Rivet Question

Thread starter #1
I am in the process of replacing the eye straps on the boom due to one being bent w/ half-pulled, corroded SS rivets and the forward strap being held on by standard aluminum rivets.

Given the issue of galvanic corrosion w/ 316 SS rivets, I've been using my background in professional auto racing to find a suitable aluminum rivet that would work.

I think I have a solution but I need to know how aluminum rivets typically fail in this application. Do they pull through the boom or do the heads shear off when they fail?

If the solution I've found will work, it will make everyone's life much easier when it comes to replacing blocks and straps.

Thanks in advance!
It's more often the body pulling thru, but I've seen a couple heads shear off..
There are ways to mitigate the corrosion, tef-gel works well as does clear packing tape (not only do you want to isolate the rivet, but the SS strap is also causing corrosion), monel rivets are another option.

IMHO though, can't go wrong with thru bolting..
Thread starter #3
Thanks for the reply. I've seen the solutions you mentioned in other threads. I actually purchased 316 SS rivets and SS M5 hardware to thru-bolt along w/ some LanoCote. Then I got the idea to call on some industry folks and see what is possible.

I like the idea of thru-bolting but, if you ever need to replace a bent eye strap or bad block, it could be difficult. Of course, you could notch the end of the bolt w/ a Dremel and use a flat head to keep it from turning as you loosen the nylock nut...

I'd like to hear from other's experiences regarding Aluminum Rivets for boom block eye straps. However, if pull through is the main issue, I think I've found a solution. They are sending samples to test. Anyone know the grade of aluminum for the spars? If I can get some scrap, I might be able to get these rivets load tested vs. normal Aluminum and 316 SS rivets.
I would make my own post, but its on a similar topic so i will ask here, In terms of replacing the blocks on the boom with the new laser preformance blocks that came out last year, if i drill out the old rivets to take off the old blocks and to put on the new ones, will the de-strengthen my boom?
Thread starter #5
It shouldn't as long as you don't drill all the way through. Just drill w/ a 3/16" bit until the head pops off. Then take a punch and pop the remainder of the rivet into the boom.
Thread starter #9
OK, here's what I've found thus far. Peter at aDP has been a big help. Also, I found an article where someone else had shear tested aDP's Ultimate Rivet. This is interesting. The 316 SS rivets have ~1,300 lbs shear strength and ~1,600 lbs tensile strength (according to McMaster Carr’s site). From the testing, it looks like the Ultimate Rivet has between 948-1322 lbs of shear strength.

Article and test results:

Video I found on YouTube (not the best quality but, you get the idea):

Thread starter #11
I realize that 316 SS and monel rivets are strong and help reduce corrosion but, they don't eliminate it. Plus, they're expensive comparatively.

I guess my thoughts behind searching for an aluminum rivet that's strong enough are:
- cheaper
- easier to replace (easier to drill & any rivet gun will work)
- no galvanic corrosion to damage/weaken/enlarge holes in boom (can still use corrosion inhibitor on eye strap)
i hadnt realised how expensive thet are £2.25 for 4 we just use them in customers spars all the time with paste between the fitting and the spar and dip the rivet in so that it goes between the rivet and the fitting so yer at that price i would just get some aluminium ones and when they go just replace them they wouldnt have to be anything special but try to get high tensile or heavy duty ones.
Thread starter #13
i hadnt realised how expensive thet are £2.25 for 4...
Hence the use of the word "comparatively" ;). A pack of rivets won't break the bank, regardless of the options mentioned. On the other hand, I found some aerospace rivets that could definitely hurt a wallet. Especially if you purchased the special tool required to install them...
Thread starter #14
Well, the generous sample pack arrived from aDP Rivets today. I decided to mount the blocks using the black coated Ultimate rivets. Not only do the black rivets look really sharp, the coating should serve as another barrier against corrosion. You can't get that w/ 316 SS or monel. Just in case, I coated both sides of the SS eystraps w/ LanoCote. I wish I could find a way to get a pic from inside the boom. There is no way these rivets will pull through.

Another bonus is that these will apparently still work at full strength even if the hole has been enlarged where a standard rivet will not hold.

The question is, can the head of these rivets withstand the shear forces dealt to the blocks by Mother Nature. From the testing I've seen, they seem to be very close to the shear strength of the 316 SS rivets. So, we'll see. I'll post if anything happens.

