End Mills  
 

DESIGN CRITERIA

techdata

A - mill size or cutting diameter
B - shank diameter
C - length of cut or flute length
D - overall length
  • Angular Edge - That cutting edge that is a straight line, forming an angle with the cutter axis. The surface produced by a cutting edge of this type will not be flat as is the case with a helical cutting edge.

  • Axial Runout - The difference between the highest and lowest indicator reading taken at the face of a cutter near the outer diameter.

  • Chamfer - A short relieved flat installed where the periphery and face of a cutter meet. Used to strengthen the otherwise weak corner.

  • Chip Breakers - Special geometry of the rake face that causes the chip to curl tightly and break.

  • Chip Splitters - Notches in the circumference of a Corn cob style End mill cutter resulting in narrow chips. Suitable for rough machining.

  • Core Diameter - The diameter of a cylinder ( or cone shape with tapered End mills) tangent to the flutes at the deepest point.

  • Counterbore - A recess in a non-end cutting tool to facilitate grinding.

  • Cutter Sweep (Runout) - Material removed by the fluting cutter (or grinding wheel) at the end of the flute.

  • Cutting Edge (A) - The leading edge of the cutter tooth. The intersection of two finely finished surfaces, generally of an included angle of less than 90 degrees.

  • Cutting Edge Angle - The angle formed by the cutting edge and the tool axis.

  • Differential pitch cutters - A specifically designed variation in the radial spacing of the cutter teeth. This provides a variation in tooth spacing and can be beneficial in reducing chatter. This concept is based on reducing the harmonic effect of the tool contacting the part in an exact moment of vibration.

  • Entrance Angle - The angle formed by a line through the center of the cutter at 90 to the direction of feed and a radial line through the initial point of contact. As this angle approaches 90 degrees the shock loading is increased.

  • Entrance Angle: Ramp-in - Angle or radius value to enter the cutter into the part surface

  • Fillet - The radius at the bottom of the flute, from which core diameter is found.

  • Flute - Space between cutting teeth providing chip space and regrinding capabilities. The number of cutting edges. Sometimes referred to as "teeth" or "gullet". The number on an end mill will determine the feed rate.

flutes

  • Flute Length - Length of flutes or grooves. Often used incorrectly to denote cutting length.

  • Shank - Projecting portion of cutter which locates and drives the cutter from the machine spindle or adapter

  • Straight Shank - Cylindrical shank, with or without driving flats or notches, often seen on carbide end mills

  • Weldon Shank - Industry name for a specific type of shank with a drive and location flat. The flat on the cutter provides positive ( non slip ) driving surface to the End mill.

  • Tooth - The cutting edge of the End mill.

  • Tooth Face - Also known as the Rake Face. The portion of the tooth upon which the tooth meets the part.

 

END MILL TECHNICAL FEATURES

  • Back taper - A slight taper resulting in the shank end of the cutting diameter being smaller than the cutting end. This condition aids not only the plunging or drilling condition but also tends to compensate for deflection.

  • Clearance - Space created by the removal of additional tool material from behind the relief angle.

flutes

  • Clearance Angle - The angle formed by the cleared surface and line tangent to the cutting edge.

    • Clearance: Primary (1st angle, 5-9) - Relief adjacent to the cutting edge.

    • Clearance: Secondary (2nd angle, 14-17) - Relief adjacent to cutting edge

    • Clearance: Tertiary (3rd) - Additional relief clearance provided adjacent to the secondary angle.

  • Concave - Small hollow required on the end face of an End mill. This feature is produced by a Dish angle produced on the cutter.

  • Convex - An outward projection radius feature on the end face of a Ball mill.

  • Dish Angle - The angle formed by the end cutting edge and a plane perpendicular to the cutter axis. Dish ensures that a flat surface is produced by the cutter.

flutes

  • Gash (Notch) - The secondary cuts on a tool to provide chip space at corners and ends. The space forming the end cutting edge, which is used when feeding axially.

  • Gash angle - The relief angle of the gash feature.

  • Gash width - The width of the gash feature. The space between cutting edges, which provides chip space and resharpening capabilities. Sometimes called the flute.

  • Heel - The back edge of the relieved land. It is the surface of the tooth trailing the cutting edge.

