milling machine t slot operation

Milling Machine Operations You Should Know

You’ll find a milling machine in nearly every machine shop and manufacturing facility, and the machinists working on them complete an array of cutting operations to produce finished parts. One of the primary reasons for the popularity of the milling process is its ability to remove more material per cut than single-point cutting tools on a lathe machine, shaper, or planer.

The following are fifteen of the milling operations you can expect to perform on one of the many types of milling machines. Although this is not an exhaustive list, it will cover most of them.

1. Face Milling

The face milling operation is one of the simplest. The workpiece’s dimensions determine the size and type of the face mill. The teeth are on the outside and do most of the work, while the cutting edge on the face removes a tiny bit of material of stock left from the springing of the workpiece or cutter, providing a better surface finish.

The facing operation is used only on flat surfaces perpendicular to the axes of the milling cutter. It removes the material by rotating the facing tool in the counterclockwise direction as the table feeds the workpiece across the cutter.

Face milling can be set up on either a vertical or a horizontal milling machine with the cutter mounted on a stub arbor.

2. Plain Milling

Plain milling is another common type of milling machine operation, producing a simple, flat, horizontal surface parallel to the axis of rotation of a plain milling cutter. Also referred to as slab milling or surface milling, the operation is done on a horizontal milling machine with the plain milling cutter adequately mounted on an arbor.

An operator sets the depth of cut by cranking the vertical feed screw to raise the table. After determining the correct feed and speed, the table is moved along the X-axis into the rotating cutter to remove material.

3. Side Milling

If you are trying to produce a flat vertical surface in the workpiece, side milling is the option. The side milling cutting tool is fastened to the horizontal arbor, and the table is raised to determine the depth of cut for milling slots or anything with a vertical wall.

Although the side milling cutter’s size, type, and diameter will depend on the machining, you should remember to use the smallest diameter cutter that will work properly and allow for sufficient clearance between the arbor support and workpiece or vise to keep the cutter’s flex to a minimum.

4. Straddle Milling

Straddle milling is used when you must have two or more parallel vertical surfaces machined in one cut. You accomplish this by mounting two side milling cutters on a horizontal milling machine on the same arbor. The cutters are kept apart by a spacing collar that’s the same dimension as the parallel sides so that they “straddle” the workpiece to produce the flat vertical surface.

You can use the straddle milling operation to cut splines, squares, or a hexagon on the end of a round part.

5. Gang Milling

The gang milling operation involves two or more milling cutters secured together on one arbor to machine several surfaces simultaneously. Typically, milling cutters of different diameters, shapes, or widths are mounted on an arbor with spacing collars. The combination of cutters is determined by the requirements of the part and is virtually unlimited.

Gang milling saves machining time and is often used in repetitive work. The cutting speed of a group of cutters is calculated from the cutter with the largest diameter.

6. Angle Milling

The angle milling operation can be accomplished in several different ways: with special form cutters mounted on a horizontal arbor, using end mills ground to the specific angle required, or by tipping the milling machine’s head to the proper angle. The last method is often used on Bridgeport-style vertical knee mills using a straight end mill and side-milling the workpiece.

The angle cutter for the horizontal milling machine could be ground to a double angle for producing parts such as V-blocks.

7. Form Milling

The form milling process allows for machining contours made up of curves and straight lines in a single cut. Formed cutters are ground to the shape of the contour of the workpiece and used on both vertical and horizontal milling machines. Sometimes, the contour will be ground on a single-point fly cutter.

The irregular shapes can be convex, concave, or any other shape and are usually inspected using a template gauge. After machining, the formed surface is checked by a template gauge. Feed rates and spindle speed for form milling are typically 20% to 30% slower than for plain milling.

8. End Milling

End mills are the standard vertical mill cutting tools, producing a vertical, horizontal, or angular flat surface. You can hold end mills in standard holders or collets. (You should only hold single-ended end mills in a collet). The two most common end mills are 2-flute and 4-flute. Most machinists use 2-flute, high-speed steel end mills for aluminum since the flutes are less liable to clog with chips. The 4-flute end mills with reduced cutting speeds are recommended for cutting steels.

