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hey all:

I haven't built a rosewood necked guitar in a while (neck not fingerboard) and i have a question about clamping pressure. when using tightbond i usually just clamp the living %^&*( out of the joint. but i was considering using epoxy for this joint because of the oils in both parts and to fill some minor fissures, etc in the rosewood neck. 1) good idea? or just stick with tightbond original; and (2) do you clamp more gently with epoxy or same as usually - the more pressure the better

I'd appreciate your thoughts

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Gauge Guitars
www.gaugeguitars.com

thanks gents

sorry about the bad day - that sounds like one of those times when you just shut the lights and walk out of the shop (for the safety of tools)

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Gauge Guitars
www.gaugeguitars.com

I'm looking at a Rosewood fretboard glued with epoxy as I type. I use epoxy to glue any kind of oily wood. It's aggressive and therefore, lessens the risk when any kind of bond issue is present. Scuff sand and wipe with acetone prior to gluing. I use a formulation that allows a lot of open time but cures overnight. I can't vouch for what you are using since I don't know the brand or system. The manufacturer ought to be able to give you a suitable cure time. If they can't, find a manufacturer that can.

Clamp it hard. There's no such thing a too much pressure. Just make sure you measure and mix well...and thoroughly cover both surfaces prior to gluing.

Stick with me...I'm going to make a point.

If you had a polished aluminum plate and poured Titebond on it, you could easily peel it off after it dried. If you sprayed a polyester or polyurethane you'd need to apply a wax mold release to the plate prior to spraying in order to get them released. If you prepped the plate with wax release and poured a typical structural epoxy on it, chances are good it would eat through the wax and bond to the plate, albeit non-optimally. It would require numerous wax coats to release the epoxy properly.

Titebond really IS fine for oily woods with good prep....but I thought I'd give you the picture of what epoxy does in that oily environment. I use it because I don't want to worry about bonds.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

When I said there's no such thing as too much pressure I should have included the rest of it.

Think of a pile of ping-pong balls. If you press down on the pile with a flat surface they'll spread out until there's only one layer of them...and then there is no force to move them laterally any more. Now let's say you could make two perfectly flat surfaces, down to a molecular level. Could you squeeze them together hard enough to result in a layer of epoxy one molecule thick? No...neither could you ever prepare a wood surface even remotely close to this...but if you could there would still be a bond.

Epoxy crosslinks to cure. Without a solvent carrier there is no theoretical minimum thickness to create an effective glue joint. I'll venture to say, however, that even with Titebond or any other glue there is no amount of pressure between two pieces of wood that will squeeze out glue to the point of "glue starvation". A few things CAN happen with high pressure on compressible materials though. You can compress wood when gluing and then upon the removal of pressure, weird stress accumulations can occur.

I have a hydraulic press that can deliver 160,000 lbs. of pressure to the two surfaced plates that comprise the front body plate of my guitars. This is about 580 p.s.i of compression...which crushes some species. Even with crushing pressure I haven't seen anything remotely close to "glue starvation". I need about half that much to make a very consistent glue joint though.

My press delivers EVEN pressure. A typical 8", cast iron C-clamp can make about 2500 pounds of pressure...all focused on a small point. This is where too much pressure is going to be bad...not from glue starvation but from highly localized compression and therefore, localized stress accumulation when the clamps come off. A thick, hard, FLAT layer on each side of a laminate to homogenize the clamp pressure is the ticket. Of course, applying pressure, backing it off, and then re-applying pressure is a no-no.

When considering pressure on a laminate...it's not the glue that's the issue. It's the distribution of pressure. The more you do to homogenize pressure on a laminate, which includes the surface prep to create flat surfaces and the even application of glue, the more pressure you can apply to the laminate...and the better your glue joint.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Yeah, use cauls as Stuart mentioned to evenly distribute the clamping forces to minimize a "scalloped" look or put a bend in the neck.

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wah
Wah-wah-wah-wah
Wah

I aways do. Thx guys

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Gauge Guitars
www.gaugeguitars.com

Stuart,
Great, extremely educational post. Thanks for sharing your knowledge. Can you address what Filippo said? I don't know if your knowledge of adhesives includes glues like Titebond, but if so, that would be great.
Also, I had read somewhere, possibly in one of your posts here, that clamping, unclamping, and then clamping again is bad for joint strength. Can you elaborate on why that is bad? I am not questioning that it is, I would like to understand why.
Thanks,
HGHIC
(Head Goat Herder In Charge)

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http://www.CostaGuitars.com
PMoMC

It's not necessarily bad...but it can be in a number of circumstances. Imagine two grossly concave boards facing each other. You can squeeze them together with clamps and in doing so, you'll squeeze out all excess glue. If you then loosen the clamps and then re-tighten you no longer have the excess glue in there and it becomes critical to re-tighten at least as tight as the original torque (assuming c-clamps here) or there could be a gap between the two thin films that are left.

Applying clamp pressure once, in one direction and holding it, makes sure whatever gaps might exist in boards that are not perfectly planed remain filled with glue.

I don't know too much about PVA glues like Titebond...and honestly, I know little about the chemistry involved with any adhesive. I just have a lot of experience releasing gobs of different materials from polished surfaces. I did R&D for a long time...all practical molding experiments. Epoxy is THE hardest thing to release from a surface. Because it's highly aggressive, even in the presence of release agents that easily release other materials, it's my choice when oily woods concern me.

I use Titebond all the time for joining edges. On light colored woods it disappears whereas epoxy, being aggressive, soaks into the joint and can create a discolored looking line.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I should add that the epoxy formulation I use stays open in a thin film for many hours before it cures. Then, when I want it to cure, I kick up the temperature and the cure completes. The press I mentioned has heated platens so the epoxy is guaranteed to reach a full cure overnight set at 120F. The cure cycle of this epoxy allows a lot of time to get it spread thinly and evenly. I'd use Titebond in more applications but often the open time of epoxy is the main consideration with glue choice.

You can adjust the cure cycle of epoxies with different catalysts and temperatures...which offers a degree of latitude not found with some other glues. Often a process idea will work or not work based solely on the cure temperature or cycle time of a glue. I kind of learned to depend on, and design with, the control of those variables...so today epoxy is my "go to" glue.

Lastly...I have a specific formulation I understand well. Other epoxies have different characteristics. Most store bought structural epoxies that claim an "overnight cure" are about right for guitar building. They'll stay open longer than Titebond Extend, have several "speeds" of catalyst available, and will have accelerated cure cycles with the application of heat. If you want a faster cure you'll sacrifice open time to get it.

If you want to use epoxy and think it sounds right for you, I suggest buying System Three or West Systems. Both companies offer systems with several catalysts. They both also publish the cycle times of their products. Understanding these variables give you a LOT of latitude when solving gluing problems.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

A fabulous article on epoxy for use in guitar building, Stuart. Thanks for breaking it down!

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