Rivets or SS machine screws

[Dan L]

I am resealing windows in a 79 scamp 13 and also replacing some leaky rivets. I am seeing alot of discussions on rivets vs. SS machine screws. They both seem to have pros and cons. Some like to think that rivets will break before they ruin the fiberglass but have a tendency to leak. The SS hardware would be much easier to install and would make a better seal and it would be easier to work with for future repairs. I am thinking about using SS for the windows but sticking with the rivets with snapcaps for the cabinets. Any insight into this would be much appreciated.

[Perry J]

I've refurbished several Eggs over the last few years.
My philosophy is, if something has worked for last 20 or 30 years why change it.

I just bought an 82 13' Scamp with no snapcaps.
I'm going to reseal the side windows and they will be riveted as well as the rest of the trailer.

Some one along the line used nuts and bolts on the kitchen base cabinet to the outside.
I have two very large holes to repair because of the bolts crushing and cracking FG.
I think the problem with bolts is they may not allow the flexing of the shell as the rivets do.
John

[Donna D.]

Hi Dan, welcome to FiberglassRV. We're glad you're here.

Just remember, if you mate SS bolts to an aluminum frame window, you'll eventually have a corrosion problems because of using dissimilar metals. If you still decide to go this route, use a non-corrosive (plastic, rubber, poly) between the bolt and the window frame.

Once again,

[ruscal]

In a perfect world the inner cabinets and stiffeners would mate perfectly with the outer skin. Since the world ain't perfect we have gaps between the parts. That is where the problems of holding and sealing arise. If you pull the parts together with a bolt the outside skin will be pulled into the other part distorting the outer panel and building stress into the assembly. The stress could in time allow the screw head to eat through the skin from shifting and vibration. Best result would probably come from shimming the gaps between the parts and bolting it up snug.
The dissimilar metal issue isn't too pronounced with Stainless steel and aluminum. I have been using them together for many years and have not seen any galvanic action.
Russ

[Brian B-P]

Originally Posted by ruscal

IIf you pull the parts together with a bolt the outside skin will be pulled into the other part distorting the outer panel and building stress into the assembly.

It seems to me that a rivet will do the same thing.

Originally Posted by ruscal

The dissimilar metal issue isn't too pronounced with Stainless steel and aluminum. I have been using them together for many years and have not seen any galvanic action.

Good to hear, but there are many stainless steel alloys, and they will behave differently.

Also, the oxidation of aluminum forms a desirable and protective surface barrier (unlike rust on steel) - anodizing aluminum is just doing this carefully and deliberately. Raw aluminum (such as a freshly drilled hole) should be more vulnerable than an oxidized surface.

[Carol H]

Originally Posted by ruscal

The stress could in time allow the screw head to eat through the skin from shifting and vibration.

Or it can crack the fiberglass. I have had a few rivets snap due to stress of traveling long distances on dumpy roads and not all of them where back roads. Had two rivets snap last year after doing a long journey on highways through areas that clearly needed resurfacing

Personally would much rather have the rivet snap than have the fiberglass snap.

[ruscal]

Originally Posted by Brian B-P

It seems to me that a rivet will do the same thing.


Good to hear, but there are many stainless steel alloys, and they will behave differently.

Also, the oxidation of aluminum forms a desirable and protective surface barrier (unlike rust on steel) - anodizing aluminum is just doing this carefully and deliberately. Raw aluminum (such as a freshly drilled hole) should be more vulnerable than an oxidized surface.

There are also several aluminum alloys to complicate things more. Some are much more corrosive than others. Window frames on our trailers are probably not made of 2024 or 7075 which corrode easily. I'll use common stainless steel hardware to fasten my windows without worry.
The raw aluminum where the holes are drilled though the anodizing will corrode without any help from stainless steel hardware. If I were building aircraft I would be properly concerned.
If you use zinc or cad plated hardware it will rust after a few years anyway. And as Neil said "rust never sleeps."
Russ

[ruscal]

Originally Posted by Brian B-P

It seems to me that a rivet will do the same thing.

In my experience pop rivets do the same thing, but are controlled by the tensile strength of the rivet shaft. When re-riveting my Scamp I found the rivets were snapping before the parts were pulled together. I had to employ my son as a rivet bucker to push the cabinet or brace up tight to the outer skin before drawing up the rivet. Perhaps high tensile rivets should have been used. I don't have the strength anymore to snap them though! With a screw you can torque up any tension you desire to achieve holding and watertightness.
Russ

[Daryl and Wendy]

Originally Posted by ruscal

The dissimilar metal issue isn't too pronounced with Stainless steel and aluminum. I have been using them together for many years and have not seen any galvanic action.
Russ

I will defer to people with more experience than me; but, in my experience with a f/g runabout on saltwater, we had never ending electrical problems - until I replaced all the fastening mounting and trim screws and bolts with stainless. The aluminum / stainless combination didn't seem to be any better or worse, but our electrical maintenance went to zero.

