Learn CNC The Hard Way

Operating a CNC machine will make you a better designer and engineer. Understanding how a machine works is the first step to designing parts for it.

I wrote this guide to provide a clear path for using CNC machines. Machining requires a lot of effort and study on your part and one person can't explain the entire process to you - the knowledge you gain comes from lessons learned by your own trial and error and guidance from an experienced mentor. In short, it's a journey or marathon, not a series of pushing buttons. I think you will find this to be a very rewarding experience.

Your ability to read and understand every word written here will make you successful in machining and much more. Take your time and it's OK to be totally lost at first. Stop and think about what you have read and maybe read it a second time. As you are relaxed and contemplating new information this is called learning. And when you think about that new information later in that same day or even first thing when you wake up in the morning this is also called learning. Your self-discipline to keep your mind trained on relevant information and not other stuff is the beauty of human intelligence. You can do it.

This Instructable gives you a place to look for answers. I want you to be self-reliant; I want you to be able to learn on your own; I want you to know how to find answers yourself.

When searching for machining answers on the internet, I've found it to be very noisy. That's why I put together the list of books below - they are proven to be good stuff and they have the real answers. If you are lucky enough to learn machining at Autodesk Pier 9, I have plenty of these books for you to borrow.

Anything worth doing is difficult at first. Some of the days I'm good and I design and make my parts without any mistakes and other days I'm not so good. Take your time, go slow, and enjoy the new territory and experience. If I'm not around to answer your question that was either by design or accident - take advantage of it and use the books and your experience to think about a good solution. If you are right, it will work. If you aren't, it won't. Repeat. Never give up (Submarine Officer talk).

Each day you should go home struggling to remember or recount the days work and learning. Start a notebook and take good notes and review them frequently. Try to recall that information at a moments notice without looking at your notes. It should be a struggle to recall the information perfectly each time. Challenge yourself.

BTW, it's The Hard Way because, again, anything worth doing is hard at first. If you want respect as an engineer or maker, knowing where to find stuff or at least attempting to figure it out on your own will show you care. You will get more help that way. The day I win is the day I watch you navigate the shop and calmly make something extremely complicated and great. Go make great things!

Pier 9 CNC Tool Library Instructable


Pier 9 Haas Training Videos


Dan's CAM Training Videos

Introduction - https://screencast.autodesk.com/Main/Details/90232...

2D Adaptive Clearing - https://screencast.autodesk.com/Main/Details/07cce...

Learn Inventor HSM



NextGenCAM Training Videos


Learn HSM Express


Pier 9 CNC Book Library

Machine Shop Essentials by Frank Marlow

CNC Programming Handbook by Peter Smid

Sandvik Coromant Academy (See attached .pdf)

Precision Machining Technology

Machine Tool Practices

Manufacturing Processes for Design Professionals

Learn CNC The Hard Way
MCT.pdf34 MB

Step 1: Make Something On The Manual Mill

Learn CNC The Hard Way

You made it, you are officially on step 1! Welcome. So, should you follow these instructions? Sometimes it's hard to take input or hard to believe that this is really the right path. What if they are wrong? What if they don't know what they are talking about?

Those are all great questions. I'm convinced a great learning experience only comes from people you trust. If you don't trust them you won't really learn as much. A good teacher will work to earn that trust as they give you what you need to grow. That's not always easy to do for either person, but it is the right thing to do. So, I hope you stick with this plan and go as far as you can. It is worth it.

So, it's very important to make two or three things on the manual mill! This will give you an understanding of the cutting forces involved (strength needed to rotate the handle) and speeds and feeds for different materials. It is essential to calculate speeds and feeds (Appendix B in Smid) for various materials. This is the most accurate speeds and feeds table. Don't trust the internet when it comes to speeds and feeds.


Speaking of the internet, search YouTube for machining videos! TrubalCain is an interesting guy to learn from


Cutting Tools

It's also important to learn about the different types of cutting tools. Read this article from Make: http://makezine.com/magazine/make-40/endmills/

Work Holding

Securely clamping your work piece in a vise is also very important. Holding something in place while forcing a cutting tool through it is the most important skill in machining. Read Chapter 10 - Milling Setups in the CNC Handbook by Autodesk.

