Barstool Philosophy - My Lessons From a Dog-Eared Notebook.

 A few years ago, I developed what some might consider an odd habit as I started to learn aircraft mechanics. 

Every weekend, I'd sit at the local watering hole, enjoy an "adult beverage" (responsibly of course), and do something not many people see in a pub.

I'd pull out a composition notebook, and write down a few things I learned. 

You read that right, a notebook, writing with a pen and paper. 

Sometimes it took me five minutes. Sometimes it took me thirty minutes, but I always tried to get those notes record that lesson learned..  

It might be something I learned not to do, or some pearl of wisdom from a silver haired mechanic who had been working on airplanes since Kennedy was President of the United States. 

I don't recall what prompted me to do it. But I found the act of putting my thoughts on that paper with ink helped me slow down and rethink the lesson. It gave me the ability to relive the lesson, and hopefully commit it to a deeper memory. 

Eventually, after a few years of collecting notes, I've got a very well used, and nearly full notebook full of lessons. 

Looking at that somewhat beat up notebook, I realized it's a collection of knowledge and experience, something I can look back, and reflect on. 

At some point I plan on transferring those lessons electronically, I may even do that on on this blog. While this lessons aren't CAD related, they at the very least may teach transferable lessons to the CAD world. 

For now, I'll leave you all with this thought. consider coming up with your own version of the dog-eared notebook. We all learn something every day. 

Maybe we just need to take a few minutes to slow down, and remember the lessons. 

They can pay off one day, either for yourself, or perhaps for the next person that comes along. 

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

Barstool Philosophy - When Did I Become the Expert!

Every once in a while, I responsibly enjoy an "adult beverage" and ponder life. 

I call it "barstool philosophy".  

The beverage over which much
wistom is shared

Recently,  I celebrated my 51st time riding a giant rock around a "gianter" ball of fire floating in the vast expanse of space. 

Only a few days after that, I found myself helping seal the fabric envelope on a 1940s vintage  Taylorcraft. 

The Taylorcraft with fabric
over its steel tube frame

But this time "helping" meant handing the brush to someone half my age and saying, "you're up, kid".  

Somehow, when someone said, "he's the expert", and we looked around for that guy, I realized the eyes were looking at me. 

It didn't seem right. There's so much I don't know, so much I haven't done yet. 

I learned, or rather re-learned, teaching is a different mindset.

It's watching, guiding, stepping in, but not too much. It's saying, "if you do that, this bad thing will happen. Ask me how I know."

But we reached the finish-line in that milestone. The end product was pretty good 

The kids looked at me and said , "I hope we did good. "

Little do they know, the thought going through my mind was...

"I hope I did good."

So what lessons did I learn from this anecdote? \ "old guy with experience". I'm not sure when that happened. 

But happened it did. And I realized I had something to offer. While I don't know it all, the years had taught me more than I realized. Things that had become second nature by me were new, valuable lessons to those just starting out. 

Somewhere, without my realizing it happened, I became a mentor. 

I learned patience. I learned to look at a student and say, "You made this mistake. This is what you did wrong." And with a wry smile I'd say, with accurate self-deprecation, "Ask me how I know. I did it too.' 

And finally..

This post is pretty far removed from the Computer Aided Design Posts I've done in the past. My life and career has evolved. I'm not as deep in 3D modeling tools as I once was. The versions I use are old, and I don't use them at the level I did a few years go. 

But the lesson shares common ground.

For those of use who have a little more gray in our hair, and find ourselves squinting a little harder at our screens because "someone made the fonts smaller". 

Look to the fresh faced kids who were born after we graduated high school. 

You might have something to teach them. 

Drilling for Truth - Implied Drill Tolerance

First, I have to start with my big disclaimer.

While I've had experience with drawing standards, I don't consider myself a full blown expert. There is so much detail in standards, I can't say I'm an authority on all of them. 

Also, living in the United States, I work in the ANSI/ASME standards.  

My apologies to those who are living the ISO life (which is basically everyone who isn't the United States), I'm only acquainted with that standard. 

