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. 

New in Fusion 360 - Improved Thread Notes

 Sometimes it's the little things that make a guy happy. 

A thread note placed
on an external thread

In this case, it's the improved thread annotation tool in the January/February Fusion 360 update. 

In short, Fusion 360 can now create an annotation for a thread note placed with the thread tool, not just the hole tool as was the case in previous updates 

That opens up the field to place thread notes onto external features. It's a capability I've personally been hoping would get added for some time. 

Admittedly, applications like Inventor have been doing this for what seems like eons, so it's hardly a "ground-breaking" feature. 

But it sure is a nice feature to have! 

All you have to do is place the note using the "Hole and Thread Note" command, and you're off and annotating. 

Locating the "Hole and Thread Note" tool

One little cool thing I noticed in my evening of poking about. 

The tool works with threads created using the "modeled' setting too! 

A modeled thread with a thread note.

I've been waiting for this enhancement for a while! I'm glad it's finally here! 

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 Milestone Creating a Fusion 360 Title Block!

I have completed the task I challenged myself with in my previous post. I finished up my reproduction of a 1940s era North American Aviation title block in Autodesk Fusion 360!

The original, and Fusion 360 Title block together

It was a little tedious at times, it's a lot of repetitive sketching geometry and inserting text and properties. 

But it's completed, and ready for use. I'm sure I'll find a few more things to adjust as I test it out. 

Ultimately, I was able to recreate nearly every feature of the title block. It's not an exact match. I couldn't find a solid fill to block out the box above the part number for example. But it is close, and it will serve it's purpose just fine. 

As more features get added to Fusion 360, I'll update the title block accordingly. 

The North American Aviation tile block finished

So now, it's time to start creating drawings! From there, I'll learn more lessons and make more adjustments!

Credits:

Title Block Sourced from my Aircorps Library subscription.

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. 

A Trick - Creating Fusion 360 Title Blocks from an Image

 Happy 2022! Here's to hoping for a prosperous loop around the sun. 

One of my latest endeavors has been recreating 1940s aviation prints as 3D models in Fusion 360. The drawings are available via my Aircorps Library subscription, and they're a great look into how parts and assemblies were documented nearly 100 years ago. 

A piston for an actuator on a North American P-51 Mustang.
Model created in Autodesk Fusion 360

The models are the fun part for sure, but I also decided to recreate the drawings themselves too. 

The first part of recreating the drawing, is to recreate the title block of course. 

The title block image, ready for import into Fusion 360

\

It's still a work in progress, but I thought I'd spare a moment to document my progress.

It almost goes without saying, the process can be tedious. Since the original drawings are hand drawn, they have to be recreated from scratch. 

The thought of trying to "eyeball" the title block wasn't very appealing, but finally an idea dawned on me that made the process much less challenging. 

I imported an image of the title block, scaled it to a suitable size, and laid out the geometry on top of the image.

The title block in Fusion 360. The lines sketched in Fusion 360 are highlighted.

Overall, I felt pretty well. But there was one thing I did have to overcome

There's no image opacity setting like there are in other parts of Fusion 360. But I was able to see where my sketched lines were by highlighting them. I also extended the lines beyond the edges of the image. I can always trim them later. 

Finally, I'd also use the good old, "Delete, Inspect, Undo" trick by deleting the image, inspecting, and undoing the delete.

Overall, its working pretty well. I've found the process is much faster, accurate, and less frustrating than trying to scale by using the title block in a separate window. 

As I said earlier, it's a work in progress.  I'll share my final product when I'm done. Give me time, it might be a while! This is an "evening here and there" project! 

One Final Note

The team at Aircorps Library have done a spectacular job collecting, scanning, and sharing these vintage documents. Out of respect for their work, I won't be sharing any documents or models. Please, don't ask me to do so.

If you are really interested in their documentation, feel free to check out their site and investigate a subscription yourself! 

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. 

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

Lessons from the Shop Floor - Helical Inserts do more than Repairs.

Many technicians, designers, and fabricators are familiar with helical inserts, often referred to by their trade name "Heli-Coil". 

A helical insert in an exhaust manifold

These inserts are made of a coil of diamond shaped wire. Looking like tightly wound spring, they can be installed in a special threaded hole to create standard metric and imperial threads.

In my early experience, I only saw them used to repair a damaged thread. As a matter of fact, they were used for thread repair so often, the name "Heli-Coil" became a verb. 

"Curses! This thread is completely boogered up! I'm going to have to Heli-Coil it! This why you always start a screw with your fingers!"

But as I gained more experience, I saw two additional uses for helical insert, and that's what I thought I'd share in this post. 

Wear Resistance

A 3D model of a free running (non-lockng) 
helical insert in an aluminum block

The first is to create a wear resistant hole in softer material, such as aluminum. Instead of waiting for the hole to get worn out, a helical insert is installed in the hole at the time of fabrication. The helical insert is made of a more wear resistant material such as stainless steel, although there are other materials available. This creates a more durable hole better suited if repeated installation and removal of the fastener is expected.

You might see this on a panel that needs to be removed periodically for inspection. Naturally, once the inspection is competed, the panel needs to be reinstalled. The more wear resistant helical insert lasts longer, and resists damage caused by cross threading. 

And if you have a really bad day and damage the insert, it's possible to remove the insert and install a new one without damaging the base material. 

Create a Locking Element

A 3D model of a locking helical insert.
Note the deformed thread in the middle.

Another element is to create a hole with a locking element in it. Locking helical inserts have a distorted thread in the middle that resists the screw backing out. By using a locking insert, the need for a screw with its own locking element, such as a nylon pellet, can be eliminated.

While this may seem like extra work for not much gain, this can be advantageous since you don't need to purchase fasteners with their own locking elements. Another advantage is in higher temperature applications where a nylon locking insert's performance may degrade to the point where it loses effectiveness.

And just like it's non-locking (also known as "free running") counterpart, it can be removed and replaced ,when it's locking element loses effectiveness.

 Wrapping it up

I've written this post based on helical inserts, but there are many styles of threaded inserts. Far more than I know about, let alone discuss in one post. So if the helical insert isn't your speed, there's likely another that will do the trick.  

For a sampling of just some of the different types of threaded inserts available for different applications and materials, take a look at the McMaster Carr catalog!

I hope you found this post helpful and informative. 

Let's get out there and design, fabricate, and maintain some stuff!

Appendix and Credits

• 3D models created in Autodesk Fusion 360.
• Threaded insert models downloaded from McMaster Carr
• Threaded insert models are based on the NASM/MS21208 standard for non-locking inserts, locking inserts are based on the NASM/MS21209 standard, although several standards, both imperial and metric, exist.

Finally! Looking for a video on how to install a helical insert? Check out this video here! 

Photo Credit: rustyheaps Repairing exhaust manifold, XK engine via photopin (license)