why no match drilling?

When I started on my -7, I was taught that the reason we final drill all the holes is that the punching process can leave micro-cracks on the edge of the holes which can propagate over time. Drilling and deburring the holes fixes this problem and assures that you won't get cracks starting to spread from around your rivets.

Now, if I understand correctly, on the -12, all of the holes are punched to size and you just fill 'em up with rivets. Why is it that drilling out the holes is no longer needed?

I'd appreciate it if someone can enlighten me.

Thanks!

I think you need that answer from the 'horse's mouth', otherwise you will just get speculation. Please ask VAN's, then please post it here as well I'd like to know the answer as well.

I'll give you this little bit of speculation, someone somewhere told me along the way that the water jet cut parts as supplied by some European kit manufactures don't exhibit these cracks and don't need match drilling/deburring. I don't know what process Van's is using on the 12, but then again the info I just gave you is hearsay, get it from the Man himself ;-)

Thanks
Rudi

Again, speculation, but it may be because the holes aren't dimpled. During dimpling, the hole is stretched slightly larger in diameter and deformed in general. This does create stresses that initiate the cracks where the micro scratches are. Without the dimpling, there are less stresses to begin with. That MAY be the reasoning, but a quick call to van's would clear that up.

Pre-dimpling

On the RV-12 kit that is being built at our Chapter, it looks like a some of the skins are pre-dimpled...

no dimple!

Micro-cracks typically occur when you dimple (not punch) an undersized (3/32) hole without first drilling it out to the final (#40) size of the dimple. In the other RV kits, the holes were undersized to allow a better "fit" when drilled out to the final size. Since the RV-12 does NOT use flush rivets and will not need to be dimpled, I surmised this is why NO match drilling is required.