Acoustic Guitar Construction

Steve -- "kevininca" used regular epoxy as filler and he reported problems that showed up months later.

It would be a good idea if you asked this question again but please do it in the "finishing forums" topics that way it is in the right place and likely will get more attention.

In a pinch Wrigleys sprearmint gum will work.

David L

Spearmint, eh? I'll try it. I think stewmac sells it for $10 a stick..

Is a smooth joint better than a rough joint? (No puns here!)
Something interesting that was forwarded to me by a woodworking friend who choose to try to get to the bottom of this often asked question the other day regarding the "Joint" Here is his letter and the response from Tite-bond:

"From time to time I hear someone comment about a woodworking practice that runs totally contrary to what I've been taught. One of these is what kind of wood surface yields the strongest joint when using wood glues, typically white or yellow glue, but also hide glue.

This came up a few weeks ago. And while I thought I was right, that the best surface is smooth, I thought I’d get to the bottom of the question. I mean, maybe I was wrong. So I went to the folks who know a lot about this, Franklin International, makers of the Tite-Bond and lots of other adhesives. I received the following from Bob Behnke, the company’s Senior Technical Specialist. There’s great information here that every woodworker must know. And by the way, the section on Franklin’s web site on woodworking glues is a great resource for woodworkers. You should check it out.

Hi Steve,

Our work has shown that a smooth surface will always have higher strength than a rough surface. Two-hundred grit or higher sanding to get flat or tight-fitting joints works well.

Wood glues work by attaching to cellulose on the wood and the smoother (tighter) the joint, the less adhesive is needed to bond the surfaces. Less adhesive gives fewer areas of imperfections (bubbles, skips, dust and gaps) where stress can accumulate and cause glue line failure. Also, wood glues tend to be around 50% solids and therefore shrink when they dry. If the rough surface is too “gappy,” as the adhesive dries and shrinks, it will pull away from one surface or the other leaving gaps in the glue line, which again will concentrate force when the joint is stressed. This is why wood glues need to be clamped. Clamping keeps the surfaces in contact as the glue shrinks and dries.

A note of caution on smooth surfaces: Burnished areas may be smooth, but will not bond. Burnishing causes the cellulose to change chemical characteristics and thus not bond to the polyvinyl alcohol portion of the wood glue. This can be tested by putting a drop of water on the surface of the wood, if it doesn't soak in, the surface is burnished or sealed and should be sanded until cleaned of the burnishing.

For hammer veneering, you can use either hot or liquid hide glue. I have read that roughing the surface of the substrate and veneer gives better strength. But our work shows that too much roughing of the surface can cause loose fibers and fiber tear which can weaken the bond. As above, the adhesive bonds to the cellulose so a roughed surface is not necessary, but as long as it doesn't damage the wood surface to be bonded, it will produce good results on veneers.

Bob Behnke
Sr. Technical Specialist "

The "Top Dogs" aren't always right...but I personally have found this to be true in my own endeavors.

It may be a bit "Off topic" but the fact remains that the glue world is continuing to evolve, things change, and STILL workmanship has a LOT to do with the end result, not necessarily the brand or type of product. IMHO.

Ray

Well done, Ray.

Another great thread.

With all this, it still leaves me confused concerning the best approach to successfully gluing Cocobolo.

Looks like many are having great results with both PVA and HHG (instead of epoxy), but the bigger disagreement seems to be the wood prep before gluing (whether to wipe with acetone or not).

Norm Abrahms the "New Yankee Workshop" guy is in favor of wiping with acetone and then gluing as soon as it evaporates.