"alexy" wrote in message
...
I am getting ready to do a bent lamination, and have questions about
adhesives and springback.

I have heard that urea formaldehyde or plastic resin glue is the best
to use for this application because of the long open time and lack of
creep once set. I am having a hard time finding it, though. I can get
a gallon from Highland Woodworking but because of its relatively short
shelf life, I would end up throwing away 95% of it. Anyone know a good
source for small quantities (Atlanta area desired, but online source
okay, too) or whether another type of glue would work as well. My
application is not load-bearing, and in fact will be "captured" by
another structure. I'm laminating 4 pieces of 1/8" thick poplar for
edge banding of the inside of an elliptical arch cut in plywood.

I think the stuff you're looking for is Weldwood Plastic Resin Glue,
http://www.dap.com/product_details.aspx?product_id=42 which is a
urea-formaldehyde water-activated dry powder FAA approved for aircraft
construction (in other words this is seriously good stuff). You can get it
online in one pound containers for about 8 bucks a pound and shipping. Two
reliable sources are Aircraft Spruce and Specialty
http://www.aircraftspruce.com/catalog/wppages/weldwood.php and Jamestown
Distributors
http://www.jamestowndistributors.com/userportal/show_product.do?pid=2432&familyName=Weldwood+Plast ic+Resin+Glue&BASE.

It used to come in pint cans but now the smallest seems to be a pound. I
don't know what the real shelf life is--officially it's "1 year minimum" and
I wouldn't use it older than that for an aircraft, but for noncritical uses
I have a can that I've been using up gradually that is at least 15 years old
and still seems to set up fine.

Ace Hardware lists it online, but only in 4.5 pound containers for over 20
bucks--you might want to call around and see if they have the one pound size
in the stores.

Read the instructions carefully--the stuff is reasonably forgiving but it is
possible to screw it up. That part about "cannot be successfully removed
from most surfaces once set", they _mean_ it--don't wear clothes you care
about. The only way to get it off wood once it cures is to scrape or sand.
Also, when the squeeze-out sets up it's _hard_. Doesn't stick to metal
though, at least none that I've dripped it on. Nice thing is that if you
get to it before it sets you can clean up with water.

I have a form for bending my lamination, that I made slightly
undersize, anticipating that there will be some "springback" when the
lamination is removed from the form. Anyone have any ideas or formulas
for estimating how much that will be in advance, or is it just a case
of trial and error?

I haven't used it so can't say how good it is, but try
http://www.woodweb.com/knowledge_base/_Spreadsheet_Calculation_Program.html
which is an Excel spreadsheet that purports to calculate springback for
laminations.

If you google "lamination springback calculator" you'll find some others.

--
Alex -- Replace "nospam" with "mail" to reply by email. Checked
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