What is the right glue to use?
Boy, you folks sure know how to pick good subjects. I think the
discussion about glue will be like telling someone which motor oil to
use or which person to marry :-).
There is a huge range of adhesives available to us, even if we just
stick to the ones sold for hobby use (I did a quick inventory and I have
9 different kinds). I'm not sure what all the concerns are for
"museum quality" models, but the typical
model, even an RC boat that is frequently in the water, is generally in
a fairly benign environment. Here are some of the things I consider
when picking the right glue:
-
What is the direction and nature of the load on the joint? Is the
joint loaded in peel, tension or shear? Is the load per unit area
of the joint high or low? Is the load constant or cyclical over
time; is there vibration or shock?
-
What is the temperature range? This might surprise you. A
model left in a car in Tucson, AZ in the summer could see 150
degrees F. One left in an unheated area in Alaska might see -30
degrees F. Does the temperature cycle from hot to cold in a
short or long time?
-
What is the humidity range? This one is relatively easy, assume
100% non-condensing humidity for most static indoor
environments.
-
What is the nature of the objects to be bonded: porous,
non-porous, wicking, rigidity, slick, rough, the same or
drastically different?
-
Is the bond line visible or hidden?
-
How fast do I need the bond to set and/or cure?
-
How thick is the bond line? (This one is very important)
I think the original question was about bonding wood to wood, but in the
completion of any model there are typically lots of different materials
to be joined. Even for wood to wood, one could pick several different
glues depending on the nature of the joint. For my Typhoon, I
used 5 minute epoxy for the motor mount parts and thick or thin CA for
most of the rest. I'll probably use the epoxy for gluing the pin type
joints for most of the deck hardware (windshield posts, vents, step
plates, etc) These bond lines are probably relatively thick and there is
a large coefficient of thermal expansion difference between the
materials, which requires a bit of flexibility in the bond lines.
As far as longevity goes, the environment plays a huge part in this,
regardless of what glue is used. My opinion is that most of the good
quality CAs will last a long, long time in this application. FYI, violins
are assembled with hide glue, and some of these might go more than
a hundred years without failure of a bond. I imagine nearly everyone
used so that with the proper application of moisture and heat, the
violin may be disassembled for repair.
One might also ask the same questions of other materials in the model,
especially the paint used.
This is a fun area to deal with and one that for me evolves all the time
as I learn about materials. Everyone gets to do a bit of engineering!!
{John Witt}
When all else fails, go to
This To That; a website where you enter the two materials you want ot attach
and it will recommend the best adhesive fo that purpose!
{John O. Kopf}
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