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  #1  
Old 11-24-2019, 08:16 PM
RV701775 RV701775 is offline
 
Join Date: Jul 2019
Location: Boston, MA
Posts: 95
Default Rudder Stiffener Rivets - Drill Out?

I finished setting the AN426AD3-3 rivets on that holed the rudder stiffeners to the skin. I did the math and these rivets area almost exactly the correct length for a 1.5 diameter head. About six of my rivets fit in my cleaveland rivet gauge tightly, but are not significantly over driven. The issue is that on one side the rivet may be 0.033in height and on the other side the head height may be 0.045+. The rivet looks acceptable except for on side of a head is a bit short.

Should I drill these rivets out or is it acceptable to have one side below the Mil-R-47196A minimum head height of 0.038in for a -3 rivet? Not sure how much this matters on the stiffeners.

https://eaabuilderslog.org/?blprojec...=7YL1dRvO9&add
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  #2  
Old 11-24-2019, 08:33 PM
Girraf Girraf is offline
 
Join Date: Dec 2017
Location: Southern Maryland
Posts: 227
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May be strange coming from another user who just today asked a similar question albeit for blind rivets......but I wouldn't even think twice here. Those look more than adequate. There will be so many more rivets in your future that you'll never be able to measure as precisely and have to rely on just a visual inspection or by touch only to determine acceptability.

In the course of building, I often repeat two mantras, both from Vans.

1. Your building a tractor with hand tools in your garage, not an F-22. (also rephrased often as "Your building an airplane, not a watch)

2. More problems have been created than ever solved by drilling out rivets.

I found it helpful to carefully examine other RVs and aluminum planes to create my own basis for workmanship that clearly was acceptable for flying aircraft.
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  #3  
Old 11-25-2019, 08:31 AM
iwannarv iwannarv is offline
 
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Location: Olathe, KS
Posts: 511
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Take note, work on driving square, and build on!
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Last edited by iwannarv : 11-26-2019 at 07:13 AM.
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  #4  
Old 11-26-2019, 10:04 AM
sblack sblack is offline
 
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yes agree with the others. they are fine. Work to improve, but if you drill them out you will elongate the holes and make a mess. These are structurally sound.
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  #5  
Old 11-26-2019, 07:39 PM
RV701775 RV701775 is offline
 
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Location: Boston, MA
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One issue I noted is that the dimples on the stiffener are slightly tipped inward. I believe this is due to the proximity of the bend in the stiffener. I also tried using a dimple die that was ground down on one side and did not see much improvement. I believe this tilt in the dimple may be why, that although the rivet is set straight, the outer side of the shop head is shorter than the inside side.
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  #6  
Old 11-26-2019, 10:10 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Review Section 5 in the construction manual regarding shop heads on rivets.
Pay particular attention to the Referenced MIL Spec for rivets. The minimum and maximum shop head size is much broader than "Must be exactly .5D thick and 1.5D in diameter.

Something else to keep in mind.....
With the experience level that most people are at when building the empenage, 9 times out of 10 if a removal is done, the rivet hole will get messed up and the second installation attempt will be even worse than the first.

I'm not saying that a rivet should never be removed. Just don't do it without serious contemplation. Especially early in the project with a lower skill level.
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  #7  
Old 11-27-2019, 04:33 AM
mturnerb mturnerb is offline
 
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Location: Jacksonville, FL
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Quote:
Originally Posted by rvbuilder2002 View Post
Review Section 5 in the construction manual regarding shop heads on rivets.
Pay particular attention to the Referenced MIL Spec for rivets. The minimum and maximum shop head size is much broader than "Must be exactly .5D thick and 1.5D in diameter.

Something else to keep in mind.....
With the experience level that most people are at when building the empenage, 9 times out of 10 if a removal is done, the rivet hole will get messed up and the second installation attempt will be even worse than the first.

I'm not saying that a rivet should never be removed. Just don't do it without serious contemplation. Especially early in the project with a lower skill level.

Experience is helpful here for sure - you start to get a feel for which rivets look "right". I find this part of Section 5 particularly useful in this regard:

"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. To relieve the anxiety sometimes associated with an imperfectly set rivet and to avert potential problems arising from ill-advised attempts at repair, (not to say 'never repair a rivet'), guidance in the form of an excerpt from the Alcoa Aluminum Rivet Book, dated 1984, is provided here.


"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 percent 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 [is] likely to be more defective than the first because the hole is enlarged and [the] 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."
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  #8  
Old 11-27-2019, 09:16 AM
RV701775 RV701775 is offline
 
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One side of the rivet heads is below the 0.038in min thickness in listed in the mil-spec and the 0.5 dia thickness. So what I am trying to say is that they were also below the mil-spec on one side (i.e. 0.033in head thickness). The only way I can think to fix this is to increase rivet size
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  #9  
Old 11-27-2019, 06:21 PM
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gmcjetpilot gmcjetpilot is offline
 
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Quote:
Originally Posted by RV701775 View Post
I finished setting the AN426AD3-3 rivets on that holed the rudder stiffeners to the skin. I did the math and these rivets area almost exactly the correct length for a 1.5 diameter head. About six of my rivets fit in my cleaveland rivet gauge tightly, but are not significantly over driven. The issue is that on one side the rivet may be 0.033in height and on the other side the head height may be 0.045+. The rivet looks acceptable except for on side of a head is a bit short.

Should I drill these rivets out or is it acceptable to have one side below the Mil-R-47196A minimum head height of 0.038in for a -3 rivet? Not sure how much this matters on the stiffeners.
Short answer is, it is acceptable (not seeing the rivet). Rivet has no other defect? One or few rivet or many rivets? Is the rivet shop head centered over hole? (hard to determine sometimes) Cracks in rivet? (Get light and magnification).

It sounds OK. A stiffener on thin sheet metal is not loaded but is subject to vibration and thin skin flexing. Worst case is (after lots of flight hours) a rivet can get loose and "smoke". Will these smoke? Unlikely, but the best prevention is a perfectly driven (or slightly over driven) rivet.

You risk more drilling out the rivet. Structurally as you point out it is a stiffener. Set a standard and stick to it. Takes the head scratching out of it.

If you have not drilled rivets out in thin sheet metal make some practice parts and have fun. You know to only drill head off and try and punch the rest out.

Really up to you.
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Last edited by gmcjetpilot : 11-27-2019 at 06:24 PM.
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  #10  
Old 11-27-2019, 07:30 PM
RV701775 RV701775 is offline
 
Join Date: Jul 2019
Location: Boston, MA
Posts: 95
Default How do I fix this?

No matter what I do the rivet seems to tilt to the inside of the stiffener. I have tried different pressures, tilting the back rivet set slightly outward, two different back rivet sets (big black one and small Cleveland one). I didn't have this issue during the sports air workshop but I wasn't back riveting a stiffener. I attached some additional photos of the same stiffener to see if I can get any ideas to correct the issue prior to continuing. Thanks for all the input!

https://eaabuilderslog.org/?blprojen...cat=^empennage
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