Sheet metal screws: good enough for this?

I wouldn't trust them on a bike. Try welding or brazing nuts to the back. Use lockwashers and loctite on the screws.

I wouldn't count on it.

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.

to hold things together in the presence of

What you want are aircraft nutplates.

Kevin Gallimore

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.

Tim.

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.

Pem nuts

Martin

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 <

>

Ted

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.

[ ... ]

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 metric sizes:

Auction #3880108987

and here are some more:

Auction #4534138893

They come also in aluminum, typically with a greenish finish, though I have seen plain aluminum. Here are some of them:

Auction #3879123472

As for the tooling to install them -- here is an example of the kind which I prefer:

Auction #3880590104

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:

Auction #4533826680

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.

Good Luck, DoN.