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. 

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.