Do you think like a machinist? Not every CNC’er does. If I had to guess, based on what I see out on the internet, a surprisingly large number don’t. But it’s worth learning to think like a machinist.
Joe Pie, from his YouTube Channel
Joe Pie Thinks Like a Machinist
I was reminded of what it is to think like a machinist when I started watching Joe Pi’s (Joe Pieczynski) YouTube channel.
I saw one video about a particular insight Joe had into a difficult fixturing situation. I thought it was pretty good, and immediately YouTube pitched me another Joe Pie video called, The Best Mill Tip You Will Ever Get.
I don’t know if it was the best ever, but with a title like that I had to watch it and sure enough, it was worth checking out.
At that point I was hooked, because Joe Pie thinks like a machinist. Even better, he clearly communicates what that means really well in his videos, so you can learn.
I wound up sitting down and going through his whole catalog of videos over the course of a couple of days just to get back in touch with that pure expression of thinking like a machinist.
What is Thinking Like a Machinist?
What does it even mean to think like a machinist? It’s a particular mindset. Manual machinists are much more in touch with it than CNC machinists. Experienced professionals are much more likely to think like machinists than hobbyists. Those who learn as apprentices are more likely than those who are self-taught and just figured things out.
Years ago, when I was learning manual machining, I was trying to learn how to think like a machinist, though I didn’t realize it. Back then I craved the insights into how real machinists would tackle machining tasks. It was less about “How do you do that?” and more about “Why did you do it that way?”
I read as many accounts of machining as I could, seeking those rare insights. I was particularly interested in learning everything I could about fixturing, setup, and measurement. As it turns out, those are the tasks where thinking like a machinist really helps.
After a couple of years of intense focus, I noticed a change. I’d read a machining account and see ahead of time what they were going to do. Or, even better (and this is what Joe did in the first video I watched) I’d came up with a better method.
Coming up with better methods is what thinking like a machinist does for you. When you think like a machinist, your solutions to machining problems work better because:
- They’re automatically more accurate
- They’re automatically more consistent, or perhaps idiot proof
- They save time, and they’re often easier. Great machinists are lazy. They have so much to get done they can’t afford to be any other way.
Seeing Joe’s videos reminded me of those lessons I’d learned those years ago, and how I had internalized that thinking almost to the point where it had become automatic.
It also motivated me distill with much better hindsight and knowledge what it is to “Think Like a Machinist.” It hadn’t really become a conscious thought that this was a thing to talk about, and maybe teach others about.
Okay, How do I Think Like a Machinist?
First, a little bad news–there’s no simple recipe I can teach you in this article that will leave you thinking like a machinist.
A good analogy comes from music. There’s no simple recipe that’ll teach you how to solo with a guitar or piano. But, I can show you a little music theory along with some examples, and then encourage you to get started trying to think like a machinist.
With time, experience, and trying, you will get there just like our budding guitar player.
Thinking like a machinist requires just two steps plus your toolkit of techniques. Here are the two steps:
Let’s go over these steps.
Think Like a Machinist: Step 1 – Solve the Geometry
To think like a machinist, think geometrically and very visually. Start by boiling down your problem to pure geometry. Sketch it on a yellow pad or white board.
When Joe Pie gets up there on his white board and starts sketching triangles and trig, you know you’re in the right place for this. You can’t think like a machinist if you can’t think geometrically.
If you are naturally a visual thinker, this is going to be pretty straightforward. If you’re not, I don’t know how to turn you into a visual thinker, sorry. But I would still try to sketch out that geometry. Keep working problems until the circles, triangles, and lines become second nature. If you missed basic geometry in high school (or wherever it was taught in your curriculum), get an old textbook and go through it.
You’re going to see Joe using most of what you remember from Geometry class at some point or another in his videos. For example, draw two parallel lines. Draw a line that slashes across them. Do you know off the top of your head which of the eight angles that creates match each other? At some point in Joe’s videos you’ll see him using that stuff to figure out a machining problem!
There’s a little more to it than just having the geometry drawn up. As machinists, we need numbers. We need coordinates. We need diameters. These are the things we measure, set our machines to, program in our G-code, or create in our CAD programs.
