Captive Nuts?

[Porthandbuoy]

I've just made a new teak cockpit sole to replace the delaminating ancient ply that was there before. Historically, the cockpit sole has been fastened in place using self-tappers (~5mm). The evidence for this is the number of epoxy filled holes around the GRP flange the cockpit sole sits on.

The GRP flange is 25mm wide and from 6mm to 8 mm thick. Google has thrown up a bewildering number of options, so can anyone recommend a captive nut system I could use to securely locate the cockpit sole?

 

[Fr J Hackett]

Thought this was a Brexit thread You could epoxy the nuts to the underside of the flange, if you can weld then weld them to a large penny washer to give a greater surface area. Then secure the sole with countersunk machine screws.

 

[coenvanwyk]

You could try SISO in Denmark, they have an online catalogue of knock down fittings (page 63), including brass inserts. I am not sure they will go into a relatively thin fibreglass flange, but you might be able to beef it up. I ended up using something they no longer have in their caralogue, a screw-in brass insert that takes a m6 bolt, but this is about 10mm deep. They also do a nylon bushing/insert, this may also be an option for you.

http://siso.dk/Files/Images/Catalogues/Documents/Knock%20Down%20Fittings.pdf

 

[Poignard]

Big Heads

https://www.ecfibreglasssupplies.co.uk/category/inserts-and-fasteners

 

[Porthandbuoy]

Big Heads

https://www.ecfibreglasssupplies.co.uk/category/inserts-and-fasteners

They look like they might do. Thanks.

 

[Ian_Edwards]

You could try SS rivet nets, the are designed for sheet steel, but work well epoxied into GRP, just drill a hole with minimal clearance and glue in with Araldite, making sure you clean any oil or grease off the rivet nut with acetone or IPA.

Then use a standard machine screw, with a CS head (or hex head if you prefer). I've used CS with allen key socket heads, they seem to be more robust if you have to take them out.

I've used them extensively for fixing the floorboards in the saloon.

Just Google "SS rivet nuts" and you'll see a wide variety for sale.

 

[Pagetslady]

How about rawlplugs that way you can reuse the screws and existing holes, if you get the correct size for the screws, the rawlplug will open out on the under side and make a very strong fixing.

 

[Porthandbuoy]

Thanks Ian.
You gave me a good lead with 'SS rivet nuts'

Looks like THESE are just what I'm looking for.

 

[Ian_Edwards]

Thanks Ian.
You gave me a good lead with 'SS rivet nuts'

Looks like THESE are just what I'm looking for.

Yes, that's what I use, it's worth countersinking the hole, so that the rivet nut sits flush the the GRP.

They are very good in shear, don't take any load in compression, but I'd be wary of using them in tension where the strength depends on the quality of the bond between the GRP and SS. But fine for fixing floor boards or gratings.

 

[crisjones]

You might want to have a look at Rawlnuts - http://www.rawlplug.co.uk/products/...ut-flexi-plugs/rawlnut-flexi-plug-with-screw/ they have a brass threaded insert so corrosion is not usually an issue and when tightened up they will form a watertight seal around the screw and the hole - they work really well and are very easy to use.

 

[DinghyMan]

Yes, that's what I use, it's worth countersinking the hole, so that the rivet nut sits flush the the GRP.

They are very good in shear, don't take any load in compression, but I'd be wary of using them in tension where the strength depends on the quality of the bond between the GRP and SS. But fine for fixing floor boards or gratings.

And it might be worth popping a stanless repair washer on them before pulling them tight to prevent pull out so you have stainless washer, GRP, countersunk part