"Wild_Bill" wrote in message
...
Numerous responses have suggested nut-sert type fasteners with machine
screws for applications in sheet metal, which is what you're attempting.
They're what the automotive and commercial equipment manufacturers use
because attaching parts to sheet metal isn't as simple as using a screw.
The majority of steel fasteners aren't intended to COLD FORM tight
(binding) threads in steel, which is the part that you seem to be
ignoring. Steel isn't like wood, and sheet steel has more limitations.
If the screw is hard, it will snap.. if it's mild steel, the threads will
smear.. no worky.
There are self-drilling screws that work well with thin steel, but may not
work well (100% of times tried) for everyone.
With many of the fasteners you're hoping will work, you end up with a
small portion of one thread (10-30% of a single thread) holding a load.
This is exactly correct -- essentially "camming" the two pieces together.
Also, I've resolved the shear part of the load (shear will essentially be
zero), so there will only be pullout/axial loads, and those are inherently
minimal.
So even tho the loads on the bar itself could be quite heavy, the screws
themselves will feel almost none of these loads, so this method may be
suitable.
Ito of the other attachment methods, what I didn't mention is that these
bars will often be installed by end-users, so fancier rcm-type stuff is not
a practical reality. Even riveting, which in principle is a good fastening
solution, is a very very long shot, so I think I'm stuck with making the
best of a screw solution.
I'll review your links more fully tomorrow, and greatly appreciate your
detailed responses, and the others' responses.
What I"ve learned so far ito screw-type fasteners is that "deep threads" and
"sheet metal" do not go together, as deep threads are a wood-type
application.
Which is OK, except that now there is no option of a drill point, which is
handy to have in the installation process.
McFeely's was surprisingly inept at answering my Q's. Tech support was
measuring an 8-32 screw and telling me the root diameter was .035!!!! The
good news was the major diameter was .11, so whatever that screw was, it did
have some bite!
The installation I did a day or to ago, with the screw not of my choice,
seems sound, nevertheless -- knock on wood/sheetmetal.
I'll post back after reviewing your links.
--
EA
You'd get
better contact with a nail, as in woodworking, but not appropriate for
metal.
You're most likely either going to need threads in the base material
(nut-sert), or screws that can CUT threads.. self-tapping screws, also
suggested in earlier responses. Trouble is, there isn't much thickness for
a reliable connection.
Self-tapping screws are intended to be installed with a specific (ideally
punched) hole size, which isn't easily made with a hand drill.. the
3-sided hole in thin metal, everyone's seen that, right? Or the DIY-types
that work the drill around in a large orbit as a matter of habit.
http://www.theindustrialdepot.com/ri...llow-zinc.html
http://www.youtube.com/watch?v=Wf-mwytdurQ
A gurl (with dimples) can do it
http://www.youtube.com/watch?v=p8oMHuLxCcs&NR=1
Installing the rivnut/nut-sert type fasteners doesn't actually require
special tools.. a stud, washer, nut and wrench will usually suffice. There
are styles with ribs to grip the sheetmetal hole to prevent the fastener
from spinning while installing them.
http://www.rivetdirect.com/
An alternate fastener might be a drive rivet, which provides all of the
fastener's diameter for shear strength (unlike hollow pop-type rivets).
http://www.rivetdirect.com/driverivets.html
Machine screws/bolts with a very short shoulder on them (not threaded all
the way to the underside of the head) will have a greater shear strength,
used with the above rivet-nut inserts.
The nut-sert-type fasteners are a solution, not something that needs to be
analyzed.
The ultimately cheap, reliable solution will be MIG wire, properly applied
with a welder.
BTW, threads on most fasteners are rolled (displaced), not cut.
--
WB
.........
"Existential Angst" wrote in message
...
Awl --
I think the whole sheetmetal/drywall screw thing is resolved with the
"deep thread" class of screws:
http://www.gardensheds.greenhouses.a...ew-threads.htm
http://www.theindustrialdepot.com/de...ead-screw.html
For example, a coarse sheetrock screw measures .094/.146 minor/major
diam
The drill-point sheetmetal screw (that I wound up using) measures
.130/.165.
So the SR screw, being a deep thread, has *a lot* more bite.
McNeely's has a variety of deep thread screws. One section is he
http://www.mcfeelys.com/search/fsl , altho it's not clear just how deep
is deep.
In http://www.mcfeelys.com/tech/dimensions.htm , it's not clear if "B"
(their body diam) is the same as the root diam.
If so, this is not as deep a thread as the name suggests.
McNeely's deep-threads (inch length) are about $20/1,000 -- McNeely's
seems pretty reasonable.
But here's the Q:
Can I get REALLY deep thread screws? What would they be called, or their
application classification?
I'm thinking on the order of .125/.200, ie, about .040 grabbing on the
radius.
I've hunted around, but haven't come across anything deeper than the reg.
deep thread spec.
Any ideas of what a custom run of screws might cost? Quan, $$ ?
I'm thinking if I ordered a standard #12 or #14 screw, and asked them
just to set the machine to cut a little deeper, I'd get the screw I
wanted....
Iny ideas on who might do this?
--
EA