The task is to join two overlapping pieces of 22 gauge steel, but they
will have to come apart once in a while, and one side is not accessible
when closed. Would sheet metal screws be alright here?
There will be a neoprene gasket between the steel pieces, and I'm
thinking that may help to hold things together in the presence of
vibration. This for a motorcycle chaincase I'm constructing.
"Jim Stewart" wrote: I wouldn't trust them on a bike. Try welding or
brazing nuts to the back. (clip)
I agree. Furthermore, after they have been removed and retightened a few
times, the holes will begin to enlarge, and possibly release. Threaded
pop-rivets might be an easy way to make the threaded holes.
Please explain a bit about threaded pop-rivets. I've not heard of them. Do
they leave a threaded nut on one side, or a threaded screw; or maybe a
threaded member on each side.
Bob (pop rivet is an oxymoron) Swinney
Not really pop-rivets. what you want are called "Rivnuts".
They fit in from the near side, and the tool draws the threaded far
side towards the near side, expanding a section in between. They often
have a rib which gets oriented in a notch cut from the hole to prevent
rotation if you don't pull it down tight enough.
You *can* pull them down with a stud in a pop-rivet tool,
thought there are much better tools for the purpose.
You can find some sizes at MSC, and perhaps some tooling, but I
go to eBay for this.
Here is an auction which has some steel Rivnuts in several
and here are some more:
They come also in aluminum, typically with a greenish finish, though I
have seen plain aluminum. Here are some of them:
As for the tooling to install them -- here is an example of the
kind which I prefer:
Pull out on the mushroom head on the end of the handle, hold the Rivnut
on the screw at the other end, and push the mushroom back. This will
run the screw up inside the Rivnut. Place the Rivnut in the hole
(orienting it properly if there is an anti-rotation rib) and squeeze the
handle to set the nut. Then pull on the mushroom again to unscrew the
tool from the Rivnut. (Note that for a given size of Rivnut, a given
grip range, and a given thickness of sheet metal, you have to adjust
the threaded sections of the nose anvil to get it so it sets properly --
not too loose, and *especially* not too tight, which can rip out the
threads from the inside. With experience, you can develop a feel so you
won't strip them without adjusting, but this is meant as a production
tool (though there are air-powered tools for faster production), so it
can be set so the full squeeze does it right.
Each one of these is for a single size, so be sure to get the
one to match the screw size which you wish to use -- or collect them
all. That particular style ranges from 4-40 through 1-4/20, along with
a corresponding set of metric ones, which are much less common.
There are similar tools (tubular handle with lever to actuate)
which will notch for the orientation/anti-rotation ridge. They will not
have a mushroom handle, and they, also, will be for a specific size.
You *can* rebuil these for different sizes with kits of parts,
but I find it more convenient to have one of each size on hand.
There is a smaller one which is drawn up with a wrench, but it
does not appear in my searches today. I have a few of these (6-32,
8-32, and 10-32 IIRC) for use where there is not room for the
mushroom-handled tools -- but they are slower.
The air-driven one looks really nice at the moment, but it has
over six days to go, and already has several bids. :-)
I also have a hand-pumped hydraulic one, for pulling up the
larger steel Rivnuts.
However -- there are cheaper designs, which I personally would
avoid, which show up regularly. Here is an example of what I avoid:
Note that I have no financial interest in any of these auctions,
though I may have purchased from some of the vendors in the past.
Email: < email@example.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
I really don't think so. And when they do fall out, they'll end up in
your or somebody else's tire... I have a snowblower that manages to
shake several sheet metal screws free every winter and by spring
they're all in my wife's tires!
Carrol Smith's book shows a variety of captive nuts and nutplates. For
what you're doing (which is non-structural, right?) I think pop-rivets
would be fine too.
No. Sheet metal screws are a one-time deal. If removal and replacement
is contemplated, go for another solution. They are also not to be
trusted where there is vibration. And their sharp points will be
waiting to savage an unwary mechanic's hand, even yours.
Maybe, but not much.
Use captive nuts, or nuts brazed to one of the pieces. Or a long thin
strip of metal with holes drilled and tapped at suitable intervals.
Think about using cheese-head screws with holes drilled for locking
wire. Or put the screws through and braze their heads to the side
that's inacessable when assembled and run castellated nuts or
nylon-insert locknuts on from the accessable side.
I would use "riv-nuts", "thread-serts" or similar. See:
Nut plates are higher quality, possibly overkill for your present
application but if you use them it's well worth taking the time to make
the tool shown in
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