Best adhesive for Rosewood and ebany

[Jack Lord]

What is the preferred adhesive for a rosewood bridgeplate (to spruce) and for an ebony fingerboard (to mahogany)?

[Greg Mirken]

Hot hide glue has a proven track record for both of those tasks. Some find the water introduced by the glue can cause a neck back-bow so they prefer epoxy for the fingerboard-to-neck joint. I've never had an issue with it, though.

[Hesh Breakstone]

And Titebond original or Fish glue - used these glues as well on the woods mentioned and never a problem.

HHG is wonderful stuff but sometimes the requirement and/or user may not be condusive to the short open time of HHG.  It's nice to have lots of choices.

For new builds my plates are always glued with HHG but for some repairs where access, positioning, and pre-warming are an issue fish and Titebond original work well too.  I also like LMI white but never have any this time of year because of my climate and the risk of it freezing in shipping.

[Mark Pollock]

When I make pen blanks with these materials, I first give the sides to be glued a wipe with acetone to remove any surface oils that might weaken the joint. It really seems to help - between the natural oils of these woods, and the accumulation of fingerprint oils and whatever dust lurks in the shop, a little wipe down seems to be good insurance.

[Andrew]

Ditto the acetone. Never had a problem here. I use either lmii's white glue or hide glue.

As for water based glues causing backbow in the neck when gluing a fingerboard, Ive had this happen. You can either use a caul that will put a bit of relief into the neck when you glue it, or you can wipe the back of the neck with water to counteract the water in the glue. This is pretty variable though, not real easy to predict.

[Hesh Breakstone]

A couple more comments:

Regarding wiping oily woods with acetone prior to gluing some report that this only encourages more oils to migrate to the surface as the current surface oils are evicted.  Instead they say, and I agree, that a fresh scrape or two or three is a better bet in that it removes oil soaked surfaces while not tearing up the surface and pores on a microscopic level prior to gluing.  The term I believe is "joint energy" (no jokes please, well maybe a few....) where freshly scraping a joint prior to gluing produces more joint energy than sanding, wiping, wishing, etc.

I originally used water based glues, Titebond original and Fish, on fret boards but then had one back bow on me.  Good thing I had a double action rod in this instance.  After that I went with West Systems epoxy and no more issues.  Then my good friend Link Van Cleave who is a master woodworker and now Luthier made the very good argument that epoxy is a tone sink in the sense that it does NOT dry crystalline hard like HHG and Fish do and that the fret board is a pretty important piece of real estate on an instrument.

Link made his case and convinced me that perhaps I was leaving too much on the table with epoxy as my fret board glue.  So I went back to water based glues with the only difference being that I would clamp the entire neck and fret board assembly to my Stew-Mac radiused sanding beam (nice to find some use for this sucker since I now do compound boards...) and left it clamped for about four days.  Results, dead straight assembly and something that likely will be how I do this going forward until someone else makes a better case for another method.

What I learned from this exercise, I think, is that water based glues can work well on things such as fret boards, after all that's all that was used for decades back in the day, and that it's extra insurance to clamp to a solid caul that will not flex and leave things clamped up long enough for the water to dissipate from the two dissimilar woods.

[Andrew]

Interesting about that acetone wipe. It would be good to see tests done..

Also, if Im using a pva type glue, I score the gluing surface of oily woods.

[Russell Vance]

"Hi Hesh,

"Regarding wiping oily woods with acetone prior to gluing some report that this only encourages more oils to migrate to the surface as the current surface oils are evicted."

My understanding is contrary to this statement with a couple of important and relevant expansions:  oils (a loose generic) are classed as extractives because they can be removed by organic compounds  (acetone for instance) and these oils are one of the factors  which affect the "activation" of the surface to be glued. 

Activation of the gluing surface is optimized by freshly skimming the surface to be glued (for a number of reasons) and this coupled with the removal of the newly exposed extractives gives the best surface possible for adhesive bonding of most types of glue in common use.   Scraping (with a proper hooked scraper) is the same as skimming with a plane or shearing with a helical head cutter and this should be done immediately before the wood is glued.   If  the fresh surface is exposed to light or heat or atmospherics for any time the surface will deactivate (which is the technical term for how the newly exposed molecular surface reacts with these things) and the glue bond will be weaker.    Removal of surface extractives will assist the activation if the process is conducted properly (quickly).

"Joint Energy" appears to be a contradiction of terms and will slow down the process, if it gets to happen at all.

We use an aluminim crenelated caul (we pre-fret fingerboards) to glue fingerboards on and pre-load it with a few thou of positive relief to counteract the tendency of the water based glues to back-bow a neck.  But we also use double action trussrods and we do need them to take out the back bow from timeto time (god bless em).

For Andrew: if you follow the above procedure you will not need to "tooth" woods like mahogany/rosewood/alder ash etc - but I still "tooth" ebony and maple as a tradition (even after scraping) and I should know better.

Regards, and have a good one. Rusty.

[Andrew]

Ive had questions about the need for scoring oily woods when prepared properly as you stated, but I still do it for similar reasons. One other reason, which Im entirely uncertain about, is that the scoring seems to reduce the tendency of the piece to squirm around when using pva type glues. But this might be my imagination.

[Mark Pollock]

A suggestion once given to me to reduce squirming to to drop a few salt grains into the glue prior to attaching whatever you are gluing.

[Hesh Breakstone]

Well we agree on scraping and that's something...;)  Just want to differentiate scraping from sanding where as sanding is far more damaging to that surface that we speak of than scraping with a freshly sharpened scraper.  This can be seen under magnification where sanding tears up the surface, pores, etc. and to some degree leaves more dust in place too.  Conversely scraping is more like a well placed blow by the Highlander.... - there can be only one.... ;)  Sorry, watched the Highlander last evening so this morning I'm going around chopping off heads.... :)  Is it me or is the Highlander's voice just a bit too high to be saying "there can be only one...?"  Sorry, I digressed....

Now toothing is a whole subject unto itself and there are lots of opinions here too.  My impression is that toothing is also a function of the glue of choice or more specifically glues that benefit from very thin glue lines such as fish, HHG, perhaps even Titebond original toothing is counter productive.  Where as if the application calls for epoxy which can have thicker glue lines toothing may be helpful.

I'ver seen older guitars that had the bridge undersides toothed but HHG was used.... seems counter productive to me.

[Andrew]

Yes, i have preferred scraping over sanding in most circumstances for a long time now. Seems a lot of woodworkers these days dont understand the difference it makes to the structure of the wood at the surface. It also improves clarity, depth, and probably adhesion in relation to finish preparation as well (in my opinion). Also, I friggin hate sanding for any length of time lol.

Now I want to make some scraper sharpening jigs Ive been putting off and get my collection of them tuned up!