In article ,
"Wild_Bill" wrote:

I don't think that zinc plating involves any high temperatures for
electroplating. A prep acid bath may have been part of the process, as a
cleaning step prior to plating.

Plating itself (regardless of the metal being plated) generates hydrogen ions
and drives them into the plated item, all at low temperature. One way to remove
the hydrogen is to heat the plated item up, allowing enough hydrogen to diffuse
away to prevent brittleness. This is done only for critical items.


If surface embrittlement had been a factor, I think cracking, probably
leading to a full break/snap would have taken place.

True. Preventing this bad outcome is why one slightly anneals plated items that
may be vulnerable to hydrogen embrittlement, or doesn't plate in the first place.


Most quality hex keys/allen wrenches are already fairly hard, though I would
think of the twisting failure as a feature for tighening fasteners, to let
the user know the screw was as tight as it should be.

But the Craftsman hex key hasn't twisted yet.


I agree with JR, that screws this size shouldn't be torqued to the tighness
of cracking when they let loose.
I prefer to use medium-hold blue threadlocker for small fasteners.. easy
enough to remove for disassembly when required.

The screw and threaded hole (in 1018 steel) don't seem unhappy.

The intent is accurate fixing of one part with respect to the other. Great
strength isn't required, just great stability. And, it would be a real nuisance
if the screw backed out, as it will take some disassembly to get at these screws.

I may well use locktite (or epoxy) for final assembly.

I designed the assembly to allow for soft soldering, if needed to fix the parts
together stably, but it does not appear that soldering will be needed.


In high quality equipment (aerospace), the countersink angles of the screw
head and the base material could create a taper lock, but that's probably
not the case in this situation. Medium hold threadlocker would likely
eliminate a taper lock if applied to the countersink area.

From the look of the countersunk holes, some taperlocking may be happening.


All that may have happened was that the key had a soft spot, or that it was
one of the Unbrako-type keys.

I buy the soft-spot theory. I think all vendors endeavor to make Unbrako-style
keys, but with varying degrees of success.


I'd feel fortunate that the key twisted insead of snapping off, which can
result in a very sharp projection which fingers may have come in conact
with.
Additionally fortunate that the screw didn't require drilling to remove it.

I don't think there was any danger that the key would snap off. It twisted at
least one full turn axially quite nicely, without pretzeling. Nor did it break
when I twisted it back to more or less straight.

Drilling would be a nuisance, but not that hard because the whole assembly is
easily removed and clamped in the mill vice. A small carbide drill bit would
make short work of the screw.

Joe Gwinn



"Joseph Gwinn" wrote in message
...
In article ,

The hex socket screw seems OK, and has been done and undone many times so
far. If I wear the 10-32 screws out, I'll just replace them.

The Craftsman hex key is standing up nicely too.

The weak link is the old hex key. I wonder if the plating had something to do
with it, as they may have had to heat the keys to allow hydrogen from plating to
diffuse away, to avoid hydrogen embrittlement. The Craftsman hex keys are
black oxide finished, as are the hex socket screws.

http://en.wikipedia.org/wiki/Hydrogen_embrittlement

Joe Gwinn