  • Helical - A cutting edge or flute which progresses uniformly around a cylindrical surface in an axial direction. The normal helical direction is a right direction spiral.

  • Helix Angle - The angle formed by a line tangent to the helix and a plane through the axis of the cutter or the cutting edge angle which a helical cutting edge makes with a plane containing the axis of a cylindrical cutter.

  • Hook - A term used to refer to a concave condition of a tooth face. This term implies a curved surface rather than a straight surface. Hook must be measured at the cutting edge, making measurement difficult.

  • Land - The narrow surface of a profile sharpened cutter tooth immediately behind the cutting edge,

    • (A) Cylindrical - a narrow portion of the peripheral land, adjacent to the cutting edge, having no radial relief.

    • (B) Relieved - A portion of the land adjacent to the cutting edge, which provides relief.

  • Lead - The axial advance of a helical cutting edge in one revolution.

                        Lead = (Cutter diameter x Pi) / Tangent Helix Angle

  • Length of Cut (Flute Length) - The effective axial length of the peripheral cutting edge which has been relieved to cut. 

  • Radial Rake angle - The angle made by the rake face and a radius measured in a plane normal to the axis.

flutes

  • Rake - The angular relationship between the tooth face or a tangent to the tooth face at a given point and a reference plane or line. An angular feature ground onto the surface of an end mill.

    • Axial rake - The angle formed by a plane passing through the axis and a line coinciding with or tangent to the tooth face.

    • Effective rake - The rake angle influencing chip formation most is that measured normal to the cutting edge. The effective rake angle is greatly affected by the radial and axial rakes only when corner angles are involved.

    • Helical rake - For most purposes the terms helical and axial rake can be used interchangeably. It is the inclination of the tooth face with reference to a plane through the cutter axis.

    • Negative Rake - Exists when the initial contact between tool and workpiece occurs at a point or line on the tooth other than the cutting edge. The rake surface leads the cutting edge.

    • Positive Rake - Exists when the initial contact between the cutter and the workpiece occurs at the cutting edge. The cutting edge leads the rake surface.

flutes

  • Relief-Space - Provided by removing material immediately behind the cutting edge. Done to eliminate the possibility of heeling or rubbing.

    • Axial angle relief - The angle made by a line tangent to the relieved surface at the end cutting edge and a plane normal to the axis.

    • Axial relief - The relief measured in the axial direction between a plane perpendicular to the axis at the cutting edge and the relieved surface. Helps to prevent rubbing as the corner wears.

    • Concave relief - The relieved surface behind the cutting edge having a concave form. Produced by a grinding wheel set at 90 degrees to the cutter axis.

    • Eccentric relief - The relieved surface behind the cutting edge having a convex form. Produced by a type I wheel presented at an angle to the cutter axis.

    • End relief - Relief on the end of an end mill. Needed only for plunging cutters and to relieve rubbing as the result of corner wear.

    • Flat relief - The relieved surface behind the cutting edge having a flat surface produced by the face of a cup wheel.

    • Radial relief - Relief in a radial direction measured in the plane of rotation. It can be measured by the amount of indicator drop at a given radius in a given amount of angular rotation.

  • Tangential rake angle - The angle made by a line tangent to a hooked tooth at the cutting edge and a radius passing through the same point in plane normal to the axis.

 

 

 

 

End Mills

 

The most frequently used tool on a vertical milling machine is the end mill. End mills are made in either a right-hand or a left-hand cut. Identification is made by viewing the cutter from the cutting end. A right-hand cutter rotates counterclockwise. The helix of the flutes can also be left or right hand; a right-hand helix flute angles downward to the right when viewed from the side. An illustration of the cutting end of a four flute end mill, which is an example of a right-hand cut, right-hand helix end mill is shown below.

The end teeth of an end mill can vary, depending on the cutting to be performed. Two flute end mills are center cutting, which means they can make their own starting hole. This is called plunge cutting. Four flute end mills may have either center cutting teeth or a gashed or center drilled end. End mills with center drilled or gashed ends cannot be used to plunge cut their own starting holes. These end mills only cut with the teeth on their periphery. End mills can be single end or double end (see table). Double end type end mills are usually more economical because of the savings in tool material in their production.

