What a Mason Jar in a Strange Place....

There is an elegance in simplicity.

Not long ago, I was helping with the annual inspection on a Vultee BT-13 Valiant. It's a World War Two era primary trainer.

As I'm walking around, lubricating pulleys with my trusty can of LPS2, something catches my eye.

It's in a bracket, bolted to the firewall. Inside is about an inch of white powder.

To be clear, this is not "Tony Montana" brand white powder. I know somebody out there was thinking it. 

It's a mason jar, specifically one made by Ball Corporation.

Even to this day, this type of jar can be found in your local grocery store. 

There's a hose leading from the cap to the battery box. The powder is baking powder used to neutralize battery acid.

I learn from a mechanic smarter than me that was how the airplane left the factory during the World War 2.

It was designed with a ball jar from a grocery store as a part of the battery venting system.

I laugh. I find it entertaining, but also I admire the brilliance of how simple, yet effective the solution is. I even searched my AirCorps Library account and found a scan of the Vultee Print that specs out a mason jar.

The Callout for the Mason Jar

It was indeed called out from the factory! A mason jar! A humble mason jar!.

Is it inexpensive? Yes.

Is it easy to source? Yes.

Is it easy to maintain? Yes.

Is it resistant to battery acid?

Yes. You could literally go to your pantry, rinse the contents out of the jar, and repair the airplane.

But it's a lesson for all of us designer types.

Keep it simple. And one doesn't get much more simple than that.

While there are times we need to spec out the "unobtanium fraffernator with chrome plated galloping rod adjusters", there are other times something as simple as the jar in your pantry will do just as good a job. 

100 Degree Countersunk Screw Saves the Date! - Lessons from the Red Notebook

This blog post is going in a slightly different direction than what I've historically done. 

My work these days is less "CAD-Centric". I'm not teaching and supporting CAD anymore. I now use CAD as a tool to create and update designs. I/m back in the trenches, if you will. 

Instead, this post is a journal on a lesson I've learned "on the job". The kind that I record in a tattered old composition book I've had for years. 

I present my "Lesson from the Red Composition Book".

My battered red composition notebook.
Next to an after work beer.
Enjoyed responsibly of course!

It started as an interesting challenge to modify ab design. 

DISCLAIMER! I can't share the actual design, due to proprietary issues, so the images I'm showing are a facsimile. 

My sample wear plate in
its base plate

The design was already created, and needed a hardened wear plate added to increase the product's durability. 

So far? So good? Right? 

But there was a challenge. The plate the wear plate wasn't very thick.

That meant the wear plate would be even thinner. 

In  turn, that meant the countersunk screws required to hold the wear plate in place wouldn't have a lot of room for the countersinks required to hold the wearplate in place. 

They have an 82 degree head, and in this case, it mattered.

A countersunk screw with an 82 degree head.
There isn't much wall there!
The solution? Take a cue from the aviation world, where 100 degree countersinks are more common. For those looking for the screw, you can look up MS24693.

Thank goodness for the aviation part of my experience! 

A countersunk screw with a 100 degree head.
Now there's room to work with! 

With a little CAD work, the models and drawings were updated, and off to review. 

To conclude, I suppose there are two lessons to be learned here. 

First, don't forget to use all your experience to help solve a problem. 

And second? Those 100 degree fasteners can really come in handy when you're dealing with thin walls!

Finally, I think I'll add some more lessons from that battered and tattered red composition book. If only to move them from a disintegrating book to a more robust solution. 

Hopefully, they help a few other designers along the way. 

Acknowledgements:

Sample models built in Autodesk Fusion

Screw Models Downloaded from McMaster-Carr

The Rivnut - Just Another Blind Fastener Among Many

Recently, I found myself in a situation where I needed a fastener in thin sheet metal, where I didn't have access to the other side of the material. 

That rules out the typical nut. I was going to need a blind nut that could be installed from the outside of the part. 

Enter the "Rivet Nut", more commonly called a "Rivnut". 

An Autodesk Fusion model of two rivnuts in a piece of sheet metal.

Available in  a variety of materials, they can be installed using a variety of tools that all work on the same principle.  

The rivnut is installed into its hole, and a threaded mandrel is drawing by a tool to compress the nut tight against the parent material. 

One type of Rivnut tool. There are more than one option, though

An uncompressed Rivnut threaded onto the mandrel, ready for installation.

It's similar to a "pop" rivet for those familiar with with those. 

It's a pretty quick and easy way to create threads in a part.

An orthographic view of an uncompressed (left) and
compressed (right) rivnut,

An isometric view of the same view above.

I've only used aluminum rivnuts, so my experience is limited to those, but here are the drawbacks I've encountered

1) They're easy to cross thread if you're not careful. I've learned to start the screw with my fingers to ensure the threads are running true. Starting the screw with a socket or any kind of power screwdriver is a recipe for trouble (ask me how I know). 

