Terry Phillips
Joined: 11 Jan 2006
Posts: 346
Location: Corvallis, MT
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 Posted: Fri May 28, 2010 8:53 pm Post subject: A Riveting Experience: Some Insights(?) (Long) |
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Moving ever so slowly, I have finally riveted the extruded angle to my right wing spar cap. I think that I learned some things that may be useful to others who are upgrading even more slowly than I.
I started rivet practice way back in February using two different 3X rivet guns with AN470AD-6-16 rivets from Spruce and some aluminum bars from Pacific Steel. After going through almost half a pound of rivets, I concluded that I could not drive those rivets consistently with a 3X gun. I could count on 10 or 11 out of 12 good ones. I concluded that I was just a klutz, because I knew that other builders had used 3X guns with success. Fortunately for me, a builder from EAA517 loaned me a rivet tool that he had built years ago to set the rivets in an RV-4 spar. That tool plus 4 whacks from a 4 lb sledge will really set a AN470AD-6-16 rivet--perfectly, every time. All one has to do is not hit the spar with the hammer--but that's another story.
Before I began setting the AN470AD-6-16 rivets in my wing, I had one last practice session with my bars. Just for sport, I also set one of the AN470AD-6-14 rivets supplied by Zenair with the upgrade kit. I checked the length of the -16 and the -14 rivets using the handy dandy Avery rivet length gage. Sure enough, the -16's were ~1/32" or so too long, and the -14 was ~1/8" (probably 3/32") too short. When I checked the shop heads with the Avery shop head gage, the -16's were just fine, but the -14 head was just under the thickness spec and was definitely deficient in diameter.
Hmmm .....
Of course, Zenair does not recognize the Avery rivet gage--Zenair has their own Construction Standards. So, I measured the -14 shop head (D=6.6mm & h=1.7mm) and found that the shop head does meet Zenair's Construction Standard CS#403. It does not, however, meet the Mil Spec Standard. Zenair's construction standards for AD-6 rivets (6.0<=D<=8.1mm and 1.4<=h<=3.8mm) are more permissive than MIL-R-47196A (D>=6.2mm and 1.9<=h<=2.7mm) where D is the shop head diameter and h is the shop head thickness. (It turns out that the Avery gage measures D=7.1mm and h=2.4mm, which are Zenair's "nominals." You can see photos of the Avery gages in my Kitlog entries).
So, what's going on here? Here are some conjectures: - Zenair chose to supply rivets which are really too short for the application. Possibly these are the same rivets used in the upgraded wing reported on in the load tests of 9/28/09. Of course, the spar-root-doubler thickness in those tests was 0.063" vs. 0.125" in the upgrade specs.
- I believe that one of Zenair's major objectives was to make the upgrade process as easy as possible for their customers. Since the -14 rivets can be driven to meet CS#403, Zenair may have supplied the -14 rivets instead of -16 rivets to ease the upgrade process.
- The standard solid rivet shank height above the base metal is 3/2 times the shank diameter. So, the volume of aluminum that must be formed with the -14 rivet equals ((3/2)*(3/16)-1/
 /(3/2*3/16) = 5/9 = 56% of the metal in the -16 rivets. Thus, to a first order approximation, the -14 rivets need ~56% of the energy input from the rivet gun that is required for a -16 rivet gun. - So, it is very possible that a 3X gun would do an acceptable job on the -14 rivets for some builders who would need a 4X gun to drive the -16 rivets consistently.
My conclusion from all this is that if you use the Zenair supplied AN470AD-6-14 rivets, then a 3X rivet gun may give you satisfactory results--mind you, I haven't tried it. But if you are using rivets that meet the (3/2)*(rivet diameter) rule for rivet shank length, you may have a lot more problem with a 3X gun.
Terry
Terry Phillips
ttp44~at~rkymtn.net
Corvallis MT
ZU-601XL/Jab 3300 s .. l .. o .. o .. w build kit - Tail & flaps are done;
Upgrading wings & ailerons per the AMD Safety Directive
http://www.mykitlog.com/N47TP/ [quote][b]
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Terry Phillips
Corvallis, MT
ttp44<at>rkymtn.net
Zenith 601XL/Jab 3300 slow build kit - Tail feathers done; working on the wings. |
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