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Rivet nuts


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#1 MatsNorway

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Posted 29 October 2012 - 11:18

I am about to use rivet nuts for the first time. Is there anything that needs to be mentioned about them? i know nothing about them. I learned about their existence today.

We are going to use a slightly bigger drill tap to make the top of the rivet plane with the profile.

http://www.wurth.co....-knurled-st-m10

Very cool and neat solution, i think im going to use this more if there is no obvious weaknesses.

Edited by MatsNorway, 29 October 2012 - 11:18.


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#2 mariner

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Posted 29 October 2012 - 12:16

Rivnuts are great, I didnt know they existed until I had done half my car with either bolts behind panels - unreachable after assembly or crude studs. Some thoughts ( sorry if a bit "jack and Jill"

- there are two kinds - aluminium and steel - you can pull up the ally ones up to the 6mm ( internal thread) size easily. I HAVE pulled up 6mm steel ones with a hand tool but its really hard work and , I suspect, could break the hand tool eventually.

So if you want to use steel rivnuts above 6mm you may want to get the power tool ( not cheap!)

The alloy threads arent that strong and there is no locknut so use Loctite every time if you can.

Don't make my big mistake!! - I had to attach an aluminium undertray/venturi so I installed the rivnuts on the chassis and planned to offer up the undertray and screw the capscrews into the captive rivnuts. Because the undertray was large and floppy it was hard to start each capscrew and I crossed the rivnut threads ruining them. In the end I ran a screw from the inside through the rivnut so it stuck out as a locator stud. Then teh undertray can be pushed over a steel thread and a locknut run on afterwards.

I imagine that if I had used steel rivnuts it would have worked OK.

Also there are countersunk and non countersunk ones . To get a panel to fit perfectly flush you need the countersunk kind

#3 MatsNorway

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Posted 29 October 2012 - 14:39

The ones we are using is M8 stainless i think.

They are going into a 3000 x 80 x 80 T=4mm profile.

Im not sure he got the countersunken ones. I think hes just gonna drill with a slightly bigger bore to make em sit lower.

Edited by MatsNorway, 29 October 2012 - 14:40.


#4 mariner

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Posted 29 October 2012 - 18:45

I think you will need a power tool to pull them.

One thing I didnt mention - probably obvious - is to be very, very careful to deburr the holes both sides.

The probelm is that the rivnut relies on its crush generated clamping force to resist torsion. Thats exactly what happens as you tighten the bolt up. The stronger the bolt to rivnut meshing the bigger the problem unles you use torque wrenches every time.

What happens is that the rivnuts will gall on the softest material and then rotate. If the bolt gets corroded a bit in the rivnut hole duriing service you rotate the rivnut and cant ever get the bolt out if its into a blind space because there is nothing to grip on.

Guess exactly what I did !!

#5 chunky

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Posted 29 October 2012 - 20:35

I think you will need a power tool to pull them.

One thing I didnt mention - probably obvious - is to be very, very careful to deburr the holes both sides.

The probelm is that the rivnut relies on its crush generated clamping force to resist torsion. Thats exactly what happens as you tighten the bolt up. The stronger the bolt to rivnut meshing the bigger the problem unles you use torque wrenches every time.

What happens is that the rivnuts will gall on the softest material and then rotate. If the bolt gets corroded a bit in the rivnut hole duriing service you rotate the rivnut and cant ever get the bolt out if its into a blind space because there is nothing to grip on.

Guess exactly what I did !!


Get a bolt/setscrew plus a loose nut and washer. Screw the bolt - full thread depth - into the rivnut, run the nut down and push the washer against the rivnut. Hold bolt stationary with a spanner, screw nut down with another spanner. This sets the rivnut. Don't just pull up the rivnut by turning the bolt - result is stripped threads & much cursing. Experiment a few times. Add Loctite/sealant to taste.


Also follow all Mariner's advice.

#6 bigleagueslider

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Posted 30 October 2012 - 00:47

Rivnuts are convenient for quick installation in thin panels, but they should not be used where high strength is needed. As others noted, they tend to strip out very easily. And when they do strip out, they can be a real pain to remove.

A much more reliable solution is the floating nutplate commonly used in aircraft applications. However, nutplates do take a bit more effort to install.

Regards,
slider

#7 DogEarred

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Posted 30 October 2012 - 07:33

JCB successfully use quite a few rivnuts (rejoicing in the name 'Bollhoffs') on their machines to secure some quite bulky components.

They work well but the heavy weight does have an adverse affect their lap times...

Edited by DogEarred, 30 October 2012 - 12:41.


#8 rbm

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Posted 13 November 2012 - 15:31

Rivnuts are convenient for quick installation in thin panels, but they should not be used where high strength is needed. As others noted, they tend to strip out very easily. And when they do strip out, they can be a real pain to remove.

A much more reliable solution is the floating nutplate commonly used in aircraft applications. However, nutplates do take a bit more effort to install.

Regards,
slider



as slider states, rivet nuts should never be used in high load, potential high load (think carefully about shock created high G loading) or safety situations - they come out letting quite easily whatever is attached to them fly around loose - have first hand experiance of a large extinguisher flying about, complete with bracket and the fixing bolts and riv-nuts in an incident.

#9 MatsNorway

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Posted 13 November 2012 - 16:05

It was ditched in favour of my original design. who was just extra holes on the side to get access to the nuts.

However rivet nuts would have suited this type of application.

#10 Anthem

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Posted 14 November 2012 - 01:59

FYI

http://www.pemnet.co...sheetmetal.html
~pressed into ductile metal, displaces the host material around the mounting hole, causing it to cold flow into a specially designed annular recess in the shank of the fastener~


Been using "PEM nuts" for many years. Only issue we had come across, is a loose fastener can act like a hammer and drive the "PEM nut" out. Fixed by always using "loctite", teflon tape or lockwasher on the fastener.