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Old 14-07-2016, 17:14   #31
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Re: Blind rivets for mast - stainless steel or monel?

What diameter would you advise for mast step?
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Old 14-07-2016, 17:18   #32
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Re: Blind rivets for mast - stainless steel or monel?

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Lots of bad info in this thread.
Aircraft rivets retain their mandrels but they are not "pop" rivets. So not the same thing at all.
If you note the title of this thread it's" Blind rivets" not "pop" rivets. I don't get why you would want to use something of lesser quality? If you have to compromise, do what you can but why would you argue to remove the key strength element of a "pop rivet"? Try and picture a 3/16" rivet with a hollow core in a shear load, you just don't have anything there.
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Old 14-07-2016, 17:36   #33
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Re: Blind rivets for mast - stainless steel or monel?

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What diameter would you advise for mast step?
If you mean mast steps ours are 3x6mm monel.

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Old 14-07-2016, 19:01   #34
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Re: Blind rivets for mast - stainless steel or monel?

I asked a retired sail-maker friend and dock mate, Jerry, just today what to use to mount a solid vang to the boom. Sheet metal screws or rivets? Jerry: rivets. Long discussion about holding power and the like.
Stainless or aluminum? Jerry: anodized aluminum.
Of course there was lots of discussion about galvanics.
Jerry's suggestions come from long experience working on and sailing boats. I went with aluminum rivets, (couldn't find anodized).
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Old 14-07-2016, 22:33   #35
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Re: Blind rivets for mast - stainless steel or monel?

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If you note the title of this thread it's" Blind rivets" not "pop" rivets. I don't get why you would want to use something of lesser quality? If you have to compromise, do what you can but why would you argue to remove the key strength element of a "pop rivet"? Try and picture a 3/16" rivet with a hollow core in a shear load, you just don't have anything there.
"Blind rivet" is just another name for pop rivet. I am unsure what kind of rivet you are taking about. Maybe you are thinking of the "push pin" style where the mandrel is pushed in from the outside expanding the body of the rivet. This type of rivet is not a good choice for a mast step.

A pop rivet tool breaks off the mandrel and leaves the head inside (usually). The shear strength of a pop rivet joint comes not from the rivet material but from the friction caused by the high pressure of the joint. If you have a pop rivet (or any rivet) where the joint is slipping and thus putting the rivet in shear then it is not safe and the rivet should be replaced ASAP.
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Old 14-07-2016, 23:23   #36
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Re: Blind rivets for mast - stainless steel or monel?

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"Blind rivet" is just another name for pop rivet.
POP rivet used to be a trademark.


Story goes that Hamilton Neil Wylie (b. 1885), an engineer and reserve member of the UK Royal Flying Corps/Royal Air Force applied in 1916 for a patent for a tubular aluminium blind rivet formed around a wire mandrel (patent GB 106169, granted 1917).


In 1922, Wylie joined the Sir W. G. Armstrong Whitworth Aircraft Company and refined his blind rivet further for construction of the metal-framed Siskin III fighter and gained patent GB 2864711 in 1927. In 1933, the Armstrong Whitworth Aircraft Company transferred the intellectual property of Wylie’s blind rivets to the George Tucker Eyelet Company, which had developed in 1928 a ‘cup’ rivet that had to be assembled from two parts before use, for production of a one-part blind rivet to be used in Armstrong Whitworth aircraft. Stanley Engineered Fastening bought Tucker Fasteners, and their POP brand, in 1975.


Trouble is what is sold as pop rivets includes almost anything. If you want a blind rivet of which you know the metallurgy of the mandrel and rivet, and have a clue about the sheer strength, you have to buy a brand named blind rivet, not a generic pop rivet. I think generic pop rivets are only good enough for non-structural use. I think that is one of Guy's points.


