Lessons from Life's Workbench - Selecting a Solid Rivet

In my last Wednesday, I talked briefly about how rivets are sized.  But what about how to choose a rivet for a given application?

There are requirements for how to select a solid rivet, and while they may vary slightly from application from application, the FAA publication AC43-13-1B is a good guideline for selecting a solid rivet.

The pages referenced are 4-20 and 4-21, and can be downloaded at this link.

So what do those instructions tell us?

For my example, I'm going say I'm riveting one sheet of .032 thick material to .040 thick material, using a MS20470 "universal", or button head rivet.   

The Sheet Metal Thicknesses shown
in red and cyan.  The rivet is in gold

The first step to choosing a rivet is to select a rivet diameter.  By referencing the document, you can see that it states that we should use a rivet with a diameter 3 times the thickness of the thickest sheet.  

So if the material is .040 thick, then 3 times that thickness is .120, which is close enough to a 1/8th (.125) inch rivet.  

So there we go!  The diameter is selected!  But now, how long of a rivet do we need?

The dimensions of the rivet needed for this application.

AC43.13-1B states that we should use a rivet that extends 1.5 times its diameter beyond the underside of the material.  

Adding .032 and .040 we end up with a total material thickness of 0.072.  Extending 1.5 rivet diameters beyond that we get a total length of .2595 inches,

which is close enough to 1/4 (.250) inches.

So this application calls for using a MS20470-4-4 for this particular application.

Now the rivet can be driven with a rivet gun and bucking bar, and the parts can be fastened! 

A typical rivet gun and bucking bar set.

I hope you find this tip helpful!  

A sample of the approximate dimensions of the set head.

One final note, the documentation I've used is an "Advisory Circular".  If you have engineering documentation, such as a manufacturer drawing or a maintenance manual, do what it says!  The manufacturer's data always wins in this case!

Lessons from Life's Workbench - Finding Rivet Diameter and Length from the Part Number

A few counter sunk rivets corralled
on my laptop

One thing I've learned about aircraft fasteners is that their part numbering system is like speaking another language.  But if you can understand the language, it all begins to make sense.   

Although I admit, it might take a little while!  But if you work with it, the patterns begin to emerge.  

For my sample, I'm going to use solid aircraft rivets.  It's the first fastener I learned the part numbering system for, and it gave me a basis to become familiar with other fasteners as I encountered them.  

So let's say we're given the part number MS20426-AD4-5.  You're first reaction might be: That means absolutely nothing!!

But in reality, it does mean something, once you learn to speak the language.  

Here's how to begin to break down the seemingly cryptic system.

I'll start by separating the part into it's key components. Each group of the number means something, although some mean more than others.

MS20 * 426 * AD * 4 * 5

MS20 - This part of the number tells us it's part of the Military (MS) standard

426 - This designates the head style for the rivet.  In this case, 426 tell us this is a countersunk rivet. The other common rivet style is designated by the number 470, for a universal (domed) head. 

AD - This designates the material of the rivet.  AD is 2117 aluminum.  Other examples of material and designations are: 

          A - 1100 or 3003 Aluminum

          DD - 2024 aluminum

4 -    This designates the diameter of the rivet in 32nds of an inch.  In other words, this example has a diameter of 4/32nds of an inch.  In other words, 1/8th (.125) inches.

5 -     This final number represents the length of the rivet in 16ths.  For our example this rivet is 5/16ths (.3125) inches long

A sample of  universal (MS20470) rivets
on the left, and countersunk (MS20426)
rivets on the right. 

So that's a quick example of a rivet part number.  Granted, not all of the numbers are intuitive.  Why 426 and 470 to designate head styles?  I have no idea.

And while there will be differences from fastener to fastener, the diameter and length can be derived from the part number.

So bear it in mind!  I hope that helps you out when you're thumbing through another catalog! 

Acknowledgments and Additional Resources

Aircraft Spruce - I've gotten a few tools and supplies here.  I've linked to their page on rivets not because you can buy them here, but because their page breaks down the part numbers clearly. 

Aviation Maintenance Technician Handbook - Right off the FAA website.  Check Chapter 4, Page 4-31 for more information on the rivets I touched on here. 

World Fasteners - Another site I like because they have a visual guide of different fasteners and their root part number.  You can see their visual catalog here:

Placing an Assembly into a New Design in Fusion 360

Last week I talked about how I used the Paste New functionality in Fusion 360 to quickly create a continuous hinge. 

A close up of the continuous hinge as it was finished in my previous post. 

My goal in creating this hinge, was to use it as a template so I can reuse it later.  However the thing with continuous hinges is that they're cut to size.  So even though the original hinge stock starts out 36 inches long, it can, it is often cut down to a much shorter length.

So what I'd like to do is insert the hinge into an assembly and cut the hinge to the length needed for that particular application.

The finished hinge placed into position.

I started out with my target assembly opened and saved.  For the sake of keeping the example simple, I'm going to use an empty file for the target assembly, but the steps are the same if there are other components already placed.

Now, I locate the hinge I intend to use in my data pane, right click on it, and choose "Insert into Current Design".

That will insert the file into the current design. 

The next thing I have to do is cut the assembly to size.  This required me to break the link with the template, so I can make the part independent from its parent. 

I can do this by right clicking on the part in the browser and choosing "Break Link". 

Breaking the link to the original hinge.