End mills are ideal for cutting various slots, grooves, and keyways. End mills can be re-sharpened several times, making them an economical cutting tool.

9. Conventional Milling and Climb Milling Operations

No article on milling operations would be complete without discussing conventional and climb milling. It is essential to understand how the cutting action of a milling cutter changes when the feed direction changes.

Also referred to as up milling, conventional milling is the cutter rotating against the direction of the table feed. Contrast this with climb milling, also called down milling, where the cutter rotates with the direction of the table feed. In one case, the tool tends to climb onto the work, while the other wants to move away from the cut.

Except for light finishing cuts, conventional milling is the safer of the two milling operations.

10. Saw Milling

In this operation, thin cutters make a narrow slot in the workpiece, or they can cut it in two. Feeds and speeds will be slower since rushing the cut could cause the blade-like cutter to break. The workpiece may be held in a vise or clamped directly onto the worktable with the cutter positioned directly over one of the T-slots.

11. Milling Keyways, Grooves, and Slots

Keyways milling operations are made for vertical and horizontal milling machine. Standard keyways are machined on a shaft using a side milling cutter on the horizontal milling machine or an end mill on the vertical mill. Dovetail slots, T-slots, and woodruff key slots require special cutters of the same name, while open slots can be cut with a plain milling cutter, a metal slitting saw, or a side milling cutter mounted on an arbor.

12. Gear Cutting

Gear-cutting operations can be performed using a form cutter mounted on a horizontal arbor or an end mill ground to the proper profile and held in a vertical spindle. The cutter profile fits precisely with the tooth space of the gear, and the equally spaced gear teeth are machined on a gear blank by holding the workpiece on a universal dividing head and indexing it.

13. Thread Milling

Although not used as much as thread turning, machine shops prefer thread milling in specific applications, such as when the threads are against a shoulder, close to the bottom of a blind hole, or they do not want to risk breaking a tap in an expensive part.

The operation is performed with either a single thread or multiple thread milling cutter. It requires three driving motions in the machine: one for the cutter, one for the workpiece, and the third for the longitudinal movement of the cutter.

14. Cam Milling

Cam milling produces cams on a milling machine by using a universal dividing head and a vertical milling attachment. The blank is mounted on the dividing head spindle, while an end mill is held in the milling attachment.

The axis of the cam blank and the end mill spindle should always remain parallel when setting for cam milling. The dividing head is geared to the table feed screw so that the cam rotates around its axis while feeding against the end mill. The axis of the cam can be set from 0 to 90° to the surface of the worktable for the various rises of the cam.

15. CNC Milling

Computer Numerical Control (CNC) milling is a cost-effective way to perform most of the operations on this list (and a few more). CNC mills have become a valuable asset for manufacturers because those processes requiring additional equipment, such as rotary tables and dividing heads, are no longer needed.

Versatile CNC milling machines have boosted productivity, nearly eliminated human error, saved money, and provided safety by enclosing the operation, protecting machinists from flying chips and splashing coolant. These machine tools cannot only take on the most complex milling operations but also drill, bore, ream, and tap without removing the part and completing them as a secondary operation.

Milling Operations are Performed on Several Different Types of Milling Machines

There is also no shortage of cutting tools for the many operations possible on these machine tools, and several different types of mills add to their reputation for versatility. Let’s look at some standard milling machines and the most often used milling cutters before looking at the top 15 machine operations performed on the typical workpiece.

Different Types of Milling Machines

Although milling machines can be categorized into several subsections, the column and knee type machine is the most common. The table is mounted on a knee casting, and the knee is mounted on the vertical slides of the main column. The table moves up and down depending on the size of the workpiece.