I think Guy is accurate and correct on his other point: the shear strength of a blind rivet does depend on whether the mandrel core remains or not. The trademarked blind rivets sold as 'breakstem fasteners' are all divided between non-structural ones (often not rated by shear strength and not carrying specs about whether the mandrel core remains or not) and structural ones that are rated as to shear strength and that definitely retain the stem of the mandrel.


My position is to only use blind rivets on my mast in nonstructural or non-critical ways. That includes fixing in place the cable conduits that run inside the mast.


And because I don't know for sure what the metallurgical composition of the mandrel is, I knock out the mandrel cores and count them. The blind rivets I have used for the job are for sure some aluminium alloy, but without any certification as to which alloy. So I coat them with isolating goo (e.g. Duralac) before inserting.


If I had access to rated breakstem rivets/rated blind rivets of known composition, I might consider them for structural use.


I prefer instead to attach load-bearing fittings to mast and boom using machine screws into tapped holes. Those screws are removed, inspected, and recoated with isolating goo (Tef-gel et al.) every 1.5 to 2 years (it takes me 6 months to do all of them, unless I happen to have the mast horizontal).


Stainless steel machine screws are well understood tech. Inexpensive. Readily available. Easy to replace. And easy to inspect, remove and replace.


Compare that to strength-rated blind rivets. Not carried by my local fasteners shop.
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Old 15-07-2016, 08:17   #37
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Re: Blind rivets for mast - stainless steel or monel?

Some of the information above was general and correct but misleading in the narrow context of say mast steps on an alloy extrusion.

"...These types of blind rivets have non-locking mandrels and are sometimes avoided for critical structural joints because the mandrels may fall out, due to vibration or other reasons, leaving a hollow rivet that has a lower load-carrying capability than solid rivets. Furthermore, because of the mandrel they are more prone to failure from corrosion and vibration. Unlike solid rivets ..."

I hope this is clear we are discussing not just strength but possibly primarily corrosion, once the strength of the joint is taken care of. And so you punch out the mandrel. (Which otherwise VERY often pops out by itself.)

YES, you remove the remaining part of the mandrel to limit corrosion in an alloy mast.

ALSO, you will use different type of rivet NOT a pop rivet, when ultimate strength is the target.

There are very many factors and we can only discuss them one variable at a time. You cannot get a rivet of differing metal that will have best strength and lowest corrosion at the same time. Or if you can PLS manufacture and sell, you will retire rich.

Rivets are not the only method of attaching gear to the mast. They are just one option that is good for some equipment and poor choice in other aspects.

See the whole picture but discuss one property at a time. Or we get lost in misunderstandings.

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Old 15-07-2016, 09:10   #38
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Re: Blind rivets for mast - stainless steel or monel?

Anodised aluminum rivets? Interesting. Must shop around. I was not aware of their existence.

THX for sharing!

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Old 15-07-2016, 10:35   #39
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Re: Blind rivets for mast - stainless steel or monel?

If you want to isolate dissimilar metals from coming into contact with each other and galvanic corrosion.

Google dissimilar metals isolation tape, there are tapes made specifically for this purpose.
Whatever fastener used of course often completes the circuit though.

As far as blind fasteners go, there are many other than "Pop" rivets, Pop rivets are generally the cheapest and weakest available and require the cheapest of tools to pull them and require essentially no training.
A blind fastener that is much stronger than Cherry Max rivets is a Huck bolt for example.

Shooting a real rivet "Wet" does work much better, it forms a waterproof seal for the rivet and does not allow water or other fluids to seep into the joint, since it is a waterproof and I assume oxygen proof seal, I bet it does an excellent job of preventing corrosion.
Main purpose I had for shooting rivets wet was to prevent hydraulic fluid or oil from penetrating the joint and allowing the rivet to begin "working" or fretting, evidenced by what looks like a smoke trail coming from the rivet, that is aluminum oxide that comes out once the rivet begins fretting.
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Old 15-07-2016, 10:43   #40
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Re: Blind rivets for mast - stainless steel or monel?

