Rivnuts and fibreglass skins

[tanuki.himself]

Has anyone any specifically tried rivnuts as a blind fixing into fibreglass skin/ composite panels? I'm figuring that they would probably give a larger, more consistent flange on the back side than pop rivets and be stronger all round than self tapping screws into thin sheet material. But i'd like to learn from other peoples experiences before investing in a tool and deciding what material would be best - steel, aluminium or stainless....

 

[john61ct]

Not direct experience with composites, but have widely read positive user reports for fiberglass skin alone.

Of course lots of variability in the skin strength as opposed to metal sheeting

So I would do testing if you're hanging heavy loads, how many you want supporting a given weight.

Combined with L-track gives lots of flexibility.

Stainless is the best.

Plusnuts from BOLLHOFF RIVNUT
http://www.bollhoff-usa.com/static/pdf/downloadcenter/EN/RIVNUT-US-version-EN.pdf http://www.rivetnuts.com/plusnuts-rivnuts.htm

Call for your local distributor, they can supply a cheap tool too if you aren't doing thousands

 

[S2DM]

I’d personally recommend against it. I’ll skip the detailed explanation of how a fiberglass skin bonds to its core, but the take home point is that is strength is from the aggregate of its bonding surface. Adding a point load to the skin alone does not result in a very strong fastener and really increases your chances of delamination.

a much better choice would be to epoxy in threaded inserts into the core material. What I do is is drill my hole through the skin and the core material. Then dig out the core material around the hole such that you have a big plug of open space behind the skin, atleast .25” greater diameter than the hole in the skin. An easy way to do this is to drill the hole, then take a router bit the same size as the hole, sink it so the shank is in the hole and then run the router to chew out a larger hole in only the foam.

Next step is to back fill the core with toughened epoxy, tape over the hole, and let it dry. Now redrill the original hole, and then epoxy in your threaded anchor.

doing it this way bonds the point load down into the core material and really increases the area over which the point load is exerting it’s force, which makes for a much stronger bond, and one unlikely to delaminate.

 

[headingwest]

I always use rivnuts in composite panels. Strongly recommended.

If you have an air compressor get an air nut riveter from eBay. Much easier to use.

Rivnuts are a bit stronger than screws and allow you to remove the bolt/fitting repeatedly.

For slightly added strength I drop some adhesive into the hole I drill for the rivnuts.

For lots of added strength I glue a small sheet/strip of thin aluminium over the area I need to mount things on. This aluminium might anything from an inch to 5 inches across.

I use flush mount rivnuts for interior eg light fittings. I use flanged rivnuts for exterior as in my mind they appear stronger.

I carry 2 different depth rivnuts depending on whether I'm going into just fibreglass or both alloy + fibreglass.

Sent from my SM-N975F using Tapatalk

 

[tanuki.himself]

If you can deal with a protruding surface flange, You might try Jacknuts.

i hadn't seen these before - i have used something similar but much bigger for plasterboard (sheetrock?) but didn't know they came in smaller sizes. thanks

 

[tanuki.himself]

I’d personally recommend against it. I’ll skip the detailed explanation of how a fiberglass skin bonds to its core, but the take home point is that is strength is from the aggregate of its bonding surface. Adding a point load to the skin alone does not result in a very strong fastener and really increases your chances of delamination.

a much better choice would be to epoxy in threaded inserts into the core material. What I do is is drill my hole through the skin and the core material. Then dig out the core material around the hole such that you have a big plug of open space behind the skin, atleast .25” greater diameter than the hole in the skin. An easy way to do this is to drill the hole, then take a router bit the same size as the hole, sink it so the shank is in the hole and then run the router to chew out a larger hole in only the foam.

Next step is to back fill the core with toughened epoxy, tape over the hole, and let it dry. Now redrill the original hole, and then epoxy in your threaded anchor.

doing it this way bonds the point load down into the core material and really increases the area over which the point load is exerting it’s force, which makes for a much stronger bond, and one unlikely to delaminate.

thanks - i understand the logic of epoxy anchors and how the load is distributed through the material, but its a bit overkill for my needs. I'm looking at 3-4mm screws for light switches, small brackets, towel hooks etc, and for holding and locating glued on mounting strips in place while the adhesive dries...

 

[Peter_n_Margaret]

Not very tidy, but you get the idea....

I use this method occasionally for attaching stuff to the skin where the load is relatively high but requires removal from time to time.
I have also used aluminium pop rivets with aluminium stems (so the pull up force is limited).
Simple self tapping screws are fine for light loads.
Cheers,
Peter
OKA196 motorhome

 

[Peter_n_Margaret]

and for holding and locating glued on mounting strips in place while the adhesive dries...

I use double sided foam tape.
Not only does it hold the part in place while the adhesive sets off, but it also establishes and maintains the glue thickness that is required to combat differential thermal expansion.
Cheers,
Peter
OKA196 motorhome

 

[Peter_n_Margaret]

Couple more pics...
This build was in 2004 and is still going strong.


Cheers,
Peter
OKA196 motorhome

 

[Victorian]

If you are only using screws to mount light switches and such without creating a point load (hanging cabinets....) you are fine by just pre-drilling and screwing. If it's for something like a coat hook, I would use a base plate and adhesive.

At Unicat, we have used riv nuts a lot but sometimes it's just not an option as the space is confined or hard to reach.

 

[ExpoMike]

I would look at these types of rivnuts as they are slotted on the compression part and create 4 large flanges on the backside of the part. I have used these in plastic panels and they work well for applications where you want to spread the load a little more but are not trying to hold a lot of weight.

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