This blog is for entertainment purposes only, and is not meant to teach you how to build anything. The author is not responsible for any accident, injury, or loss that occurs as a result of reading this blog. Read this blog at your own risk.

Saturday, July 18, 2015

“Tooling up” - sheet metal

Aluminum sheet metal tools

Everyone knows that difficult jobs are made easier by using the appropriate tools, but in the case of sheet metal work this is true ten times over. I would go out on a limb and say that you shouldn’t tackle sheet metal work at all without proper tools, which are expensive by the way, since the risks of hurting oneself, damaging the delicate aluminum, incorrectly shaping parts, or improperly fastening them is very high.

Sadly, the higher cost of equipping a sheet metal workshop was one of the reasons I originally steered away from metal airplanes. With two kids in college, and a B scale airline salary, there was just no room to spare at the time. Ten years later though, with the kids gone and two new Union negotiated contracts under my belt, life has gotten a little easier.

So, why are we even talking about sheet metal anyway?

Well, no airplane is purely sheet metal, composite, or else, rather they all have parts made out of "competing processes". So, many metal planes incorporate fiberglass parts like engine cowls and canopy skirts, on the other hand even the Long EZ has a few things that need to be riveted.

I am coming up with a section of the build where I will have to use rivets, so the time was right to spend some money in new tools, and sharpen my limited riveting skills.

Here’s what I bought…

Various sizes of flush and dome-head solid rivets, Cleco fasteners and clamps.

You might have noticed a couple of things missing from the photos, like rivet gun and bucking bars. For the time being, I decided to go for the hand squeezer rather than a rivet gun, since all my rivets will be located near an edge.

Five years ago I attended a sheet metal construction EAA workshop, but never got to finish the wing section project because we ran out of time. I did however take home the leftover aluminum bits and pieces, so I decided to complete the work in order to freshen up the skills I’ll need to use very soon.

My unfinished EAA workshop project

To make it easier to decide what rivet length to use, I created a small Excel spreadsheet that will calculated automatically exactly what rivet to use in most situation one might encounter, and conform to AC 43.13-1B standards. 

Source AC 43.13-1B chapter 4

The range of calculations for length goes from a 1/16” (dash 1 if it existed) to a 5/16” (dash 10) (second dash in the rivet name). All one has to do is enter the thicknesses of the metal sheets (up to 3) one is trying to join. 

The results are expressed in half sizes, and where those are not available, the next size up would be chosen. In this manner for example one would use a AN426AD-4-5 if he didn't have a AN426AD-4-4.5

The appropriate rivet diameter from 3/32” (dash 3) to 3/16” (dash 6) (first dash in the rivet name) must be chosen based on the application. All 4 diameters are calculated.

Source AC 43.13-1B chapter 4

You are welcome to download it and use it at your own risk... rivet chooser.

If you were interested to learn more about riveting, let me direct you to AC 43.13-1B chapter 4, a fantastic source of aeronautical information, riveting knowledge starts on page 4-31.

In the end, I found out that I still suck at sheet metal work, and that my 2.5 days of total practice time is not enough to avoid making mistakes, but it is just enough to allow me to complete my limited tasks satisfactorily, and that is all I really need right now.

Using the rivet fan to uniformly space out the holes for the rivets

Rivet holes drilled (note the Cleco clamps and fasteners holding the project together)

Getting ready to rivet the structure

Riveting complete

Hinge functional

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