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.