The Harmony Guitar Company used at least five adhesives during the run of Sovereign guitar manufacturing. This was from late 1950’s to early 1970’s. Harmony changed manufacturing procedures very little during those years. Those adhesives are hot hide, PVA, and red glue and a solvent based adhesive.
Red glue bonds the liner blocks to the sides, top, and back. The neck block and tail block are glued to the sides with this adhesive. Also, they glued little 5/8 inch wide stick braces to the sides. Approximately 50% of the time, red glue bonds the braces to the top. Red glue bonds the back braces in most cases
I call this "red glue" because I have no idea what this adhesive is made of. It is most definitely not hide glue. Red glue is tough stuff. When dried it is very brittle. It is impervious to water, PVA glue remover, steam, paint stripper, alcohol, and lacquer thinner. And it is very long lived. Sovereign guitars made in the 50’s are just as good as new. So, this is my plea for information on this adhesive. As a long time stick and tissue model builder and production wood worker, I have never seen this for sale anywhere.
Harmony used hot hide glue in four places: 1) neck to body dovetail joint 2) bridge to top 3) gear head wings to the gear head, 4) Fret board to neck. In newer Sovereigns, there is a 1/4 inch maple dowel glued into the heel perpendicular to the fret board. I think they used hide glue, though I am not sure if this is true in all cases.
After examining hundreds of neck to body joints, I can state with great confidence that Harmony employees used a paint brush to slather hot hide glue into the dovetail cavity. In every case, there is way too much glue in the dovetail joint. In many cases, the glue sure did not stick very well as way too many neck joints are coming loose. Possibly this was because the glue was old, or too cold. A contributing factor is a poorly machined joint. By comparison, when you steam a Gibson J45 neck apart, the joint is perfect. The Gibson dovetail joint is so tight that it is very difficult to get the steam into the joint. And steam wants to flow everywhere. In the Sovereign, if you clean out all glue from the dovetail joint, the resulting joint is very sloppy compared to a Martin or Gibson joint. You would think someone in management would have noticed this and fixed the problem. But no, they made hundreds of thousands of otherwise excellent guitars with poorly fitting neck to body joints. What on earth were they thinking? Possibly this is why Harmony Sovereigns cost around $85 in the day, and Martin D-18 cost $500-600 and this is likely why Martin is still in business and Harmony is not.
To me, the most interesting adhesive used by Harmony was PVA (Poly Vinyl Acetate). This was the earliest form of PVA. It is similar to Elmer’s white glue as is used in elementary schools these days. I don’t think Titebond glues existed when Harmony started using white PVA. They used PVA in the later years of Sovereign production to adhere braces and bridges to the top planks. Oddly, we don’t see many instances of top braces coming loose when adhered with PVA. I say "oddly" because it sure is easy to pull these braces loose from the top. On some guitars I can pull them out with bare hands.
In some cases, they used PVA to adhere the bridge to the top. Many of these bridges are coming loose. That is because those early PVA formulations were not strong enough for such a high tension application. (Hot hide glue is much better.) Furthermore, PVA prefers fresh cut or scrapped wood. I suspect that Harmony stacked hundreds of ready made tops and bridges on shelves somewhere. Months after these parts were prepared, they were glued together on the assembly line. PVA likes fresh cut smooth, clean surfaces. This is most probably why these bridges are now coming loose or lifting.
They often use PVA to adhere the braces to the back.
I think they used PVA in preference to hot hide glue because it dries much faster, thereby shortening production time. Time is money in the guitar world.
I am at a loss as to what was used to bind plastic bindings and the white plastic heel cap to the guitar woods. My guess is they used something like Duco or other solvent based adhesive. The use of solvent based glues raises an assembly line question: how carefully did they ventilate the areas where solvents were used? Lacquer was bad enough, but Duco and similar are seriously bad to breathe. I wonder how many employees went home with raging headaches each day, not to mention brain damage from inhaling the fumes.
There is one more adhesive used by Harmony. They used some sort of rubber or latex based adhesive to attach the pick guard. This adhesive is now failing at nearly 100 percent.
©2017 D.R. Hanna