 

  

 

 

 

End mills are manufactured with two, three, four, or more flutes and with straight flutes, slow, regular, and fast helix angles. A slow helix is approximately 12 degrees, a regular helix is 30 degrees, and the fast helix is 40 degrees or more when measured from the cutter axis. Most general purpose cutting is done with a regular helix angle cutter.

Aluminum is efficiently machined with a fast helix end mill and highly polished cutting faces to minimize chip adherence.

If large amounts of material need to be removed, a roughing end mill should be used.  Ball-end end mills have two or more flutes and form an inside radius or fillet between surfaces. Ball-end end mills are used in tracer milling and in die sinking operations. Round bottom grooves can also be machined with them.

 

Various End Mills

Standard Endmill

Ball Nose Endmill

Standard Long   (Length of flute almost

                                         double over standard)

Ball Nose Long  (Length of flute almost

                                         double over standard)

Stub Double-End Square

Stub Double-End Ball

Aluminum-Cutting

Rougher/Finisher

60 Degree Helix

 

 

 

 

 

 

 

Micro End Mills

Standard Decimal Micro Endmill

Ball Nose Decimal Micro Endmill

Standard Long Reach Micro Endmill

Ball Nose Long Reach Micro Endmill

 

Accu-Hold End Mill Extension Holders

 

 

 

 

 

 

Burrs

Aluminum-Cutting

Angle Burs

Cylindrical

Egg/Tree-Shaped

Long Shank

Pointed-Cone

Tapered

Solid Carbide

1/4" Burs

 

 Types and Characteristics of End Mills

 

Flutes - Spiral cutting edge on the end mill. 2 and 4 flute end mills are the most commonly used.

           2-Flute - Allows maximum space for chip ejection. Used for general              milling operations.

           3-Flute - Excellent for slotting. Used for general milling operations.

           4, 5, 6, and 8 Flute - A greater number of flutes reduces chip load             and can improve surface finish, if feed rate remains the same.

 

Ball End - Used to mill die cavities and fillets, round bottom holes and slots.

 

Carbide - This tool material combines increased stiffness with the ability to operate at higher SFPM. Carbide tools are best suited for shops operating newer milling machines or machines with minimal spindle wear. Rigidity is critical when using carbide tools. Carbide end mills may require a premium price over the cobalt end mills, but they can also be run at speeds 2 1/2 faster than HSS end mills. For best results mount in a hydraulic type holder.

 

Coatings - The use of Titanium coated tools will increase the surface hardness of the tool to near 85 Rc. This will allow for greater tool life at increased cutting speeds & feeds (15 - 25%). Titanium Nitride (TiN), Aluminum Titanium Nitride (AlTiN), and Titanium Carbonitride (TiCN).

 

Cobalt - Type of high speed steel tool which has a 8% cobalt content (M42). This material has excellent abrasion resistance for improved tool life over standard high speed steel (M7).

 

Corner Radius - Conventional end mill with radius ground on the tips of the flutes to help reduce chipping on the tip. For mold applications, radius tools can remove more material faster than ball ends.

 

Corner Rounders - Cutters having form ground radius with relieved clearance.

 

Double End - An end mill that has teeth on both ends of the cutter. End mill holders must have sufficient clearance to allow for the use of a double end cutter.

 

Drill Point - Multipurpose tool which can be used for drilling, milling, or chamfering.

 

High Helix - Usually a 40 to 60 degree spiral on the tool's flutes. Effective for rapid chip ejection in milling of aluminum and other materials.

 

HSS - A baseline tool steel. In the past, a majority of end mills were made from standard High Speed Steel (M7). Usually inexpensive, but do not offer the tool life or speed and feed advantages of Cobalt and Carbide end mills.

 

Left-Hand Spiral - Used for milling multiple layers of thin sheets where chip flow is directed away from work.

 

Rougher (Hoggers) - End mill with interrupted shape on outside diameter to remove large amounts of material quickly. Typically can remove material up to three times the rate of conventional end mills with different types available to achieve the desired finish on the material. Melin offers roughers in Coarse Pitch, Fine Pitch, Rougher/Finisher, and 3-Flute for Aluminum styles.

 

Single End - Teeth on one end of the cutter only. This style is the most common available.

 

Stub Length - Used for milling of shallow slots in all types of materials where heavy feeds are required and tool deflection is minimized.