Fastening into epoxy plugs, having difficulty.

[rkarakai21]

Hey there. I am in the process of re-bedding my Genoa sheet tracks on my Roughwater 33. To give you an idea of the set up on this boat, there are 5 inch tall by about 2 3/4*" thick fiberglass bulwarks (with some kind of wood underneath the overlapping fiberglass top of the bulwarks. On top of that there is fastened a 2 inch thick solid teak caprail, the Genoa sheet track from the factory is fastened on top of the caprail with 4 evenly spaced oval head machine screws, about 12 inches long, that go right through the caprail, through the fiberglass top and main body of the bulwark and through to inside the cabin. The rest of the fasteners (about 20 some odd) are 5/16 inch thick 3 inch long stainless steel lag style screws that penetrate the teak caprail and the overlapped fiberglass bulwark top only.

Yes I’m aware not the most ideal system. Anyway. Some of the lag screw holes were stripped and water was leaking down through some of the bolt holes, so I wanted to air it out, strengthen and waterproof the holes and fill any voids with epoxy.

I bored all the fastener holes twice their diameter and filled them with west system epoxy, as I’ve done before on smaller projects, and this time I packed each hole with chop strand fiberglass for reinforcement.

So I’ve drilled 1/4 inch pilot holes, one size down from the lag screw thickness, and have started to fasten, trying to do a full turn in and a quarter turn back as if I’m threading a tap into steel, well the lags get 3/4’s down and hold like crazy but they are so tight I broke the end on my flat blade screwdriver trying to get them right down. I’m apprehensive of driving them with a power drill, might twist the heads off.

What am I screwing up here, can I get a metal tap with the right thread pitch for lags so I can pre tap these holes? There is no doubt in my mind that these reinforced epoxy bungs are far stronger than the teak around them. Seems to me that if I drill to 5/16 there won’t be enough thread bite. They are alot head lags.

[GreenWave]

Why not drill one at the same size as screw and see how that goes? Generally that would be the approach.

[Cheechako]

Use proper threaded bolts/lags. Not wood lags if that's what you mean. Drill and tap.
I sure don't like the idea of an epoxy plug with no bolts & backing plates/nuts though. You're just relying on the bond strength of the plug to hold it?

[capt jgw]

Originally Posted by Cheechako

Use proper threaded bolts/lags. Not wood lags if that's what you mean. Drill and tap.
I sure don't like the idea of an epoxy plug with no bolts & backing plates/nuts though. You're just relying on the bond strength of the plug to hold it?

WEST system calls that the "bonded bolt" system. They do it all the time and it works. They do it a little differently though, they drill the oversized hole and fill it with silica thickened epoxy then set the bolt in before the epoxy sets. They leave a little bit of the bottom of the hole the right size to thread the end of the bolt in, maybe a quarter inch. That keeps the bolts tight till the goo sets.
Since you already have these filled I'd change the process a bit. Drill the quarter inch hole as you did, then redrill bigger, maybe 3/8 leaving the last 1/4" undrilled. Coat the bolts and insides of the holes with silica thickened epoxy and screw them in. Make sure you put in enough to get some squeeze out. It's messy but the only way to know you used enough. Another thing they recommend is waxing the threads first if think you ever might want to disassemble. You'd have to use heat otherwise.

[Bowdrie]

Originally Posted by capt jgw

WEST system calls that the "bonded bolt" system. They do it all the time and it works. They do it a little differently though, they drill the oversized hole and fill it with silica thickened epoxy then set the bolt in before the epoxy sets. They leave a little bit of the bottom of the hole the right size to thread the end of the bolt in, maybe a quarter inch. That keeps the bolts tight till the goo sets.

That's basically the same process I use.
I spray the fastener with "Boeshield", shake off the excess and let it dry, it leaves a waxy coating that the epoxy won't stick to.
After set-up, unscrew the fastener, clean it, apply sealant, re-install hardware.

[Flatswing]

Or you could get drills in smaller increments 9/32 +/- 1/64. Increase the drill size by 1/64 until you can just turn in the machine screw by hand. With the length you are working with, there will be plenty of purchase.

[catsketcher]

I do this a lot but I would caution you on understanding how the process works.

Like posted above, I usually put the machine screw into a large hole. Often I will bore a hole out to 20mm for a 6mm machine screw. I leave a small bit of 5.5mm pilot hole down the bottom to tighten up on.

I put the screws in wet. Syringe some epoxy glue into the hole and then put the fitting on and screw away, then clean up. It is not the best method but it is fast and pretty strong. To get my anchor winch out I needed to use heat to remove the machine screws. I have not had as good as bonding with the tapping method but that could just be because I only used an all in one tap instead of having three for each size. I think that epoxy needs an exact fit or the lower strength will be an issue and cause stripping. There have been a few cats that have pulled out tracks and padeyes done with this method, so make the fasteners long and if they don't need to come out regularly, put a little clear epoxy on them and on the hole sides, even if you use tapped plugs, to ensure the bolt fits perfectly.

I would ensure that there is a long distance of contact between the screw and the epoxy. Epoxy has a far lower shear strength than metal, so you need a lot more of it in contact with the fastener to ensure that it can hold without stripping.

I have done some tapping of epoxy but find that regular removal reduces strength far more than it would with metal nuts, but that is probably not a concern most of the time.