Getting those numbers, except for the simplest cases, often means either the Pythagorean Theorem or Trigonometry.
When Joe talks about trigonometry, he says a lot of folks are afraid of it, but that you really need it to be a good machinist. He’s absolutely right, but you don’t need a PhD in trig to get the job done. There are plenty of aids to help you work around it that are far short of going back through a trig class again. You don’t need to be able to derive all of those theorems. You just need to be able to apply it to figure out some pretty common problems.
Joe mentions his approach to it, which involves a handy “cheat book.” You can also use software like our G-Wizard’s handy geometry calculators.
Here’s G-Wizard’s right angle calculator:
Special any side and any angle, or any two sides, and it will tell you all the rest about that triangle. No theory required.
Or, how about circle chords? They’re another useful tool that Joe uses:
With a tool like G-Wizard’s chord calculator, you can figure out a number of interesting things. For example, Joe used circle chord math to figure out dimensions of a conical bore by dropping a ball down the bore. Given the diameter of the ball and how far it protruded above the bore, you can tell the diameter of the bore from that trick.
Another handy tool for hard geometry problems that need numbers is your CAD software. Draw it out and set the dimensions to the numbers you know. The CAD software will figure out the rest. Doing it in CAD is probably the slowest approach. You can rip through these problems on a whiteboard with some calculator help (like G-Wizard) faster. But sometimes CAD is the only thing that you can figure out that’ll work, so keep it in mind.
So, the first step to Think Like a Machinist is to sketch out the Geometry and get all the numbers filled in.
Convert the Geometry to the Physical World
An abstract geometry sketch with numbers might be enough, or so close it doesn’t matter. For dropping a ball down a conical bore, it’s almost enough.
You do have to “Convert the geometry to the physical world” by realizing the ball can’t be in contact with any chips or edges that have been chamfered or broken. Those are two ways the physical world interferes with our pure geometrical thinking.
So, are you always cleaning things carefully before you measure?
Knowing the limitations of your machine is another way the physical world intrudes. Joe goes through an entire video talking about how to find the center of a circle with an edge finder and one of the biggest issues is backlash.
That’s a limit of your machine that you need to be aware of and work around. Even CNC machines have backlash–it’s just a lot smaller. If a bore is to be accurate, or perhaps if a probing routine is to be accurate, you must program around that backlash.
Another issue with the physical world is making it accurate, convenient, and idiot-proof.
Are you an idiot? I’m not either, or so I tell myself. But give me a moment of lapsed concentration and somehow the idiot in me takes over and I screw something up. Good machinists follow practices that guard against their inner idiot. The Lean Manufacturing world even has a fancy name for it–Poka Yoke.
Some time ago I developed a defensive machining technique. I developed an instinct to be reluctant to take parts off the machine. Don’t pull that part out of your lathe chuck or out of your milling vise until you have stopped, thought hard, taken any measurements you can, and otherwise verified all is well.
And if you do take it out, try to make it possible to put it back exactly as it was. I wrote a whole article about it and you’d be surprised how many machinists got in touch off line and thanked me.
Another basic insight I picked up a long time ago is that the best way to make something accurate, convenient, and idiot-proof is to use a stop. If you can get a stop set up properly for your needs, you can repeatably put work up against that stop with an accuracy of just a few tenths. Keep things clean and temperatures stable and you may even do better. Stops are almost magical.
Joe’s no exception. He uses stops in all sorts of places. For example, he’s got a stop when he goes to return for the next threading pass on his lathe. Or, when he makes his custom angle block to machine angles in the mill, he has a stop for the part to rest against. He’s got a vise stop and is careful so that when he places the part on the angle block it pushes the angle block against the vise stop. Stop on stop and everything is quick and repeatably accurate.
Okay, let me touch on one more broad area, and that’s workholding. If you’re Thinking Like a Machinist, you start out most any job thinking about workholding:
- How do I hold this part accurately? I need to know it’s orientation because any machining I do is relative to that.
