CNC Knee Mill Guide – Knee Type Milling Machine Info

CNC Knee Mill Guide – Knee Type Milling Machine Info


CNC Milling is the precision process of machining three dimensional objects through Computer Numerical Control. This process controls the work piece and cutter bit movements to less than 0.001 inches, or 0.025 millimeters. This article will give a brief description of CNC Milling, explain the basic knee type milling machine designs, and discuss the process of retrofitting older machines.

CNC Milling

Typically, a CNC milling machine will have four axis. The table moves forward and back (y-axis), side to side (x-axis), and up and down (z-axis). The fourth axis is the milling head or bit, which moves vertically on another z-axis.

Larger knee type milling machines may include a fifth axis upon which the milling head may pivot horizontally, and a sixth axis that allows horizontal pivoting perpendicular to the fifth axis.

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Variations on the CNC milling machine or the CNC engraving machine are represented within their names. These variation range from size, design, and overall intention of use. A CNC Knee Milling Machine, or knee-and-column mill, refers to any milling machine whose x-y table rides up and down the column on a vertically adjustable knee.


CNC Knee Mills are generally separated into two categories based on the orientation of their main spindle; whether they are vertical or horizontal.

Vertical mills orient the main spindle vertically, and are further designated as turret mills or bed mills. Turret mills have a stationary spindle, though the milling head may move up and down. The table on a turret mill can move forward and back, as well as up and down. The difference of the bed mill is that the table only moves forward and back, and the spindle itself moves up and down.

Horizontal mills place the cutter on a horizontal arbor which extends over the table. Many of these types of mills will include a universal table, or rotary table which enables milling or cnc engraving at multiple angles. While the turret mill has the advantage of more axis between spindle and table, the horizontal mill can be outfitted with different cutters and even multiple arbors.


Retrofitting is the process of converting older manual milling machines into Computer Numerical Control units. Many of the older mills are favored for their heavy design and quality construction, providing better stability and over all durability. The controls on these older machines are dated, but they can be retrofitted with modern controls to add precision and quality to old durability and design. Retrofitting can save a lot of time and money by breathing new life into old machines.


Milling machines and engraving machines have come a long way in their design, use, and precision. They range in size from small workbench mills to full room sized machines. Horizontal designs evolved to include vertical mills, and as their abilities increased, so did the precision of their controls. Originally manually operated, they soon became mechanically automated. Now, CNC (Computer Numerical Control) Milling Machines are holding the stage.