Aliphatic resin gives me the creeps!
Heat Testing Glue Joints
© Frank Ford, 4/25/98; Photos by FF, 1997
I'd heard so much discussion about the various qualities of glue joints that I finally decided to do a little testing of my own. As you may know, my goal is to make luthiers aware of the tendency of aliphatic resin and white glue (I tend to use Titebond as a generic term) to creep under even mild heat.
My testing methods were not as precisely controlled as I might want before publishing a monograph in Fine Woodworking, but I think I got some pretty clear results.
I glued and clamped a plain lap joint in some clear heart redwood. In all the samples the joint measured the same length and width. Then I made up a very simple testing fixture which held the joint vertical as I loaded the end with lead bricks. I have these lead bricks which weigh in at about 3 lb. each, so I simply clamped one on to the end of each stick:
Pretty simple, eh?
I tested the samples at room temperature and found that if I loaded seven pounds on each, the joints would break immediately, splitting off wood fully across the face of the joint. I'll talk more about that shortly.
OK, on to the heat stress test. My kitchen oven's lowest setting
is very nearly 200 degrees Fahrenheit, so I chose that for my test. When I can sometime,
I'll run this test at about 150 degrees. I used a good standard thermometer to calibrate
my oven setting over a couple of hours, so I'd be sure it was very close to 200 degrees
for the test.
I opened up the door, slipped in my fixture, and waited. In only a few minutes I heard a loud "clunk" as one of the weights hit the board:
Within seven minutes the Titebond joint failed utterly and cleanly. (By the way, I did repeat this test with the same results.)
Then I figured I'd measure how long the hide glue would take to fail at 200 degrees:
That's right, it didn't. After waiting all day (Mind you, I was doing other things) I finally couldn't stand it and had to try a higher temperature, so I cranked the oven up. I had to stop the test with an oven setting of 375 degrees because the wood charred and my smoke detector went off!
So you could say that hide glue resists heat better that Titebond and its aliphatic cousins.