[Steve L.]

Originally Posted by ruscal

...The dissimilar metal issue isn't too pronounced with Stainless steel and aluminum. I have been using them together for many years and have not seen any galvanic action.
Russ

Not my experience however. I've put stainless screws in aluminum spars on my sailboat and have had real problems removing the screws or breaking them (due to corrosion) while trying to remove them. And I sail in freshwater. I would expect even quicker corrosion in saltwater which is probably not a problem for most of us.

After a few lessons learned I used Tef-gel after and never had another problem.

[David and Nancy]

I bought a new 04 Casita and broke a rivet attaching an overhead cabinet through the roof. It happened within a couple of hours after leaving the Casita factory. I replaced it with a rivet provided by the factory, the same one soon broke again. After the third time, I used a stainless steel bolt in that one problem spot. I assumed it was an unusual stress spot issue. I also thought bolting it might lead to gelcoat cracks or worse, but it never happened. That trailer went up and down the Alaska Highway several times, but never broke another rivet. That said, I have often wondered if the Scamp and Casita factory use rivets for a faster production line. It would take two technicians to install bolts. I suppose there would also be more inconsistency in torque with nuts and bolts, compared to rivets. If you decide to use nuts and bolts, a little loc-tite to prevent loosening would be a good idea.

[ruscal]

I stand corrected!
Years ago I was fabricating bicycle frames from aluminum and needed to improve the seat post clamping method. Some of the welded on clamp bosses were breaking. I asked a metallurgist what materials would be strong and would have anti corrosive properties that I could use to make the clamp. He said stainless steel would work well, so we used it successfully from then on. We also used stainless steel fasteners for bolting on accessories.
I just went onto Wikipedia and researched the electrolytic properties of metals.
The galvanic series chart shows the electrical potential differences of the various metals. The farther apart the metals are on the chart the more corrosive action you could expect. The metals lower on the chart would be expected to be sacrificial to the ones higher on the chart.
I was very surprised to find stainless steel so far above aluminum on the chart due to what I was told years ago, and all those years of successful use of the metals together. As others above said stainless could cause aluminum to corrode. One element necessary for electrolysis is for the metals to be exposed to an electrolyte. Sea water would be a good one. In drier environments the corrosion would be lessened, and may be why I have had such good luck here in San Diego. I did have a catamaran that had hard anodized aluminum spars. It had stainless steel parts fastened all over the spars. I owned it for 3 years and saw no corrosion during that time. The boat was trailered, not docked and was washed with fresh water after use. It was stored outdoors within 3 miles of the coast. On the bicycles we saw no corrosion due to the stainless clamps or hardware. If threading stainless steel directly into aluminum the use of antiseize may be a good bet to aid removal later. Stainless also welds to itself during tightening, so loctite or antiseize is a good idea to prevent galling and sticksion.
Russ

[Dan L]

Thanks for all the input. Seems like a good idea to stick with rivets.

[Jared J]

Jets are covered with stainless steel screws in aluminum panels. The amount of corrosion problems...ZERO.

[Steve L.]

Originally Posted by Jared J

Jets are covered with stainless steel screws in aluminum panels. The amount of corrosion problems...ZERO.

I apologize but I don't believe this is true. Everything I can find says aluminum panels on aircraft are aluminum rivets (frequently an AD rivet, usually solid). Some have steel pins to pull blind rivets where back bucking is not possible.

From Wiki:
Typical materials for aircraft rivets are aluminium alloys (2017, 2024, 2117, 7050, 5056, 55000, V-65), titanium, and nickel-based alloys (e.g., Monel). Some aluminum alloy rivets are too hard to buck and must be softened by annealing prior to being bucked. "Ice box" aluminum alloy rivets harden with age, and must likewise be annealed and then kept at sub-freezing temperatures (hence the name "ice box") to slow the age-hardening process. Steel rivets can be found in static structures such as bridges, cranes, and building frames.

What structural use screws I can find are also aluminum.

[Jared J]

Originally Posted by Steve L.

I apologize but I don't believe this is true. Everything I can find says aluminum panels on aircraft are aluminum rivets (frequently an AD rivet, usually solid). Some have steel pins to pull blind rivets where back bucking is not possible.