(in pic 3/16" rivets, from left to right: black coated Ultimate rivet, aluminum Ultimate rivet, std. aluminum rivet, 316 SS rivet)
This is an interesting subject and one which has been covered many times. In my opinion, the fundemental problem is not the galvanic corrosion, because you and the rest of us have rightly found ways to minimize that. The problem is that there is no way other than through-bolting to distribute the pulling force over a larger area of the inside of the boom. Remember, the most common failure mode is the rivet pulling out of the boom - not the eyestrap. This is exactly why I through-bolt using SS fender washers that have been matched to the curviture of the ID of the boom tube. The reason for this is as follows. If you assume that the diameter of the fender washer is only 50% larger than the head of the screw (bolt) or rivet , then the area which the bolt is pulling on is increased by 125%. Simply put, the pulling force exerted by the block(s) via the eye straps is now spread over an area 125 times larger than if a rivet or bolt was used alone. This means that the force per unit of area is drasitcally reduced to the point where the plastic block itself would probably be compromised before the bolt ever pulls out of the boom. I don't care if the rivet is made out of unobtainum, it is impossible to spread the force over such a large area without using a washer on the inside of the boom, and the only method I know of at the moment is through-bolting.
Thread starter #16
Pete: I like your argument. I read it before and it is what convinced me to go the thru-bolt route initially. Though, the hassle of replacing bent eye straps or potentially a bad block made me think there's an easier way.

So here's my train of thought. Since 316 SS and monel rivets are of acceptable strength and don't seem to fail when installed in a new boom or boom w/o corrosion damage, then we can agree that rivets will work. However, when you add your argument in, there really isn't much expanded surface retaining the rivet. Then you consider the numerous advantages of a standard aluminum rivet vs. the one main disadvantage of being weaker, ie. more likely to pull through or shear a head. Thus, the search for a better mouse trap, or... aluminum rivet.

Now, back to your point. I wanted an aluminum rivet of stronger stock material for better shear strength that also provided more surface area to eliminate pull-through. One option was to use backup washers. That would have been much like thru-bolting but, easier to remove. Next, there are the aerospace options w/ crazy rivet designs of multiple parts and expensive tools.

Then I came across aDP's new design. If you watch the video, you can see that their ultimate rivet doesn't just create a "bulb", it actually expands the rivet body as it compresses and collapses it. Thus, creating it's own heavy-duty "backup washer" of sorts and distributing the load over a larger area. Another advantage of the 5052 Al they use is that it gets stronger when "cold worked". So, the compressing of the rivet body actually strengthens the rivet. I looked inside the boom w/ a small super bright LED and the back of the rivet is rather amazing. It looks just like it does in the video. Plus, I was able to use a cheap rivet gun purchased from Amazon for $23 to install 'em. There is no way it will pull through. While it isn't likely that the head will shear either, it is a possibility. But, pull-through won't be an issue.

If aDP's ultimate rivets holds up, it seems like the best of both worlds. Time will tell...
I would generally agree with your assessment regarding a new boom or one w/o corrosion. I guess I keep forgetting that I am mostly in the "antique business" and generally don't wotk w/ new stuff. I do like the idea of rivets, particularly if they are superior to hardware store or GP variety.

Question - I wonder if there is a way to place a backing washer inside the boom after the rivet has been inserted. I'm thinking that a special tool could be rigged up to do just that. if so, then it truly would be the best of both worlds. I will give it some thought.
Thread starter #18
Well, mine is a '92 w/ original spars. While not antique, it's a only a couple months from being a classic :cool:

I thought about the backup washer and if I were to go that route, here was my first stab at how to do it.
-I would take some very thin fishing line, (something like Stren Superbraid 8lb or lighter), push it through the hole (outside to in)
- suck it out the gooseneck opening (be sure to tie something to the outside portion so it doesn't pull through)
- apply some type of light adhesive, maybe even blue Loctite, to the backup washer
- place washer onto bolt or rivet*
- secure washer to rivet by wrapping enough tape around the bolt or rivet to keep it on but still easily go through the hole
- tie fishing line securely to end of bolt or rivet opposite the head
- pull through until washer is securely against boom (maybe even clamp to let light adhesive dry)
- then, gently push bolt or rivet back through, leaving the backup washer in place
- repeat as necessary

*I think a rivet would work better since there are no threads to disturb the washer when pushing back through. To use a rivet, I would cut the mandrel off flush w/ the head and superglue the mandrel in place from the head side. Then you have a nice groove created by the head of the mandrel to tie the fishing line to.

Now, at this point, you've done half the work of through bolting. But, repairs will still be much easier. This is why I'm praying the aDP ultimate rivets will hold up as there is no need for a backup washer with these. Here's a better quality video showing how they expand and even fill oversize holes:
Pretty cool. I think they are worth a try. The only thing I didn't see was how much they mushroomed in the back. I will check out the website for views.

Never been to the PRI show but always wanted to go. Some of my former colleagues were regulars.
Thread starter #20
PRI is cool. More racing/performance industry specific. However, if you're a car nut in general, SEMA is a must. My feet, knees and back have never hurt so bad as they did from being at SEMA for a week :eek: It's nearly impossible to explain how big the SEMA show is. If I'm not mistaken, it's the largest in the world. Something like 1,000,000+ sq. ft.