December 27, 2007

Riveted Leading Edge to the Spar - 6.0 hrs.

Today I reached another mini-milestone. It's time to start riveting this wing together, starting with the leading edge to the wing spar. The ribs are riveted to the spar first. That's the hard part because they can't be easily reached, and the clearance underneath for the rivet gun or a bucking bar is very tight. You really need a helper for this part of the task if you can find one, unless you just use pop rivets.

Above and below: Here's the leading edge clecoed in place for the last time.

I mentioned this idea briefly in my entry of December 4th. My desire to avoid pop-rivets wherever possible led me to thinking... what if I could come up with a modified backriveting method for setting the rib-to-spar rivets inside the leading edge? I spent some time thinking about this method and I thought I would give it a try. I used this old hammerhead as a bucking bar of sorts... it certainly has adequate mass. I polished the top on one side, and drilled a 3/16" hole to accept a typical rivet set as shown above. The hole was near the edge so that I could put this in tight places. The duct tape is to protect the primed surfaces of the ribs while riveting.

My idea was to hold this thing inside the leading edge on the manufactured head of the rivet, while hammering the bucktail from below. My thinking was that this allows you to follow the standard protocol of using the manufactured head on the thinner material, and keep the shop head, or bucktail, on the thicker material side (the spar in this case).

I used an offset mushroom-head rivet set to reach the rivets, since they're so close to the main ribs underneath. I even ground down one side of the rivet set, as seen above, to allow close reach. Again, duct tape was used on the rivet set and also on the gun to avoid scratching the ribs or spar.

This picture shows why I ground down the rivet set. These rivets are very close to the main wing ribs. This is the only way I can think of to reach them.

So how did this method work? Honestly, I had mixed results. I had to drill out quite a few of the rivets and try again. Why? Because when you're riveting, the bucking bar normally bounces on and off the rivet with each blow of the rivet gun. It happens so fast... 2,100 beats/minute... that you don't see it or think about it. And it doesn't matter. With flush rivets or bucktails, it isn't an issue. But in this case, with round-head AN470 rivets, if the rivet set moves a fraction of an inch between blows, the edge of the rivet set hits the top of the rivet and you end up with cuts or creases in the rivet heads. It must be held precisely in place for success. And that's hard to do. The problem is, the help I have available around here are family members, none of whom have any experience at riveting. They don't understand any of this. I tried to figure out which job was the most difficult... holding the bucking bar/rivet set combo, or running the rivet gun, so I could give the easier job to my inexperienced helper. Those of you who are experienced riveters know that running a rivet gun isn't normally that difficult. But these offset rivet sets are another matter entirely. The rivet set wants to twirl around in the gun while you're hammering away, and it must be held in place with your fingers to keep it from rotating, to keep the proper angle on the work or you'll end up with smilies. Or in this case, damage to the spar web (yikes!). So I ended up giving the bucking bar task to my helper while I did the shooting.

If you look closely in the picture above, you can see that in spite of all my care I managed to ding up the inside edge of the hole in the wing rib with the spring on the rivet gun. This required some careful fine filling and buffing out, followed by application of more primer to fix it when I was done. I should have had a longer offset rivet set.

In the end, I managed to git 'er done with several of the ribs, but I'm not sure I'll try this again. Above, you can clearly see that the rivets look good, but you also see the minor damage I caused to the main rib lightening hole. If you have someone to help you who is experienced at riveting and/or bucking, you can probably use this method with great success and minimal problems.

The ribs in the middle bays of the leading edge are hardest to reach, and I decided to go with pop rivets here. It's hard to try and reach clear in there to buck them with this difficult method, let alone inspect the rivet heads and drill them out if necessary. I decided it wasn't worth the risk. I have no regrets for using these pop rivets here.

After all the work getting the ribs riveted in place, squeezing the skin rivets to the spar was a breeze.

Looks great from here! Interesting perspective.

All done! It really feels good to finally have something permanently attached to the spar

<< Previous | Home | Next >>

Contact me: swayze "at" (replace "at" with the @ sign... no spaces... you know the deal)