So this post will be based on "freedom units", that is feet, inches, and bald eagles. 

Joking aside, I hope this post is entertaining at least. Onward to the post. 

My current place of employment has a lot of legacy drawings. It's not uncommon to find a scanned drawing from the 1970s in our data management system.

It's like digital archeology! 

One of the things I find can be a big challenge, and very interesting, is interpreting dimensions, notes, and callouts that have fallen out of favor over the years.

Recently I was part of a discussion regarding a hole callout on one of these old drawings. 

The callout stated "Drill" and called out a specific drill size. In the case of the screen capture shown below, the drill size called out is a #30 drill, which is .1285 inches in diameter. But even the diameter is called out as a reference dimension. 


The really interesting thing about this callout is that it implies it's own tolerance, in accordance with AND10387.

The tolerances are based on the size of the drill, and a screen capture is shown here from Engineers Edge. You can even see that it has a link to AND10387




But now comes a plot twist. 
According to Everyspec, AND10387 was cancelled for new design and is only used for "replacement purposes". No new standard is shown to supersede this one. 

So what does that mean? 

I wasn't able to find a specific standard that states specifically how to handle drilled holes now. But my experience has taught me that, if required, a tolerance will be implicitly stated next to the dimension. If no tolerance is stated with the dimension, then the block tolerance will be used. 

A hole with the tolerance implicitly stated
Since AND10387 is only valid only for replacements, there's a good chance you may never see a drawing with an implied drill tolerance. But there's always a chance an old drawing will rise from the depths. So perhaps it's a good reference to keep in the archives!

And if anyone is aware of a standard that calls out standard drill tolerances, or if you just "do it another way", feel free to leave a comment.

Lessons from a Mentor, a Quarter Century Later

 Sometimes, a lesson learned from long ago comes to pass. 

Recently I was working on a project that required I transfer the location of four threaded holes to a piece of aluminum so clearance holes could be drilled. The question was, how to do it? 

Sure I could measure out the holes, but the threaded holes were t-nuts pressed into plywood, and the holes for the t-nuts were measured using a tape measure. So the hole placement was made to more of a carpentry accuracy than an aerospace tolerance. But I still wanted to keep the clearance holes as tight as practical.

A 3D model of the T-nut that was pressed into Plywood

But I remembered watching an old tool maker when I was a young engineer fresh out of college. And if you haven't guessed by the title of this post, that was about 25 years ago.... Ouch. 

He showed me a "threaded hole transfer punch". It's a small tool that stores threaded screws that look almost like set screws. However they have points in them instead of the hex that one would expect from a set screw. 

I had my solution! I placed an order with McMaster Carr for the punch I needed, and I had it in my hands the next day. 

They're screwed into the holes you need to transfer. You then position the workpiece that requires the holes, give it a quick strike with a hammer. And now you have marks where you need to drill. 

Then it's off to the drill press to drill the holes you need. 

The transfer punch tool and two of its inserts.
The inserts are stored inside the tool. 
The tool also doubles as a wrench for the inserts.

The transfer punch with two punches threaded into the T-nuts

The marks left in the aluminum from the punches.
I'm afraid I didn't get a chance to get a picture of the drilled holes.

Using the tool that old die maker showed me, in the way he showed me how to use it, I had the holes I needed in no time flat. The whole process took about fifteen minutes. And that includes walking to another building where the drill press was kept! 

That's a lot quicker than trying to match the holes by measuring it out.  

And, in a strange case of deja vu, a young intern looked over my shoulder and asked me, "How did you mark those holes?"

So it was my turn to pass along the lesson I learned 25 years ago from an old die maker about the "threaded hole transfer punch". 

Other than sharing a cool story, what's the lesson? 

I would say to look for those small mentoring moments that can sometimes come from the most unexpected places. It might be from someone on the shop floor, an analyst in the corner of that dark office, or a program manager who's "been there and done that". 