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I'm no metallurgist, but I think that s/s can loose its passive state when exposed to stagnant water, etc, and this process is what leads to some forms of s/s corrosion. I suspect that this also leads to accelerated corrosion of aluminium it the rivet case. I hope that someone with greater knowledge will pipe up here, for I'm out of my pay grade.

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Eactly correct !

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Old 15-07-2016, 10:48   #41
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Re: Blind rivets for mast - stainless steel or monel?

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Anodised aluminum rivets? Interesting. Must shop around. I was not aware of their existence.

THX for sharing!

b.
I would have thought the stretching would breach the anodized surface and render it pointless..... no ?
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Old 15-07-2016, 10:55   #42
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Re: Blind rivets for mast - stainless steel or monel?

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Originally Posted by barnakiel View Post
Anodised aluminum rivets? Interesting. Must shop around. I was not aware of their existence.

THX for sharing!

b.
They are used in Aircraft I believe, not sure of the spec and they are a bit different than "pop rivets". I might be wrong, I have seen them finished in some way, maybe it's not anodizing though...
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Old 15-07-2016, 11:04   #43
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Re: Blind rivets for mast - stainless steel or monel?

Never seen an anodized aircraft rivet, anodizing I believe actually changes the physical property of the metal I doubt it would be allowed, however, EVERY aluminum aircraft rivet I have used that I can think of is alodined, often anodized and alodine are confused, they do sound a lot alike

They two commonly used aircraft blind rivets that I can think of are Cherry Loc and Cherry Max, the Loc rivet has an aluminum stem that breaks off at a pre weakened spot and has a steel loc ring that firmly hold the stem in, making it structurally part of the rivet.
The Max differs I believe in that the stem is steel, the max rivet is I think stronger than a solid aluminum rivet.

Getting rivet length correct is critical as well as having the hole dimensioned correctly, sounds like BS, but it's tough to drill a perfectly straight, round hole, very few people can do it without a lot of practice, if a hole is critical, it's best to ream it to size.
If you shot a Cherry Max or Loc wet and then painted the head with zinc chromate primer and a top coat, I can only imagine that is about the best that can be done to prevent corrosion, and have a strong joint.

When I installed my Whisker pole track, I drilled and tapped and used SS screws with lots of Tef-Gel, seems to be fine so far?
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Old 15-07-2016, 11:06   #44
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Re: Blind rivets for mast - stainless steel or monel?

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Never seen an anodized aircraft rivet, anodizing I believe actually changes the physical property of the metal I doubt it would be allowed, however, EVERY aluminum aircraft rivet I have used that I can think of is alodined, often anodized and alodine are confused, they do sound a lot alike
In aircraft work I see Alodine specified usually when the part is going to be painted. My understanding is it's like a low level anodizing, thin and not hard coat.
"Alodine is an international brand name for Henkel Technologies' conversion, anodizing and functional coatings suitable for use on aluminum, magnesium and other non-ferrous alloys. These coatings provide improved corrosion protection and paint adhesion."
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Old 15-07-2016, 11:31   #45
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Re: Blind rivets for mast - stainless steel or monel?

Aircraft I build, everything aluminum is alodined. It's an Ag plane and aircraft wise the only aircraft that sees worse corrosion than an Ag plane is one that lands in salt water
Its a zinc chromate conversion process that converts a very think layer of the aluminum to something else chemically, it is an excellent paint prep, but it's primary purpose is corrosion prevention.
Aircraft skins and structure are usually also Alclad, which is a thin, pure aluminum coating on the metal, pure aluminum is apparently much more corrosion resistant than alloys.

One of the biggest reasons there are so many US made WWII aircraft flying around and very few Japanese and German is the metal, the Japanese aircraft in particular have literally rotted away. I believe only the US used Alclad metal.
My little airplane that I kept is a 1946 Cessna C-140, she is in excellent shape corrosion wise and I am certain she will out live me.
Alclad I am sure is somebody's trademark
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