Also read Chapter 8 - Milling Operations in Marlow.

Step 2: Make Something On The Manual Lathe

Learn CNC The Hard Way

Yep, get to know this piece of machinery too!

Again, calculating speeds and feeds and using your hands in a coordinated and controlled manner will pay dividends down the road.

Read Chapter 7 Turing Operations in Marlow. Types of turning tools.

Step 3: CAM Software - Introduction to Inventor HSM

Learn CNC The Hard Way

Warning - If you skipped steps 1 and 2 and think you don't need to know it you are doing yourself and everyone around you a disservice. Manual machining will teach you the fundamentals of cutting metal and you need those skills to successfully operate a CNC machine. Find a manual machining project and make it.

Ok, let's talk about the software that controls a CNC machine! This is where all the fun starts and you'll need easy-to-use CAM (Computer Aided Machining) software to get the job done.

Our next goal is to create instructions for the machine to follow. These are called tool paths. And I'll create tool paths using Inventor HSM.

There are three main steps in CAM programming: Setup, Tool Paths, & Simulation.

Step 4: Setup

Learn CNC The Hard Way


Open the attached file '2D Strategies.ipt' and select the CAM tab.

First, you'll need a piece of raw material or stock to machine. This is called the Setup and we'll select it on the ribbon. Note: Inventor HSM buttons are positioned like reading a book - you'll most likely use buttons starting from the left and working to the right. Click Setup.

Work Coordinate System (WCS)

What is a Work Coordinate System or Work Offset? Peter Smid explains this well in his CNC Programming Handbook on page 127:

"Work offset is a method that allows the CNC programmer to program a part away from the CNC machine, without knowing its exact position on the machine table."

By default, there are multiple points to select for our work coordinate system. It's common to select the upper left corner as your Work Coordinate System. Click the upper left point. This defines the X, Y, & Z coordinates, known as the Work Coordinate System, of the part. Note: The x-axis travels along the long axis of the part, the y-axis points away, and the z-axis origin, notably z-zero, is at the top of the stock pointing up. We'll need to remember this orientation when positioning our stock in the CNC machine. For a more detailed explanation of the Work Coordinate System, watch this video Setting up a Work Coordinate System and read Chapter 4 Coordinate Systems in the CNC Handbook.

Learn CNC The Hard Way
2D Strategies.ipt275 KB

Step 5: Setup

Learn CNC The Hard Way


With the Setup dialogue still open select the Stock tab. Note the dimensions of our default stock in the bottom dialogue box labeled Dimensions. By default, the software created stock material surrounding our part and the dimensions of the stock are 6"x4"x1.5". We need to change this since raw material is normally purchased a little thicker and our z-dimension is 2 inches not 1.5 inches.

In the Height (Z) field change 1.5 to 2 and press tab on your keyboard (we are working in inches so it'll automatically add the correct units). Tab is a handy way to input values and move to the next drop down menu. In the graphics window, notice the thickness of our stock (z-axis).

Next, in the Model Position drop down menu, select Offset From Top (+Z) and press tab on your keyboard. This allows you to position the model inside the stock. In the Offset field enter .05. This offsets our model .05 inches below the top of the stock. This offset is necessary for the first machining operation in the next step, Facing. Your screen should match the picture above. Notice the additional stock on the bottom of our part; we will use this additional material to hold our part in the vise.

Note: our stock dimensions are now 6"x4"x2". Remember that number.

Step 6: Install Pier 9 CNC Tool Library

Learn CNC The Hard Way

So far so good, right? This 'programming a CNC machine business' isn't so bad after all. And, to make this even easier and more awesomesauce I have the coolest tool library on the entire planet and you get to use it!

So, let's install the Pier 9 CNC Tool Library. If you happen to be one of the lucky contestants who won a Golden Ticket to Pier 9, you'll need to install this amazing set of milling tools that will make your life easier.

