Ahh but you leave out the key comments. The thinner the glue layer the
better the stronger the bond. The comment was made and as I have pointed
out, that extra clamping pressure is only needed if the surfaaces do not
touch evenly along the joint line. If you have flat mating surfaces,
squeezing the glue tighter is not going to strengthen the glue.
No, the effect of the extra gluing pressure contributes by helping in
creating the thinner bonding layer as well as inducing (as the above
alluded to as well) more integrated into the wood pores.
As noted above, these results have been verified over and over and over
w/ identically prepared samples taking out the variable of the quality
of the jointing surfaces, etc.
If you put the proper amount of glue on in the first place there is no need
to squeeze excess glue out. If you are working with flat mating surfaces
and don't use excess glue there is no need to clamp except to keep the
pieces properly aligned.
And for the last 30 years I have verified by my own practice that the joint
is fine if properly set up to start with. Clamps are not necessary. Try
this, put some glue on a "flat" scrap, and "lay" another flat piece of scrap
on top, let set a few hours, see if you can break apart with out the wood
No, but there was lots of response to the OP's that I think wasn't quite
right...addressing the difference between ultimate and "adequate"
strength and effect of clamping pressure thereon.
I'm not disagreeing it's possible to get "adequate for most
circumstances" glue strength w/ moderate to even minimal clamping force
but otoh there is a relationship between clamping force and ultimate
strength obtainable that seems worthy of being recognized...
Isn't glue a pass/fail kind of situ? You either do it right and it
survives punishment or you get it wrong and it fails catastrophically.
Adequate = ultimate in this instance, wot?
No matter how cynical you are, it is impossible to keep up.
There is lots of practical info published on this for PVA glues
(Titebond wood glue, etc.). FWW magazine had a study a while back. a
few hundred lbs clamping force is what is needed. The most important
things the study show is that various types of clamps have widely
different capacities to generate clamping force. The modern parallel
clamps can get to a thousand + pounds. Thin bar clamps can struggle to
get to 150 lbs. Pipe clamps IIRC can also create quite some force.
Strangely they report the pistol grip clamps also generate huge
amounts of force but I just can't believe it. I just use them for
positioning and lite work.
So use good clamps and there is no need to overtighten. Clamp until
you see squeeze and give it another little twist just to be sure.
Trust me, masking tape ain't gonna do it with PVA glue.
If you are edge gluing panels, you should envision a 90 degree V
extending from the location of the clamp at the edge, 45 degrees on
either side of centerline of the clamp bar. The V's of the clamps
should overlap at the glue joint, so wider boards in the panel require
fewer clamps becaus ethe V covers more area as it extends away from
the face. I actually have some outer cauls I have been using lately
that essentially widen the panels that give me the side benefit of
needing less clamps sometimes.
Yeah - I actually read that article once upon a time but then last night
I was watching the weekly online version of New Yankee Workshop classics
and Norm was talking about not clamping too tight to avoid squeezout...
so I just wanted to get some additional perspective on these seemingly
I guess I tend to believe the science, but on the other hand real life
doesn't always follow theory ;)
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