Early 60's Harmony Tenor Guitar
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This elegant early 60's Harmony Tenor guitar is all original, with solid spruce top, solid mahogany back, sides, and neck, and brass frets. The fingerboard and bridge appear to be "ebonized" maple. As with every old Harmony I've seen, the neck joint has failed and the neck needs to be reset. This one's bridge is also coming up. So begins the restoration ...
I'm using a silicone-coated heat blanket from Omega Engineering to heat the fingerboard extension. I've covered it in aluminum foil to help distribute the heat and keep it from sticking to the fingerboard due to oils in the wood. It gets plugged into the temperature controller in the next slide
I built this temperature controller from a JLD-612 digital temperature controller module from Amazon, and parts from the local electronics surplus store. It uses an H-type thermocouple for the feedback signal, and will self-calibrate its coefficients for different heating applications. I also use it to control my hot hide glue pot (made from another Krups cappuccino maker). I'm heating this fingerboard extension to 250 deg F.
I now have good clean gluing surfaces on both the bridge and top. I will use hot hide glue, not only because it is period-correct but it has incredible strength and has the amazing property known as the "death grip" which actually draws the two pieces together as it cures. It also dries glass-hard for better acoustical transfer. Amazing stuff, but can only be used in quick gluing situations because it gels very quickly.
I've decapitated another Krups cappuccino maker to use as a glue pot. I fill the aluminum chamber with water which the temperature controller keeps at a perfect 145 deg F in which I soak small plastic cups of pre-soaked hide glue (1.8-to-1 water-to-glue ratio). It ramps up quickly since the Krups has a robust heater element. The temp controller has been self-calibrated so overshoot is kept to a minimum. I use a K-type liquid probe thermocouple with a small piece of silicone tubing on the end to keep the tip from directly contacting the aluminum. This system works amazingly well.