Lessons From Life's Workbench - The Blind Rivet

Over the last few weeks, I've mentioned how solid rivets are sized by part number and selected for diameter and length.

Solid rivets joining two pieces of
aluminum together. 

Solid rivets are amazing little pieces of metal.  They've been used in aircraft for decades, and if you've flown on an airplane, the odds are you've been depending on these little pieces of metal to ensure your safe flight.

And while these pieces are amazing in both their simplicity and effectiveness, like anything, they are not without their drawbacks.

They're inexpensive, but they require a certain amount of skill to properly set.  Proper riveting takes practice, and I found if I don't do it for a while, I have to shoot a few practice rivets to get "back into the groove." 

The other problem is access to both sides of the part are required.  The rivet has to be "shot" with a tool from one side of the part, and "bucked" or set, from the other.

If you're curious about seeing how solid rivets are set, the Experimental Aircraft Association has a great video explaining that here!

Moreso, it's likely that one person won't be able to reach both sides of the parts to be joined.  That means that two people are needed to set the rivet, a "bucker" and a "shooter".

Two workers setting solid rivets.

If you take a couple of moments to think about that, what you have is a rivet that maybe inexpensive, the workers required to place will be where the expenses will be found.

The blind rivet, also known as a "pop" rivet or "Cherry-Max" rivet solves both of these issues.  'For trivia's sake, the name "Cherry-Max" is derived from Cherry Aerospace, a prominent maker of  blind fasteners.

These rivets have a metal stem (mandrel) that is drawn through the rivet by a special tool.  The metal stem expands the rivet as it's pulled expanding the rivet and setting it in place.  The stem breaks off inside the rivet, adding to the rivets strength.

A blind rivet diagram.  Image from FAA Advisory Circular
AC43.13-1Bhttps://www.faa.gov/documentLibrary/media/Advisory_Circular/AC43.13-1b.pdf

The advantage of these rivets is they don't require the skill that a solid rivet requires. They also don't require that the part be accessible from both sides.   The drawback of these rivets is they are much more expensive than their solid counterparts.

A blind rivet tool, with unset blind rivets under the
"Design Differently" sticker on my laptop.

So like in so many cases in design and manufacturing, a benefit isn't seen without making a concession somewhere else.  So when all is said and done, you can still find both types of rivets in widespread use.

If you're curious about how to set blind rivets, here's a link to a great video here.

For more information on selecting blind rivets, check out the process guide  provided by Cherry Aerospace at the link here.

I  leave it to them to provide the info for you!   Mostly because I have to review it myself to refresh in my own memory!

But there you have a few of the "wheres and whys" of rivets.  I hope the info I've compiled here helps you out!

Photo Acknowledgements:

photo credit: The Library of Congress Riveting team working on the cockpit shell of a B-25 [i.e. C-47] bomber at the plant of North American Aviation, Inc., Inglewood [i.e. Douglas Aircraft Company, Long Beach], Calif.   (LOC) via photopin (license)

A Quick Tip on Creating a New Drawing in Fusion 360

The Thanksgiving Holiday here in the United States and some studying for a class have been keeping me busy, but I've been starting to get a little seat time creating drawings in Fusion 360 for a wooden rack I've been working on.  

The Fabric Rack in it's current state.
There's still some adjusting to be done! 

The tip I'll share is a simple one, but one that not everyone may realize is there.  

I know I haven't been using this tool nearly as much as I should have! 

If you right click on a component in the model tree, you can create a drawing for that component by choosing Create Drawing. 

Creating a drawing from the model.

Choosing that option, a dialog box appears that gives the following options. 

1. Create a drawing of the full assembly found in the model, or just selected components in the model. 

The first step to creating a drawing

2. Create a new drawing from the selected component(s), or add a component to an existing drawing. 

3. Choose a template drawing or start from scratch. 

4. Choose to use the ASME or ISO drawing standard.

5. Choose the default units for the drawing.

6. And finally, choose the sheet size for the drawing.  

Once you hit OK, the drawing will generate and you'll the opportunity to place the views on the darwing.  These options include

1. View Orientation

2. View Style, such as Visible Edges, Visible and Hidden Edges, Shaded, or Shaded with Hidden Edges.

3. Scale so you can size the view to the page.

4. Tangent Style, which include Full Length, Foreshortened, and Off. 

5. Toggle Interference Edges on or off. 

6. Toggle thread display on or off.

I found it can be a slick way of creating a view, some of which I'm still testing out!  But I think it's well worth taking a deeper look!  

I'll keep you posted! 

Lessons from Life's Workbench - Penetrant Inspection

Happy Thanksgiving to those in the United States.  Enjoy the holiday!  Here's a quick post on penetrant inspection for your consideration! 

In my aircraft maintenance classes, I've been able to try my hand at dye penetrant inspection.  

An example of cracks in a part.  This is actually from
magnetic particle inspection test.  But the tests are similar,
and it's the best picture I have! 

There are a few variations of the process, but the one I performed soaked the part in an light oil containing a phosphorescent dye.  

The dye soaks into cracks and voids in the material.  After soaking, the part is rinsed to remove penetrant on the surface of the part, and finally, it's sprayed with a powder like developer to draw some of the remaining penetrant out of the flaws so they can be seen with a UV light.  

After inspection, the part is thoroughly cleaned and returned to service, assuming it passed inspection of course.  

It's a quick, fairly easy to perform test, and can be a great to find surface flaws on a part.  

It's also messy, at least where I learned how to do it!  But a little mess never hurt anyone. 

But my experience, isn't vast by any means.  It's something I've tried enough to gain some familiarity with.  

For a little more information, check out these resources.  