- How do I deal with repositioning the part for future ops? Oy, this is a can of worms. I need to make sure the machining establishes the orientation I will need for future ops as I reposition the part. I need to be able to access any part datums needed by the future ops. The latter is how I got started watching Joe’s videos in the first place!
- How do I hold this part securely? If the part flexes in the workholding, it is hard to machine it accurately. Flex is one of those Physical Limitations that doesn’t exist in Geometry. Everything flexes, it’s just a matter of knowing how much and how to minimize it.
- How do I do all this efficiently? For production, especially on CNC, I need to be able to put a raw workpiece into the workholding quickly. I need to be able to machine as many as possible within the travels of the machine. And I need to get the part back out again quickly.
Solving some of those problems is about geometry, and some is about having the right set of techniques to deal with the physical world’s limitations. Stops of one kind are another are often your friend for workholding. Vise jaws and chuck jaws are little more than stops combined with clamps in some sense. Or they can be if you need them to be.
Are you getting an idea there is a grab bag here? Yes, there is. These are techniques to overcome the limitations of the inaccurate error prone physical world versus the perfect dead nuts spot on geometric world. One is real, one is imaginary. As machinists, we’re going to be judged based on how well we can make the real world mimic that imaginary world.
Here’s what Joe Pie had to say after reading the original draft of this article:
I’ve had the pleasure of training a lot of apprentices over the years. I’ve somehow always found myself in a position where I could pull CNC operators that showed great potential and run them through a higher level program. I have found its easier to make a manual machinist, a CNC guy, than it is to make a CNC guy, a manual machinist. The core skills and mindset seem to be different.
My entire career has been focused on prototypes, repairs, product development and jigs and fixtures. I knew early on, I didn’t want to do the same thing every day. Same trade OK, but same part or activity, Big nope. I am formerly an associate knee product development engineer from Sulzer ( now Zimmer ) orthopedics. In my capacity there, I organized and ran an internal course for our 3rd year mechanical engineering co-ops, from the University of Texas at Austin. Design for manufacturability. These guys were book smart, but totally naïve to machining. Time, cost, accuracy, etc. I noticed during that time, just because you went to school for something, and maybe have a degree, doesn’t mean you are cut out for the job. Some are naturals, some have to work harder at it. If you’ve ever taught a mechanical based class, its easy to tell who should be there, and not.
I think that ‘thinking like a machinist’ and excelling at this trade, has to be in you from the start. As an infant, I’d spend my time playing with the Tupperware containers and lids to see how many I could match and hide inside each other. The pots and lids didn’t stand a chance. My Father traveled a lot for his job and always came home with a mechanical puzzle for me. So I guess I was programmed right from the start. I still have every one he ever gave me.
Joe’s remarks about play as an infant resonate with me. At those ages I was all about Legos, Tinker Toys, Erector sets, and anything similar I could be making things from. I think that all goes to the visual/geometry thinking thing I have focused on here.
So, going forward, let’s do a few things:
Second, cultivate your geometry thinking, and cultivate your bag of tricks for making the real world behave like the pure geometry. Those are the things that will make you think like a machinist. The more you can do along those lines, the more proficient you’ll be as a machinist. It’s a lifelong journey, honing these two skills. You’re never done. Just when you think you are, someone like Joe Pie or many others will pop up to show you something new.
Let me leave you with one final exercise. I have an article on all the different ways you can set up Part Zero on your CNC Machine. It’s something that has to be done for every CNC job, so it’s worth getting good at it and having a good-sized bag of tricks to support it.
Go through the article and try to think like a machinist as you review each method. What’s the geometry there? On many, you’ll see they probably were thought of because some machinist was thinking about geometry first. Also, how are they dealing with translating that geometry to the physical world? What are their tricks?
The last part is the best–how did they eliminate work by rearranging the problem in some clever way?
For example, if you can let the fixed jaw of your vise be part zero and position the workpiece against a stop there, you eliminated nearly all the work in finding part zero.
You clever machinist, you!
And just like that, you’ll be a clever machinist too.
This post was written by Bob Warfield and originally appeared on the CNC Cookbook blog.