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back riveting top flap skins

Tom Martin

Well Known Member
I have been following Van's instructions pretty closely on this RV14 kit but when I started to rivet the top flap skins to the ribs using a gun and bucking bar as suggested, I just was not happy with the results. I found it difficult to get a smooth finish on those thin .020 skins. The plans do make allowance for back riveting the final two rivets in the top skin.
One method I have used over the years to back rivet tight spots is to set up a bucking bar as shown in the picture below. Just tape a 1/8" piece of wood, to the one end of a flat bar and set the other end on top of the rivet. Hitting this cantilever bucking bar close to the rivet end will make a very nice shop head.
Be careful to make sure that the "wood" strip on the bucking bar is also resting on your back rivet plate. This will make some really nice perfectly smooth top flap skins, and is also kind of fun to do. As always, practice and some scraps first.
zksk.jpg
 
looks good...do you have any problems with proud rivets or gaps in the sheets since there is nothing to press down on the material on the shop side like the spring sleeve on a standard back rivet set?
 
No, there are no issues with that, you do have to make sure that the rib is pressed down tight to the skin, and the whole affair tight to the metal plate.
I had some weights on boards on either side of the rib being riveted to keep the flap from moving.
 
Gun Size?

Tom -

What size gun and how much air - please?

It seems like a lot of potential energy would be lost in the contact point between the gun and bar, and that the mass of the bar itself would absorb some as well. Your experience?

Thx

David Howe
 
I use a 3X gun on 99% of my work. I keep trying the 2X gun but I am never satisfied. I have much more control with a few harder hits of the larger gun then with that buzz of the 2X gun. On this particular job with the 20 thou skins I tried the 2X gun an attempted to set the rivets with a bucking bar. It is hard to get a smooth surface, for me anyways, riveting a light skin onto a small rib. Even though I have the flap secured in the reccomended fixture the skin and ribs are a bit of a moving target. Back riveting the top skins removes this potential for error. Back riveting control surfaces is the norm for Van's parts it is just that the rib requires that you modify your technique and I have presented one way of doing this that worked for me.
As for air pressure I use the pressure that is required for the job at hand. Turn the air down until you cannot set the rivet properly and then turn it up until you are satisfied.
When I was a bit younger I never changed air pressure as my reflexes were good enough to get the number of hits required for the rivet be it a - 3 or a -4. Now I am finding that turning the pressure down gives me a bit more control.
 
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