November 15, 2019

Flush Rivet Process

Among other things, this past weekend I came up with a tool to dimple the holes where I intend to install flush rivets. I received my supply of AK41H countersunk rivets from SW Anderson Co, and performed some tests on a scrap piece to ensure I would be happy with the results; the pictures are below. Happy with the results, I turned to the aircraft to start looking at which holes need to be dimpled, and I quickly realized I didn’t have a way to dimple the channels that fit behind the side skin – due to the U-shape of the channel, the dimple die I bought from Aircraft Spruce that uses a nail and a pull riveter doesn’t work, because the channel blocks access for a nail. I don’t have a squeezer and dimple die, nor did I want to invest in a squeezer at this point. I’m also not sure it will work, the standard dimple dies are fairly big, so it may not fit either. So, I came up with my own solution: a modified Pop dimple die temporarily attached to a set of locking pliers. Admittedly, this is not completely my own idea; such devices exist, but not one that will fit into a tight space, nor one the proper die for a 120 deg dimple.

This is one of the channels that will be difficult to dimple using standard tools – the U-shape of the channel prevents direct access to the back side of the hole
Starting point – a 120 degree dimple die purchased from Aircraft Spruce that uses a common nail (bottom). Instead of the common nail, I’m going to use a 1 inch roofing nail (top), modified to turn it into a pilot – see next few pictures
After cutting the nail to right length and some filing to get it to fit through the hole in the dimple die
View of the roofing nail through the dimple die from the other side. I also rounded off the end of the nail using a deburring wheel
Some standard locking pliers – I used this because you can squeeze with pretty decent pressure, enough to make a nice crisp dimple in the skin
Dimple die hot-glued onto the end of the pliers
What the die looks like with the pliers jaw open
The rivets I’ll be using: AK41H POP Rivets. 1000 rivets doesn’t look like very much in a bag like this!
View of the finished rivet – it’s nice and flush!
Side view of the finished rivet. Notice that this is a closed-end rivet, which is the only option I could find in a -1 grip length for 1/8″ size holes.

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