Rivets or Machine Screws When Splicing a Mast?

[team karst]

neither is perfect, but bolts have replaced rivets in most steel beam building construction. You won't mess up a bolt temper, but a rivet has to be malleable during fastening and therefore can't be made as strong, given the size. Even worse strength performance for hollow rivets. But, bolts could loosen with vib.

I thought fine threads are stronger than coarse??

[stormalong]

Mine is welded. A bunch of small holes, each with drip of a weld. Then the joint is welded. 37 years old now. So far so good.

Painted mast of course.

[sailormed]

Using our “friend” Gxxgle I found a lot of manufacturers of ingenuous bolts for instances of one sided access for installation. But they look expensive and rather large.

[Breaking Waves]

Originally Posted by stormalong

Mine is welded. A bunch of small holes, each with drip of a weld. Then the joint is welded. 37 years old now. So far so good.

Mine was plug welded also. That has its own pros and cons - ruins the heat temper of the aluminum extrusion so you need a beefy inside sleeve to add strength back. And probably more skill is needed than machine screws or pop rivets. But is 'forever' when done well.

[Cheechako]

The Pro's use rivets and structural epoxy on assembly between the sleeve and the two mast sections. I had one done years ago by Chesapeake Rigging. They did a lot of this type of custom work for expensive racing yachts etc.. The sleeve should fit closely.

Anything threaded will become threadless in short order anyway from corrosion.

[thinwater]

I did a bunch of testing (shear and tension, bolts and rivets, in mast sections) for an article some years ago. Although the result depends on mast thickness and grade of rivets, if high strength (yes, there are many types) are used they are stronger than machine screws. But the difference is tiny.


As for chafe, again it depends on the rivet. Generally the edge would go to rivets.


Really, it's not going to matter, since any differences are on the order of 10-20%, and the fasteners are not going to be what fails. This is why the mast manufacture did not have a strong opinion.


Good rivets are NOT a cheap production substitute. I've have just as many machine screw failures as rivets, and a bad rivet is easier to remove; drill it out, takes seconds.

[Baby tug]

Originally Posted by stormalong

Mine is welded. A bunch of small holes, each with drip of a weld. Then the joint is welded. 37 years old now. So far so good.

Painted mast of course.

Welding hands down for me

[thinwater]

Originally Posted by Baby tug

Welding hands down for me

If the mast is a heat treated alloy, which it almost certainly is, this will weaken the mast and is, in most cases, the worst possible way to do this. Which is why mast makers do not do it that way and do not recommended it. See post 20.


Ask an engineer. Welding is not always the best way, and if high strength alloys are involved, post heat treatment is required.


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More interesting is the spacing of the fasteners, and whether they are combined with epoxy, which they commonly are.

[stormalong]

Originally Posted by thinwater

If the mast is a heat treated alloy, which it almost certainly is, this will weaken the mast and is, in most cases, the worst possible way to do this. Which is why mast makers do not do it that way and do not recommended it. See post 20.

Ask an engineer. Welding is not always the best way, and if high strength alloys are involved, post heat treatment is required.


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More interesting is the spacing of the fasteners, and whether they are combined with epoxy, which they commonly are.

Well, I am not a welder or an engineer but as I said this mast is 37 years old and doing fine.

Each individual hole is about 1/8 inch in diameter and from a cutout I did with a hole saw I can see a drop of aluminum in each hole. The joint between the sections is also welded. The sleeve is the same thickness as the mast. The strength is in the sleeve. The welds just hold the sleeve in place. Guessing from the number of welds in the one inch hole plug I would guess there are a lot of welds.

I have put about 130,000 sailing miles on this and I am the second owner. It has been stripped and repainted twice in the 32 years I have owned it and even stripped and grit blasted I cannot see the welds.

So my experience says it can be welded.

[Breaking Waves]

Originally Posted by thinwater

Which is why mast makers do not do it that way and do not recommended it.

Rondal welds - they are one of the top (European) superyacht spar makers.

