"Existential Angst" wrote in message
...
Awl --

First, is "two-part epoxy" redundant? Does "epoxy" nec. imply two parts?

Next, does the strength of a two-part epoxy vary with its setting time?
Intuitively, I would think the longer the stronger.

The classic is "5-minute epoxy", but I believe I have seen 60 sec epoxy,
and I have 90 minute epoxy.
I find 15 minutes to allow for a few parts without rushing, and without
waiting forever to cure. Altho I have also found that the epoxy is not
really hard in that time.

The stuff I have now is Permatex (a 30 min epoxy), but DevCon and Loctite
are big players, with big-time industrial uses, such as epoxying
bearings, instead of press-fitting them into their housings. I believe
DevCon stated that epoxying bearings is in fact the preferred method,
being stronger than press fit.

The shear strengths are enormous, but require at least .010 on the radius
for good bonding. So a slip-fit for epoxy would be counterproductive.

In some of my proposed assembly methods, I could use set screws, pins,
epoxied pins, or just epoxy -- typically nominal 7/8 alum round in 16 ga
SS tubing, or some such.

I thought epoxying would be slam dunk, and indeed it saves machining, but
goddamm, you gotta pick yer poison, it seems. I could see arguments for
actually using a mechanical method AND epoxy, in some applications.

A feature of epoxy, which could be both good and bad, is its instability
to heat. I think boiling water, or at least not that much hotter, can
undo epoxied parts.

Iny thoughts?

I did some side-by-side trials of epoxies and for steel-to-steel I like JB
Weld best of the commonly available ones.

I have changed some of my joints so that there is mechanical advantage
making the epoxy joints stronger (e.g. recessing a cylinder into a flat
plane even slightly makes the joint much stronger than just gluing the flat
of the cylinder to the said plane). I think it is worth looking at what
forces will be present and how to minimize them in any particular design.

I made a few stone statues for the garden. The epoxy joints were strong
indoors but all fell apart in the hot sun outside. Not all of them were
exposed to UV light so I assume heat was the primary factor.

--
Michael Koblic,
Campbell River, BC