A lesson can be learned in a few minutes can take years to pay off. But when it  does, it can be a life saver! 

Wow, that lesson was twenty five years ago.... Thinking of that I'm suddenly overcome by the urge to yell at some kids to get off my lawn....

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

Why I chose to use Autodesk Fusion 360

Part of a Hydraulic Valve for 
a P-51 Mustang

Recently, I was asked why I used Autodesk Fusion 360 for my side project of modeling vintage aircraft parts. Why not use Autodesk Inventor? Or Dassault Solidworks?

Sitting down one evening, I decided to take a few moments to share my thoughts. These reasons are purely my own, as one guy cranking out models on evenings and weekends. I'm not an evangelist proclaiming my choice is better than yours. It's just that, my choice. 

Also, I do pay for a Fusion 360 subscription. I chose to take advantage of one of the promotions a few years back. I know this is likely still a hot button issue for some, but in my case, I'm glad I did. I thought it was

important that I mention that, in the interests of full disclosure.

 So, why did I chose Fusion 360? 

Accessibility

 A hydraulic housing in the
Fusion 360 mobile viewer

 The first reason I chose Fusion 360 it's easy for me to get. Yes. It's as simple as that.

Even if I chose not to subscribe, there's a free version that covers most of what I would choose to do. Sure, there's a cost associated with my subscription. But my cost for a yearly subscription is less than I'd spend on a weekend snowboarding. So for me, it's worth the expense to indulge my hobby.

Sure, there are probably ways I could get an educational copy of Inventor or Solidworks. Some are probably above board, others, more "gray market". 

At least in this case, I don't have to worry about stepping on anyone's

EULA (End User license Agreement). 

Capability

As far as bang for the buck. Fusion 360 does everything I need to do, plus more.

Most of what I do is currently limited to the parts, assemblies, and drawings. I haven't delved into the manufacturing or simulation space. But it's good to know I can do it should the time come!

I have used Fusion 360 to create *stl files for 3D printing and dxf files for a waterjet (see that post here), and overall, I've been happy with the results.

One thing I really like is the way Fusion 360 models threads. More than once I've been able to 3D print a usable thread out of Fusion 360.

A 3D print created with Fusion 360.
The fitting is threaded into 3D printed threads.

Ease of Administration

I've configured installations for Autodesk Inventor, Autodesk Vault, and to a lesser degree, Solidworks. All these tools are incredibly powerful. But with that, comes a great deal of setup and configuation. Where are the templates placed? How are you configuring your data management system? When you upgrade, what's your migration strategy? What are you using for a server?

For Fusion 360, the server is on the cloud, so there's no data to move when it's time to update hardware. 

When I purchased a new laptop, I installed Fusion 360 on my new computer, logged into my account, and had instant access to all my designs.

There was no need to migrate files or remap file locations. It was already there. In about an hour's time, I was up and running.

In Summary

In conclusion there isn't much, really. 

My big reasons why I chose Fusion 360. It works for me! Does that mean it would work for you on whatever projects you're working on? Maybe, maybe not! That's for you to decide. And whichever way you decided to go, happy 3D modeling!

Using Fusion 360 to Create Parts for a B-17 Restoration

A portion of the original print used to 
create the model.

 For many years, I've created models in Fusion 360. On occasion, I've 3D printed a few of my Fusion 360 models as "desk ornaments". 

But a few weeks ago, I had a fantastic opportunity to create a model that would be used to make a part for the restoration of a B-17 Flying Fortress. 

The part was a "friction washer" for use in the throttle quadrant. And the team needed geometry that could be cut on a water jet.

It started with a reproduction of the original Boeing print. Having the original dimensions made the modeling easy. It was interesting to note that even though standards have changed in the nearly 80 years since that print was created, it's not too different from the prints I work with today. 

The model of the friction washer, created in 
Fusion 360

Next, was to place the view on a drawing. The first goal was to dimension the drawing as a way of verifying all the dimensions were correct. Second, the drawing is what creates the 2D DXF file for the water jet. 

