tkatc

tkatc

Well Known Member
I am about to close up my HS with the rear spar. I was hesitant to do this without having someone look at it for fear I had overdriven or under driven some rivets. In my research here, I have read that even poorly driven rivets are within say 5% maximum strength of a properly driven rivet. I've also read that unless the rivet is seriously misdriven, the risk of drilling the rivet out is greater than leaving the imperfect rivet in place for fear of enlarging the hole.

Can anyone shed some light on this theory? Setting the rivet enlarges the rivet body to fill the hole be it a proper hole or enlarged. So why is it thought to be inferior?
 
The tolerances for the specific rivets shop head are pretty large. Take a micrometer and check a few rivets against the specifications. You will be able to quickly learn how to "eyeball" the rest of them.
Leaving a few hang nail, cracked, grossly over driven or under driven rivets here and there is not considered that big of a deal by most.

However, standards exist for a reason. When you start to deviate from them, where do you start, and where do you stop. Experience and good judement would guide you from there. If you don't have the experience, or someone to rely on to help make a good decision, stick to the standards called out in AC 43-13.1b and your builders manual.
 
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Understood JonJay....but why are rivets into enlarged holes worse than proper holes?
 
Why?

Like Jonjay said, we need to draw the line somewhere.
Where to draw that like varies due to:
Function, what does it do, how likely and what happens if it lets go.
Location, will I be able to do a better job.
Options, are there other acceptable type fasteners
Type, rivets in dimpled holes in lighter sheets tend to swell open the hole. oversize rivets can do the same thing.
I imagine all this kind of muddies the water. In reality good judgement and common sense usually are a lot alike.
 
tkatc said:
Understood JonJay....but why are rivets into enlarged holes worse than proper holes?
Click to expand...

A sloppy rivet in a too large hole may not drive properly. It may look ok on the surface but you can not tell if the shop head was formed off center. The specifications call out the length of rivet, acceptable shop head size, and hole tolerance. That clamping force inside the hole is a "controlled" event. I am not an engineer so that is the best explanation I have for you.

I can suggest that we RV builders obsess about our riveting, and that is a good thing. You would not believe the number of bad rivets in my Fiat projects and they never fell out of the sky, but I am rebuilding properly with the confidence that it will be better than when it was new.
 
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Drilling out rivets isn't worth the risk

Your original supposition is correct; Vans endorses Alcoa's statement that the risk of re-drilling is greater than the value of a replacement rivet:

(From Section 5: CONSTRUCTION MATERIALS, PROCESSES AND USEFUL INFORMATION http://www.vansaircraft.com/pdf/Section_5_R11.pdf )

"DRILLING OUT RIVETS
One of the common calls we get is ?I had to drill out a bad rivet and now the hole is oversize. What do I do??.

Sometimes this is done multiple times in the same hole and now the hole is so large that the builder has to use a bolt and nut instead of a rivet. See below.
EXCERPT from Alcoa Aluminum Rivet Book, dated 1984.

?The standards to which driven rivets should conform are frequently uncertain. In addition to dimensions and perfection of shape, inspection is concerned with whether the drive head is coaxial with the shank (not ?clinched?) and whether there is excessive cracking of the heads. It has been determined that even badly cracked heads are satisfactory from the standpoint of static strength, fatigue strength and resistance to corrosion. (Poorly set and cracked) rivet heads were tested in tension to determine how well formed a head has to be in order to develop full strength. The tensile strengths of all the rivets were within five per cent of the strongest. The test indicated that minor deviations from the theoretically desired shape of head are not cause for concern or replacement. The second rivet that is driven in any one hole likely to be more defective than the first because the hole is enlarged and rivet will be more likely to buckle and form an imperfect head.
Tests have shown that very small rivet heads are sufficient to develop the strength of the rivet shank, even when the rivets are subject to a straight tensile pull?.where a large head is not needed for appearance, smaller sizes of drive head should be used to decrease the required driving pressures.?

YMMV

Ron
 
Tony,
If you are using those anodized "rivet gauges" as your go/no go, you are being to critical. As already mentioned, you need to actually READ that section of AC 43.13 Shop heads that are 1.3 diameter [rather than 1.5d] still meet the mil-spec. Shop heads that are only 0.3d tall [rather than 0.5d] still meet the mil-spec. You are also allowed 1 "non spec" rivet, in every 10. However, you can not have 2 next to each other.
Over-sized holes and botched rivets are what 1097 rivets are for. If the botched hole is in the sub structure [not a skin] simply drill it out and install a 5/32" diameter rivet.
Charlie
 
Good stuff guys. I was not really talking about my work. I believe my rivets to be acceptable according to the AC 43.13 although they are not all perfect. I was just mulling over the theory as to why enlarged (or oblong) holes are taboo. This discussion had shed a few ideas on the subject. I never thought that the enlarged hole would possibly not be filled by the rivet. I suppose that is possibly and this would allow movement of the joined pieces under various pressures.

Just thought I would ask the masses the theory behind the taboo. As I become better and better at setting my own rivets I am wondering how many bad ones are out there. I figure it took me a dozen or so rivets to get the feel for what I was doing. You can definately feel AND hear when the rivet is set close to proper.
 
I am coming tomorrow morning to check. I will take Big Uptiks with me to show everybody here on VAF the truth :D
 
Tony, sounds like good news / bad news. On the good news side, Vlad can give you an experienced first hand opinion. On the bad news side, I'm guessing Vlad needs to perform another oil change :D
 
I have had my times. Practice!

I am very good at drilling rivet heads off and not touching the hole.

The skill came over years of fixing planes.

I do it best with a new or very sharp 6 inch drill bit.

It is hard to explain but the best I can say is you will do well to imagine where the tip of the bit is when going through the rivet head. I try not to drill all the way through, as I want to crack the head off with the back of the same size drill bit or better yet the correct diameter sharp edged Pin Punch.

I do not try to drill deeper than the rivet head/shank juncture.

The smaller the rivet, the more difficulty you "may" run into.

As the bit wanders from center you will need to adjust from perpendicular to keep the tip of the drill on center.
 
EAA Counselor

Tony, I had an EAA counselor sign off on every piece I built before I closed it up, and an airworthiness report gets sent into the EAA office. Something to consider for your build.

T.
 
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