Anchors for a fiberglass door?

[triangleforge]

A friend of mine was watching the construction Rat's door knocker in progress and wants something similar for his house. To work for him, though, I'm going to have to change the mounting system, because his front door looks like a heavy, solid oak door, but in reality it's fiberglass over a foam core. The fiberglass shell seems fairly substantial, but it's not going to work to mount the knocker with wood screws, which will pull out in fairly short order.

Are there products out there that would work to anchor a door knocker on 'glass? Would some sort of an expanding bolt like a toggle screw or molly bolt work over the long haul? The weight & torque on the anchors won't be that much -- they'll probably get more stress over time from the door opening & closing and from freeze/thaw cycling than from people using the knocker -- but they do need to stay stable and snug for years.

[sno_duc]

These might be the ticket 
http://www.clipsandfasteners.com/Nutsert_10_24_Uss_p/a10270.htm

The Auveco Nutsert was developed to offer both the production-oriented designer and engineer a unique and versatile anchor nut-type insert for high-speed installation. This Auveco system gives the designer the option to design for blind or open applications, eliminating and simplifying his design problems.
The Auveco Nutsert system provides a cost-saving method of installing clean, load-bearing steel threads in castings, fiberglass, fiberboard, plastics, wood or almost any ductile material more than .030" thick.
A simple hand tool installs the Nutsert...it is ready for use in seconds... no finishing is required after installation.
Auveco Nutsert's advanced design offers unlimited grip range in a minimum of sizes...inventory is minimized to one body dimension per thread Size; ideally suited for blind...buried... and through holes. The ingenious taper-lock principle locks-in the Nutsert preventing spin or twist; installs in flat or curved surfaces and is self-tightening with repeated use. The unique design of the installation tool eliminates marring of the parent material surface.

[geoffduc]

I've been using that type of threaded insert for quite afew years with no problem at all in all types of materials.

Over here in the UK they are known as Avdel captive nuts.

Geoff...

[The Architect]

You can thru-bolt it and use fancy cup washer on the inside.  If the house is located in a cold area, you might get sweating on the thru-bolts. 

[ducpainter]

A nutsert will put it together...

a properly installed one will allow dis-assembly...maybe.

Take it for what it's worth.

[MendoDave]

At United airlines we used a "floating" Nut cert. It gives you a little more flexibility since the threaded part can float inside the casing about a millimeter or so. That helps the screw holes line up.

You need to counter sink the hole and then whip up some resin and "micro balloons" Then put the inserts in, wipe off any excess resin and then stick a little vellum or plastic or tape on it. That will keep the expanding resin flat. Be careful not to use too much because it will expand. Then shine a heat lamp on it if you can, or go easy with a heat gun. If not just let it cure longer.

It's best if you can take the door off and lay it flat.

[rgramjet]

Thru bolt.  Whip up a couple wrought iron spiders or whimsical bugs, bored and threaded to act as the nuts on the inside of the door.   

[ducpainter]

Thru bolt.  Whip up a couple wrought iron spiders or whimsical bugs, bored and threaded to act as the nuts on the inside of the door.   

You can thru-bolt it and use fancy cup washer on the inside.  If the house is located in a cold area, you might get sweating on the thru-bolts. 

He isn't blowing smoke you know.

[Speedbag]

Thru bolt.  Whip up a couple wrought iron spiders or whimsical bugs, bored and threaded to act as the nuts on the inside of the door.   

Yep.

Can't beat a through bolt....

[rgramjet]

He isn't blowing smoke you know.

Hey, every once in a while a contractor and an architect can agree!

[ducpainter]

Hey, every once in a while a contractor and an architect can agree!

It's one of those 'special' moments.