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Rivet Shop Head Cracking

CFI1513840

Well Known Member
Has anyone seen cracking in the rivet shop head during the forming process? I have a batch of AN470 AD4-5 rivets where I occasionally get a tiny crack on the circumference of the shop head. In this case, I'm using a pneumatic squeezer. This is the first time I've seen this and I'm well into the Fuselage. I worried about the crack propagating and destoying the integrity of the rivet. I checked with Van's and although they didn't have any idea what was causing it, they didn't think it would be a problem. I just wondered if there was anyone else out there that had any experience with this sort of problem.
 
I've had this happen as well. It's a pain, but I drill out and replace cracked ones. So far I've only seen it happen on squeezed rivets, and not on bucked rivets.

I've taken a few of the drilled out shop heads and tried to pick them apart with a punch and pliers, but no luck. They're still stuck together pretty well.
 
Funny you bring this up, I had three rivets do this when working on the tail cone, all of them were bucked. I also drilled them out, which was a little tricky because the head just falls apart.
 
Or you could check the MIL-Spec....

...which does allow minor cracking around the periphery of the shop head.

...Cracks in driven heads (1) which fall within a circle which is concentric with and 1.10 times the nominal shank diameter, or (2) intersecting cracks, or (3) five or more cracks...

The full specification is here -

http://www.rvproject.com/MIL-R-47196A_MI.pdf

If it meets the specification, it's OK....:)
 
...which does allow minor cracking around the periphery of the shop head.

...Cracks in driven heads (1) which fall within a circle which is concentric with and 1.10 times the nominal shank diameter, or (2) intersecting cracks, or (3) five or more cracks...

The full specification is here -

http://www.rvproject.com/MIL-R-47196A_MI.pdf

If it meets the specification, it's OK....:)

Gil, thanks for the information. It proves that I should do more reading because I have a copy of the Mil Spec, come to think of it. It's conveniently located in the front of my construction manual. I just have to remember it's there. I have a similar problem with my cleco pliers.

Even if the Spec allows some cracking, I think we would all prefer to have crack-free rivets, but it's nice to know we have some leeway. I drilled out a couple of them, but they were easy to get to. I worried about those tight places where drilling out would be a lot harder than setting them, so I wanted to wait until I had more information before proceeding.

I wondered if the rivet batch had anything to do with it. So I examined them and found that I had at least two different batches of -5 rivets with different markings. One batch had an "nr" marking, the other had a "P" symbol. The ones that had cracked were all "nr" so I tried using rivets from the "P" batch and had much better results, no cracking.

My rivet bin contains a mix of stuff from the empenage, wings, fuselage and maybe a few from Aircraft Spruce. Some of them could be a few years old. I don't know if this proves anything, but I'm thinking that I might chuck the whole batch of "nr" markings and order a bunch of new ones.
 
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Yes...

......

Even if the Spec allows some cracking, I think we would all prefer to have crack-free rivets, but it's nice to know we have some leeway. I drilled out a couple of them, but they were easy to get to. I worried about those tight places where drilling out would be a lot harder than setting them, so I wanted to wait until I had more information before proceeding.
........

...but be careful that you might do more damage reworking a cracked rivet that is within specifications....:eek:

I'm awaiting the "old rivet" and "DIY heat treating" postings, but the MIL-Spec for our specific rivets quotes no age limits or storage limits.

This specification is good for fighter aircraft and NASA, so it should be good enough for our RVs. They form the basis for the strength tests referenced in Mil-Handbook 5 that I am sure Vans staff uses for loading calculations.
 
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Funny you bring this up, I had three rivets do this when working on the tail cone, all of them were bucked. I also drilled them out, which was a little tricky because the head just falls apart.

John, this is an interesting point because it might indicate that the rivets became too brittle. That brings me back to my question about rivet batches and whether it's possible to have a bad batch of rivets.
 
...but be careful that you might do more damage reworking a cracked rivet that is within specifications....:eek:

Gil, this point is well taken. I'm very reluctant to replace a rivet that might meet Spec but is not too pretty. In that case, I prefer to leave well enough alone.
 
this happend to me last week and i drilled out about 10 rivets all done with a squeezer. got frustrated and just went inside. the simple solution was just backing off the set half a turn and squeezing slower. fixed!!! now i dont hate -5's anymore funny it only happend with 470-5. i thought i was going crazy!!
 
My AN470AD4-5 rivets are cracking too

It's really weird that this thread would pop up one day before I had the very same problem with some of my AN470AD4-5 rivets. I squeezed about a dozen of these today and nearly every one had a 45 degree crack around the outside of the shop head. :eek:

Here's a photo:

20090509-10-tn.jpg


They really acted like they were especially hard. Before I found the problem, I remember thinking it was odd how my pneumatic squeezer hesitated for 1/4 second or so after clamping on the rivet, but before it actually squeezed it.

I also had driven a few of these with the gun today. Here's a close up of one done with the gun. Notice how the sides are very bumpy and there appear to be some voids in the end face of the rivet.

20090509-08-tn.jpg


In contrast, here is one done with the gun today, but from a differnt batch. The sides of the shop head are much smoother and there don't appear to be any voids in the end face of the rivet.

20090509-09-tn.jpg


I had two more compartments full of this sized rivet in my storage container, so I just discarded all the ones in the compartment I had been working out of.

