bluescreek wrote: The higher the gram strength the less viscosity you have. Hot Hide Glue 192 is plenty strong and you will have the most open time with this.
I also suggest to warm the area to gain as much open time as you can. When I tried higher gram strengths I have a few failures due to the clamping issues.
They are easy to reglue but I now use almost all 192 and 215
Given the same amount of water per weight of glue, I'd agree, but it's easy to add hot (150-160 deg F) distilled water to adjust viscocity, or simply heat the glue to a higher temperature as is done when better penetration is needed. Sure - the strength of the glue is compromised if that glue is reheated and then used again, but a quick boost to 185 degrees for 192g gives a 90 degree cushion on gel temp versus the usual 50 degree cushion for 145 degree glue... with a little thinning, that gets 192 gram strength glue much deeper into a neck break.
All of the common gram strengths are technically strong enough in a perfect joint, but bridge joints on repairs and even new guitars are seldom perfect, so the better the gap filling capability and tolerance to thicker glue lines, the better. This is why we used 315g for bridges, as we saw plenty of 192 and 251 glued bridges on previously repaired or custom built guitars (NOT ours) part company after a few months or years. 315 does not make sense for any application where the joint can be perfected AND where the clamping is perfect, but for the average bridge joint - under constant loading and operating near strength limits - it is cheap insurance. Preheating the bridge handles imperfect technique on glue-up by providing a reservoir of additional heat energy to remelt the glue on the bridge patch as the joint is closed. A plate warmer does a nice job of bringing the bridge up to about 165 degrees... heat for 10 minutes, which is enough to get a consistent temperature, but not long enough to cause resin bleeding on rosewoods and some ebonies.
315 gels at about 130-135 degrees, so without a secondary source of heat (i.e., the thermal mass of the bridge at 160-165 deg), open time is measured in tens of seconds (allowable cooling during assembly = glue temp - gel temp = 145 deg - 135 deg = 10 deg!!!), which is too little time to close and clamp the joint. Therefore, 315 requires a method to add supplemental heat which 192g (95 deg gel) and 251g (115 deg gel) usually avoid through good technique and a bigger temperature range between glue temp at application and gel temp.
192g for everything else.
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