Wednesday, February 12, 2014

Mechanical Fasteners: (Blind) Rivets

I have recently become aware of a strong, efficient, and economical way to fasten metals together: the blind rivet. I have always heard about how rivets were used in aircraft production, and for some reason I never seriously considered using them in my own mechanical projects. I wrongly assumed the cost and complexity was too high for someone with a hobbyist's budget. It turns out blind rivets are very practical and economical even for me.

As I am working with aircraft-grade aluminum (7075 T6), I cannot weld pieces together. Aluminum is notorious for being difficult to weld well, and this applies even more so for the stronger aircraft-grade aluminum alloys. Welding these alloys are usually deemed ineffective, especially when the resulting material strength is important. With welding out the window, I racked my brain for alternatives to heavy screw and nut arrangements, and came across the blind rivet.

As you noticed, there is a specific type of rivet I am referring to: the 'blind' rivet. A regular rivet is a solid pin-looking thing where you have to hammer down and flatten one end. A blind rivet is a rather complicated-looking thing if you have never seen one before, but it can quickly and easily be implemented with a tool that you can buy for less than $20 at your local hardware store. Also, with blind rivets you do not require access to both sides of the joint, only one side is required, hence the name 'blind' rivet. You can Google up many great explanations and visual demonstrations of how blind rivets work.

Blind rivets are economical. On McMasterCarr, I can buy 1/8" diameter aluminum blind rivets at 250 for less than $10. It was actually more economical than the alternative for me, which were socket cap screws of similar size.

I would argue that the space and weight efficiency, for a given bore size, of the rivet is greater than that of screws. Strength of screws are diminished because of the required space for the threads. The screw nuts can be heavy when many screws are needed.

The downside of a rivet compared to a screw is more complicated dis-assembly. You have to destroy the rivet if you want to unfasten something, but it is not too difficult to remove a rivet.

Blind rivets today are the product of many years of improvements from field use. They are extremely effective if welding is not an option and you need a strong, lightweight bond between metal plates.

2 comments:

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