage of hide glue, but someone has experienced failure due to humidity so I'm a little scared to use it. I also glued an african blackwood bridge with titebond because I'm not sure if hide glue will stick to it properly.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Titebond is only yellow because they dye it, to make it seem different and better. (newsflash ) The white color doesn't necessarily indicate that a PVA is going to be a soft drying craft glue like Elmers. You may want to test some locally available adhesives for hardness and joint strength, especially if they are sold for woodworking. As you say, qualities of PVA vary widely.

AFA hide glue - I'm currently in the same camp. I use HHG for braces, bridges and anything that might creep, and use titebond for everything else.