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Old 09-02-2015, 04:37   #1
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Rivets in Mast Cleat Question

I managed to bung up a composite mast cleat mounted with a type of heavy duty pop rivet. Is this a rivet that is readily available, and installed with a standard puller? No way to install a machine screw/nut that I can see.
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Old 11-02-2015, 20:40   #2
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Re: Rivets in Mast Cleat Question

Rivets hell yeah, a common bad practique for many mast makers and some riggers , cleats never ever ever should be used with rivets,,, best way is to use screws...is quite common to found lots of gosenecks and cleats working loose thanks to cheap rivets.... just my 2 cents...
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Old 11-02-2015, 21:23   #3
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Re: Rivets in Mast Cleat Question

All kinds of pop rivets are readily available. Unfortunately your description is entirely too vague to determine exactly what kind you're referring to.

If you want to avoid using a rivet use a tap to cut threads in the hole and use a machine screw to mount the cleat. Fine threads are preferred.
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Old 14-02-2015, 12:58   #4
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Re: Rivets in Mast Cleat Question

The rivet tool used to mount your cleat originally was pneumatic or hydraulic. These are not the tools hobbyists use around the house. I'd just do as advised already and replace the rivets with machine screws after tapping new holes.
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Old 14-02-2015, 13:37   #5
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Re: Rivets in Mast Cleat Question

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Originally Posted by Jim Walsh View Post
The rivet tool used to mount your cleat originally was pneumatic or hydraulic. These are not the tools hobbyists use around the house.
I ran into this problem of oversized rivets in an automotive application. But I found out that there are many types of screw type rivets available. Instead of using the standard pop tool you cinch down on a screw to collapse the body of the rivet. Some are available in stainless and in the larger sizes which I had to use.
I'm not advocating these for the cleat I'm just saying they are there.
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Old 14-02-2015, 14:12   #6
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Re: Rivets in Mast Cleat Question

More details and pictures.

On the thinner spars of small boats, rivets can be the very best answer, better than threads, and properly installed will outlast the boat. Look at beach cat masts. They have the addvantage of leaving nothing sharp inside to snag lines and cut wires.

On thicker spars (over 1/8") threading is good. But it must be done very well to be better than a rivet. Coat the threads with Tefgel or Teflon pipe dope.

If you are to reuse rivet holes, you must drill the old one out cleanly. A sharp 3/16" drill (most common size) will remove it perfectly; just drill down the center hole until the head shears off. Drive the rest through. Much easier than removing a stuck screw. Use only SS or monel rivets. Hand rivet tools work fine to 3/16, but a quality tool is required.

I've used hundreds and can't remember a failure... but like anything, they must be properly and appropriately used.
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Old 14-02-2015, 14:19   #7
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Re: Rivets in Mast Cleat Question

[QUOTE=skipmac;1746859]All kinds of pop rivets are readily available. Unfortunately your description is entirely too vague to determine exactly what kind you're referring to.

If you want to avoid using a rivet use a tap to cut threads in the hole and use a machine screw to mount the cleat. Fine threads are preferred.[/QUOTE]

So I was always told to use coarse threads in aluminum.....? I think because the fine don't cut well and just smear leaving little grip...?
What"s the consensus?
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Old 14-02-2015, 19:07   #8
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Re: Rivets in Mast Cleat Question

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Originally Posted by Cheechako View Post
So I was always told to use coarse threads in aluminum.....? I think because the fine don't cut well and just smear leaving little grip...?
What"s the consensus?
Good question. I have seen the question addressed somewhere before (maybe an old thread on Cruiser's Forum) but don't recall for certain the conclusion.

I went with fine threads on the last mast repair I did because my buddy that's a machinist and all around fix anything guy wanted to use fine threads. We discussed it a bit and his reasoning: higher number of threads engaged in the thin wall of the mast and more total surface area in the screw and hole that are in contact.
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Old 14-02-2015, 19:14   #9
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Re: Rivets in Mast Cleat Question

FWIW, I have always believed soft metal - coarse thread & hard metal - fine thread...BUT wall thickness has to be considered.

I'm not a machinist so this might just be wrong
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Old 14-02-2015, 21:05   #10
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Re: Rivets in Mast Cleat Question

My preference has been to use pop-rivets to secure important hardware to our aluminum mast and boom. I just think they offer a better hold than screws into thin aluminum, and would be less likely to work loose. I have also used coarse self-tapping SS screws into aluminum for less critical hardware.

I've mainly used aluminum pop-rivets on the spars of our small boat, but we're on freshwater. I haven't seen corrosion issues with our SS fittings and some of it is going on 35 years old.

