Flush riveting experiments

Before getting to building my empennage, I still need to determine whether I will be able/willing to attempt a flush riveted Sling 4.

I tried a number of things, and took lots of pictures, but I'll try to summarize the process and keep it short. Don't hesitate to contact me if you want details.

General process:

  • Take some spare sheet metal 6061-T6, 0.016 thickness (That's the skin material).
  • Make two parts that I will rivet together.
  • Drill 1/8th holes (3.3mm), one in each part.
  • Dimple each part with a standard 1/8th dimple die.
  • Rivet the two parts together with a CherryMAX oversize flush head pulll rivet CR3242-4-2.
  • Observe closely.
  • Cut down the middle, and observe closely again.
  • See if I think such a joint will hold up.
Here is what one will see when analyzing the hole and dimpling process:

Pretty! Right?

Note that there are 2 edges. As later testing revealed, this is chamfer from the deburring tool. This is magnified 200x.

The diameter of the post-dimpling hole is .148 to .150. Maximum allowable is .146, with .143 being ideal.

You can clearly the gap between the rivet and the hole. I knew this would happen, so let's see how much of a problem this will end up being.

The first sample I assembled, I kept for eventual shear testing.

The second sample gave something like this:

There is a slight malformation of the bulb. This is OK as per CherryMAX documentation.

Note how the shop end (the "bulb") doesn't seem to quite cover the full dimple edges. As it turns out, my riveting technique wasn't quite right, and the rivet wasn't being pulled in as straight and forcefully as ideal. Alright, so let's keep going anyways.

I try to cut through it and the rivet goes flying! It clearly did not have a very good grip at all:

Note the two sheets, the gap with the rivet, the unevenness (See my first post on riveting to understand why this is bad). This is admittedly after me putting in the rivet my hand back in its spot, since it flew away, but is still a good illustration of the challenge.
Demoralizing! But like I said, I had riveting challenges, and I have some more spare parts, so let's keep trying.

So I went back to my first sample, and did the same thing:

Note the left side, you can see the same thing as with the pictures earlier. Did not do a very good cutting job on this one ... but enough to see some useful things.

Closer, but a little blurry. You can see gaps, and uneven grip.

Finally with my last sample, things looked better:

Note how the chamfer still appears, and it's uneven.

All around, I was pretty satisfied with this! At least looking at it as-is, without inspecting internally.

Next post, my thoughts and conclusions on all this!