Now it comes time to cut the part down to size.  Naturally, this may vary for different parts.  In the case of the hinge, I used an offset work plane to split the solid bodies that make up each hinge leaf.

Splitting the hinge leaves using the split tool and a workplane.  The workplane is
off screen (it's why the background is blue). 

Now each hinge leaf is split into two bodies, which can be removed from the model using the "Remove" tool.  You'll have to locate the bodies underneath each component.  I've numbered them in the image below.

Hint!  Don't use the delete tool!  It can cause your features to blow up!

But now, with the hinge sized, it can be positioned as needed in its new home!

The hinge is completed!

In conclusion!

Personally, I like how this workflow allowed me to take an assembly, place it, and modify it quickly.  I can cut the hinge down, add holes, all without harming the original. 

I'm particularly pleased with how I can contain the hinge in a single design, and not create three separate files (two parts and an assembly).

I do feel a few pangs of guilt about breaking the link to the parent, since if the parent changes, the hinge derived into this assembly won't be updated.  But for the most part, standard parts such as this don't change often, so I think I can live with that possibility. 

All in all, I think there is much more to be gained with this flexibility!

Galvanic Corrosion - Lesson's from Life's Workbench

In the last few months, I've been spending a lot of time reading for my aircraft maintenance class.  I've been through my General text, and I'm halfway through my Electricity book.

These two books are well worn from reading. 

Naturally, that takes away from my time working on things like Inventor and Fusion 360.  So I thought to myself, why not share a few of the lessons from my studies?  It'll help me study, and maybe help out someone else who's trying to learn themselves.

Consider it paying forward!  So every Wednesday, I intend to post a tip on a little something I've learned about design in my studies.

Without further delay, here's a lesson that had faded into the archives of my mind, only to be relearned.

A Life Lesson on Galvanic Corrosion

When two different metals are attached to each other, there can be an electrical potential between the two metals.  One metal will act as an anode, the other will act as a cathode.  If an electrolyte, such as water is added, a chemical reaction known as galvanic (or dissimilar metal) corrosion will occur.

When that happens the anodic material will be eaten away by the cathodic material.  For my tests, I remembered it as the "cat" the one that does the eating.

Galvanic Corrosion between Copper (Cathode) and Iron (Anode)
By Ricardo Maçãs - Own work, CC BY-SA 3.0,
https://commons.wikimedia.org/w/index.php?curid=17645877

Galvanic corrosion can be mitigated by isolating the two materials from each other.  Another solution is to use materials that have similar galvanic potential.  Several charts can be found in textbooks and on the web.  Here's a basic one from Wikipedia.

Just remember to keep the two materials as close as possible!

Yet one more is to attach a third, more anodic material to the assembly.  This sacrificial material will corrode away first, saving the other two.   You can see some good pictures of sacrificial anodes on a ship hull here.

No matter which method is chosen, designing for corrosion is something that can make a difference between a product having a long life, or a painfully short one.

I hope this first little tip is one that helps you out! I'm hoping to post some more soon!

Using Fusion 360's "Paste New" to create Similar Parts

Before diving into my next post, I wanted to say that I'm glad the solution I shared to fix the broken threads issue in Autodesk Inventor helped so many.  When it first occurred earlier this week, I thought it was just me.  Little did I know that so many others would run into it!

I originally found the issue on the Autodesk Community, so credit where credit is due.  The link to the post where I found the information is in the original post, as well as linked here.

Now, I'm back to a little Fusion 360 work I've been doing.

As part of an ongoing project, I've been slowly building different parts here and there, mostly off of vintage prints from AirCorps Library. 

One of the challenges I ran into was building a model of a continuous, or piano hinge.  It's based on the AN951 standard, which has since been superseded by the MS20257 standard,

One hinge leaf.  A little examination shows how it's mate has to
vary to mesh correctly.

Modeling the hinge isn't a difficult task, building the individual hinge leaves is easy, but they need to be made to mesh correctly.   That means the hinge knuckles have to be offset, and that's where the knuckles have to be different.


But other than that, everything is the same only the hinge knuckles vary.  So it would be ideal to be able to create a new copy of the existing hinge leaf, and make the appropriate changes. 

It turns out that Fusion 360 has a functionality known as "Paste New", and it's exactly what I needed.  It will create a new, independent copy of first hinge leaf, while leaving the original alone.  That means being able to reuse as much of the design as possible, while only changing what has to be changed.

I started with an assembly with one of the leaves modeled as its own component.  You can see that in the browser..  Now it's time to make the other side of the hinge so it can be changed so it can mesh with its mating hinge leaf.

The browser with the new part modeled

 All that needs to be done is to right click on the existing component and choose "Copy".  It's just a good old Windows Copy.

Copying the part is where it all starts. 

Now move the cursor onto the modeling canvas, right click, and choose "Paste New".  A new, independent, hinge leaf can be placed and positioned. 

Pasting the new copy using the Paste New command

I'd suggest getting the part as positioned in it's "nearly" correct position.  Then you'll be able to make changes to key features, the hinge knuckles in this case.

Positioning the part. You can use the handles, or dialog box.

Now all that's left to do is activate the new copy, modify it so it meshes with the original, and assemble.  And we're off to the races!

There it is!  All done! 

So keep this in mind when you have similar components to build, and modify it for your needs.  It can really help in not recreating extra work!