Re: [ATM] Bonding components i.e. glues

[Daniel Fundo <fundo@bellsouth.net>]

<< I have been building scopes for quite  few years and one point I am
having trouble improving on is glues.   For example overtime sticky
backed Velcro fails,  rubber cement bonds of ebony Star to wood fails.
etc.  My question is, what do the commercial guys use?  What does
Obsession use to bond Ebony Star to aluminum bearings?  Or, what is the
best way to bond Velcro to wood? I'm looking for solutions that won't
have to be revisited in five years.  >>

Pete,  While the pros in industry have access to some products that the
amatuer doesn't, the biggest problem is the difference between
professional application and amatuer usage. They use the exact quantity,
evenly applied to a clean/preped surface, followed by the correct
pressure and temperature.  They have a completely controlled work
environment, and surfaces that match very well.  

In a former job, I had to deal with several 3 M adhesives.  The one we
used the most, we called "the adhesive from hell"; an "extreme
conditions" type of contact adhesive that is only available to
industry.  Touch a surface to which it has been commercially applied and
in 3 seconds you will have to leave skin behind to get your finger
back!!! NO <G>!!!  In a controlled application, it had a 7 year(?)
guarentee against failure.  In the application we used it for, placing
labels on existing outside surfaces, it had a prorated life of only 5
years!  We couldn't really get the existing surfaces clean enough or
control the temperture or the pressure needed to ensure proper contact.

Most contact cements begin to fail around the edges where moisture
infiltrates.  This is especially true with particle board where the
moisture swells the small wood chips and breaks the wood-to-wood
adhesive.  (Wood is actually one of the most stable building materials
available ***IF*** you waterproof it!!)  You may try to butter the wood
surface twice with the contact cement when attaching the Ebony Star.

Another source of failure is a poor match between the surfaces being
glued.  A clean smooth surface is need for most glues.  The exceptions
are epoxy glues and the new urethane glues, both of which have excellent
gap filling characteristics.

As far as epoxies are concerned, the slower the set time, the stronger
the bond will be.  The 5-15 minute quickie epoxy glues do not set up
hard.  They take on a resilient texture that can creep and eventually
fail under load.  

As for attaching Velcro to wood, I would stick it on with the adhesive
it comes with (make sure the wood surface is clean and sealed), and add
a staple or two.  Use a nail set to get the staple down far enough.

And attaching Ebony Star to aluminum, that must be a bear due to the
differences in CoE.  I'll bet they use a silicon based adhesive for
that.

If you want a source of good adhesives, find a hobby/model airplane
store, though they are getting harder and harder to find.  I use a lot
of gel type C-A to connect oak and maple.  In a hurry to build something
one weekend, I made a jig from maple and aluminum angle, all set
together with gel C-A.  That jig has been used for over 10 years now in
my unheated-unair conditioned shop and its still as solid as the day I
made it.

*****-----
Dan F.
Secretary/MAS
Memphis, TN
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