  • Machines within this category include:
  • Vertical milling machine (Manual and CNC milling machines)
  • Horizontal milling machine
  • Universal milling machines
  • Benchtop milling machines (a.k.a. hand milling machines)

Another category includes heavy, rigid machines where the table is mounted on the ways of a fixed bed. The table movement is restricted to the right-to-left direction (X-axis) and in-and-out (Y-axis), with vertical movement (Z-axis) provided by the head. These fixed-bed milling machines are further classified as simplex, duplex, and triplex based on the number of spindle heads.

Types of Milling Cutters

Since no milling operations can happen without a milling cutter, these cutting tools play an essential role in the milling process, and they are used to machine parts on various types of milling machines. Milling cutters are of numerous sizes and shapes, and here are the most recognizable of them:

  • Face mill cutters have replaceable carbide inserts with cutting edges on the sides of the cutting head. They are ideal for milling flat surfaces.
  • Slab mills are placed on the arbor of a manual horizontal milling machine to machine large surfaces and increase the depth of cut.
  • End mill cutters have cutting edges on the end and the circumference of the cutter. End mills work well for small milling operations such as cutting slots and profile milling operations.
  • Ball mill cutters are ideal for 3-dimensional milling operations.
  • Woodruff cutters have teeth perpendicular to the outside diameter and are used to cut keyways into shafts and other parts.
  • Thread mill cutters produce threaded holes, although taps can do that faster.
  • Fly cutters are single-point cutting tools that work much like a face mill.
  • Angle milling cutters can be in the form of an end mill, or they can fit on an arbor and be used on a horizontal milling machine.
  • Formed cutters have irregular profiles on the cutting edges to create irregular shapes such as concave, convex, corner rounding, and gear cutting.
  • Dovetail cutters are special cutting tools for machining trapezoidal-shaped grooves (dovetails) into the workpiece. You can also use them to cut angles, undercuts, and deburr parts.
  • Helical plain milling cutters have a coarse pitch and a helix angle on the teeth, and it’s helpful in profile milling work.
  • Side milling cutters have teeth on the periphery and one or both of its sides. They are typically used on an arbor with the horizontal milling machine, and end mills serve the same purpose on vertical milling machines.
  • Sawmilling cutters produce narrow slots or grooves on a workpiece or can be used as a parting tool.

What is the Difference Between a Milling Machine and a Drill Press?

In the not-so-distant past, it was easy to distinguish a milling machine from a drill press by its operations. Milling machines executed one or more of the fifteen operations we will detail below, and drilling machines drilled, tapped, reamed, and bored holes.

However, with the advent of Bridgeport-type vertical knee mills, these versatile machine tools began taking on the operations of a drilling machine and the milling machine operations of a vertical milling machine. And when these knee mills became CNC mills, their capabilities were nearly limitless.

Talk to an Expert in CNC Technology

CNC Masters offers a Bridgeport-type CNC vertical knee mill in two sizes. Called the Supra, our CNC milling machine quickly transitions between manual and CNC milling to perform numerous milling operations. We sell only high-quality, USA-built machine tools with ball screws, a warranty, excellent service, and all at a competitive price!

Please email us directly at, call us at 626-962-9300, or visit our contact page. You’ll be happy you did!

About Peter Jacobs

Peter Jacobs is the Senior Director of Marketing at CNC Masters, a leading supplier of CNC mills, milling machines, and CNC lathes. He is actively involved in manufacturing processes and regularly contributes his insights for various blogs in CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general. You can connect with him on his LinkedIn.

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29. Create a Peck Drilling Program in Circular or Rectangular Patterns
Using the Circular or Rectangular Drilling Wizards, you can program the machine to drill an un-limited series of holes along the X and Y planes. Program it to drill straight through to your total depth, use a high-speed pecking cycle, or deep hole pecking cycle. You can program the cut-in depth and return point for a controlled peck drill application to maximize chip clearance.

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20. Change up to 30 tools with compensation, and store your tool offsets for other programs
The MX supports…

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21. Use the optional ATC rack up to 8 tools for milling, drilling, and rigid tapping applications
The CNC Masters Automatic Tool Changer Rack and Tools (US Patent 9,827,640B2) can be added to any CNC Masters Milling Machine built with the rigid tapping encoder option. The tutorial will guide you through the set-up procedure using the ATC tools.

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22. Use the optional Rigid Tapping Wizard without the need for tapping head attachments
When you order your CNC Masters machine, have it built with the optional rigid tapping encoder. You can take any drill cycle program and replace the top line with a tapping code created by the wizard to tap your series of holes up to 1/2” in diameter.

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23. Use the optional Digital Probe to scan the profile and/or pockets of your fun/hobby type designs to write your tool path program and machine out a duplicate of your original design To “surface” scan an object, you can program the probe along the X or Y plane. The stylus will travel over the part starting on the left side front corner of the object and work its way to the end of the part on the right side. Depending on how the stylus moves, it will record linear and interpolated movements along the X, Y, and Z planes directly on the MX Editor.
To “pocket” scan an object containing a closed pocket such as circles or squares, the scan will start from the top front, work its way inside of the pocket, and scan the entire perimeter of the pocket.
Under the Setup of the MX software you will find the Probe Tab which will allow you to calibrate and program your probe. Your “Probe Step”, “Feed”, and “Data Filter” can also be changed on the fly while the probe is in the middle of scanning your object.

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24. Use work offsets G54-G59 for nesting applications
The work offsets offer you a way to program up to six different machining locations. It’s like having multiple 0.0 locations for different parts. This is very useful especially when using sub-routines/nesting applications.

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25. Create a Rectangular Pocket / Slot with our selection of Wizards to help you build a tool path program
The Cycle Wizards for the mill or lathe makes it easy to create a simple tool path without needing to use a CAD and CAM software.
On this Wizard, the Rectangular Pocket / Slots, can be used to form a deep rectangular pocket into your material or machine a slot duplicating as many passes needed to its total depth.

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26. Create a Circular Pocket Wizard
Input the total diameter, the step down, and total depth and the code will be generated.

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27. Do Thread Milling using a single point cutter Wizard

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28. Cut a gear out using the Cut Gear Wizard with the optional Fourth Axis

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19. Disable the axis motors to manually hand crank each axis into place
Easily de-energize the axis motors by clicking [Disable Motors] to crank each axis by hand, and then press [Reset Control] to re-energize the axis motors.

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30. The MX interface can easily be interchanged from Mill Mode to Lathe Mode
Use this interface for your CNC Masters Lathe. It contains all the same user-friendly features and functions that comes in Mill Mode. Simply go to the Setup page and change the interface.

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31. Use Tool Change Compensation or the optional Auto Tool Changer Turret if your application requires more than one tool in a single program
You can offset the length and angle of each tool and record it under Tools in your Setup. The program will automatically pause the lathe’s movement and spindle allowing you to change out your tool, or allowing the optional ATC Turret to quickly turn to its next tool and continue machining.
On the MX interface, you also have four Tool Position buttons. Select your desired T position, and the auto tool post will quickly turn and lock itself to that position.

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32. Use the Lathe Wizard Threading Cycle to help you program your lathe’s internal or external threads in inches or metric

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33. Use the Lathe Wizard Turning / Boring Cycle to help you program simple turning and boring cycles without having to go through a CAM or writing a long program with multiple passes

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34. Use the Lathe Wizard Peck Drilling Cycle to help you program your drill applications or for face grooving

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35. Facing / Grooving / Part Off Cycle Wizards – with Constant Surface Speed
These cycles can be used with Constant Surface Speed allowing the spindle speed to increase automatically as the diameter of the part decreases giving your application a consistent workpiece finish. With CSS built into the wizard, there is no need to break down the cycle into multiple paths and multiple spindle speed changes.

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36. This is our list of supported G and M codes which can be found under Tools > G Code/ M Code List in the MX
If you plan to use a third-party CAM software to generate your tool path program, use a generic FANUC post processor and edit it to match our list of codes. As an option, we also sell Visual mill/turn CAM software which comes with a guaranteed post processor for our machines to easily generate your tool path programs based on your CAD drawings.

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37. Our pledge to you…

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10. Run each tool path independently to study its movement
1. Run the machine on Trace mode. You can run each tool path independently, one line at a time to study the tool path movement on the machine to verify the position of the application and if any fixture/vise is in the way of the cutter’s path.

2. You can also verify your program by clicking on the Trace and Draw buttons together. This will allow you to view each tool path independently one line at a time in the Draw Window.

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2. Clutter Free Interface
The MX is engineered for the CNC MASTERS machine so you do not have to fiddle with a detailed complicated configuration that can be overwhelming. Just load in the MX and start machining!2. Clutter Free Interface
The MX is engineered for the CNC MASTERS machine so you do not have to fiddle with a detailed complicated configuration that can be overwhelming. Just load in the MX and start machining!

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3. Features Tour and Tutorials Included
The Features Tour will give you a quick run-down on all the features the MX can do for you. The Tutorials are easy to follow even for the first time CNC machinist.
Feel free to download the MX on any of your computers. We recommend downloading the MX along with your CAD and CAM software there at the comfort of your office computer to generate your tool path programs. You don’t need to be hooked up to the machine either to test your program in simulation mode.

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4. Navigate and Edit Your Program through the MX interface with Ease
With a few clicks of the mouse or using touch screen technology, you can easily navigate through the MX interface importing saved programs into the Editor from the File drop down menu. Using standard windows features to edit your program you can then lock the Editor Screen to avoid accidental editing, and if you need to insert a line in the middle of a program, just click on [ReNum] to re-number your tool path list.
You can create a program or import CAM generated G-code tool paths into the Editor
The X Y and Z W arrow jog buttons are displayed from the point of view of the cutter to avoid confusion when the table and saddle are moving. You can also adjust your spindle speed and coolant control while jogging each axis.

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5. Feed Hold – Pause in the Middle of your Program
Feed Hold lets you pause in the middle of a program. From there you can step through your program one line at time while opting to shut the spindle off and then resume your program.
You can also write PAUSE in the middle of your program and jog each axis independently while your program is in pause mode.

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6. Hot Keys
Hot Keys is an alternative method to easily control your machine using your hard or touch screen keyboard. One can press P to pause a program, press S to turn Spindle On, G to run a program, Space Bar to Stop, J to record your individual movements one line at a time to create a program in teach mode.

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7. Pick Menu – for conversational mode programming
Write FANUC style G-codes directly into the Editor or select commands off the [Pick] menu and write your tool path program in conversational mode such as what is written in the Editor box. You can even mix between conversation commands and G-codes in the same program.

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8. Pick Menu List of Options
Use commands such as MOVE, SPINDLE ON/OFF, COOLANT ON/OFF, PAUSE, DELAY, GO HOME…. to write your tool path programs in conversational mode.

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9. Draw the Tool Path to verify it before pressing Go
Hit Draw to view your tool path program drawing, check out its run time, or even simulate the tool path in 3D mode. This can be helpful to quickly verify your program before running it. You can also slow down or speed up the drawing or simulation process.
You can also hit Go within the Draw Window itself to verify the cutter’s position on the machine. The current tool path will be highlighted and simultaneously draw out the next path so you can verify what the cutter will be doing next on the program.

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MX Software – Easy to Use, Easy to Learn – Included with your machine purchase
The MX software is designed to work seamlessly with your CNC Masters machine. It is made to work with Windows PC – desktop, laptop, or an all in one – on standard USB. Use it on Windows 8 or 10 64-bit operating systems.
No internal conversion printer/serial port to USB software or additional conversion hardware is used with the MX.

