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Improving connection for stanchion base


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I’m replacing my stanchion bases and bedding them with Bed-It. 
 

The bases are secured with 5 - 1/4” bolts: one at each corner of the base and one in the center of the base. 
 

On two of the bases, one of the holes in the corner of the stanchion falls over a bulkhead. To overcome this, the manufacturer used a 1/4” sheet metal screw in that hole. I don’t like this arrangement because it’s not likely to provide a good enough purchase in the deck to compress the Bed-It and because it seems an invitation for water intrusion into the core. 
 

I’m looking for ideas on how to deal with this. 
 

It seems I could drill an oversized hole, epoxy fill and thread but in my experience, that doesn’t seem to provide a tremendous amount of holding power. 
 

I could try to notch the corner of the bulkhead to be able to use a through bolt, but it’s really close quarters where that bulkhead meets the deck, so that’s not ideal either. 
 

You guys always come up with clever suggestions. Got one more?

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I'd do your first suggestion.  Drill the deck hole but you need to dig out the core beyond the deck hole, so when you fill the cavity with epoxy it is basically going under the deck skin.  The typical way to dig out is to grind down the short leg of an allen key so its sorta blade like, chuck it into a drill and then snake it into the hole.  Grind away, vacuum, fill with epoxy, pilot hole, drive self tapper home.

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Is 404 the best thickener for this application?

Also, do you think I can tap the epoxy for a 1/4-20 bolt, or is it best to use a bigazz sheet metal screw??

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Fiberglass method is to overdrill the size with a taper/flare on the inside, fill the hole with a high strength filler and resin, then drill the proper size hole. You could do the same with epoxy.

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Neat resin to start, try to coat the core and skins using a small brush.  Then fill with epoxy thickened with 404.  Yes you can tap.  If it strips you can always overdrill and refill.

 

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One thing that occurs to me is that since I don't have access to the underside, there is no way to get a piece of tape on there to prevent the epoxy from running through. Any ideas?

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6 hours ago, Quickstep192 said:

One thing that occurs to me is that since I don't have access to the underside, there is no way to get a piece of tape on there to prevent the epoxy from running through. Any ideas?

Candy pop stick, paper or plastic. Glue it through a plastic tab/disc smaller than the hole, you could use tape or paper in front of it that you can push through the hole. 

Now find someone who did something bad to hold the stick in the center of the hole until the epoxy kicks off and can hold on its own weight. Drill through the center of the stick. 

Do try to taper the inside of the hole a bit if you can.  

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Why has no-one has suggested removing the stanchion, filling all the holes and remounting it an inch or so away so all the fasteners clear the bulkhead?

 

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1 hour ago, SloopJonB said:

Why has no-one has suggested removing the stanchion, filling all the holes and remounting it an inch or so away so all the fasteners clear the bulkhead?

 

The initial post only describes that issue for 2 of the stanchions, if it is a solid railing that connects them (with 4 or more stanchions in total), is that actually an option?

Myself, I do not like holes that go through wood, the less holes the better. More backing plate can only help to disperse the pressure load, in this case it would mean cutting a slot in the bulkhead to slide the plate through. That could be a viable method as well, in that case they could use a waxed card/plywood to back the initial hole filling before re-drilling and the blind holes could be tapped in the backing plate.

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5 hours ago, SloopJonB said:

Why has no-one has suggested removing the stanchion, filling all the holes and remounting it an inch or so away so all the fasteners clear the bulkhead?

 

Agreed! You’d think the manufacturer might have thought of that!! 
 

In this case, the old stanchion and the bedding that was used have left a considerable shadow that would stand out like a sore thumb. Also, on one side, the fuel fill is in the way. 

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Put a nut on the bolt after you coat the bolt in vaseline. Glue the lot in. Once cured the bolt will undo leaving the nut so you can fit the stanchion, or have the bolt on the stanchion to help position it correctly , but undone sufficiently to make sure the nut is as deep as possible in the glue .

You will just have to remove enough core to make sure the load is adequately distributed. 

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Tha is everybody for the suggestions. 
 

Embedding a nut in the epoxy seems ideal,  but if I’m not able to make that happen, do you agree that a #14 sheet metal screw will get a better bite in the epoxy than tapping the epoxy 1/4-20?

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Maybe, maybe not, maybe Gougeon did some withdrawal tests? Tradeoff between deeper threads and fewer of them, factor in high density filler.

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Great points. All the articles I’ve read from Gougeon show machine threads, not screw threads. I’ll call them tomorrow  and see what they say. I’ll report back

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Drill and tap the epoxy plug full depth, no need for an embedded nut.  Plenty strong enough, it will rip the deck out before letting go. Most people dont realise that in a typical machine screw of the same metal for example you only need 3 threads engaged to get full strength. Obviously with epoxy its very different but if you have ever tried to extract a machine screw tapped into a solid glass deck without undoing it you will understand. 

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While I’m waiting for the weather to be a bit more conducive to working on the boat, I’ve conducted some experiments.
 

