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Captive nut in thick fibreglass
matty h - 1/9/14 at 08:40 PM

I need to put a captive fixing in some thick fibreglass but have no way of getting to the back of the panel, it did have a rivnut in it but due to the thickness this did not hold and has pulled out.
The hole is around 10mm for a m6 rivnut.
Any ideas ???
Thanks Matty

ReMan - 1/9/14 at 08:51 PM

For anything more than cosmetic load I'd have thought you need to put a bonded in substantial tapped plate of some description at production.
Are you trying to do this into an existing piece of fibreglass?

twybrow - 1/9/14 at 09:53 PM

Google 'Big Heads'. They are fasteners for composites. They bond to the surface using PU or similar. You can even apply for free samples of what you want from their website! I have several on my car. I also made my own when I needed something oddball.

MikeRJ - 1/9/14 at 09:56 PM

For fibreglass you can use rubber "well" nuts. These expand behind the fibreglass when tightened, but being rubber the distribute the stress around the hole so you don't risk cracking.

Easily available on eBay in various diameters and lengths and they are fairly cheap.

inkafone - 1/9/14 at 10:07 PM

Plasterboard anchors work - like Heavy Duty Gun Hollow Dry Wall Cavity Fixing Anchor Setting Tool Not Silverline. Or use a threaded insert, use masking tape when screwing in to minimise any gelcoat cracking.

matty h - 1/9/14 at 10:07 PM

Seen the big head fixing was looking at using one of these until I found out I could not get in behind the panel.
The rubber well nuts could look like the way forward or the cavity wall fixing.
Thanks everyone for the suggestions.
Matty

[Edited on 1/9/14 by matty h]

twybrow - 1/9/14 at 11:23 PM

quote:
Originally posted by matty h
Seen the big head fixing was looking at using one of these until I found out I could not get in behind the panel.
The rubber well nuts could look like the way forward or the cavity wall fixing.
Thanks everyone for the suggestions.
Matty

[Edited on 1/9/14 by matty h]


No need to get behind the panel. Drill it and bond it to the outer surface so the threaded section is in the fibreglass. You could even grind a small recess so it is all flush.

renetom - 2/9/14 at 08:07 AM

Toggle bolts should do the job & gets something behind the panel

rdodger - 2/9/14 at 02:34 PM

I have used these in similar circumstances

http://www.modelfixings.co.uk/threaded_inserts.htm
I used a blob of epoxy on them before screwing them in.

http://www.shop4fasteners.co.uk/threaded-inserts/self-tapping-inserts-for-soft-wood/c-24/p-966


[Edited on 2/9/14 by rdodger]

[Edited on 2/9/14 by rdodger]