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Best way to add bolt threads in the board for the mast when building board?

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BWD
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Re: Best way to add bolt threads in the board for the mast when building board?

Postby BWD » Mon Oct 15, 2018 4:19 pm

Tee nut on top is stronger. Keeps full board in compression and spreads loads to deck and bottom.
Also easy to inspect and repair.
Nut hidden in middle of core relies on core strength, so needs much more core reinforcement.
And if it starts to break, you won’t know, until it fails completely. Also, every time you tighten the bolts, you will risk over tightening and damaging hidden parts.

If the nut is on deck, you can see if it is corroded, cracked, tightened too much and starts to crack the deck, etc. You have a chance to see the problem and fix it fairly easily before snapping the board or losing a foil.

It is not a problem if the insert doesn’t reach the bottom of the board.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby junebug » Wed Oct 17, 2018 12:01 pm

BWD wrote:
Mon Oct 15, 2018 4:19 pm
Tee nut on top is stronger. Keeps full board in compression and spreads loads to deck and bottom.
Also easy to inspect and repair.
Nut hidden in middle of core relies on core strength, so needs much more core reinforcement.
And if it starts to break, you won’t know, until it fails completely. Also, every time you tighten the bolts, you will risk over tightening and damaging hidden parts.

If the nut is on deck, you can see if it is corroded, cracked, tightened too much and starts to crack the deck, etc. You have a chance to see the problem and fix it fairly easily before snapping the board or losing a foil.

It is not a problem if the insert doesn’t reach the bottom of the board.
Thank you.

Another noob question: when I drill out the columns in the board and fill it with epoxy for the t nuts, should I drill the column wider than the head of the t nut (so the prongs of the t nut grab epoxy when I insert them) or narrower than the head (but wider than the barrel) so the prongs grab wood? I would assume the former, so there is less potential for water entry into the board but I’m not sure.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby downunder » Wed Oct 17, 2018 1:16 pm

This is difficult question simply because you can't see what's going on inside. A tiny imperfection in unsealed wood and you got yourself a potential problem.

To be fair, for your first build this is way to complicated. Yes, it is a steep learning curve, but worth only if you'll continue building many boards.
My suggestion would be to build a TT style board, glass it, and than if you wish, slap a foam on top of it. Providing it's shaped nicely. Than glass it again on top only.

That way your SS inserts will be fully visible and as a plus, there will be no long bolts which can pop the insert out if you drill the wide column. Ie, you hit the mast, this makes a huge leverage on insert and pops it out, b/c the bolts are long.

On TT as I see it, there is no leverage, b/c bolts are short and in level. All the time.

D.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby BWD » Wed Oct 17, 2018 7:32 pm

when I drill out the columns in the board and fill it with epoxy for the t nuts, should I drill the column wider than the head of the t nut (so the prongs of the t nut grab epoxy when I insert them) or narrower than the head (but wider than the barrel) so the prongs grab wood? I would assume the former, so there is less potential for water entry into the board but I’m not sure.
Suppose the widest part or "head" of the T nut base is 20mm.
I would drill 25mm holes all the way through the board before glassing.
Next fill them with a strong epoxy/fibers putty (microfibers, wood flour, milled glass, etc.).
Drill out so you can fit the barrel of the Tee nut in the holes, maybe 1mm oversize so it slides in easily.
If the Tee nuts have prongs, flatten then with a hammer or pliers. They aren't needed (if possible, just get flat weld-on type tee nuts).
Get some long screws to fit the tee nuts, and wrap them in masking tape or similar leaving only enough threads bare at the tips to engage the depth of the tee nut.
Don't get petroleum jelly on the barrel or head of the tee nuts.
Insert tee nuts into holes from deck side. Secure to deck with tape, being careful to get a good seal.
Turn board upside down making sure the tee nuts are supported from below.
Coat the screws with petroleum jelly, and screw them into the tee nuts.
Pour epoxy into the holes around the screws from the bottom of the board.
When cured, unscrew the screws.
You now have tee nuts secured into strong epoxy holes, with enough clearance to insert screws easily.
Plug holes with surf wax, plasticine or whatever to protect from resin, and glass the board.
After glassing, open the holes with a drill -carefully.
If you feel confident, you could try potting the tee nuts and screws directly into the 25mm holes in one go.
If you feel too cocky to get a good result, you could try doing any of this stuff without using the foil plate or an accurate template to place the screws in the holes.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby junebug » Wed Oct 17, 2018 8:32 pm

