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Old 26-05-2011, 07:30   #1
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Speed / Captive Nut Backing Fiberglass?

The top of my pedestal is attached to the base with 4 self taping screws into the thin fiberglass of the base. Naturally, the holes are wallowing out and becoming stripped. I'd like to find a clip nut/speed nut like the ones used for sheet metal. The clip over the edge over an unthreaded hole and provide a tread for a sheet metal or machine screw to fasten to.

The problem with using the stock items found in Ace, etc., is that they are designed for much thinner material than the fiberglass edge that the top to the pedestal fits down over. Does anyone know of a source for such a clip that would work for fiberglass? I don't have an exact measurement, but I'm guessing the fiberglass is maybe 1/8" to 3/16" thick (it's a stock pedestal on a Beneteau 361, if anyone happens to know).

I much prefer this to epoxying on a nut or wood backing. These nuts provide access to the underside of all the instruments on the pedestal and the steering gear, so they need to handle repeated removal and installing.

Any suggestions or hardware sources would be most welcome!
Thanks!
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Old 26-05-2011, 07:33   #2
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Re: Speed/captive nut backing fiberglass?

I don't have the answer, but if you hear of one I'd like to know it.
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Old 26-05-2011, 08:26   #3
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Re: Speed/captive nut backing fiberglass?



RTC3744 PLASTIC LOCK NUT | 101 Forward Control: Body/Fittings | shop | www.lrseries.com | L. R. Series

Any use?
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Old 26-05-2011, 08:42   #4
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Re: Speed/captive nut backing fiberglass?

Is the underside accessible? In other words, could you get a carriage bolt in there and then tighten down a nut from the top? If so you could top it off with a cap nut making it look pretty.

You want to thru-bolt this if at all possible.

Use stainless if possible. If the only option is steel then coat it in Tef-Gel. West Marine sells stainless carriage bolts.
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Old 26-05-2011, 08:48   #5
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Re: Speed/captive nut backing fiberglass?

Thanks David, but I'm not sure I have enough material thickness to put that type of nut in. I think I'm going to need something that can slide down over the edge and provide threading on the back such as a J or U type speed nut:
McMaster-Carr

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Old 26-05-2011, 08:50   #6
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Re: Speed/captive nut backing fiberglass?

A picture would help. I can't really visualize it.
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Old 26-05-2011, 08:51   #7
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Re: Speed/captive nut backing fiberglass?

There is an access panel way down at the base (maybe 2-3 feet below the screws) that could, with the right tools and bodily contortions, provide access to hold a nut while someone else screws in the bolts, but that's going to be pretty difficult.

I am definitely looking for a thru-bolt solution, and am hoping to find something like a speed bolt or clip bolt that will hold on in the right location while the top is placed and the screws applied.
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Old 26-05-2011, 08:53   #8
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Re: Speed/captive nut backing fiberglass?

Quote:
Originally Posted by David M View Post
A picture would help. I can't really visualize it.
A guick google yielded this link. At the top of the page is the type of joint I'm dealing with.
http://www.ocmulgeeblacksmiths.org/Offset_Lap-Joint.pdf

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Old 26-05-2011, 10:07   #9
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Re: Speed / Captive Nut Backing Fiberglass?

Rivit nuts, Nut-Serts, Well-Nuts all sorts of things will work. Take a look at these: McMaster-Carr
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Old 26-05-2011, 10:10   #10
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Re: Speed / Captive Nut Backing Fiberglass?

If I'm reading this correctly, you can only get at the holes from one side. So see about getting some blind nuts, which are cylindrical tubes, threaded on the inside with a flange on one end, which has some teeth in it. Usually they go into an enlarged hole from the back and when you put the bolt in from the other side, and tighten it, the teeth bite into the material and hold the nut in place. A bit of epoxy helps hold it there.

However you can put them in from the same side as the bolt if you drill a slightly smaller hole, epoxy them and tap them into the hole. Only problem is that they may get drawn out if you apply too much force to the bolts. Better to fit them in from behind.

Here's what they look like

Google Image Result for http://www.bandbhobbies.com/shop/images/prod_gpmq3327.jpg


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Old 26-05-2011, 10:14   #11
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Re: Speed / Captive Nut Backing Fiberglass?

larger washers on both sides and fiberglass repair to close the hole size works for me.. goodluck.
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Old 26-05-2011, 11:36   #12
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Re: Speed / Captive Nut Backing Fiberglass?

Quote:
Originally Posted by HopCar View Post
Rivit nuts, Nut-Serts, Well-Nuts all sorts of things will work. Take a look at these: McMaster-Carr
I'd be a little worried about the expansion pressure cracking the fiberglass. Looking further, I think Knurled rivet nuts might work better
McMaster-Carr

Thanks for the pointer! Other than clip nuts, I didn't have any good ideas about what kinds of fasteners are out there and are useful in this situation.
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Old 26-05-2011, 12:09   #13
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Re: Speed / Captive Nut Backing Fiberglass?

Helicoils epoxied in. You want machine threads for anything repeatedly removed.

If it was my boat I would buy two stainless plates, and drill and tap to 1/4-20, and epoxy them to the underside. A quick spray of teflon to keep from galling or rusting in place, and some stainless thumbscrews.
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Old 26-05-2011, 13:30   #14
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Re: Speed / Captive Nut Backing Fiberglass?

Batkins, I would be worried about cracking the fiberglass as well if the edge of the hole is near the edge of the fiberglass. Rubber Well Nuts might be a better choice in that case. I like Capn Bill's idea about the plates but you don't have to make them. You can buy them at aircraft parts stores. They are called Nut Plates. Google it.
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Old 01-06-2011, 19:03   #15
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Re: Speed / Captive Nut Backing Fiberglass?

Overkill! All you need is a screw one size up.
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