They mostly do carbon today but have a long history of welded aluminum. Interestingly, not just joins, but gooseneck fittings and tangs also.

I'm curious what specific rivets you recommend? I have difficulty believing that apples to apples (eg "size for size" and "material for material") a hollow rivet will match the strength of a solid machine screw. And current steel construction practices would seem to agree with that.

The high end riggers I know all prefer machine screws.

For the OP - any of the approaches will work just fine if properly done - quality and care of the job is the key. It is just an engineering job to ensure that whatever technique is used is strong enough.

[thinwater]

Originally Posted by Breaking Waves

... It is just an engineering job to ensure that whatever technique is used is strong enough.

For the OP, this is the point. You need to use the fasteners that the designer speced. The size, spacing, and number all matter, and they relate to the specific plug. No point in us guessing.


No, you don't use Tefgel in this application. You want a thread locker. Tefgel actually increases the chance of a screw vibrating loose, and in aluminum, you need to watch the torque.



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Yes, I am an engineer, and I tested fasteners in masts up to 3/16" thick. The OP's mast is probably thicker than this.



Extra strong rivets differ from typical hollow rivets in that the core is designed to stay in place, increasing shear strength, and this is a pure sheer application. My tests results squared with manufacture specs.

[Dave_S]

My 0.02c NOTE: I have no mast joining experience, just mechanical design experience.

It will depend on the standard of the workmanship. Don't assume a tradesman can deliver tradesman like quality of work, regardless of their reputation. If you are paying someone to do it, go the most fool proof way, this will give you the greatest chance of success and minimise the risks associated with the unknown standard of workmanship that you will get.

Rivets offer less chance of mistakes compared to drill and tapping.

I would not use countersunk fixings.

Use high end structural rivets only. A few points....
1. The optimum machine screw diameter is usually approximately equal to the material thickness. 3/16th - 3/16th (P.S. only use a coarse thread if you are using a screw made from a stronger material than the material with the tapped thread i.e if you use Cad plated 316SS screws in aluminium you should use a coarse thread, if you were using aluminium screws you would use a fine thread).
2. Structural rivets like a Huck rivet provide superior clamping force especially because you can use diameters larger than the machine screws. (6mm rivet V's 3/16 machine screw)
3. Rivets are easier to fit and less likely to be installed incorrectly. NOTE: There is a risk that swarf may collect between the two skins and reduce the strength of the assembly.
4. You need to check rivets, they can deform in use under stress and may need replacement.

[Celestialsailor]

Originally Posted by Rumrace

Rivets pull metal together screw tear at the aluminum assuring corrosion and the mast looses. The rims on my summer car have 40 rivets to hold 3 pieces of the rim together. The front ones wore out so I had all 4 rims reworked. We’re they threaded or screwed they’d be junk.

This is nothing more than a misleading opinion. I am a Toolmaker/Machinist and a Field Engineer. Screws do not tear aluminum. Properly tapped and lubed, the male thread simply pulls the adjacent female threads together. Do you even know how many blocks, fairleads and whatnot are fastened to a mast with threaded fasteners? Give it a rest chief. You're not impressing anyone here. Instead you continue to mislead them.

[MWGDVC]

Originally Posted by neilpride

Both ways are ok, monel its the answer if its riveted, air hydraulic gun, you need one, machine screws the best option, FLAT 82º, allen head, dont even try to use flat or phillips heads, Loctite , just a bit.

https://www.cruisersforum.com/forums...-a-138817.html

I would tend to agree with this except for the FLAT 82 deg. I would use 100 deg. as less of the wall thickness is removed from the mast for the countersink (most flush rivets are 100 deg).

[aqfishing]

Originally Posted by Cheechako

The Pro's use rivets and structural epoxy on assembly between the sleeve and the two mast sections. I had one done years ago by Chesapeake Rigging. They did a lot of this type of custom work for expensive racing yachts etc.. The sleeve should fit closely.

Anything threaded will become threadless in short order anyway from corrosion.

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