Thanks BWD. I really appreciate you taking the time to spell all that out for me.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby grandeand » Thu Apr 09, 2020 3:49 pm

This is tee nut?
Screenshot_2020-04-09-16-48-19.png

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby tmcfarla » Thu Apr 09, 2020 5:31 pm

I’ve had best luck potting directly into the bottom of the board, but it is really hard to get placement just right without a jig of sorts. The bolts can move around a bit on their own, or go off level. At its simplest, this jig could simply be your mast, but a piece of plywood with exact-spaced holes is better in case you screw up. Put some wax paper or similar release agent on jig, it should never touch epoxy, but you’ll be very sad if you accidentally epoxy this to your board.

1.) drill out slightly oversized holes in the board. Go all the way to, but not through, the deck skin. If you drill through the deck skin, you can tape it off, but epoxy can find its way through tape sometimes and leave a mess.

2.) Put light coat of petroleum jelly on bolts, keep it light or you’ll get it on the inserts and you don’t want that. Plan to throw these bolts away afterwards, so use something replaceable.

3.) place bolts through jig, thread on a disposable washer and nut, these will not get potted into board, they are there to hold the bolts firmly in place on the jig (they should not touch epoxy but put jelly on them anyways) . You now have bolts secured in place at the correct spacing. Are they exactly 165x90 spacing. Are the bolts all level (perpendicular to jig)? Good, now thread your inserts onto them, leave several millimeters between the insert and the nut holding things in place. Do not get petroleum jelly on inserts! Tip- while not required, putting nuts/washers on both side of the jig will allow you to adjust depth of inserts in the holes, this is usually easier than finding disposable bolts of just right length.

4.) check jig by putting inserts into holes. Alignment look good? Are the inserts all the way in the holes, and not poking out of them ? too deep is better than too shallow. Any part of the insert not filled by bolt will get filled with epoxy, are the bolts long enough to go all the way through the inserts? Are the bolts short enough to not be resting on the deck skin and throwing things out of alignment? I like to leave a bit of extra bolt poking through inserts so if you need a replacement bolt for your mast in the future, you can use one that is too long.

5.) put some filler and epoxy into holes, but leave space for inserts.

6.) place inserts in holes, you may need to use some shims to hold jig at correct height above board so it does not get epoxied there too. Remember - inserts go in epoxy, while jig and nuts hover above it.

7.) allow to cure, unscrew bolts, remove jig. Your inserts should be epoxied in place, but there will be lots of gaps in the epoxy, place your bolts back in there, and put epoxy/filler into to bring to level. You can do this along with above step, but it is hard to do with jig in place.

Edit- as others have pointed out- you can’t see an internal insert so you won’t know if it is corroded. I’ve used 316 stainless inserts with good luck, they are harder to find but more corrosion resistant than other stainless steels

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby grandeand » Thu Apr 09, 2020 11:03 pm

Thanks for the explanation .. are the tee nuts the ones I posted in the photo?

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby tmcfarla » Fri Apr 10, 2020 12:05 am

grandeand wrote:
Thu Apr 09, 2020 11:03 pm
Thanks for the explanation .. are the tee nuts the ones I posted in the photo?
Yeah the shape of those will work fine. The teeth are for wood, but as long as your epoxy is thin enough to jam into the teeth without big voids, it will be fine. However, be aware that there are different types of stainless steel. Some are rust-proof, and some are rust-resistant. While I haven't tried lower quality stainless, I would be very wary of using it, particularly if the board is carbon (galvanic corrosion). I have used 316 stainless with good results, but it is a lot harder to find.

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Re: Best way to add bolt threads in the board for the mast when building board?

Postby downunder » Fri Apr 10, 2020 2:23 am



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