On 4/17/2013 12:52 PM, -MIKE- wrote:
On 4/17/13 11:03 AM, Greg Guarino wrote:
This is mostly a "curiosity" question. My schedule allows only brief
encounters with woodworking, so anything I glue up tends to stay clamped
well past the recommended time; several days, on average. But I'm
finally assembling the (prefinished) parts of the second pair of
bookcases and I noticed something this morning.

The shelves are in dadoes, and I've been assembling the bookcases face
down. I applied some shiny packing tape to the work surface under the
areas where glue might drip out. That kept the work from adhering to the
bench, but left some hardened glue in a couple of spots (on the first
two bookcases). That wasn't too much of a problem. I scraped it down
flush before I attached the face frames, and the areas were small.

I glued up another unit last night at about 8 p.m. I decided to have a
look at it this morning, at 7 a.m. I removed the clamps and had a look
underneath. Sure enough, there was squeeze-out, but it was a lot softer
than I would have imagined after 11 hours. Is this possibly because it
was relatively sealed in by the non-porous tape? Even some that had
collected in an exposed corner was pretty soft. The temperature in the
garage would likely have been in the low 60s.

Adding to what Karl and Leon already wrote...
The actual glue joints will be very strong at the manufacturers "set
time" which is generally around 30 minutes. I would speculate up to an
hour down around their minimum temperature for use.

Those glue drops and puddles will take days to harden, fully, and
sometimes never. If they "skin-over" fast enough, that skin acts like a
lid on the bottle keeping all air away from the glue inside the bubble.

It has been my practice to try to scrape away squeeze-out before it
hardens, but after it skins a little. There's a magic time for this that
is usually right around the set time for the glue. It's when the glue is
set enough (doughy) to be scraped without spreading further on the wood
and soaking into it, yet not so hard as to pull up any wood fibers or
have to be chipped off.

The window of opportunity for this only about 10 minutes, in my
experience. But when you get good at finding it, it removes a lot of
other work from the equation, including clean-up, scraping/sanding,
masking, taping, etc.


To try to answer your practical question which I assume is how long
should you wait for a glue joint to dry before continuing the next
operation.

I make a lot of picture frames and stretchers. They are miter joints
with biscuits. After the picture frames are assembled, I apply addition
wood to the frame to complete them. I usually allow at a very minimum
of 3 hours before I remove the clamps to complete the final wood work.
I prefer to glue in the morning and finish in the evening or over night.

If the next operation are going to stress the joints I would allow
additional time. Overnight should be more that enough for most
operations that will stress the joints. The more stress to the joint
the more time after gluing.