From Wiki:
Typical materials for aircraft rivets are aluminium alloys (2017, 2024, 2117, 7050, 5056, 55000, V-65), titanium, and nickel-based alloys (e.g., Monel). Some aluminum alloy rivets are too hard to buck and must be softened by annealing prior to being bucked. "Ice box" aluminum alloy rivets harden with age, and must likewise be annealed and then kept at sub-freezing temperatures (hence the name "ice box") to slow the age-hardening process. Steel rivets can be found in static structures such as bridges, cranes, and building frames.

What structural use screws I can find are also aluminum.

You're wrong. Panels aren't riveted, skins are (99% of the time). Panels are held on with stainless or cad plated screws (99% of the time). Riveted skins aren't always aluminum rivets, either. Stainless and Monel are quite common, depending on if its on a firewall, pylon, fiberglass, carbon fiber, etc. Then we can get into if its a solid, cherry max, cherry lock, huck, blind huck rivet, or hi-loks. After that, there's button heads, countersunk heads (shear and tension head), unisink heads…all sorts of fun stuff.

[Steve L.]

I used panels interchangeably with skins which is wrong. I was thinking about skins when I responded since you mentioned that aircraft were "covered" with stainless screws which put me in mind of the skins covering an aircraft.

Monel contains very little steel. Its mostly nickel. Cadmium is a plating used to isolate steel for corrosion purposes, again, it separates steel from aluminum.

Using stainless to fasten fiberglass and carbon fiber is not the issue being discussed here but I expect you simply included it as an aside since it doesn't add anything to the stainless/aluminum discussion.

I'm not going to debate the galvanic series. I'm going to stick to my observations about stainless steel fasteners in aluminum on my boat which confirm stainless/aluminum corrosion and how an anti-sieze compound mitigated the problem. We can perhaps debate how quickly this happens but as was pointed out earlier there are many different alloys of stainless and aluminum to confound the discussion.

[Steve Hammel]

Any experience with aluminum nuts and bolts? Is there such a thing? Several of the windows in my 19' had been removed and replaced with steel not stainless nuts/bolts. I couldn't figure why they liberally slathered each bolt/nut with silicone but now I'm begining to get an idea. I'm not too overly concerned with thread strength.

[Jared J]

Originally Posted by Steve L.

I used panels interchangeably with skins which is wrong. I was thinking about skins when I responded since you mentioned that aircraft were "covered" with stainless screws which put me in mind of the skins covering an aircraft.

Monel contains very little steel. Its mostly nickel. Cadmium is a plating used to isolate steel for corrosion purposes, again, it separates steel from aluminum.

Using stainless to fasten fiberglass and carbon fiber is not the issue being discussed here but I expect you simply included it as an aside since it doesn't add anything to the stainless/aluminum discussion.

I'm not going to debate the galvanic series. I'm going to stick to my observations about stainless steel fasteners in aluminum on my boat which confirm stainless/aluminum corrosion and how an anti-sieze compound mitigated the problem. We can perhaps debate how quickly this happens but as was pointed out earlier there are many different alloys of stainless and aluminum to confound the discussion.

You're absolutely right. I've only worked on jets since I was 19, and spent 12 hours on Sunday pulling thousands of stainless screws out of aluminum panels. I'm sure I've pulled out well over 500,000 stainless screws from aluminum, and have NEVER seen corrosion under the screws, but what the hell do I know?

I didn't include the fiberglass and carbon fiber as an aside, I included them because panels made from them use STAINLESS screws to attach to ALUMINUM structure with NO corrosion. Obviously your experience with a few fasteners of probably dubious quality in your boat, has taught you otherwise, though.

As for the cad plating separating the aluminum from it, I've seen many cad fasteners completely rusted, with again, ZERO corrosion on the aluminum.

[Jared J]

Originally Posted by Steve Hammel

Any experience with aluminum nuts and bolts? Is there such a thing? Several of the windows in my 19' had been removed and replaced with steel not stainless nuts/bolts. I couldn't figure why they liberally slathered each bolt/nut with silicone but now I'm begining to get an idea. I'm not too overly concerned with thread strength.

I'm sure they exist, but I haven't seen them on our jets. At worst, those bolts will rust like any other exposed bolt eventually will. They probably did it to stop leaks. If you don't need to take the windows out, I wouldn't bother. If you do, you can use the rivets or stainless fasteners. If it corrodes your windows, I will buy new ones. It's not happening.