Basic Principles of Liquid Penetrant Inspection

Exposing 10 Common Misunderstandings About Penetrant Testing

Lessons From Life's Workbench - Intergranular Corrosion

One of the most insidious types of corrosion I learned about in my classes is intergranular corrosion.  Aluminum alloys containing copper, such as 2024 aluminum, particularly if it's been improperly heat treated.  

The copper in the alloy comes out of the solution, and creates tiny galvanic cells that begin corroding the metal. 

The sneaky part of this type of corrosion is that it can happen deep inside the material, and may not become visible until the corrosion breaks the surface of the material in a process called exfoliation. 

 

Here are some pictures of aluminum that has some serious exfoliation.
The metal has completely disintegrated.

Another angle of the same extrusion.
You can see how the material has flaked away.

It goes without saying that intergranular corrosion is bad.  But if it can start in the interior of a material, where it can't be seen,, how can it be found?

That's where nondestructive tests (NDT) such as ultrasonic inspection or eddy current inspection can be employed to locate and eliminate this type of corrosion before it affects the strength of the structure. 

That's it for this weeks tip!  Have a great week! 

 

Using Your Resources to Design in Fusion 360

I've had a mental idea to build a simple rack to hold bolts of fabric in Fusion 360. 

It would look similar to this mobile pipe rack found on the McMaster Carr Website

But naturally, the store bought version doesn't quite meet my needs.  Murphy's Law wouldn't allow that!  So that leaves me in the position of designing and building one. 

Here's one side of the rack, mostly done,

And seeing how I don't want to work on it evening upon evening, that means I have to take advantage of every step I can to increase the efficiency my design time.

Now I should mention that many of these steps I've shared before, so this will be a link back to these posts.  But I think it's a good example of how these processes can come together and become greater than the sum of their parts. 

Here are the tips!

1) Don't Create a Model if You Don't Have to!

The rack needs to be mobile, so it needs to rest on casters.  Fortunately, Fusion 360 has a link to the McMaster Carr website that lets you insert models from their website into your design.  The part number is included, so you can always order the part from McMaster Car if you like.

Downloading these casters was more accurate and less time
consuming than trying to build my own versions

Here's the link to a previous post if you want to read more!

2) If you have to build it, reuse it! 

Every wooden piece pictured here was built and resized from
one source model.

The frame is going to be made primarily of 2x4s.  And while this isn't a complicated part, why keep drawing rectangles over and over again if you can just Copy and Paste New?  This tool allows you to copy a part, paste a new, independent version, then resize and reposition it where needed.

You can find a link to more details there. 

3) Don't rebuild what you don't have to! Redux!

I couldn't find the joist hangar on the McMaster Carr website.  It might be their, but I couldn't find it.  So instead I tried GrabCAD and found it here.

The joist hanger inserted into the model.

The download wasn't quite as slick as the one on the McMaster Carr website, but it was still a lot quicker than building the model myself. 

In Conclusion!

The design still has a long way to go.  It's not even complete, and I can already see a few changes I'll probably want to make.  But being able to reuse and download parts got me a lot further down the road in a couple of hours than I otherwise would have been.

So I hope these ideas inspire you to try a few things, and get a little further down the road yourself!

A Life Lesson - My Inspiration from a Little Black Cat

Foreword

This post is far off my usual topics.  It's a reflection on a little inspiration coming from the strangest places.

But who doesn't need that once in a while!

*******

This week has been one of those weeks.  You've probably had them, where nothing seems to go right.

In work and play, I've had projects go sideways, problems big and small plague me.  Like zombies from the grave, rookie mistakes I made months, or even years ago came back to bite me.

It was one of those weeks that leaves you asking yourself "Why am I doing this?"  (Looks at bank statement).  "Oh yeah, that's why.'

But even in this week of frustration, a ray of inspiration came to me.  And strangely enough, that inspiration came in a form I would have never expected.

A couple of nights ago I saw two of my cats, who are brothers and littermates, get into a little playful "rough and tumble". It's not uncommon, they like to roughhouse with each other.

The contenders were...

"Runtley" earned his name because he's the runt of the litter, he was born a little guy, and now, fully grown, he's small and slight of build.

This is "Runtley the Runtling"

His brother, "Scar", earned his name because he was missing a chunk of fur under his eye when we adopted him, a product of an unknown kitten misadventure. The wound has since healed, but the name remains. Scar is bigger, bolder, and stronger that his smaller brother.

This is Scar.  He's the bigger and bolder one.

The two cats wrestled on our hardwood floors, rolling about and pawing at each other as they played.

Naturally, I expected the bigger, tougher Scar to come out on top.  He had every reason to.  He has a size advantage, he had a weight advantage, he's even the more confident of the two cats.

Scar as a kitten. Bearing the mark that named him

But to my surprise, the Runt twisted and rolled, wrapped his front legs around his bigger brother, and with a heave from his back legs, rolled Scar and threw him to the floor.

The Runt's "baby picture". You can see how tiny he was.

My mind's voice shouted in it's best UFC tone: THERE'S THE TAKEDOWN! 

Scar got up and ran off, the fight knocked out of him for now, the round going to the undercat.

The victorious Runtling gave chase, as if to say "How 'bout another round!"

I instantly thought of the Mark Twain quote, "It's not the size of the dog in the fight, it's the size of the fight in the dog."

Perhaps in this case, it was a cat instead of a dog.

But in a few minutes, a runt of a black cat taught me that we all have disadvantages.  We've made mistakes, and we've all suffered setbacks.  Some of us were given a disadvantage from the very start. 

It's easy to give up and make excuses, but if you stick with it, you might just beat the odds.

Sometimes you have to be the scrappy little runt in the room, who isn't the biggest, strongest, or most confident.

Sometimes you just have to be too stubborn to quit.

Scar (left) and the Runtling.  In spite of their wrestling matches, they get along!

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: