Posted March 2, 2021

What Tools Are Needed for CNC Machining?

 Different types of CNC machining tools

Computer numeric control (CNC) machining, a subtractive manufacturing process, sequentially removes material from a raw block to achieve the desired geometric specifications. The machine tools are an integral part of the subtractive manufacturing process, removing material through milling, grinding, or drilling techniques. Machine shops use milling and lathe tools for precision CNC machining applications to achieve specified accuracy, tolerances, and finishes.

CNC Machining Tools

A CNC machine provides the advantage of accomodating a wide range of cutting tools for fabricating materials of different shapes and sizes. Cutting tools can rotate, cut, and remove the material from the workpiece using shear deformation. Each tool has its unique properties and benefits. Understanding the basics of CNC machining tools helps design engineers design better parts. Most cutting tools feature flutes, which refers to the tool’s cutting edges. Cutting edges have helical grooves along the exterior length of the tool. The tiny piece of metal chipped away during the machining process travels along with the flutes as they eject. Different cutting tools have varying numbers of flutes. Machinists select the tool with the desired number of flutes depending upon the workpiece’s material and surface finish desired. 

From drill bits and end mills to reamers, tool selection for CNC machining is vital to get the desired fabrication and finishing. 

End Mills

Different types of end mills

Industries widely use end mills for their vertical CNC machining applications. Vertical machining applications create details along the workpiece’s surface, such as rounded contours around the edges or cutting a keyway in a shaft. 

End mills have one or more sharp flutes for various cutting and removing large amounts of materials quickly. There are different types of end mills depending upon their anatomy and function.  These include:

  • Flat end mills are flat-faced tools for cutting 2D features on the workpiece.
  • Ball nose end mills are tools with a round cutting end, suitable for milling 3D contour surfaces.
  • Bullnose end mills have a flat bottom and rounded corners, suitable for cutting rounded edges.
  • Roughing end mills have a serrated tooth design, suitable for removing a large amount of material quickly while leaving a rough finish.

Drill bits

Drill bits

Drill bits are the most common CNC machining tools and not unlike the drill bits found at a local hardware store. They consist of a shaft with one or more flutes and a conical cutting edge for rapidly drilling holes in the workpiece. Operators fit different types of drill bits with CNC machines for various cutting operations.

  • Twist drill bits: For drilling holes on materials, most suitably on metals, woods, and plastics. 
  • Center drill bits:  Suitable for precisely centering and drilling the holes 
  • Ejector drill bits:  Tool for drilling deep holes, with preferable diameters range of ¾ inches to 4 inches.

Thread Mills and Taps

Thread mills

As the name suggests, thread mills are tools for cutting internal or external threads in a material. Taps serve a similar purpose, but they only cut internal threads. Thread mills produce threads of at least ⅛” (3.175 mm) up to the thread holes about three diameters deep. Taps, alternatively, can reach up to 20 diameters deep. Threading with a large diameter tool can cause the CNC machine to show poor results at ½” (12.7 mm) or higher tap diameter.   



Reamers are rotary cutting tools used in metalworking applications to drill small or deep holes and widen or expand the size of existing holes using an angled bevel process. Precision reamers enlarge holes with high accuracy, smoothing the edges, while non-precision reamers perform basic enlargement and remove burrs. They classify based on the arrangement of cutting edges into single or multi-blade reamers. Single-blade reamers offer high accuracy and size consistency for precision but can be expensive. Standard multi-blade reamers have multiple carbide edges and circular land, which performs a burnishing action. Machinists prefer reamers for dimensional accuracy and tight tolerance as compared to other cutting tools.

Hollow Mills

Hollow mills are pipe-shaped cutting tools with three or more cutting edges on the inner face. It closely resembles an inverted end mill, and machinists use it for applications such as preparing workpieces and threading applications. Hollow mills can perform multiple operations such as facing, centering or chamfering in a single pass. It can have anywhere between three to eight cutting edges, which facilitate a relatively faster feed rate. In this operation, a workpiece is fed into a hollow mill to produce a cylindrical part.

Gear Cutters

Gear cutters are specialty cutting tools used to make metal gears for manufacturing industries. Hobbing machines sometimes replace milling machines to cut gears. With gear cutters, machines can fabricate several gear types:

Spur gear

  • Cylindrical gears with a tooth line parallel to the shaft.
  • No loads in an axial direction.
  • Preferred for high accuracy and easy production.

Single and double-helical gear

  • Winding tooth line parallel to the shaft.
  • Preferred for high-speed applications.
  • Creates force in an axial direction; thus, the use of thrust bearing is required.

Bevel gear

  • Cone-shaped gears transmit the force between two shafts at the point of intersection.

Worm gear

  • Constitute of a hard metal worm and soft metal work wheel with self-locking ability.
  • Used for applications requiring speed reductions.
  • The reduction rate is dependent on the number of teeth on the worm and wheel.

Screw gear

  • Similar to helical gears with the tooth angle of 45°.
  • Low load-carrying capacity.

Fly Cutters

Fly cutters are single-point cutting tools primarily utilized for their ability to machine large flat surface areas. The cutting process with fly cutters is not as fast as a face mill, but it provides a uniform and smooth finish. A standard fly cutter can adjust to cut up to a 2” (51 mm) diameter and for aluminum and can make .0010” (0.25mm) deep cuts.

Face Mills

Before applying other milling tools, a machine must flatten a workpiece to meet design specifications. Face milling facilitates the preparation of a flat surface on the workpiece with a wide array of tools. The face mill tool consists of a solid body and multiple interchangeable cutter inserts. The interchangeability of cutter inserts allows variation in cutting profiles without having to change the entire tool. Variously angled cutters produce different outputs:

  • 10°- 65° cutters are the typical range of tools face milling applications. Manufacturers mostly use a 45° cutter for its reduced vibration and thin chipping.
  • 90° cutters form a right-angle. This cutter is suitable for thin-walled and weak fixtured components.

Large radius or round insert cutters, square shoulder cutters, and side and face mill cutters fit operations ranging from demanding complex face milling to simple profiling. 

Slab Mills

Slab mills, also known as plain mills or slab cutters, cut broad flat surfaces. In this process, the milling cutter axis is parallel to the part’s surface. Slab mills only have teeth on their periphery, and either wide or narrow cutters can make deep or wide cuts. Wide cuts correspond to larger surfaces. Slab mills are more popular for manual milling than with modern machines. However, universal milling machines can also accommodate it for machining large, broad surfaces. 

Deciding What Tools are Needed for Your CNC Machining Application

Machine shops leverage advanced software to select the right tool to go with a CNC machine for fabricating the final product with the desired specification. A typical machine shop has an extensive tool library on hand, with the option to order specialized tools when needed. Every fabricated part has unique geometry that a shop analyzes manually or with proprietary software for the optimal tool selection. Plethora’s online quote system facilitates selecting optimal machining tools for your fabrication process and provides a price quote in seconds. The online part ordering system runs through their extensive tool library and multiple manufacturing scenarios before concluding what tools they’ll use for machining your part. 

Plethora is an ISO 9001-certified machine shop specializing in precision parts using various CNC machining tools and techniques. Give us a call today at 415-726-2256 to learn more about what tools are needed for CNC machining. You can upload your design files to Quote My Part and get started on your project today.

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The Plethora Team

The Plethora team is your go-to CNC manufacturer for hardware done right the first time. We have the tools and experience needed to create high quality custom parts quickly and with precision, whether you need a prototype or production run.

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