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How to choose an Endmill

When choosing an endmill for a particular milling operation, there are many possibilities as to which tool is best for the job. Tool material (the actual substance the tool is born from), the specific characteristics of the tool, and whether or not you want a coating on that tool all play an integral role and can have a significant effect on whether these things add value or significant cost to your milling application.

Tool Material

High Speed Steel (HS): HSS is a baseline tool steel used for many basic machining applications and for short runs on older milling machines. However, it does not offer the speed and feed advantages of HSS-Cobalt and Carbide tools.

Cobalt: With a typical cobalt content of 8 percent, this tool is usually priced a bit higher than standard HSS. It allows for increased speeds and feeds because of greater hardness, though it still falls far short of the speed, feed, and durability advantages of carbide.

Carbide: Carbide tools can be run at speeds 2 to 2 ½ times faster than HSS tools and HSS-Cobalt and thereby provide the opportunity for substantially improving production output. If you are using or considering a carbide tool then keep in mind several things.

  • Ensure that your machine tool is rigid with a solid spindle and that holders have little or no runout. Due to the brittle nature of carbide and the speeds at which carbide tools are typically run, rigidity is critical to prevent tool breakage.
  • The initial cost of carbide tooling over HSS products is easily offset by savings in production costs due to increased output and fewer tool changes.
  • Carbide is more sensitive to chipping than HSS, so handle with extreme care.

Tool Characteristics

The endmill’s basic design can be altered in many ways to tailor the tool for a specific application. Here are some basic characteristic considerations:

Length

Select an endmill that is as short as possible to minimize tool deflection during the milling operation. Select stub lengths, if possible, to save on tool cost.

  • Stub Length – Used for milling of shallow slots in all types of materials where heavy feeds are required and tool deflection is minimized.
  • Regular Length – Used
  • Long Length – Used
Number of Flutes

More flutes reduce chip load and improves surface finish if feed rate remains the same. The most common flute numbers for general milling operations are two (maximum space for chip ejection) and four (better surface finish).

2-Flute 3-Flute 4-Flute
  • 2-Flute – Allows maximum space for chip ejection. Used for general milling operations and on softer metals.
  • 3-Flute – Excellent for slotting. Used for general milling operations. Also good for a cross between higher chip removal and finish.
  • 4-Flute – Use for better rigidity and finish on ferrous metals.
  • 6 & 8 Flute – These larger number of flutes reduces chip load and can improve surface finish. As such these tools are excellent for putting the final finish on the application, and removing any rough spots from previous milling.

Certain materials respond better to various flute configurations. Below is a chart to help you decided what number of flutes is best for the material you are milling.

Materials 2FL 4FL 3FL 6FL Straight
Aluminum
Brass, Bronze
Fiberglass
Iron
Plastics
Steel nickle, chrome
Steel, Carbon
Steel, 39-48Rc
Steel, 46-86Rc
Steel Stainless
Steel Weldments
Titanium
Zinc
Rake Angle

Endmills typically have a 10-12 degree positive rake angle. This allows for efficient cutting performances of soft, gummy materials as well as high tensile strength materials. Depending on the material to be machined, it is possible to change the rake angles. Used in conjunction with variation of rake, clearance angles can be altered to provide added support and strength directly behind the cutting edge.

Helix Angle

The standard helix angle of an endmill is usually 30°. Higher helix angles provide better chip ejection and are useful in machining materials such as aluminum at a much faster rate.

End Types
The most common endmill end types are Square End, Ball End, Corner Radius
Square Ball End Corner Radius
  • Ball End: The tip of the tool is rounded or in the shape of a half-ball. These endmills are used to mill die cavities and fillets, round bottom holes and slots.
  • Center Cutting and Non Center Cutting: Center cutting square endmills are essential for plunge milling. Use non-center cutting mills only for side milling.
  • Corner Radius: Since the sharp corner of the endmill is its weakest point, a ground radius on the cutting tips is useful to prevent chipping of the tool tips. These corner radius tools remove more material faster than the traditional ball nose endmills, but consideration must be given to the shape of the cut. Best use is for mold applications because the ball end can remove more material faster than ball ends.
  • Corner Rounding endmills provide a uniform finish on corners. They have a ground radius with relieved clearance.
  • Single End – Teeth on one end of the cutter only. This style is the most common available.
  • Double End – An end mill that has teeth on both ends of the cutter. Endmill holders must have sufficient clearance to allow for the use of a double end cutter.
  • High Helix – An endmill with a helix angle greater than 30°
  • Drill Point endmills are multipurpose cutting tools. Use them for drilling, slotting, chamfering, and profile milling.
  • Chamfer Mills can eliminate hand deburring operations and provide uniform material finish.
  • Roughers, or “hoggers”, are useful for rapid removing of large amounts of material. The chip grove design allows more cutting fluid to the cutting edges and dissipates heat better. There is a wide range of variations in rougher profile forms for different material groups. The coarser the pitch of the roughing edge, the more material removed and the less smooth the finish. In addition, most roughers have eccentric relief so regrinding can be done by grinding only the cutting face. This saves you if you have access to regrinding equipment.
  • Left-Hand Spiral – Used for milling multiple layers of thin sheets where chip flow is directed away from work.
Tool Coatings

Tool Coatings can enhance the performance and life of carbide endmills. Base your coating selection on the material you are machining. Keep in mind, however, that the surface hardness increases with coatings. If the substrate material has poor surface finish, the coating follows the same contour. Visit the Tool Coatings page for more detailed information on coatings.

PowerA – AlTiN Coating
PowerT – TiN Coating
PowerN – nACo Coating