I think I'd only tap aluminum spars for a machine screw if the wall was decently thick.
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Old 14-02-2015, 23:03   #11
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Re: Rivets in Mast Cleat Question

I had a mast which had solid, shaped heavy alloy plates added to the exterior of the mast by multiple screws and the cleat screwed through the piece thru both. Very secure. Can melt some alloy in appropriate mould to make your own.


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Old 14-02-2015, 23:22   #12
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Re: Rivets in Mast Cleat Question

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Originally Posted by neilpride View Post
Rivets hell yeah, a common bad practique for many mast makers and some riggers , cleats never ever ever should be used with rivets,,, best way is to use screws...is quite common to found lots of gosenecks and cleats working loose thanks to cheap rivets.... just my 2 cents...
However, the choice is not simply between cheap rivets, and screws. How about using GOOD rivets? McMaster Carr have high strength SS rivets, rated for 2200 lbs each in 1/4". That means you could lift my boat by the boomvang, as 6 of them hold that on.

Bristol used rivets to hold my boom to the mast, and it's been working for 35 years.

Finally, here is the incredibly exotic piece of equipment you need to install 1/4" rivets. Hardly out of the reach of the ordinary mortal, is it? :

Astro Pneumatic 1/4 Hand Riveter - Walmart.com
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Old 15-02-2015, 10:54   #13
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Re: Rivets in Mast Cleat Question

Coarse threads were told to me by a Millwright... I guess that trumps a machinist! haha.
This seems to support that:
"In relatively low strength materials such as cast iron, aluminum, magnesium, brass, bronze, and plastic, coarse threads provide more resistance to stripping than fine or extra fine threads.
If subjected to heat, they are less likely to seize than fine threads.
A larger tap drill is required for fine threads, shallower thread depth."
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Old 15-02-2015, 11:08   #14
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Re: Rivets in Mast Cleat Question

[QUOTE=Cheechako;1748876]
Quote:
Originally Posted by skipmac View Post
All kinds of pop rivets are readily available. Unfortunately your description is entirely too vague to determine exactly what kind you're referring to.

If you want to avoid using a rivet use a tap to cut threads in the hole and use a machine screw to mount the cleat. Fine threads are preferred.[/QUOTE]

So I was always told to use coarse threads in aluminum.....? I think because the fine don't cut well and just smear leaving little grip...?
What"s the consensus?
Choosing the thread form is a simple engineering calculation. The limiting factor is the shear strength of the base material. In reality we pragmatic engineers rarely do the math.

Some rules of thumb are:
1) use coarse threads in soft materials (eg aluminum) and fine threads in harder materials (eg ss)
2) thread length at least as long as the thread is wide for pure axial loads. Use a backing plate wherever possible.
3) if the joint is subject to a radial load then you either need a much larger diameter thread or thread depth greater than 2 x thread width. Also see 7).
4) for coarse threads you need at least 4 or more threads. This limits in how big a diameter you can go to.
5) threads need to be full depth. Most taps are tapered. You need a finishing tap for blind holes.
6) the 55 degree whitworth thread form is generally the strongest.
7) select bolt diameter so that you can sufficiently torque the fastener. Yielding of the fastener in the elastic region is required for dynamically loaded fasteners. This typically leads to a minimum diameter fastener. This opposes 4)
8.) to the experienced eye 'what looks right is right'.

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Old 15-02-2015, 11:16   #15
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Re: Rivets in Mast Cleat Question

Quote:
Originally Posted by Cheechako View Post
Coarse threads were told to me by a Millwright... I guess that trumps a machinist! haha.
This seems to support that:
"In relatively low strength materials such as cast iron, aluminum, magnesium, brass, bronze, and plastic, coarse threads provide more resistance to stripping than fine or extra fine threads.
If subjected to heat, they are less likely to seize than fine threads.
A larger tap drill is required for fine threads, shallower thread depth."
I would have to agree, would follow a millwright over a machinist. Plus my guy isn't a formally trained machinist just one of those jack of all trades though is truly a master of some. For his day job he rebuilds Steinways and I mean rebuilds, not just a tuning job and a coat of paint.

I think the idea of the deeper threads in coarse screws certainly would be better in soft metals but what does your guy think about fine vs coarse into a short hole in a thin piece like a mast? Not at the boat but from memory I think the mast section is around 3/8" thick. With a large diameter, coarse thread screw you might only have 2-3 threads in the hole where a fine thread might have 5-6 threads engaged.
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