Once the drawing is created, delete any information that isn't required for the waterjet. This includes borders, title blocks, dimensions, centerlines and centermarks, etc. You might even consider creating a second page in the drawing for this purpose. 

Also, make sure to save the drawing before you export. I learned the hard way when I realized that the first file I exported still had all that extra geometry. Save the file before export!

The dxf geometry sent to the waterjet

Once I recovered from my snag. I sent the files off to my colleague for cutting. 

A few days later, we had our part and it fit perfectly, making for a very satisfying little journey. 

And while this little project was well worth a victory lap, there were three minor challenges that are worth mentioning. 

1) Drawing standards have changed over the decades, and while the drawing wasn't hard to interpret, some information wasn't where I'd expect it to be. Modern 3D modelers have spoiled us. We can "slap down" a new view in seconds. For the drafters of old? Adding the simplest view would take minutes. A more complicated one? Hours. 

The number of views was kept to a minimum. A part of single thickness, such as this one, will likely have the thickness dimension called out in a note. 

2) Not only have drawing standards changed, industry standards have changed. That material specification called out in 1943? It's been long superseded by a new standard. It's even possible that the standard that superseded the 1943 standard has, in turn, been superseded itself. 

Be prepared to spend a few minutes Googling the updated standards. Thank goodness for the internet! 

3) Finally, how does one interpret the tolerances called out on the drawing? Symmetric, +/-.005 for example, is easy. Model to the nominal. But what about a tolerance such as +.010/-.000? Do you "split the difference"? Do you aim for nominal? 

In my case, I decided to aim for the dimension as it was called out on the print. I figured that was the target dimension, after all. 

And in my case. It worked! Fusion 360 gave me an excellent dxf file that the waterjet used with no issuee, and the part fit perfectly into its intended position.  

It was a wonderful opportunity to contribute to a restoration. And a wonderful learning opportunity!

Acknowledgements

Print Reproduction via my Aircorps Library Subscription

Models and drawings created in Autodesk Fusion 360

My Tool Won't Fit! A Design Lesson From Life.

A typical aircraft brake disk.
There's not much room for a socket!

Hands on experience is often the greatest teacher. 

And, while helping work on a friend's change tires on a light aircraft. 

In looking at the brake disk, bolted to the tire rim, I saw that there was no way one could get a socket, the ideal tool for the job, onto the bolt. 

Fortunately, my friend, having run into this case many times before, had a wrench he'd cut to fit inside the disk. So in the end, it was job that was still very easily accomplished. 

But there lies a lesson for those of who sit behind a desk and design the machines we use every day. 

Just because the fastener fits, doesn't mean the tool will! So when designing, think of ease of maintenance. 

The maintainers, who are sometimes your customers, will thank you for it! 

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

So Solidworks Happened at Work Today - A Musing

I've spent just over 20 years working with 3D CAD programs. That experience has been nearly exclusively with the Autodesk manufacturing product line, starting with Mechanical Desktop (shortly after the earth cooled), and followed by Autodesk Inventor. 

We've all seen the ubiquitous, 3D model, floating in space.

A couple of years ago, my company decided to experiment with switching to Siemens NX.

That experiment, unfortunately, failed. Siemens NX, while a good program, wasn't the right program for the needs of my employer. 

A few months ago, my company announced that we would be going to Solidworks. 

Other than dabbling in it a few times, I've never touched Solidworks. This could be an enormous change for me. 

Or not, perhaps? 

CAD Tools - Is it just
a Virtual Toolbox?

I completed an abridged "transfer training", where we were shown where all the buttons were and how Solidworks ticks. After that, we were released upon the world. 

And what did I find? Were my eyes opened to a brand new world? Was Solidworks so much better that I wondered what I was missing? 

Did I wail and gnash my teeth because Inventor was far better and I was being forced to use this inferior product?

No. I left that training and thought, "Wow! They're really similar." 

Sure, Solidworks has an Extrude and and Extrude Cut button, while Inventor has the same options combined within one Extrude command. But they both add and remove material in the end. 

