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Pour or Tap threads into epoxy??

Kenneth K

1985 32-3, Puget Sound
Blogs Author
I'm working with a deck fitting that I'd rather screw into the deck (with 1/4" machine screws) than through-bolt. I've over-drilled the holes and am ready to fill with thickened epoxy. What's the preferred method for threading the holes; lube up the screws and insert them into the wet epoxy or drill and tap the threads after it hardens?

I'm afraid if I screw up the first method I'll never get the screws back out.
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Well, you can just drill a pilot hole and put a screw into glass or epoxy. Holds fairly well.

I'm not familiar with using machine screws without nuts and backing plate--which is pretty much required for most deck fittings.
 

markvone

Sustaining Member
Ken,

I would use a stainless threaded insert epoxied into the deck. I've used these for a similar situation:

https://www.ezlok.com/threaded-inserts-for-plastic

To install them, I used the piece I wanted to be bolted down as a jig. I neatly greased up my screw threads and the end of the screw, inserted them through the fitting and threaded them into the threaded insert to a point where the inserts extended as far into the epoxy filled hole as I wanted. I greased anything else that might get epoxy on it (the bottom of my fitting and around the insert holes in the deck) to keep it from bonding. I then filled the recesses with epoxy and placed the fitting with screws and screw inserts extending into the epoxy and let it bond. I then carefully unthreaded the screws and pried the fitting free (it had bonded slightly due to epoxy on surfaces). I've removed the screws since with no problems. I can get you pictures of the install if you want to see. This was for a G10 bilge pump base.

Mark
 
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tenders

Innocent Bystander
I’m with Christian - better to throughbolt and nut. But if you must, I’d fill/drill/tap so you know as much as you can about the quality of the hole and threads; you’ll always wonder with the pour-around approach. The inserts are clever but a critical piece of metal that can’t be inspected feels wrong for marine use, and might be hard to remove someday.

I don’t think I’ve directly tapped epoxy, but I can confirm that tapping G10 works amazingly well.
 

Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Betcha an epoxy-molded nickel that the lab guys at https://www.westsystem.com
have done this research long ago, and can relate the general holding power of threaded bolts in XX fractions of an inch of epoxy.
Note that there is a huge difference between the shear (sideways pull) load and a pull straight up or closer to straight.

(One example that comes to mind was the install of our new engine riser pieces/bars last year. Securing bolts were threaded down thru about 3/8 inch of molded frp and then into the oak beneath each side. Of course the loads are in shear.... and since we could not break any threads loose with a fairly long bar they appear to be as solid as possible.)
 
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Tin Kicker

Sustaining Member
Moderator
1/4" screws won't hold much of any load in epoxy without something to add strength or greatly increase the bearing area. This is especially true in tension. They will hold a light casual load without these steps, but not much more than that. Plus, if you unscrew them you very likely will remove some epoxy, further reducing their capability when the screw is put back in.

I'd strongly suggest mixing a substantial amount of micro fibers into the epoxy to bed some inserts similar to what Mark Vone shared.
 

toddster

Curator of Broken Parts
Blogs Author
I was planning to go with inserts for an upcoming project, but a West Systems web page just about convinced me to do it their way instead. With a new cast epoxy plug in the deck, one could probably achieve up to an inch of secure threads. But I’ll probably spin the research wheel again before drilling the holes. IIRC, the issue that pushed me that way was corrosion. Most of the inserts aren’t designed for saltwater environments.

FWIW, I have a lot of small hardware items screwed down with 8-32 screws self-tapped into slightly undersized holes in old fiberglass. Most of them are doing just fine with or without backing washers and nuts. In contrast, all of the original Ericson hardware was screwed down with coarse-thread tapered wood screws into the fiberglass. It’s possible that most or all of those were inserted before the plastic was fully cured. Pretty much all of them have pulled out by now. Worth noting that the deck hatches and the rubrails were only secured by those tapered screws. :0
 

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
Kenneth, you didn't mention what deck fitting it is....

Interesting thread, we'd all like to know the options.

I had an issue with the cockpit eye straps that turn the self steering lines 90 degrees. Difficult access for bolts and the pull is all wrong--directly "out," not lateral at all. I just screwed the eye straps into the seat-back fiberglass, figured if they pulled out I'd reinstall another way.

They're still fine after many miles. So sometimes you can cheat, if failure isn't a critical issue. Ericson glass is pretty thick....
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
Thanks for all the great ideas. The fitting is just for a new cowl vent the foredeck, so it won't take a lot of stress, especially because it's protected by stainless steel railings on three sides.

I tried to unscrew the existing deck fitting but it was pressed into place thoroughly with some kind of sealant so I'm sure it's not coming out without damaging the fiberglass. Instead, I just drilled through the existing stainless fitting, and I'll mount the new stainless flange on top of the existing one. But that does rule out putting in oversized inserts. I can't drill the holes that big through the existing flange.

The original flange was just held in with 4 screws--wood screws or sheet metal screws. But those went into a combination of wood and fiberglass. I'll be refilling with pure epoxy. I have some hesitation about screwing into epoxy, it doesn't seem like it would give and stretch to hold screw threads like wood. Am I wrong?
 

bgary

Advanced Beginner
Blogs Author
I tried to unscrew the existing deck fitting but it was pressed into place thoroughly with some kind of sealant so I'm sure it's not coming out without damaging the fiberglass.