2) "Permanent" is a relative term. While reusable, rivnuts always seem to loosen over time. Eventually you end up with the dreaded "spinner". That rivnut that spins inside it's hole and must be carefully drilled out. 

Fasteners out of other materials may be a little less prone to the above problems, but not having used them, I'll avoid speaking "out of class". 

In conclusion, the rivnut is a fastener that has it's niche. If you made it this far, you may be thinking "That could be really handy!" or "That thing is useless and the universe will be cold and dead before I touch one".

Either way, that's fine! It's just another tool in the tool box! 

As a wise 1980s cartoon once stated, "And now you know." 

Acknowledgements: 

Rivnut models downloaded from McMaster Carr and modified in Autodesk  Fusion to create compressed version.

Fast vs. Effective. There is a Difference!

This post originally appeared on my LinkedIn profile, it proved to be a far more popular post than I could have guessed, so I decided to share it here as a post.  

Lessons of "Fast vs. Efficient". A lesson learned from a new tool, and an old tool

Old school versus new. The speed handle (left),
and the electric screwdriver

While removing and installing inspection panels on an aircraft, I found I love the electric screwdriver for running out the screws.

An example of inspection panels on the wing of a
North American B-25 Mitchel. The quantity required is "P" for plenty.

But I've found for stubborn screws, held in by"Nature's Threadlock" (aka corrosion), or with a boogered up screw-head throws a wrench in the works, you can't beat an old school speed handle.

Why? it has its own advantages.

I have placed the tail end of the speed handle and leaned into a stubborn fastener like a mob enforcer "balancing the books".

I've also have found I prefer the speed handle to install screws.

Why? I can better feel when the screws is run down, and I don't strip out the fasteners

Is the speed handle, with its 100 year old, muscle powered tech as fast as the lithium-ion powered, electric counterpart?

In a word? No.

Do i find that the old speed handle, with its better feel, resulting in fewer stripped screw heads and making quicker work for the next guy?

Arguably. Yes.

The thought it leaves me considering... That job might have been completed fast, to the joy of many who "made the number" this quarter.

But if a year down the road, hours are wasted undoing the minutes saved "getting it done quick".

Was it efficient?

When building a CAD model, there is quick. That means slapping the shape together, and can include:

Under-constraining sketches

Building features on top of features instead of editing the feature (think filling a hole with an extrusion instead of deleting the hole feature)

Creating uber complicated sketches that are difficult to edit. 

Over-complicated sketch. I don't like 'em!

Many times, this can allow us to "spank a shape" quickly. But when that shape needs to change? Oh. The horror. 

What can help make a model easy to edit? Here are some of my thoughts:

Fully constrain features. It makes model updates much more predictable.

Don't create unnecessary features. By that, I mean if a hole is going away, delete the hole. Don't "plug" it with an extrusion. Don't create a new extrusion on top of another if you can edit the feature and make it longer.

Keep sketches simple. I'll take more simple sketches over one that requires 283 constraints.

And finally, try (as much as possible), to build parts and assemblies in ways that mimic how they'll be made. One place I worked at strived (again as much as possible) to dimension their sketches in the same way as the part would be dimensioned on the drawing. 

Are we always able to do this? No. Sometimes, the realities of deadlines force us into a corner. Can we get away with it if it's a "one and done" model that won't change in the future? 

Trying to build models efficiently, may not be fast out of the gate, but as the edits, revisions and updates can become much easier.

Future you might be grateful. 

Observations of a clever 1940s Design - The Trunnion Nut Socket

One thing I find fascinating, is looking at old designs and seeing how the designers of the past tackled a problem. 

I love vintage aircraft and as part of that passion I like to look at vintage prints for these aircraft. 

A drawing that caught my attention was for a "Main Landing Gear Trunnion Nut" for a P-51 Mustang. 

A P-51 Mustang at Chino Airport in Southern Californai

In short, it's a big socket that tightens a big nut that holds the landing gear on the airplaane But what I found most interesting was how it was made. 

The socket was made in two halves and welded together. The side intended to accept the ratchet is one piece, and the side intended to drive the nut is another piece. 

An image of the two separate socket halves

The square drive and 12-point drive geometry are made by broaching. And by making each half separately, it allows the tool clearance to create the geometry. (Not familiar with broaching? Here's a video that shows an example!)

The Welded Socket

Given what I know of 1940s manufacturing, it was a clever way to tackle the problem and design for manufacturing. 

Today, the part could be made by using EDM (Electro Discharge Machining), but I can see how the same process could be used to make the part. 