There's functions where I think Inventor has it down better, and others where I have to give it to Solidworks. 

In the end, I see it as an opportunity to learn a new skill, enrichen myself, and be more marketable in a competitive world. I think that's going to take me further in the long run. 

So I suppose the point of my writing this is to muse about how CAD programs are tools. They're not the endgame, there the means to create our designs, drawings, and help us build our products. 

And there's nothing wrong with learning a new set of tools. It can only make me a more marketable designer. 

One Final Note. 

If you're using Fusion 360, you can change your Pan, Zoom, Orbit shortcuts to reflect Inventor or Solidworks, among other programs? 

I've switched mine to Solidworks, it may not be the same as having Solidworks at home, but it does makes it easier when I switch from one to the other at work! 

The Pan, Zoom, and Orbit options in Fusion 360

 

The Chamfer Note. Does It Say What You Mean?

Many CAD tools contain a chamfer note that I would describe as a leader style. 

You've probably seen it, probably used it even. 

It utilizes a leader to point at the chamfer, and contains both the chamfer distance, and angle in one simple note.

The advantage of this style is it's compact, easy to read, and especially easy to place when the chamfer is packed into a crowd with other nearby dimensions. 

But this dimensioning style as a subtle disadvantage. This style of dimension doesn't identify the direction of the chamfer. So if the chamfer angle is something other than 45 degrees, the angle direction is open to interpretation. 

Even though the chamfers are different, the callout is is the same. 
It's also correct in both cases.

That literally means that a chamfer in either dimension meets the print. That can cause confusion, and possibly "heated debates" when a parts acceptance or rejection hangs in the balance. 

The other option is to call out the chamfer distance and angle as separate, distinct dimensions.  This identifies the direction of the chamfer much more clearly.  

Of course everything is a trade off, and this method does take a little more room on the page than the leader style. Even on the image above, you can see that the page is a bit more cluttered, and someitmes a detail view is required to ensure all dimensions can be clearly seen. 

In the end, I find I use both. The leader style is used for 45 degree chamfers, since there isn't really an angle direction to speak of. However, when the chamfer is an angle other than 45 degrees, it's time to employ the explicit style, and make sure the direction is clearly shown. 

Ultimately, it's up to you which chamfer style you use. Perhaps you have the advantage of tribal knowledge to correctly identify these features. Or you have other means to make sure the chamfer is cut the correct way. 

If anything, this is a good practice hailing from the time when "back to the drawing board" was a much more literal statement! 

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

A Musing on Modeling Safety Wire - How Much Detail is Necessary?

A question that was recently posed to me was; "How would you model safety wire in an assembly?" 

Safety wire on a fuel
divider on an 
aircraft engine

At first, I thought I'd write a post trying to summarize the standard, and how I've seen it approached in my travels over the years. But no matter how I tried to "summarize" the standard, it ended up too long, and so dry it put me to sleep.  So instead, I'm going to try writing this briefly, and hopefully to the point. 

First of all, Safety (aka lock-wire) is small diameter wire of various sizes that is used to prevent fasteners from loosening and ultimately falling out. It should always pull in a direction that tightens the fastener. It's usually twisted with 6-8 twists per inch. 

Of course there are more details, but they're covered by standards. In my aviation maintenance travels, that standard is AC43.13-1b, issued by the Federal Aviation Administration  (FAA). In my engineering travels, that standard is NASM33540.  I'm sure there are other standards.

That's important. The standards tell the installer how to secure the fasteners with safety wire.

So when it comes time to show safety wire on a model or drawing, is it normal to show the twisted wire?  Is it modeled exactly as shown in the

image to the right?

Heck no! That takes a lot of time and computer resources, which gets expensive fast. And having a standard to reference, there's little to be gained other than bragging rights for the designer. 

Instead, I've seen, and used, on of two alternatives. 

The first, is to use a sweep in the model, showing where the wire should go. This takes a little modeling time and dedication, but it will show up on the model, and propagate to the drawing when its created.

