fixing ss bolt / screw into ply using epoxy

[simonfraser]

Hi,
i have ordered 40x ss SCREW fittings for fixing into existing screw holes in ply epoxy.
this has come back as a ss bolts :-((
i can of course send it all back and get them to make up the correct items.

but, for maximum strength, should i fix them in with epoxy anyway, & if so, will it be just as strong with the bolt thread as the wood thread ??

can i use araldite epoxy, or is there better ??!!

thanks for your input, Simon

 

[snowleopard]

bolts have a lot less thread than woodscrews so will be less secure. If you use Araldite, go for the regular, not the rapid.

 

[simonfraser]

hmm, that's what i was worried about too, re the thread grip, shall send it back :-((

 

[snowleopard]

If you can get at the back of the panel the best alternative would be to stick a Bighead nut on the back.

 

[Krusty]

Obviously the strength will depend on the thickness of ply and depth of penetration of the screw thread, but there is a technique using WEST epoxy that results in a high-strength fixing:
1. Drill out the holes to at least the diameter of the machine-screw or bolt, but no more than 1mm greater.
2. Coat the threads of the screws/bolts the thinnest coating of a release-agent (WD40 works)
3. Mix the WEST, and using a small brush, or pipe-cleaner, ensure that the wood inside the holes is saturated with the resin and the holes part-filled.
4. Insert the screws to the full depth of the hole and let the resin set. It forms a 'nut' bonded into the fibres of the wood, which is itself reinforced by the resin penetration.
5. After setting, withdraw the screws/bolts: depending on the release-agent, you may need quite a bit of force, and the separation may happen with quite a crack! Thereafter, you have a threaded hole which will accept the screw/bolt almost as if it were a metal nut.

I rebuilt my old trimaran with West epoxy after storm-damage in 1978, and used this technique in places. She is still going strong. (Pic taken 1984).

 

[simonfraser]

thanks piota,

that is v. helpfull. the fixings are for keeping the netting tight.
if it all pops out i won't fall through.

can i use araldite instead of WEST ? just easier to get in small quantities.

if you are ever in essex let me know if you wish to join me for a sail.

Simon

 

[Krusty]

When I first used WEST, in 1978, it stood for 'Wet Epoxy Saturation Technique'.
The whole point about the resin was that it is (initially) very 'thin' and highly penetrating into the wood, reinforcing it. After I rebuilt Boadicea's outer hulls in 6mm ply (saturated with it from both sides) people would knock on them, look puzzled, and ask me if it was steel.
I'm afraid I have assumed that your boat's construction is also wood, and resin-bonded, if not resin-saturated. I would not endorse using Araldite; it is not thin enough. I can't help more without knowing more about the nature and thickness of the material, size of fittings and the point-loadings.
I can tell you that I fastened my 'trampoline' nets at 150mm intervals.

 

[Krusty]

I've just realised that para 3 of my post above is incomplete (failing memory cells!)
After resin-saturating the inside of the hole in the wood, more resin is mixed with one of the WEST fillers to form the glue, which is then added to the hole, screw inserted, etc.
Sorry!