Yeah.

I lost my dorade hood last year and went through the same thing. I tried to get the old fitting off so I could replace it, and... no joy. Whatever they used to glue that thing in place is impressive.

I ended up buying a new dorade hood from Defender (Nicro-Fico #N10963, about 55 bucks) and modified it to fit on the existing flange. The inside diameter of the rubber base is almost exactly the same as the outside diameter of the existing flange, so I cut off the plastic ring inside the bottom of the base with a sharp knife, and the hood press-fits nicely onto the existing flange. It stays in place with friction, but I added a hose-clamp around the bottom just to secure it bit. Probably not necessary, but.. hey, I already lost one....

https://search.defender.com/?expression=N10963&x=0&y=0

Bruce
 
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Loren Beach

O34 - Portland, OR
Senior Moderator
Blogs Author
Thanks for all the great ideas. The fitting is just for a new cowl vent the foredeck, so it won't take a lot of stress, especially because it's protected by stainless steel railings on three sides.

I tried to unscrew the existing deck fitting but it was pressed into place thoroughly with some kind of sealant so I'm sure it's not coming out without damaging the fiberglass. Instead, I just drilled through the existing stainless fitting, and I'll mount the new stainless flange on top of the existing one. But that does rule out putting in oversized inserts. I can't drill the holes that big through the existing flange.

The original flange was just held in with 4 screws--wood screws or sheet metal screws. But those went into a combination of wood and fiberglass. I'll be refilling with pure epoxy. I have some hesitation about screwing into epoxy, it doesn't seem like it would give and stretch to hold screw threads like wood. Am I wrong?

I keep a container of "high strength filler" around and mix some into the neat resin. Unless wetting out cloth or bi-ax, I always thicken up the resin some. The consistency kind of depends on the purpose.
How much to add? Oh, about that much.... :nerd:
 

Kenneth K

1985 32-3, Puget Sound
Blogs Author
Yeah.

Whatever they used to glue that thing in place is impressive.

Agreed. I think that would be a sawz-all project.

I hesitated about drilling through the existing stainless ring flange assuming it was solid SS. Turns out it is more like chromed bronze or brass so it actually drilled like butter. Just have to figure out the best way to "bed" the new fasteners.
 

markvone

Sustaining Member
Here is a look at where I used the ez lok inserts. I probably could have tapped the G10 and it would have avoided any potential stainless-stainless galing or corrosion. The load is all compression and it's small, just the weight of the pump. I need the top of the base to be removable to get at the manual pump's pickup underneath and to unbolt the pump from the G10 base. I've had no issues with corrosion of the 1/4-20 screws or inserts in the bilge. I installed this base in 2014 and it came apart in 2017 with no issues.

The first picture is the top (from the side) with the screws threaded into the ez lok inserts and the holes in a vertical where the ez loks will be bonded. I greased the top of the vertical between the holes but still got some slight epoxy bonding from overflow that I carefully pulled apart. Second picture - inserts bonded into verticals. Third - pump in bilge. It was fun making this base but it would have been faster and simpler just to tap the G10 verticals and skip bonding in the inserts.

Mark
 

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JPS27

Member III
on each of my e27 handrails I had to tap one on the port side and 2 on the starboard side because the nuts had rusted to nothing. So I filled with thickened epoxy then fastened all the other bolts so it lined up and drilled, then took off the rails and tapped. But I wouldn't do this for something that took a huge load.
 
on each of my e27 handrails I had to tap one on the port side and 2 on the starboard side because the nuts had rusted to nothing. So I filled with thickened epoxy then fastened all the other bolts so it lined up and drilled, then took off the rails and tapped. But I wouldn't do this for something that took a huge load.
I am looking at a similar problem with the replacement and rebedding of my E25 handrails.

Some of the bedded-in nuts came out, leaving a void to be cleaned up and potted.


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While others held.


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I have been struggling with how to solve the problem, because I am not sure what is between the cabin top and the inner shell. Only the bolts on the ends of the hand rails go through.

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Has anyone out there drilled through the cabin top to thru-bolt the hand rails on an E25 (or other model with the same construction)?
 

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Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
I'd probably use the inserts in Message #4. Clean up the cabin house hole and epoxy them in. Thickened epoxy ought to mate well with the house glass, which should be relatively thick, and the handrails do spread the load.
 
I'd probably use the inserts in Message #4. Clean up the cabin house hole and epoxy them in. Thickened epoxy ought to mate well with the house glass, which should be relatively thick, and the handrails do spread the load.
That sounds quite reasonable to me. I plan on following Maine Sail's potting techniques, which should provide a secure base.
And you are absolutely correct about rails spreading the load! Moreover, the direction of the load is generally lateral, which would make the connection even harder to dislodge.
 

tenders

Innocent Bystander
There’s surprisingly little complexity to the overhead construction: the order is simply handrail, about 3/16” of fiberglass, 1/2” balsa core, a thin lower layer of fiberglass, then the headliner. There’s an “air gap” of sorts between the thin fiberglass layer and the headliner.
 
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