Safety wire shown in the model.
I've colored it in red here to make it stand out. 

The modeled sweep representing the safety wire on the drawing.
A leader references the standards in the notes.

The other, is to use sketch geometry when the drawing is created. It takes a bit of time to sketch in the drawing, but the results do a good job of showing the desired result.

Sketches on the drawing calling out the safety wire
Circles and lines represent the wire's twists.

Which ever method is used, a note can call out the standard to be complied with.  So the wire shown on on the drawing and model show where the wire should go, the note calls out the standard to reference.

If the installer has any doubts, the standard should be readily available for reference. I know in many cases, it's probably even legally required to be available. 

The next logical question for a reader may be, "How does this apply to me?" After all, while safe wire isn't uncommon, there are plenty of users who live long, fulfilling lives without ever touching safety wire.

If you get anything out of this post, ponder if there's anything that can be streamlined by adding more or less detail? How detailed does the model of that purchased part need to be? Are you spending extra time showing model details that are covered by a standards that can just be shown by a note with a leader? 

Perhaps take a few minutes to think it over. You might find you save hours! 

Acknowledgements

Models created by me in Autodesk Fusion 360

McMaster Carr models used:

• Round Head Screws (wire lockable) - P/N 90350A310 
• Flat Washer: P/N 92141A011
• 45 degree elbow (37 degree flare to NPT): P/N 50715K637
• 90 degree elbow (37 degree flare to NPT): P/N 50715K413

FAA Reference for Safetying: AC43.13-1b (See page 7-19)

NASM33540: This document is only available for purchase, so I've added a link to the old standard, MS33540.  It's very similar to NASM33540, as well as AC43-13-1b

Getting Jacked - A Simple and Clever Way to Separate Parts

One thing using 3D CAD programs has taught me, programs like these can make assembling parts together a piece of cake! With just a few clicks, parts can be quickly placed into position.

3D CAD systems have many ways of assembling components

But just because a constraints allow us to easily assemble and disassemble parts, doesn't mean that it will be so easy to do on the assembly line, or during maintenance. 

 

One example is a seal, such as a gasket or packing that locks the two mating parts together. For example, in the image below, the O-ring creating the seal may cause enough friction to prevent the flanges from being easily separated. 

The O-ring sealing the components could be enough to "friction lock"
the assembly, making it difficult to take apart.

One option would be taking a screwdriver or another prying device between the flanges and pry like you're opening a casket of pirate treasure.  But while a tempting option, wedging a prybar between the flanges could result in damage to the flanges.  If the flanges are made of a soft material, such as aluminum, the odds of damaging the parts goes up significantly. 

But the designers of old did come up with a more elegant way of separating these... sticky problems. 

Many times, assemblies such as these will have tapped holes that appear to go nowhere.  They don't have a corresponding hole in any mating part.  They just appear to.... be there.

Why were these holes put there? They do have a purpose!

That's because they aren't there for the purpose of assembling parts.  They're for disassembling parts. 

They're called "jacking holes". By carefully threading screws into these holes, the two flanges can be pushed apart evenly without damaging the parts making up the assembly. 

Using a socket head cap screw to separate the flanges.

It's a simple, and elegant way of solving a challenge. 

So if you should find yourself having to disassemble an assembly similar to what I've shown here, look for those jacking holes and see if it can make your life easier. 

And if you find yourself designing a component that may present a challenge, perhaps adding a couple of jacking holes might make for a design that's easier to disassemble when the need arises! 

Opposing jacking screws help separate the flanges evenly!

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor, Siemens NX, at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

Standard Parts Used on this Project

A569-343 Viton O-ring - McMaster Carr Part Number 9464K173

Buna-N -343 Backup  Ring - McMaster Carr Part Number 5288T372

1/2-13 x .500 Long Socket Head Cap Screw - McMaster Carr Part Number 92185A712

Double Checking Your Work and Subverting Mr. Murphy

I once saw a graph that showed the cost of making a change in the CAD model vs  further down in the product design cycle

Spoiler alert! It gets more expensive as you move from design, to prototype, to production.  

