Having issues with drilling out rivets

[BGordon]

Good morning everyone, I a have a quick question about drilling long rivets out. I just put my firewall together and some of the rivets need to be replaced, however with the amount of material I need to drill through I am very ancy about doing so b/c I can see the hole getting lopsided or enlarged. I used AN426AD4-9s through the firewall, a stiffner, a gusset, and a fabricated L bracket. I have the removal tool for an AN470, but am wondering if it can be used on a 426. Any advice would be greatly appreciated
Brandon

[Don]

Brandon,

About 10 years ago a gentleman at a local aircraft shop (and fellow EAA member) let me disassemble some spam-can skins for instruction and practice. He planned to reuse the skins on a certified aircraft so he wanted the rivets removed cleanly. Here's how he instructed me and I've used the same technique on my RV build occasionally.

First, use a drill bit slightly smaller than what the original hole size was. This gives you room to be slightly off-center without enlarging the hole, and to be a bit more off-center and only enlarge it slightly (still useable). If you're off too much you'll need to redrill the hole and use an oops rivet (larger shank, same size head). I used a spring punch to mark the center of the rivet head. Fortunately all of the rivets we use have the center marked with a small dimple. You want to deepen that dimple. Here's the trick, it there is one - use a sharp bit and turn it slowly to get it started in the center. A dull bit will wander on you. Sometimes I find it handy to turn the chuck by hand to get the drill started in the center. If you don't start in the center you will have a virtually impossible time recovering. Start slow and speed up only when the drill is centered.

Ideally, (and this happens a lot, actually) you'll drill through the rivet and not touch the skin. The rivet will stay in place. When this happens, I simply smile, stop the drill and try to move the bit side-to-side to pop the rivet out. If I've nailed the center, the rivet won't pop and I need to use a small chisel to tap (shear) the head of a 470 rivet and the shop head end of a flush rivet. There's so little material left after you've drilled through, that it only takes a light tap to the side to shear the head.

I won't tell you I've never enlarged a hole but it doesn't happen often.

[rzbill]

Two comments first.
One, I am not judging whether you should or should not. That is up to you.
Two, this is the way I have done it. It is not necesarily the only way.

In my view, succesfully removing long rivets is totally a matter of skill. Before starting, you should be comfortable drilling out short rivets from across the room with your eyes closed, and not be able to tell there was ever a rivet in the hole.

The rivet body will be tight in the hole. You will very likely need to drill most if not all the way through the rivet with a 1/16" or 3/32" in order to remove enough pressure to tap it out.

Use standard techniques to properly and cleanly remove the manufactured head. As stated above, drill as far as you dare into the body with a 1/16" and follow it with a 3/32. Try to punch the rivet body out with a small pin punch.

If it is really stuck, and you can get to the shop head side, you can centerpunch the shop head and use proper techniques to remove the head and repeat the body drilling to join (or get close to) the hole previously drilled from the other side. I try to leave some metal in the rivet body for the punch to bear against.

Take your time and work accurately. I have removed -12s succesfully so it is possible.

[xavierm]

There are always several ways to do a task, but here is the one that works for me.
Use an automatic center punch on the head of the rivet.
Then use the removal tool to drill deep enough to remove the head of the rivet.
Use a punch of the appropriate size to remove the shank.

[Master Designs]

http://www.eaavideo.org/video.aspx?v=1657896937

[vlittle]

An additional tip, after drilling the rivet shank undersize and removing the manufactured head...

Rather than using a punch to drive out the rivet, use a small flush cutter (also called a dike) to grab the shop head and give it a twist. This can be done on thin material which may be deformed by punching.

It's important to use a full flush cutter... usually found at electrical equipment suppliers.

[LettersFromFlyoverCountry]

I found that patience is the key to drilling out a rivet head. Follow the tip Don suggested above and start wiggling. Resist the urge to "go for broke" and give it the big attempt to break it off before it's ready to do so. It'll break off by small wiggling moves.