It occurred to me that the users' weight shouldn't be supported by screws
(shear), but instead, by welded pins on the device's brackets that protrude
thru holes drilled in the door frame.. with the screws providing secure
attachment to the frame.

As for DW screw's binding, that's appropriate in wood or softer materials..
essentially a result of surface area contact and displaced material. Steel
doesn't compress.

As for the ductwork comment, those screws aren't intended to support loads,
only to keep the joint from separating. Ducts are generally suspended by
various types of straps and brackets.
Basically, all that sheetmetal screws need to do is pierce a hole and then
be driven in. The steel is soft and thin so very little cutting action is
taking place.
In thicker steel, even with a drilled pilot hole, most common screws (DW or
SM) will not cut threads or displace the metal enough to attach something
securely.
I know this from experience.. nearly all common screws will break before
they cut or displace thicker steel.

When I mentioned fine threads, I was thinking 32 TPI, not the difference
between sheetmetal screws and DW screws (or fine-coarse versions of each),
but forgot to mention that.

I suspect that 4 welded 1/4" pins (each side) would probably be more than
adequate for supporting most folks' weight. This would most likely require a
template for the installer, and fairly accurately positioned holes for the
pins and screws.
I think the nut-sert fastening system would probably be best, but probably
too complicated for many folks to install. They don't absolutely require a
special installation tool.. they can be installed with a stud and washer,
nut and wrench.

Aside from the methods of fastening a device to a door frame, many folks
probably wouldn't like the idea of not being able to close a door because
this thing's installed.
If they have a door with a steel frame, it's likely for security.

--
WB
..........


"Existential Angst" wrote in message
...

You should be examining real screws.. self-tapping or other style for
mounting a chin-up bar.
Generally, the most secure method will be to get as many threads as
possible into the thickness of the material that the part is being
attached to, which means a fine-thread, self-tapping type screw, most
likely (or nut-sert type products that were mentioned previously).
If the fasteners that you recommend fail, the user could sustain a
laceration, or possibly brain trauma. Good luck fending off the lawyers.


Well, the real Q is along the lines you've mentioned.
"Real" sheetmetal screws, such as hvac ductwork, really can't put ANY
threads in the material itself, ductwork is just too thin. I always
thought the tek-type screws were the wrong thread design for this
application.

Even 16 ga is sort of thin, but chassis screws seemed to have been
developed for this purpose, which is why I mentioned them in the earlier
thread, but no one picked up on this. Roger touched on these, which I'll
continue in a response to him.

Chassis screws seem to be a discontinued item, so I wonder how practical,
under load conditions (not really found on radio chassis) threads in thin
material is.

Which is why I'm asking about threading vs. *binding* of thin material
together, via a larger ratio of major to minor diameters.

I keep mentioning SR screws, because the coarse thread screws really seem
to have a much better major/minor diam ratio, and I believe I've seen
specialty-type screws that used this strategy.

If the answer is, STFU and buy a box of self-drilling sheet metal screws,
then I'll do it, but this never really seemed to be the "right" solution,
on basic geometrical/mechanical grounds, for the above threading reasons.
--
EA