One need only to cases like the Takata airbag recall, or Boeing 737 Max grounding or the impact of the impact of a a production level design change in in money, company reputation, and tragically, in lives lost. 

But I'm not here to write about such heavy topics. The example I'm choosing to document is a much lower stakes version of the same thing.  It's just a basic hobbyist example that at worst, is inconvenient and marginally embarrassing.

It's an access panel based on something you'd find on an aircraft. It's a concept for a potential future hobby project. I built one back when I was in school.

So I happily modeled away in Fusion 360, creating sheet metal parts and placing fasteners from McMaster Carr. 

After spending a couple of evenings of casual modeling, I was done! I took that moment we all love, I leaned back, looked at my work proudly, then prepared one last check before I took my little victory lap.

The completed inspection hangar, or so I thought...

And that's when I saw it. 

The countersunk rivets I had installed were the wrong ones. I'm not sure how I missed it initially, but obviously I did. 

So first, what's wrong with the rivet? 

It's a rivet with a 78 degree countersink, which means the countersink extends to the second sheet of metal being riveted.  This is a big no-no. When the countersink extends into the second piece of metal, the larger hole required in the first sheet of metal makes for a weaker joint.

The wrong rivet. I did match the countersink angle to match the rivet for clarification.

The incorrect rivet for this application. The countersink angle is too steep

The correct rivet is a 100 degree rivet. The shallower angle prevents the head from punching into the second sheet of metal. That means a stronger, and safer joint.

The 100 degree rivet, the correct one for this application. 
I know in the model the rivet does appear to just clip the second sheet.
But past experience has taught me that this combination does work.

The shallower angle of the 100 degre countersink makes a stronger joint

So that's the technical aspect of it, what's the other lesson?

I suppose the first lesson is make sure to check the hardware before you put it in. But we all make mistakes. That's where double checking comes in. 

A final check can help prevent the last little "oops" from slipping through. Even though we can't eliminate them all, we can reduce them with a little time. 

For those of us working in industry, a second set of eyes never hurts. In some places, multiple checks on a drawing are required. It's not a bad practice at all, one I think should be taken advantage of whenever possible. 

Some may argue it takes time, but it takes much less time than undoing a costly mistake. 

I've worked in maintenance shops where "second eyes" is a standard policy on items such as fuel system repairs. In other words, the person performing the work checks his work, and then a second technician or inspector checks it again. There often are even signatures required to prove that this step was performed. 

But that's it for today's anecdote. I re-learned a few lessons in a safe environment where the only bruise was to my pride. 

I hope you can take a few lessons from this musing, and keep making cool stuff! 

About the Author:

Jonathan Landeros is a degreed Mechanical Engineer and certified Aircraft Maintenance Techncian. He designs in Autodesk Inventor, Siemens NX, at work, and Autodesk Fusion 360 for home projects. 

For fun he cycles, snowboards, and turns wrenches on aircraft. 

Additional Resources: 

A nice  rundown on different types of rivets by- Hanson Rivet and Supply

A wealth of knowledge on general airframe repairs (start at page 4-31 for the Riveting Section) -Aviation Maintenance Technician Handbook 

Standard Parts Used on this Project.

.125 Diameter, 78 Degree Solid Rivet (The Wrong One) - McMaster Carr Part Number 97483A075

.125 Diameter, 100 Degree Solid Rivet (The Right One) - McMaster Carr Part Number 96685A170

10-32 Floating Nut Plate - McMaster Carr Part Number 90857A129

.094 Diameter Rivet (to Fasten Nut Plate) - McMaster Carr Part Number 96685A143

#10 Flat Washer - McMaster Carr Part Number 92141A011

10-32 Pan Head Phillips Screw - McMaster Carr Part Number 91772A826

Designing for O-Rings and Reusing Design Features in Fusion 360

O-ring seals are hard to avoid as a mechanical designer of any type. They can be found just about anywhere that fluid, gases, or debris needs to be kept in or out of something.