Visit the Pier 9 CNC Tool Library Instructable. Select the link 'Download Pier 9 CNC Tool Library' and download the file 'Haas Mill 25Feb15.hsmlib'. In Windows explorer, create a new folder on your hard drive called 'Pier 9 CNC Tool Libraries' and save that file there.

Back to Inventor HSM software. In the CAM tab in the upper right corner, click Tool Library. This opens the tool library dialogue. Click on My Libraries folder and click New Library button at the bottom left corner of the window and name this library 'Haas Mill 25Feb15'. This creates a new, and empty, tool library where we will import tools. Next, right-click this new library you created and click Import Tools from Library. Browse to the tool library you just saved on your hard drive and click Open. You just installed the Haas CNC mill library tools.

Step 7: Tool Path

Learn CNC The Hard Way

Facing Tool Path

The first step using CAM software is Setup and now we're on to the second step, Tool Paths. Let's create our first Tool Path.

Face milling from the CNC Programming Handbook on page 235:

"Face milling is a machining operation that controls the height of the machined part. For most applications, face milling is a relatively simple operation, at least in the sense that it usually does not include any special contouring motions. Cutting tool used for face milling is typically a multi tooth cutter, called a face mill, although end mills may also be used for certain face milling operations, usually within small areas. Top surfaces machined with a face mill are generally perpendicular to the facing cutter axis."

In the 2D Milling section click Face. Select the Tool button and choose Tool 171 2.5" Face Mill from the Haas Mill 25Feb15 tool library and click Select in the bottom right. Notice the Feed and Speed dialogue box is populated with the recommended feeds and speeds for beginning users machining aluminum.

Click OK at the bottom of the dialogue and look at the lines created in the graphics window - these lines are call tool paths! The face tool path is quick and easy because the software understands you want to remove all material from the top of your part. How much stock material did we remove? Take a closer look at Step 5 for the answer.

Step 8: Simulate

Learn CNC The Hard Way


This is the last of three steps for using CAM software, Simulate. Simulate what the machine will actually do with this tool path by clicking Simulate. Put a check mark in the Stock box by clicking it and press Play in the bottom middle of the screen. This simulation is very important and is exactly what the machine will do.

Step 9: Tool Path

Learn CNC The Hard Way
Learn CNC The Hard Way

Now we'll remove material from the feature in the center of the part - this is called a pocket. Peter Smid defines a pocket:

"In many applications for a CNC machining center, the material has to be removed from the inside of a certain area, bounded by a contour and a flat bottom. This process is generally know as pocketing."

There are two key words in this definition: contour and flat bottom.

In the 2D Milling section, select 2D Adaptive (Roughing). This is a roughing tool path that uses advanced algorithms to create tool paths to remove material VERY quickly and maximize tool life. This is what really sells software and this is our bread and butter. It's pretty cool and 2.5D is free!

Now we need to select a tool for this roughing tool path. Select the tool library you installed from the previous step and select Tool 114 1/4" EM (End Mill) Short.

Notice the five different tabs available in this tool path. We'll navigate these tabs just like we did when we first opened the software - it's best to use them from left to right. Select the next tab to the right, Geometry. This tab defines the geometry of our pocket.

Before we do anything else, what is the definition of a pocket? Quoting the man Smid, "the material has to be removed from the inside of a certain area, bounded by a contour and a flat bottom." Those two BOLD words again, contour and flat bottom. So, by definition, we must select a contour and flat bottom. This process is easy thanks to the great people at HSM Works.

Ok, now pay attention: Notice in the Geometry dialogue box the selection arrow is highlighted by default. The software wants you to select something. Move your mouse to the graphics window and select the bottom curve of the pocket (as displayed in the first picture above). What did we just do? We just selected the contour and flat bottom of a pocket in one click!! We did not select the upper contour of the pocket because that only defines contour of the pocket and not the depth (although there are tricks to make that work, too). Cool.