3D Printed Parts for an Aircraft Restoration - An Update

I think it's about time to update on my project 3d printing "faux gun barrels" for the restoration on a Bell P39 Airacobra non-flying display.

A restored P-39 Airacobra

The P-39 Airacobra I'm helping restore.

There's been some progress since my previous post!

The black PETG I was waiting for arrived, and I printed the new barrels using black instead of the gray I used for a test fit. 

One of the finished barrels

I found the PEtG I used worked well, but it was a little "stringy", and the finish wasn't quite as good as PLA or ABS. But it's nothing that a little sanding can't fix. It also helps that the barrels will be buried inside the flash suppressors, so a lot of them won't be seen. 

One of the guns temporarily placed in its the suppressor

What's left now is a final sanding to knock of the layer lines and a weathering to make the barrels look a little more weathered. 

Overall, it's been a pretty good first attempt!

 

3D Printed Parts for an Aircraft Restoration

Recently, I had an opportunity to mix some modern technology with the restoration of an 80 year old airplane.

The project is a Bell P-39 Airacobra, which is being restored to be a non-flying display at Planes of Fame Air Museum. One of the tasks I was given was to come up with four faux .030 caliber machine gun barrels for the wing mounts. 

An example of a restored P-39 Airacobra
By San Diego Air and Space Museum ArchivesUploaded by Bzuk at en.wikipedia - Source, Public Domain, https://commons.wikimedia.org/w/index.php?curid=24375991

The P-39 I'm helping with has a little ways to go before its finished!

All that was needed was a short length four to six inches so it looked like there was a barrel inside the flash suppressor. 

Given the tools I had available to me, I opted to 3D print the barrels. 

The first step was to get some measurements. Fortunately, Planes of Fame has an SNJ Texan that has a fake 30 caliber machine gun barrel I could use for measurements.

The SNJ and the barrel I could use for measurements.

With measurements sketched on a piece of paper,, I headed home andI created the model I needed in Autodesk Fusion. It wasn't a difficult model. I had it in about an hour or so. 

The 3D Model in Autodesk Fusion

The next step was to print it out. My plan was to print in black PETG, but it didn't arrive before the weekend, so I printed in gray PLA so I would have something to test fit. 

The PLA Print in Progress

Once Saturday rolled around, I had a chance to see how the test barrel fit. 

I was pleasantly surprised to see it fit well! It fit perfectly in one flash suppressor, and should go into the other three with a little light sanding. 

The 3D printed test part next to its "sample

The 3D printed part placed in its tube. 
Its not fully seated here.

The 3D printed barrel recessed in the tube. 
This will be its final position.

The next step? Print in the PETG I intended to, perform another test fit, and make preparations for permanent attachment.

In conclusion, it was a unique experience to be able to be able to use Fusion to create a model that could be 3D printed for the restoration. I'm grateful for the opportunity.  

But my part was indeed small, and I'm not the only one creating models that are turning into parts for this restoration. 

To see some amazing Inventor work that has turned into real parts for this restoration, check out Aviation CAD Technotes here! 

One last bit of "Legal Talk".

Any opinions expressed here are my own, and not necessarily those of Planes of Fame Air Museum. 

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. 

Why Combine Two Different Radii Fillets in One Feature? - Food for Thought for Autodesk Inventor and Fusion 360

 Once upon a time, I was asked, in reference to Autodesk Inventor and Autodesk Fusion 360, "Why would someone want to have a fillet feature with more than one radius in it?" 

An example of two different fillet radii in Fusion 360

It's a fair question. It's likely we can pick a feature in just about any CAD tool and ask, "Why is that there?"

But to that end, I did have a reason one might want to combine two different fillet radii in one feature. 

It's a matter of organization. In my design work, I often find myself modeling O-ring grooves, which nearly always have a different radius at the top and the bottom of the gland. Having the ability to combine the different radii in the same feature allows me to combine the fillets into a "O-ring Radius Feature", and maybe shave down the feature tree a little bit. 

An O-ring groove using two different radii fillets in the gland.




O-rings installed in the glands.
Just to give some context to the first image.

Another case I've used was way back when I was designing sheet metal tooling. I used it when "keying" a rectangular insert. In that example, the opening has 3 radii of one size, and the fourth is a different radius. The insert has chamfers of a similar size. This prevents the insert from being inserted in the wrong direction. Why fillets on the opening and chamfers on the insert? It was easier to machine with the tooling of the time!

An example of a sheet metal stamping insert


The"keying" feature up close. 


Admittedly, these two example are very specific to my own design experience. But perhaps it might give someone food for thought. 

While you might not run into one of these particular examples I've described, maybe there will be something similar that you can use.  

Is it life changing? Not very likely. But maybe it's a little food for thought as you make your way through the 3D CAD world.