Weird. :confused:
 
... I had the very same problem with some of my AN470AD4-5 rivets. I squeezed about a dozen of these today and nearly every one had a 45 degree crack around the outside of the shop head. :eek:

Here's a photo:

20090509-10-tn.jpg

I know this thread is from 2009, but I had the EXACT same problem last night. AN470AD4-5's cracking in the exact same way as pictured in Mike's post. About 50% of the installed rivets display some level of a 45degree crack.

I've read the MILSPEC, and my interpretation is that this 45 degree crack most likely does intersect the 1.10 diameter circle concentric to the rivet stem and therefore they are out of spec...

That being said, I'm curious what people think of the 45 degree crack (drill out or leave), and the possibility of the rivets being a "bad batch"...
 
I know this thread is from 2009, but I had the EXACT same problem last night. AN470AD4-5's cracking in the exact same way as pictured in Mike's post. About 50% of the installed rivets display some level of a 45degree crack.

Me too! NR marked AN470AD4-5's in the older tail kit I am assembling. Very grainy looking and many/most are cracking. All other 470's are setting just fine (and have the double line "R" mark) Going to go grab my 15 year old 4-5's at the hangar tomorrow. Bet they set just fine. No doubt a bad batch of NR made 4-5's got out. Grrrrr!
 
I tried several different remedies to no avail. I finally grabbed a bunch of replacement rivets from a friend at the airport... and those set just fine. I definitely think its a bad batch of rivets. Replacing them is the best bet.
 
Me too! NR marked AN470AD4-5's in the older tail kit I am assembling. Very grainy looking and many/most are cracking. All other 470's are setting just fine (and have the double line "R" mark) Going to go grab my 15 year old 4-5's at the hangar tomorrow. Bet they set just fine. No doubt a bad batch of NR made 4-5's got out. Grrrrr!

Yep, drilled out the cracked "NR"s and replaced with circa 1989 stock. They set without issue. Noticed the bag of "NR" crackers was Van's dated 2008. Seems to be in line with the manufactured date others have had issues with.
 
Resurrecting this thread since I ran into this exact issue with the same AN470AD4-5 rivets adding the reinforcement plates to the elevator front spars.

10/11 I set cracked with 3/11 needing replacement (cracking extends to within 1.1d circle). They exhibited the same odd driving behavior as noted previously (the squeezer didn't set smoothly but instead struggled then finally the rivet gave way). These were also the first time I've had to set the rivets in two stages.

Interestingly enough, only the rivets that I fully set with the pneumatic squeezer cracked. The ones that I half set with the squeezer and then fully set with the gun did just fine.

These were marked AF and have a 2018 date stamp.

Edit: I replaced 9/11. 3 had cracking within the base circle and the remainder had 5+ cracks. Generally everything cracked on the bias. The deeper cracks made a vee with its apex on the shop head.

Drilling out the rivets felt a bit odd. The heads were soft but from there I could feel layers of hard metal. It felt like I was drilling through several different layers of metal.

I think I’m going to order some replacements.
 
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Recently had cracking issues as well, but on skin flush rivets. Not sure how old the rivets were, but Vic Syracuse and some others at Sun n Fun recommended replacing the kit rivets with a new order.
 
There are strong opinions on this, but you can re-solution heat treat the rivets. I have done it and it works great, but there are risks involved. I only use it on non-critical areas. I happen to have a nice little benchtop heat treatment oven.

For instance, I re-solution heat treated some AN470AD4's that are used to secure the seat hinge to the floor panel because the panel is so thin the shop head tends to distort the metal. Also,you typically have to use a gun and buck them because they are in the middle of the panel. The freshly treated AD4's were easily squeezed with a DRDT operating as a long-reach squeezer! I wish I had used this on the seat backs. The rivets age harden back to spec.

Again, solution heat treating is not annealing!
https://materialsdata.nist.gov/bitstream/handle/11115/192/Heat%20Treating%20of%20Aluminum%20Alloys.pdf?sequence=3&isAllowed=y

<Flame suit on>
 
Recently had cracking issues as well, but on skin flush rivets. Not sure how old the rivets were, but Vic Syracuse and some others at Sun n Fun recommended replacing the kit rivets with a new order.

My bags were labeled 11-2018 but who knows how old the actual rivets were. All of the bags in the kit were labeled around then. These were the only rivets I've had issues setting and I've set 470AD4-4 through -8 at this point. I haven't had any issues with AD3 sized rivets.

There are strong opinions on this, but you can re-solution heat treat the rivets. I have done it and it works great, but there are risks involved. I only use it on non-critical areas. I happen to have a nice little benchtop heat treatment oven.

Interesting. Does it affect the coating any? I don't have any way to control the heat that closely and there are only like $2 worth of 470AD4-5 rivets in the kit. These also hold the ailerons to the HS so I'd consider them critical. There are enough in the plate that it's probably OK to have less than perfect rivets but I don't want to take the chance.



I thought it was interesting to find the exact same issue with the exact same size of rivet nearly a decade later to the day.
 
Interesting. Does it affect the coating any? I don't have any way to control the heat that closely and there are only like $2 worth of 470AD4-5 rivets in the kit.

yes, the coating dissolves into the alloy. You can re-chem film if you want, but I prime anyway, so I don't bother.
Agree that it is not done to save money. Rivets are cheap. I bought new rivets to replace the "crackers" when I was building the structure. The crackers went in the trash.
 
I received the replacement rivets today. They look exactly the same as the ones supplied in the kit (same AF head mark) but they set just fine and in one stroke instead of two and they had the ?smoke? during set that the cracking rivets didn?t have.
 
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