Better stripped screw hole filler

[Quickstep192 92]

I’ve always understood it to be standard practice to fill stripped out screw holes in fiberglass with epoxy. But in almost all cases, I find the epoxy to be too soft to really hold a screw; even when thickened with high density filler. 
 

Are there other fillers/strengtheners that are a better choice? 

[slug zitski 575]

Helicoils …threaded inserts

seat them in epoxy or lock tight

 

[Ishmael 10,553]

3 hours ago, Quickstep192 said:

I’ve always understood it to be standard practice to fill stripped out screw holes in fiberglass with epoxy. But in almost all cases, I find the epoxy to be too soft to really hold a screw; even when thickened with high density filler. 
 

Are there other fillers/strengtheners that are a better choice? 

If you don't drill the hole oversize, there isn't enough strength in the little bit of epoxy to hold much. A tapped hole in filled epoxy should be as strong as the fastener if it's done right.

[phill_nz 859]

bit hard to say

need info .. like

laminate type and thickness

what you want fixed to it

what type of screw you are using

epoxy works well for most things

but

https://www.specialinsert.it/en/prod-category/prodotti-en/compositi-en/

is the permanent solution if they are needed

 

[ctutmark 285]

A quick hit to the hole with a countersink bit before the epoxy filling helps too. Increases the surface area between the existing laminate and the epoxy. 

Also had luck with putting the fasteners into the epoxy filler while it cures but the window to get them out is fairly small- too early and it rips out the epoxy with it, too late and it can be a bugger to remove. Assuming the fastener will be replaced and using a bolt versus a screw can help the removal as the epoxy dries

[Grande Mastere Dreade 4,131]

2 hours ago, ctutmark said:

A quick hit to the hole with a countersink bit before the epoxy filling helps too. Increases the surface area between the existing laminate and the epoxy. 

Also had luck with putting the fasteners into the epoxy filler while it cures but the window to get them out is fairly small- too early and it rips out the epoxy with it, too late and it can be a bugger to remove. Assuming the fastener will be replaced and using a bolt versus a screw can help the removal as the epoxy dries

put a little wax on the screw as a release agent

[SloopJonB 12,559]

10 minutes ago, Grande Mastere Dreade said:

1 hour ago, ctutmark said:

A quick hit to the hole with a countersink bit before the epoxy filling helps too. Increases the surface area between the existing laminate and the epoxy. 

Also had luck with putting the fasteners into the epoxy filler while it cures but the window to get them out is fairly small- too early and it rips out the epoxy with it, too late and it can be a bugger to remove. Assuming the fastener will be replaced and using a bolt versus a screw can help the removal as the epoxy dries

put a little wax on the screw as a release agent

Just dip it in oil.

[Guvacine 43]

Humans also seem to have a need to over tighten things. This fractures the epoxy thread. Just nip it up and it will have a lot of holding power.

[Leeroy Jenkins 475]

Why aren't you throu bolting? 

[Ishmael 10,553]

7 hours ago, SloopJonB said:

Just dip it in oil.

Or spray it with cooking spray. Puts on a much thinner layer.

[CaptainAhab 210]

On 9/14/2021 at 10:10 AM, Ishmael said:

Or spray it with cooking spray. Puts on a much thinner layer.

Or spray it with hairspray. It works like a PVA mold release. 

[DELETED 208]

I recently saw fellow Australians Troy&Pascale of FreeRangeSailing use these Flanged,thread in timber to bolt inserts. They drilled an oversize hole in the stripped hole, filled it with hardened epoxy, drilled that, epoxied and wound in the 316insert.

The larger area and coarser outer thread provides huge anchoring potential, then they threaded a bolt into it. Clever and an alternative to full through bolting depending on application.(i forget if they used butyl tape or sealant, it was on a recent dodger install or stanchion repair i think)..

[SloopJonB 12,559]

3 hours ago, FixinGit said:

I recently saw fellow Australians Troy&Pascale of FreeRangeSailing use these Flanged,thread in timber to bolt inserts. They drilled an oversize hole in the stripped hole, filled it with hardened epoxy, drilled that, epoxied and wound in the 316insert.

The larger area and coarser outer thread provides huge anchoring potential, then they threaded a bolt into it. Clever and an alternative to full through bolting depending on application.(i forget if they used butyl tape or sealant, it was on a recent dodger install or stanchion repair i think)..

I have used those inside to bolt down infrequently removed panels - berth flats, engine box panels etc.

They work great and are easy to install. They do require very precise alignment though - drilling a pilot hole through both pieces before drilling to size is pretty well essential.

[Waiex191 64]

On my H16, the bottom screw for the drain plug fitting was stripped.  I used a thick mixure of fine sawdust and epoxy and am pretty happy with how it turned out. 

[CaptainAhab 210]

One thing to keep in mind when doing the hole fill thing with epoxy/filler is how long it takes for the epoxy to reach its full hardness in terms of days. Depending on the temperature and the other variables screwing into the epoxy may shred it. If you wait long enough the epoxy will go rock hard and provide a strong material for the threads. Straight silica or high density filler mixed into regular West System or the equivalent should be more than adequate.  

[thinwater 121]

For cored hulls, over drill as for sealing blot holes, half fill with epoxy, stuff in many small squares of 6 oz finish cloth, and then top off with epoxy. Very strong, because of the glass fibers.

[Waiex191 64]

Here is my through-hole solution for a cored hull.  I carved out some foam and filled it with flox.  Afterwards sanded it smooth.  This was for a hatch I installed on my old H16 for ventilation.

 

I 3D printed up some tooling to form the top layer, as the hatch needed a flat surface.  Then I drilled through and screwed it down.

Lots of compressive strength there and there is a nut on the backside.  We used to do similar things to composite parts at a major helicopter manufacturer on the Housatonic River, although they had better materials than my epoxy/sawdust mix.

[penumbra 23]

I've had good luck with JB Weld. I feel like it stays a little flexible instead of being hard and brittle like epoxy.