Let's move over to the next tab, Heights. In the Top Height box click the drop down and select Model Top. Since we removed material from the facing step we want this tool path to start machining from the top of the model (I wish this was already selected by default...one less thing to click).

Now let's look inside the next tab to the right, Passes. Notice Stock to Leave is selected and its values. Inventor HSM treats Adaptive as a roughing strategy - roughing means you want to remove as much material a quickly as possible - and it assumes you will come back and slow down the speeds and feeds for a nice finish pass. We'll talk more about finish passes next step, but just a heads up. Just remember, Adaptive = Roughing.

Click OK and check out your tool paths.

Learn CNC The Hard Way
2D Strategies Adaptive Roughing Tool Path.ipt619 KB

Step 10: Simulate

Learn CNC The Hard Way
Learn CNC The Hard Way

Click Simulate. Check the Stock box and press Play.

This is what you'll see in the machine and it's important to know what "right" looks like.

Step 11: The Workflow

Notice the workflow: Tool path, simulate, tool path, simulate, tool path, simulate, tool path, simulate. That's how you learn how CAM software (or any software for that matter); you first create a tool path and then you simulate it to see what happens. Repeat.

Bang your head against a laptop long enough and you will be able to operate any piece of software.

You are doing great, keep moving. Remember, any progress is progress. You should be proud of what you've done so far.

Step 12: 2D Pocket Finishing Tool Path

Learn CNC The Hard Way

Now that we've quickly roughed out our part, let's program a finishing pass.

Select 2D Pocket (Finishing). Notice the tool you used from the previous operation is already selected by default.

By default the software is ready for you to select a pocket, so there's actually no need to select the Geometry Tab. Move your cursor over to the graphics window and with one click we can select the contour and flat bottom of the pocket by selecting the lower contour. This defines the pocket boundary (contour) and depth (flat bottom).

Select the Passes Tab. Uncheck Stock to Leave since this is a finishing tool path and click OK.

Inspect your tool paths. This is a finishing tool path that will machine the bottom and sides of the part to the final dimension.

Learn CNC The Hard Way
2D Strategies 2D Pocket Finishing Tool Path.ipt618 KB

Step 13: 2D Pocket Roughing and Finishing Summary

Again, the workflow for programming a CNC machine - setup your stock, create a tool path and simulate it. We'll follow this workflow every-single-time, setup, tool path, & simulate.

2D Adaptive Roughing Commands:

1. Click 2D Adaptive.

2. Select Tool 114 1/4" EM (End Mill) Short.

3. Geometry tab. Select the bottom curve of the pocket.

4. Heights tab. In the Top Height box select Model Top.

5. Passes tab. Notice Stock to Leave field.

6. Click OK.

7. Click Simulate. Check the Stock box and press Play.

2D Pocket Finishing Commands:

1. Click 2D Pocket.

2. Tool from previous operation is already selected.

3. Geometry tab. Select the bottom curve of the pocket.

4. Passes tab. Uncheck Stock to Leave.

5. Click OK.

6. Click Simulate. Check the Stock box and press Play.

Step 14: CNC Machining Overview

Learn CNC The Hard Way

Pier 9 Haas Training Videos

Machine Startup Video

Understanding the Keyboard


Chapter 1 - Numerical Control

Chapter 2 - CNC Milling

Chapter 5 - Control System

Chapter 51 - CNC Machining (page 488 Machine Warm Up Program, CNC Machining and Safety, p489 Shutting Down a CNC Machine)


Chapter 1 - Measurement Tools, Layout, & Job Planning

CNC Handbook

Chapter 2 - Shop Safety

Start/Home Machine

Load CNC Program

Run CNC Program

Complete Project 1 - Install Vise

Complete Project 2 - Square Block

Step 15: Cutting Tools

Learn CNC The Hard Way

There are a variety of cutting tools used in metalworking. The CNC Handbook, Sandvik Coromant Academy, & Frank Marlow do an excellent job explaining the tools.

