Finally riveting some wing ribs!

It has been over 3 months since my last post. During that time I have had to endure what I can only describe as the worst experience of my 20 year career as an IT professional. It was largely responsible for my inability to work on the plane, not to mention many other things. I'll just leave it at that. I made a promise to myself that that will NEVER happen again.

My left wing spar has been clamped to the edge of my work bench during all that time, just waiting for me to start riveting the ribs. I spent about an hour planning and rigging my clamping solution to keep the spar from vibrating or moving excessively. Many builders have problems with this because they do not secure the spar properly, and when they try to rivet the ribs the rivet gun jumps off the rivet head causing smileys and all sorts of other damage. I was aware of this so I wanted to ensure that the assembly was properly secured.

Step one was provide support at the inboard edge of the spar. I used 2 of my 4x4 padded blocks and one bar clamp to provide a kind of stop block that would prevent the spar from flexing backward. The blocks are laid flush with the workbench top on both sides of the spar and clamped together. I really wanted to clamp the blocks vertically onto the workbench but this proved difficult using my bar clamps since they did not have enough depth to reach the blocks on the back side of the spar. So I relied on this approach and the remaining bar clamps locking the bottom spar flange to the work bench to give me enough support of the spar to keep it from moving too much during the riveting.

My plan was to start on the inboard side since these are the most difficult ribs to rivet because they are so close together. These first 4 ribs are the support ribs for the area where the pilot and passenger will be entering and exiting the plane, so the extra strength provided by these closely set ribs is necessary to support the weight.

For the rivet gun I chose to use the double offset rivet set for the AN470AD4-7 rivets. I can't say enough about using masking tape on the rivet set to help prevent marring the surface. I think I also followed the advise from other fellow builders before me who suggested grinding down the rivet set head by about .001 or less to prevent smileys from occurring due to holding the rivet set slightly off-angle from the work surface during riveting.I have a very difficult time judging if a rivet set is truly 90 degrees to the work surface in all directions, and holding it there while you are pounding the rivet into place. Removing this small amount from the tip of the rivet set, and using the masking tape, seems to resolve that problem quite nicely.

Here is the clamping setup for the first inboard rib:

One of the frustrating things about this is that the primer on the ribs tends to close the diameter of the rivet hole just enough so that the rivets will not insert into the hole. The only way to solve this is to run a reamer into the holes to clear the excess primer.I had had to deal with problem repeatedly on other parts of the plane. It is problematic for me because I constantly have to switch out my air line between the rivet gun and the drill, and this takes extra time between rivets. Once the holes are cleared everything goes according to plan.

Here is the front side with all but the top-most rivet in place. I am proud to say that even though I had not riveted anything in a very long time, I managed to set the rivets of the first four of 28 wing ribs without any problems, dings, or smileys. It felt really good to get back to building the plane again. My clamping solution also worked very well. I kept solid pressure on the rivet with the rivet gun the entire time, and kept the bucking bar (I use the fat man bar for most all AN470 rivets) square to the rivet shank. I did have to adjust the air pressure on the gun several times by increasing it way more than I used to for the double offset rivet set. I think the reason was because in the past I had been setting AN470AD4-5 rivets, and these rivets are about 1/8 inch longer  (4-7). So it takes a bit more air pressure and energy to set these longer rivets.

I have never had much of a problem using the double offset rivet set, but others seem to have problems working with it. The reason it is ideal for this job is that it provides the clearance needed between the rivet gun and the rib web, AND it adds enough length to the entire assembly to allow the bulk of the body of the rivet gun to clear certain areas of the ribs, i.e. lightening holes,etc. that could potentially get in the way of things like the retaining spring, handle, etc. I found it to be the right tool for the job, as long as you remember to adjust the air pressure accordingly.

Here is the shop side of the rivets. Note the top most rivet is not set. I decided to wait until all the other ribs are set and then I will flip the spar over and set the last rivet. The reason - simple - I cannot easily see the top side rivet, and since that hole is so close to the edge of the large wing spar reinforcement bars, the bucking bar cannot be centered on the rivet shank and must use the bottom third of the bucking bar. Then, the bar must be held so that it will not mar the surface of the support bars. This, combined with the weight of the bucking bar, means that it is possible to screw this up in a heartbeat. So I am choosing to let gravity assist me by setting both of these outer-edge rivets while the hole is on the bottom so I can see what I am doing and allow gravity to help me position the bucking bar along the edge of the wing spar support bar. I also added some extra tape along the edge where the support bar meets the spar web of the wing spar to prevent damage from the bucking bar.

Here is how I began the riveting process for each rib. This pic shows the start of the third inboard rib. I clecoed each hole from the back side and then removed the center cleco and began riveting from there. I wanted to ensure that any slack in the rib flange would be removed, so I applied the same process that is used for riveting the skins to the frame by starting from the center and working outward. I set the center rivet and then set the two on the bottom, followed by the fourth rivet next to the top-most rivet, which I left alone for reasons as stated previously.

And finally then end of 3 hours of work: