January 5, 2022

What is a knee mill

Milling machines are essential tools in industries that rely on precise metal shaping. They use spinning cutting tools to shape workpieces precisely. Now, knee mills are the rebels of the milling world. Unlike regular mills, they can move along the y-axis to machine workpieces of different sizes. Their versatility and unique capabilities make knee mills a topic worth exploring. So let us dive into the fascinating world of knee mills and discover their secrets!

What is a knee mill?

A knee mill is a vertical milling machine that moves along the y-axis. This is a direction in which the workpiece can move toward the milling tool shaping it. The table is not stationary like conventional milling machines that can only move along the two horizontal axes. The head drills and performs boring movements along the y-axis.

The head does not consist of the fixed top slide and spindle. What distinguishes the knee mill from other milling machines is its head, which can also move along an X axis. Due to their movement capabilities, they accept different sizes of workpieces.

Unlike a wood or metal lathe, where the workpiece rotates at high speed and through a stationary tool, milling machines operate like a shaping machine. The workpiece is held and clamped on the table while the milling tools rotate at high speeds.

This is how the machine makes precise cuts. The difference between milling machines lies in the position of the workpiece. A knee mill performs a variety of cutting and shaping procedures. Some of these processes include face grinding, cutting, and slotting. They achieve these capabilities through the use of milling tools. This is similar to drill bits. These tools come in different shapes and sizes, for different sized shapes.

The advantage of the knee mill is in machining larger objects. Sometimes the torque of the moving spindle is not enough to drill vertical holes. This operation is called drilling. Knee milling machines have fixed spindles, and all y-axis movements are made by the table on which the workpiece is located.

Rickwashburn1, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

This significantly increases the torque and allows drilling holes in harder material. The knee mill has a vertical table movement that can accommodate larger objects. This is the result of greater height capacity.

What is a knee milling machine?

A knee milling machine is a type of vertical mill. It has a horizontal X axis that also moves along the vertical Y axis. The work table is not fixed but moves along the machining axis. The spindle head of the knee milling machine performs all cutting operations on the Y axis. A knee milling machine is a flexible tool for various machining operations and workpiece types. It has a vertically adjustable work table that rests on a knee-supported saddle.

Tosaka, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons

The knee is a supportive and massive casting of the machine. The knee ensures the stability of a knee milling machine by riding vertically on the column. It also secures the column rigidly and firmly in a fixed position. That makes the milling head and spindle vertically fixed during operations.

Modern vertical knee machines have the spindle installed vertically. Sometimes it is parallel to the column face. The design is for the head to have the ability to swivel on angular surfaces. The turret and swivel head assembly gives cuts a higher precision and mobility.
For angular cuts, the setting of the head allows better precision when done on the horizontal plane. The versatility and stability of knee milling machines have made them one of the most popular manufacturing machines.

The knee milling machine is one of the most widely used machine tools in machine shops due to the unenclosed nature of the knee machine. It allows for quick setups for simple jobs. It is easy to operate. Put a workpiece into the mill, drill a few holes or tap something. Also, the tilt-able head, movable ram, and turret make it versatile.

Why is it called a knee mill?

The name comes from the way the machine works. Its design of the knee mill dates to 1936 when Rudolph Bannow’s company produced a knee-and-column vertical mill with a rotating turret and sliding-ram head.

Types of knee mills

Horizontal Milling Machine

Horizontal milling machines are also known as plain milling machines. These are more robust than hand millers and have horizontal spindles, also called horizontal milling machines.

You can feed the table in vertical, cross, or horizontal directions. The feed includes vertical, cross, and longitudinal. Feeding the table vertically, you are adjusting the table vertically. Cross feeding moves the table parallel to the spindle and longitudinal rotates the table.

Vertical Milling Machine

When using the vertical milling machine, the position of the spindle is perpendicular or vertical to the table. You can use this machine for slots, machining grooves, and flat surfaces. The spindle head is fixed to a vertical column, which rotates at an angle.
The milling cutter is fixed on the spindle to work with angular surfaces. Some vertical milling machines allow you to adjust the spindle up and down.

What Is a Vertical Knee Mill

A vertical knee mill is a versatile machine tool that allows an operator to perform various tasks such as facing, slotting keyways, drilling, or boring. A vertical milling machine is the most used knee mill due to the oriented cutting head or spindle. The spindle holds a rotating cutting tool against the workpiece and moves vertically along the Y-axis.

Vertical mills are ideal for projects on a single side, such as sectioning or finishing operations like end millwork. Vertical mills are into two vertical milling machine types: bed and turret milling machines. Each mill functions differently from the other and offers unique advantages.

Features of a knee mill

Column and Base

The column has a base, and the casting supports all other milling machine parts. The column features an oil reservoir and a pump that lubricates the spindle. It rests on the base, and the knee base has a coolant reservoir and a pump. These are required to cool off the milling machine during teaching operations.


The knee is a casting that supports the saddle and table. All gearing mechanisms are within the knee. It is secured to the column by dovetail ways, supported, and adjusted by a vertical positioning screw. That is the elevating screw. It adjusts the knee up and down, raising or lowering the lever. Use the help of a hand or power feed.


It is a rectangular casting that comes on the top of the saddle. It holds the work or work holding devices. The table comes with multiple T-slots holding the work and work holding devices. You are allowed to control the table by hand or by power. To move the table by hand, engage and turn the longitudinal hand crank. To move it through power, engage the longitudinal direction feed control lever.


It is the shaft used to hold and drive the cutting tools of the milling machine and mount the spindle on the bearings supported by the column. Move the gear trains by the electric motor. The gear trains are inside the column.
The face of the spindle lies near the table and comes with an internal taper machined on it. The internal taper at the front of the spindle allows only a tapered cutter holder. It has two keys at the front face that gives a positive drive for the cutter holder.

Advantages of Knee Mills

Machining of larger objects: Kink milling machines are ideal for machining larger workpieces, thanks to vertical table movement. This greater height capacity allows the machining of objects of different sizes.

Higher torque when drilling: When it comes to drilling vertical holes, knee mills shine. Their stationary spindles and y-axis movement through the table provide significantly higher torque, making it easier to drill into harder materials.

Vertical table movement: The ability to move the table vertically is a distinguishing feature of knee milling machines. This feature increases flexibility and allows machining workpieces of different sizes and shapes, resulting in greater versatility.

Knee Mill vs Horizontal Mill vs Vertical Mill Comparison Table

Milling Machine TypeKnee MillsHorizontal MillsVertical Mills
Features– Vertical table movement
– Stationary spindle
– Y-axis movement through the table
– Versatile and adjustable worktable
– Turret and swivel head assembly for precision and mobility
– Unenclosed nature for quick setups
– Tilt-able head and movable ram
– Horizontal spindle
– Can feed the table in vertical, cross, and longitudinal directions
– Sturdy and robust design
– Suitable for heavy-duty applications
– Excellent for machining large, flat surfaces
– Vertical spindle
– Perpendicular spindle position to the table
– Ideal for slotting, grooving, and machining angular surfaces
– Adjustable spindle up and down
– Offers oriented cutting head or spindle
– Suitable for sectioning and end millwork
Capabilities– Machining larger objects
– Increased torque for drilling vertical holes
– Wide range of cutting and forming processes
– Accommodates different workpiece sizes and shapes
– Excellent for heavy-duty cutting
– Machining large, flat surfaces
– Suitable for horizontal slotting and grooving
– Capable of angular cutting
– Ideal for slotting, grooving, and angular cutting
– Versatile for various milling operations
– Suitable for sectioning and finishing operations
– Offers oriented cutting head or spindle
Ideal Applications– General machining tasks
– Drilling vertical holes in harder materials
– Surfacing, cutting, and slot machining
– Handling different-sized workpieces
– Heavy-duty cutting operations
– Machining large, flat surfaces
– Horizontal slotting and grooving
– Slotting, grooving, and angular cutting operations
– Sectioning and finishing operations
– End millwork
– Projects focused on a single side

Applications of Knee Mills

Knee mills are the multitasking wizards in the machining world, capable of a wide range of cutting and forming processes. They perform tasks such as face milling, cutting, slotting, and more precisely and easily.

However, knee milling cutters’ versatility in workpiece sizes and shapes makes them special. Whether it’s a small, intricate part or a large, complex workpiece, knee mills can handle them all. They adapt to different sizes and shapes like a chameleon, making them the ideal choice for various machining projects.

Whether you need to shape a delicate component or machine a massive workpiece, knee mills have got you covered with their impressive capabilities and adaptability. They’re the true all-rounders in the world of machining!


In summary, knee mills are the dynamic and versatile powerhouses of the machining industry. Their ability to machine larger objects, deliver higher torque for drilling vertical holes, and provide vertical table movement sets them apart from other milling machines.

With their wide range of cutting and shaping processes, knee mills can precisely perform various machining tasks. Their adaptability to different workpiece sizes and shapes makes them a valuable tool for manufacturers in various industries.

Consider the mighty knee mill if you’re looking for a machine that can handle various manufacturing tasks. It’s a reliable companion that can easily handle complicated components and large projects. Take advantage of the power of knee mills and open up new possibilities for your manufacturing projects.

David D. Hughes

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