Pier 9 Haas Training Video

Pier 9 Tool Library Video

Inserting Tools

CNC Handbook

Chapter 3 - CNC Tools


Chapter 8 - page 332 - 334 Cutting Tools


Milling Introduction Video

Milling Section D D3 - D37 (attached .pdf)

Miscellaneous Article

The Skinny on End Mills - This is a great article

Mesmerizing Cutting Video

Slow motion machining

Machining of Hard Materials

2.7 Toolholders and Tool Clamping Systems


End Mills


Cut Style

Step 16: Speeds & Feeds & Offsets

Learn CNC The Hard Way

Pier 9 Training Video

Tool Offsets

Measuring a 3/4" End Mill

Work Offset


Chapter 18 - Work Offsets

Chapter 19 - Tool Length Offsets

Chapter 20 - Rapid Positioning (pages 147 - 149 Only)

Chapter 21 - Machine Zero Return (page 153 Only) Appendix B - Speeds and Feeds

CNC Handbook

Chapter 4 - Coordinate System

Do Project 4 - Contour Square Setup

Machine Tool Practices

Unit Two - Speeds and Feeds for Machine Tools (p275 - 278)

Precision Machining Technology

Unit Three - Speed and Feed (p336-339)

Step 17: Machining Features

Learn CNC The Hard Way


Chapter 33 - Slots and Pockets (pages 291 - 292, 294)

CNC Handbook

Chapter 7 - 2D Milling Toolpaths


Milling Summary Video

Step 18: Drilling

Learn CNC The Hard Way
Learn CNC The Hard Way

How to make a hole - spot drill, drill, & ream (if necessary)

  • Spot drill (or center drill) - This shallow pilot hole provides an accurate location for the drill. The Depth of Spot Drill = Diameter of Hole* 0.5 (for 90 degree spot drills)
  • Drill - make the hole
  • Ream - make the hole to a very precise diameter using a reamer.


    Read About Drill Bits


    Read attached Drills.pdf


    Chapter 2 - Basic Hand Tools

    Chapter 3 - Filing & sawingarlow

    Chapter 4 - Grinding, Reaming, Broaching, & Lapping

    Chapter 5 - Drills & Drilling Operations


    Drilling E3 - E47 (attached .pdf)

    CNC Handbook

    Chapter 7 - Drilling

    Chapter 9 - 3D Toolpaths

    Chapter 10 - Milling Setups

    Learn CNC The Hard Way
    Drills.pdf121 KB

    Step 19: Tapping


    Read About Taps


    They have something to say about it, too

    Step 20: CNC Programs

    Learn CNC The Hard Way

    Pier 9 Haas Videos

    Load a Program

    Run a Program Safely


    Chapter 7 - Part Program Structure

    Chapter 8 - Preparatory Commands

    Chapter 9 - Miscellaneous Functions

    CNC Handbook

    Chapter 5 - CNC Programming Language

    Step 21: Turning

    Learn CNC The Hard Way

    CNC Handbook

    Chapter 8 - CNC Turning


    Turning A3 - A32 (attached .pdf)

    Project 10 - French Curve

    Step 22: CNC Programs and Machinibility

    Learn CNC The Hard Way

    If all else fails use the Othermill...this thing is super-easy to use.


    Chapter 12 - Spindle Control

    Chapter 13 - Feedrate Control

    Chapter 14 - Tool Function


    Chapter 10 - Metallurgy


    Machinability H3 - H84 (attached .pdf)

    Step 23: Machining Laminates/Stacked Composites

    Learn CNC The Hard Way

    Minimize delamination and burrs using a compression cutter (pictured on the right). More data is available on the Harvey Tool Website.

    Step 24: End Mill Coatings

    Learn CNC The Hard Way
    Learn CNC The Hard Way

    End mills come with a variety of coatings. The above image and .pdf gives a great explanation. Website link here.

    Learn CNC The Hard Way
    CoatingsGuide_2010.pdf204 KB

    Step 25: Machining Acrylic

    Please see the attached guide from Onsrud.

    Learn CNC The Hard Way
    Routing_and_Trimming_Acrylics.pdf21 KB

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