I filled a 7/16 hole with epoxy, thickened with 404. After it fully cured, I drilled a pilot hole and then drove by hand a 1/4” stainless steel lag bolt into it. At first, it looked like it would get a good bite, but as I drove deeper, the friction from driving it created enough heat to soften the epoxy and make it strip under load. 
 

In my next experiment, I again drilled a 7/16 hole, filled it with thickened epoxy and put 1/4” bolt coated with release agent in it. I smeared thickened epoxy on the bolt before inserting it to ensure it got into the threads. I removed the bolt this morning and the thread looks great. Once it fully cures, I’ll do a strength test. 
 

I wish I didn’t have to do this at all, but I’m learning a lot along the way. 

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I load tested the thread I made by casting a bolt into the epoxy. I put bedding on the surface and tightened a washer over it to see if I could tighten it enough for the bedding to “goosh” out. 
 

As soon as I applied enough torque to make the bedding goosh, the thread stripped. I’m now trying a test with embedding a nut in the epoxy. 

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I spoke to West yesterday. They recommend Drilling a 1/2” hole and burying 2 nuts, spaced apart in the hole using a bolt coated in release agent. 
 

A test I did by drilling a 1/2” hole in a 2x4 worked well. But… this method sort of flies in the face of hogging out some core below the glass at a larger diameter  than the entry hole. Any thoughts on that?

BTW, just for some perspective, this is just one bolt in a stanchion base that is held by 4 bolts. 

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4 hours ago, Quickstep192 said:

 this method sort of flies in the face of hogging out some core below the glass at a larger diameter  than the entry hole. Any thoughts on that?

The conventional wisdom for that is to chuck an allen wrench short side out into a drill and use it to hog out the core.

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On 6/30/2021 at 3:43 PM, Quickstep192 said:

I load tested the thread I made by casting a bolt into the epoxy. I put bedding on the surface and tightened a washer over it to see if I could tighten it enough for the bedding to “goosh” out. 
 

As soon as I applied enough torque to make the bedding goosh, the thread stripped. I’m now trying a test with embedding a nut in the epoxy. 

What did you use for thickener? It will make a large difference in your results.

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6 hours ago, Caustic said:

What did you use for thickener? It will make a large difference in your results.

I used West 404 high density filler. Is there something better?

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14 hours ago, Quickstep192 said:

I used West 404 high density filler. Is there something better?

404 or 406 are both good, West lists the 404 as more suited and the only way they increase strength is to add chopped fiber/strand into the mix. 

"To increase the mixture’s load-carrying capacity, you can add chopped glass fiber or carbon fiber. However, the additional cost and application difficulty are usually not worth taking this step." High-Density Adhesive Filler - Marine Grade WEST SYSTEM Epoxy

More on Hardware Bonding - Epoxyworks

I was unable to get 404 here for a while so I have used 406 on my lower rudder gudgeons.

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Put a 3/16 stainless backing plate in place.  Use a fein or vibratory multitool to slot the bulkhead to allow it to fit.  Mark the hole locations on the plate, remove it, drill it and tap it.  If you want it to be pretty, either paint it or buff it prior to install.  Put a dab of temporary loctite on each fastener before installing it.

I HATE stantions without backing plates, and manufacturers that install stantions on a cored deck without the backing plate are point loading it and will cause the gelcoat to crack and craze and the stantion to come lose.

Editted to add:  Mix up a little epoxy and paint it on top of the bulkhead.  That way, *when* the stantion leaks, it doesn't soak into the end grain and rot the entire bulkhead.

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4 minutes ago, Grrr... said:

Put a 3/16 stainless backing plate in place.  Use a fein or vibratory multitool to slot the bulkhead to allow it to fit.  Mark the hole locations on the plate, remove it, drill it and tap it.  If you want it to be pretty, either paint it or buff it prior to install.  Put a dab of temporary loctite on each fastener before installing it.

I HATE stantions without backing plates, and manufacturers that install stantions on a cored deck without the backing plate are point loading it and will cause the gelcoat to crack and craze and the stantion to come lose.

Would slightly amend that to using thread sealer instead of general loctite, machine bolts take a lot to back out, it is the corrosion and wicking you are trying to prevent. The metal plate will not expand and contract at the same rate as the resin. 

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On 6/26/2021 at 7:44 PM, Quickstep192 said:

... It seems I could drill an oversized hole, epoxy fill and thread but in my experience, that doesn’t seem to provide a tremendous amount of holding power....

In fact, it will hold enough to break the bolt if...

... You fill the epoxy with fiberglass. Drill and remove core. Inject about half the epoxy. Take 3/4" x 2" strips of 6-ounce finish cloth and jam them in with a big cable tie. You can fit more than you think, probably 6 or more strips. Add the rest of the epoxy, poking to help the air release.  It takes some time, but not hard. Just slow.

 

This will make the threads MUCH stronger, like threading G10. Yup, I've tested the theory to failure.

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