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-   -   Rudder Stiffener Rivets - Drill Out? (https://vansairforce.net/community/showthread.php?t=177222)

RV701775 11-24-2019 08:16 PM

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

Girraf 11-24-2019 08:33 PM

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.

iwannarv 11-25-2019 08:31 AM

Take note, work on driving square, and build on!

sblack 11-26-2019 10:04 AM

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.

RV701775 11-26-2019 07:39 PM

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.

rvbuilder2002 11-26-2019 10:10 PM

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.

mturnerb 11-27-2019 04:33 AM

Quote:

Originally Posted by rvbuilder2002 (Post 1389207)
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."

RV701775 11-27-2019 09:16 AM

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

wirejock 11-27-2019 11:41 AM

Rivet length
 
I know the plans call for a certain length but I always measure and use a length that yields a Mil Spec shop head. Never used any of the 3-3s.

rvbuilder2002 11-27-2019 03:32 PM

Quote:

Originally Posted by RV701775 (Post 1389289)
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

My recommendation would be to not try removing them.

PaulvS 11-27-2019 04:18 PM

I think they are OK
 
Quote:

Originally Posted by RV701775 (Post 1389289)
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

The average shop head thickness is (.033+.045)/2 = .039 so I would consider them OK, as others have also said. I've seen worse looking on flying aircraft... yours are better.

gmcjetpilot 11-27-2019 06:21 PM

Quote:

Originally Posted by RV701775 (Post 1388794)
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.

RV701775 11-27-2019 07:30 PM

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

PaulvS 11-27-2019 09:08 PM

Couple of ideas
 
Quote:

Originally Posted by RV701775 (Post 1389434)
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

Not sure exactly what is causing it, it might be due to some sort of alignment issue rather than the rivet set... though I had no joy with a spring loaded back rivet set, it tended to slip. I had more luck with a set similar to this, although mine has a rebate on the face:
https://www.browntool.com/Listview/t...6/Default.aspx

Suggested things to check:
- are the dimples formed consistently and not lop-sided before riveting;
- are you riveting from the inside-out (i.e. starting with the centre rivet and working out towards the ends of the stiffener);
- is everything fully clecoed before riveting;
- is the stiffener pressed up against the skin before riveting (use your fingers either side of the set to press it down);

Also, what does the factory head side of the rivet look like on the skin, is it nice and flush? If not, then the dimples may not be deep enough. If you could get another builder to come look over your shoulder while you work I'm sure there will be a solution, though what you have done looks quite acceptable.

jcarne 11-27-2019 09:26 PM

Ya those look similar to the rudder I built. I found later in the build that if I took the guard completely off my back rivet set and use my fingers to hold the tip of it on the rivet I got some really nice looking rivets. This method is not without warning though, there is nothing but your fingers holding the set on top of the rivet and not slamming into your part. It works very well for me. Go slow at first and you can correct any clinching before the rivet is too far set. When I used the set with the guard I never got perfect results.

Bottom line though, them rivets look pretty good and I sure would feel comfortable flying in front of them.

Jetmart 11-28-2019 05:15 AM

I found that the guard did not let you get close enough to the centre of the rivet because it was interfering with the stiffer. I ended up grinding the flat edge more to remove the interference.

rvbuilder2002 11-28-2019 09:57 AM

Quote:

Originally Posted by RV701775 (Post 1389434)
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.

The face of many of the shop heads are not parallel to the skin surface.
The only way that can happen is if the rivet set was not perpendicular to the skin as you finished setting the rivet.
If that was the case, then there is a good chance it wasn't perpendicular as you started setting the rivet. That will make the shop head form off to the side slightly (the amount depends on how far out of square the rivet set was).

All of the rivets are more than acceptable and should be left. Just work towards improving as you go.

As already mentioned, sometimes the guard interferes with the stiffener slightly cause you to tilt the rivet set. Grinding a bit more off the flat with a belt sander can help that.

Btw, it really isn't a guard (but that is what people typically call it)m It's primary purpose is to apply a down force to the parts being riveted to make sure they are tight together as the rivet begins to set. As a secondary purpose it is there for insurance to prevent the set from accidentally wandering off of the rivet. If the tool is being used properly, that should never be able to happen though.

A common error (even by Flight Chops :o) is to operate the gun using one hand and expecting the guard to keep the rivet set in the proper position. This is a recipe for disaster.
There should always be one hand on the grip of the gun, and fingers of the other hand grasping the rivet set at the bottom. If I am using one with a guard, I just grab the guard. If no guard, grab the rivet set itself
It can not hurt you as long as you always keep the set tight against the rivet.
With practice, you can learn to put down pressure on the part right adjacent to the rivet set (a good practice to assure that the parts are in tight contact with each other) using your ring and middle fingers, and hold the rivet set with your thumb and pointer finger.

An additional tip that can help people having trouble aligning the rivet set square to the skin, is to place something right beside the rivet being set to use as a sight guide in determining if they are aligned (a small machinist square, precisely cut wood block etc.). Make the rivet set parallel to the corner edge of the object being use and you will be square every time.


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