An O-Ring on the end of a flashlight

As simple as they appear, there's enormous amounts of research invested in that simple, pliable polymer ring.

How does this affect the designer? Typically by the pages and pages (real or virtual), containing tables and tables of o-ring groove dimensions.

O-Rings from a
different flashlight.

When it comes time to apply that to a 3D modeler, that means creating the o-ring grooves, including some tight tolerances. The process can be extremely tedious, especially when there are multiple o-rings of different sizes involved.

So how can a user create these o-ring glands as painlessly as possible? Sure, many of us have placed the same feature so many times we have the dimensions memorized. But why do that, unless you like that sort of pain? 

While I can't speak for every CAD tool, many tools have wizards that will help create o-ring glands, as well as other common design features. Autodesk Inventor has iFeatures, Solidworks has Library Features.

Fusion 360 doesn't have a library feature as such, at least that I've found at this point. But, there is a way to create such a thing and make life a little easier.

Preparing the O-Ring Gland

The first step, is acquire the documentation with the necessary dimensions. Lately I've become partial to the Parker O-Ring Handbook myself, seeing how they know a thing or two about sealing. 

For this example, I'll use a -018 o-ring. It's a static (non moving) seal, and I'll use the male gland as an example (stop snickering, that's Parker's terminology). 

Gland Schematic from Parker O-Ring Handbook

Here are the dimensions pulled from the design tables

From Table 4-1

C=.860/.861

F = .750/.754

Corner break = .005 

From Table 4-1A 

W = .105/.110 

From Table 4-2

R = .005/.015 

O-Ring Groove Radius

Modeling the O-Ring Gland

Before creating any models in Fusion 360, enter the relevant values into the parameters dialog box. This seems like extra work, but I think it makes creating models with new sizes easier.

The Fusion 360 Parameters screen with the o-ring parameters started

Now, draw the profile of the o-ring gland, using the values from the parameters table. 

The gland profile sketched and dimensioned.

Next revolve the profile into a solid. Now, we have a solid representing the shape of the groove.

The o-ring groove revolved as a solid.

Believe or not, that's it for creating the gland. Saving it will make it available for other components to use.

Inserting the O-Ring Gland

What's needed next is a component in need of an o-ring. In this case, I've modeled a simple plug in Fusion 360.  It's similar to the threaded plugs found here on the McMaster Carr site.  I've just moved the gland location to make things a little more clear.

A threaded plug

To place the o-ring gland, right click on the file in the Data Panel and choose "Insert into Current Design".  This places the gland into the model

This inserts the gland into the plug.  Now it can be positioned by using the Move/Copy command, or assembled using the Joints command.

Placing the o-ring gland. The Move\Copy command is shown.

After positioning the gland, use the combine command to subtract the gland volume from the plug.  

Once the Combine Command has been committed, the plug is finished.  And you also have a -018 gland ready to use in your next design!

The finished plug. (Don't forget to hide the original solid!)

But undoubtedly, other o-ring sizes will be needed.  That's where using the parameters can come in handy.  Just copy the existing gland and rename it, then enter new values in the chart.

Summing it Up

I only used static o-ring grooves for this post.  There's also dynamic (moving) seals, face seals, glands that use backup rings (for higher pressures), and probably something else I'm not mentioning. I just can't get into them all, but the data is out there. It's just a matter of looking and asking questions.

As for desigining the gland, the steps I've shown here are for Fusion 360. But if you've made it this far, I hope it's the process you take away. I hope that you can find it helpful, and perhaps can apply it to what ever product you use for your design.

At the very least, I hope you walk away with resources that you can use when the time comes to design for o-rings.

And lastly, here's the list of resources I used in this post.

Parker O-Ring Handbook -  PDF Download

McMaster Carr - Website

Milwaukee Penlight - From the Home Depot Website 

Mag Instruments Maglite - Mag Instruments Website

Autodesk Fusion 360 - Autodesk Website