As for the OPs issues. I would check the tap is the correct size but if it is and the problem is the amount of friction in the epoxy plug, you could try lightly greasing the fastener with lanolin, for regular removal, or wet with clear epoxy, for more permanent fitting or oversizing the hole and putting the fastener in with epoxy glue. Just make sure it is long enough. (You can always get an epoxy fitting out with heat though so it does not need to be fully permanent)

I have my stanchion bases put in this way and it works well - no leaks and no rot issues. Love epoxy.

[thinwater]

With fiberglass in the epoxy plugs, as you described, just tap as for bolts. I have done pull-out testing with that method, and at 3/4-inch, it is MUCH stronger than the bolts. And there are a lot of bolts on the track. Then bed as usual.


(this is NOT as strong if it is just neat epoxy--you need to add the fiberglass)

[Jim Cate]

I've never tried this... wondering if it makes sense: using the principle of casting the threads in thickened epoxy as outlined upthread, how about potting a hex nut into the hole as well? would have good pull-out strength and rely less upon the cast threads which might become worn from occasional removal.

Jim

[thinwater]

Originally Posted by Jim Cate

I've never tried this... wondering if it makes sense: using the principle of casting the threads in thickened epoxy as outlined upthread, how about potting a hex nut into the hole as well? would have good pull-out strength and rely less upon the cast threads which might become worn from occasional removal.

Jim

Cast-in plates are fairly common. Cast in the plate, then drill and tap in-situ. Lining up a nut and potting sounds like a practical nightmare.


The down side is that if the fastener becomes seized to the plate with corrosion it is the stuff of nightmares (been there several times, have the tee shirt). There is no way to get at it.


How often do you remove a genoa track? Once?

[Jim Cate]

Cast-in plates are fairly common. Cast in the plate, then drill and tap in-situ. Lining up a nut and potting sounds like a practical nightmare.

I was thinking of the method mentioned upthread where the screw is coated in a bond release and set into uncured epoxy, thus generating female threads in the socket. My thought was to have the nut on the screw while being potted, thus eliminating the task of alignment but still adding considerable strength (all liberally coated with some reliable non-stick compound!).

And I wasn't thinking specifically of the genoa track application...just a general idea to be investigated.

Jim

[rkarakai21]

Hey there, I have been reading over all of this and really appreciate the varied knowledge here. I had read the west system approach of putting the fasteners in wet with some kind of wax or release agent on and "casting them in to the wet epoxy. I was pretty intimidated by that approach with my application, as A. I had never done that particular process before, and B. This track is about 13 feet long with over 30 fasteners (just counted), and the track has to be clamped and cajoled neatly onto the curve of the caprail. I was worried that the margin for error was high and if I screwed up the casting and things didn't line up or couldnt be tightened down sufficiently. Clearly of course this is just my lack of experience with the procedure.

Mechanically speaking though if I have heavily fiberglass reinforced bungs, and the threads cut into them, either with a tap, or the wood lags themselves, is that inherently weaker than setting them in curing epoxy, if I only screw them in once to bed them? If so i'd love to learn why (just the adhesive bond to the screw?). These arent going to be removed regularly, I hope to only have to screw them in once and forget them.

Fastener wise, I would guess more threads per inch, in the case of a bolt or machine screw is stronger because of the surface area increase of the threads, over a wood lag, but I'd love to be confirmed on that assumption or refuted.

We are fitting the boat out for offshore and I'm well aware of the forces involved and the danger of having gear not up to the task, so I want to do this once and right. That being said, I am not made of money, and would prefer not to have to replace 30 stainless 3 inch fasteners per side if it is unnecessary.

I am leaning towards getting an in between drill bit size, drilling out a fraction more and I'd be open to dipping the lags in epoxy prior to the screw in, if that makes a significant difference in strength.

I considered adding more through bolts to the existing four, but with the length needed, between 10" and 12" because of the caprail, and bulwark and deck they need to go through, into some areas that are not accessable as well, I was told both by the chandleries and a specialty fastener shop in town that stainless machine screws with the right head to fit flush to the sheet track in that length I would need to have them custom made at a machine shop, which is well out of my price range.

I'm all ears. Thanks again for all the great info.

[Patrick of M]

Given the number of screws and having to bend the track, it sounds like you are headed in the right direction.

[Rumrace]

Systems west with chopped glass is like machine grade Vinyl. You could only make it stronger with Carbon Fibre or Poly Carbon
It should be treated like cast aluminum when it comes fasteners including a loktite or sealer. Threaded inserts are an option but self tapping screws are not.

[rkarakai21]

So your saying I have to replace all my fasteners and use some kind of metal threaded inserts? Because threading lags into the glass reinforced epoxy is not strong enough?

I hate to be that guy to say it, especially knowing what I know about certain manufacturers of production boats, and corners they cut but these tracks have gone 40 years in all types of weather and not pulled up, and they were just lagged into a teak caprail. There are over 30 fasteners sharing the load per track, including four evenly spaced through bolts a side. Basically I pulled them up because of water ingress, and because a small fraction of the holes were stripped. I simply cannot afford to replace 60 large stainless fasteners at this time and I would have a hard time believing that fg reinforced epoxy (with a good bond) would be weaker than the teak that it was fastened into before.

I need to find some formulas for calculating Genoa sheet load, and pull out forces with a variety of fasteners.