How to Put Thread Inserts in a Composite Layup

[mobefive]

Hello all,
I am laying up a ski with a composite sandwich which looks like this: From the core to the top: Expanded PVC core, Aluminium plate with Chopped Strand Glass Matting Underneath the shape of the plate, then a Full layer of CSM over the top of the ski, then a layer of Uni-Directional Carbon, then another layer of CSM then a Tissue layer to finish it off. Now that process is all set up to go, but what I want to include is thread inserts (not brass, probably stainless) permanently put in place through the aluminium plate, but flush with the top layer of the laminate.

Now I can drill the plate to accept the inserts and epoxy them in place from underneath and countersink the core to accept both the plate and the inserts. BUT what my concern is, is how to lay up the next 4 layers with resin overtop of my inserts and still get the insert flush with the top of hte laminate, without being full of resin and how do i make it go through the layers of glass and carbon?

I am sure this problem is common and easy to fix, just need to know some industry secerets guys.

Regards,

Cameron Leake

MobeFive Waterski Equipment
mobefive@hotmail.com

http://www.mobefive.tk

 

[Compositepro]

Release coat the inside threads of the insert and a headless screw (set screw, all-thread, or stud) and use the screw to keep the threads clear. If this is a mold surface the insert can be attached to the mold to locate it accurately. Then remove the screw from the insert through the back side of the mold after the part has cured.

 

[mobefive]

Ok that sounds good but infortunately the side that the inserts are going to face is the one covered by the vacuum bag, and vacuum materials. Also how do I get the stud/screw through the four layers of materials whilst they are wet without loosing too much structural strength (in the uni-directional carbon mainly).

Cameron

 

[Compositepro]

Its difficult to visualize exactly what you are doing. I imagine that cosmetics are very important for a water ski so you would not put a bagged surface on the outside. So you might be planning to assemble two halves. In any case from what you describe one concern I would have is putting stiff parts like inserts into a flexible ski. It generally leads to cracking and disbonding.

It is generally not too difficult to lay-up dry fibers over a stud and then brush on resin. Having the fibers go around the insert rather than cutting a hole for it is usually prefered.