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11. Counters display in Inches or Millimeters – Continuous Feed
1. When running a program, the counters will display a “real-time” readout while the machine is in CNC operation without counting ahead of the movement.
2. The current tool path is highlighted while the machine is in operation without causing slight interruptions/pauses as the software feeds the tool path to the machine. The MX internally interprets a program ten lines ahead to allow for “continuous machining” avoiding slight interruptions as the machine waits for its next tool path command.
3. “Run Time” tells you how long it takes to run your tool path program.

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12. Use the “Go From Line” command to start in the middle of your program
If you ever need to begin your program from somewhere in the middle of it, use [Go From Line] which you can find under Tools. The Help guide will walk you through how to position the cutter without losing its position on the machine.

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13. Exact Motion Distance without over-stepping on an axis while jogging
Use “Relative ON” to enter a specific coordinate to jog any of your axes to an exact location without having to write a program. It’s like using “power feed” but easier. You can jog an exact distance on any of the axes without needing to keep the key pressed down and mistakenly over-step the movement releasing your finger too slowly off the jog button.
Let’s say you need to drill a hole exactly 0.525” using the Z. So you enter 0.525 in the Z box. Next, adjust the JOG FEED RATE slider for the desired feed rate. Then “click once” on the +Z or -Z button to activate the travel. In this case you click once the -Z button first to drill the hole exactly 0.525”. Then click once on the +Z button to drive the axis back up 0.525”.

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14. Teach Mode – Jog Input
You can create a tool path program by storing each point-to-point movement by simply jogging an axis one at a time. Click on either of the Jog Input buttons to store each movement on the Editor Screen. You can then add Spindle ON, feed commands, and press GO to run the new program as needed. This is a great feature to help you learn to create a program by the movements you make on the machine without necessarily writing out an entire program first.

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15. Override on the fly to adjust the Jog Feed to Rapid or the Spindle Speed during the middle of a program
1. Jog Feed and Rapid with Override: You can adjust feeds using the slider from slow minimum 0.1″ per minute to a rapid of 100″ per minute of travel. You can even micro-step your jog as low as 0.01”/min. The [-][+] buttons allow you to fine tune feeds in 5% increments while the program is in motion.
2. Spindle Speed with Override: You can adjust speeds using the slider from a slow minimum RPM to the max RPM according to the machine setup. The [-][+] buttons allow you to fine tune feeds in 5% increments while the program is in motion.

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16. Adjust Counters using Pre-Set if you cannot begin the program from 0.00
In a situation where you cannot begin your cutter at it’s 0.00 location, you can “Pre-Set” directly into the counters by typing in your beginning coordinate. You can press Go from here to run your program. You can also “zero all” or “zero” your counters independently. With one click of the [Return to 0.0] button, all axes will travel back to its respective 0.0 on the machine.

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17. Set and Save your 0.00 position for future runs
Set and save your 0.00 position on the machine. These coordinates will be recorded as the first line of the program in the Editor Screen. Should you desire to return to this program at a later date, you only have to click on the Set Zero Return button. This will command the machine to automatically jog each axis to its saved “set” 0.00 position according to the recorded coordinates at the first line of the program.

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18. Create a “Home” position to clear your application and run multiple times
Let’s say you need to machine one application times 100 pieces. This usually requires a jig to retain that physical 0.00 position. But in this case, you want the program to end with a clearance of the axes to easily switch out the next piece of stock and start again. With Save Home, you have the ability to save this offset (home) position while still retaining your Set Zero position where the machine will mill your part out. Pressing [Save Home] will record this new position under the Set Zero line in your program.
Pressing [Go Home] will jog your axes back to your “saved home” position where you originally pressed the Save Home command. You can also input GO_HOME from the Pick Menu as its own tool path in your program. At the completion of your program the axes will end at your Home position. Replace your part, then press [Return to 0.0] button to allow the axes to return to its zero position, and press Go to start your next run.

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