Now we will study in detail the various cutters according to shapes (Various types of milling cutters are shown in Fig. 16.36 to 16.48).
Type # 1. Plain Milling Cutter:
It has straight or helical teeth cut on the periphery of a disc or a cylindrical surface. It may be of solid inserted blade or tipped type, and is usually profile sharpened but may be form relieved also. Generally helical teeth are used if the width of the cutter exceeds 15 mm.
The plain milling cutter is generally used for milling flat surfaces parallel to cutter axis. Helical teeth cutter is used where large stock removal is required. Helical angle permits several teeth to cut simultaneously which results in smoother cutting action.
Heavy duty plain cutters have fewer teeth and helix angle of 35-45°. These are sometimes nicked on their periphery on a helical pattern for chip breaking and smooth operation.
Type # 2. Side Milling Cutter:
This cutter is similar to plain cutter except that it has teeth on the side. However, the side milling cutter may have teeth on the periphery and on one or both sides of the tool. These cutters may have straight, spiral or staggered teeth. Further these may be solid, inserted blade or tipped construction, and may be profile sharpened or form relieved.
Half side milling cutters have teeth only on one side in addition to circumferential teeth. These cutters are usually used in pair for milling both ends of work to a given dimension.
Type # 3. End Mill Cutters:
These cutters have an integral shaft for driving and have teeth on both periphery and ends. These are the cutters with teeth on the periphery and end integral with a shank for holding and driving (Refer Fig. 16.41). These are used to mill flat, horizontal, vertical, bevel, chamfer and slant surfaces, grooves and keyways, and to cut slot and in recess work such as die making etc.
The flutes on the cutter may be either straight or helical. End mills with high helix are used for milling aluminum and light metals. The end mill cutter may have either taper shank (tanged or tapped) or straight shank.
Large cutters (shell end mill cutters) have the cutter part separate and are held to a stub arbor owing to the high cost of the high speed steel. This construction results in a considerable saving in material cost.
Type # 4. Metal Slitting Saw Cutters:
These cutters resemble a plain to side cutter except that these are made very thin. These are usually profile sharpened and may be either solid or tipped. These are used for cutting off and slotting operations and are somewhat similar to the circular saw blades. Plain cutters of this type are relieved by grinding the sides to afford clearance for the cutter.
Generally there are six types of saw cutters:
(a) Plain Metal-Slitting Cutters:
These are used for fine slitting operation and have teeth of saw-tooth form with both sides slightly concave to provide clearance while cutting.
(b) Staggered-Teeth Milling Cutters:
These are similar to the staggered teeth side milling cutters and have their teeth staggered at the periphery with alternate right-hand and left hand helix angles and are made in relatively narrow widths.
(c) Side Teeth Slitting Cutters:
There are suitable for cutting off wider material or for making a deep slot.
(d) Angle Milling Cutters:
Any cutter, angle shaped, comes under this classification. These may have cutters either on only one conical surface (single-angle cutter) or on two conical surfaces (double angle cutter). Angle cutters are used for cutting ratchet wheel, dovetails, flutes on milling cutters and reamers, machining angles and Vs of 30°, 45°, 60° and 90°.
Angle milling cutters have circumferential teeth and its cutting edges lie on a conical surface (Refer Fig. 16.43).
(e) Concave Milling Cutter:
This is a formed cutter which is shaped to mill a convex surface of circular contour equal to half a circle or less (Refer Fig. 16.44).
(f) Cylindrical Milling Cutter:
This is the cutter having cylindrical shape and teeth on the circumferential surface only (Refer Fig. 16.45).
Type # 5. T-Slot Cutters:
These are used for milling T-slots in one operation and are available in special sizes for standard T-slots. These resemble plain or side milling cutters which have an integral straight or tapered shaft for driving.
Straight or staggered teeth are cut on the periphery and both sides. For making T-slot, first a side milling cutter makes the groove and then the T-slot cutter enlarges the width of the bottom of the groove of form the desired T-slot.
Type # 6. Form Milling Cutters:
These have a special curved tooth outline and are used for milling contours of the various shapes. According to the method of grinding employed, these could be classified as profile-ground or face-ground.
(a) Form Cutters:
These are designed to produce a specific shape on the workpiece. One of the examples is the side and face milling cutters (Refer Fig. 16.46).
It may be noted that it has teeth on the circumferential surface as well as on both sides. The teeth may be either staggered or straight.
Another example of form cutters is the thread milling cutter in which formed cutter is shaped to mill screw threads having pitch equal to tooth pitch of the cutter (Refer Fig. 16.47).
Various other types of form milling cutters are convex milling cutters, concave milling cutters, corner-rounding milling cutters, pocket milling cutters, spindle milling cutters, form milling gang cutters, etc.
(b) Shaped or Form Profile Cutters:
In these cutters, sharpening is done by grinding a small land back of the cutting edge. As the contour is to be exactly reproduced each time the sharpening is done, therefore, its application is limited to simple outlines. These may be either solid or inserted blade type.
(c) Form or Cam-Relieved Cutters:
These cutters are sharpened on the face of the tooth, thus preserving the original profile. These are, therefore, very suitable for complicated shapes as they can be sharpened again and again easily until the teeth are too slender to be used.
These cutters are generally of the solid type and the clearance at the back of the cutting edge is produced by a form of master tool in a cam-relieving machine, giving all teeth the contour of the master tool.
Type # 7. Fly Cutters:
Basically, the fly cutter is a cylinder with provision for mounting one or more tool bits or single point cutters on the face or periphery. This is particularly suitable for high speed operation for quick operation by giving more feed per tooth on metals like magnesium and aluminum.
Type # 8. Inserted Tooth Milling Cutters:
The use of this type of cutter allows fabrication of the main body of the cutter from machine steel which is relatively less expensive and tough. The teeth are formed of alloy tool steel, and are attached to the body mechanically with set screws or brazed in place. The teeth position can be adjusted for wear. This is very suitable for expensive cutter material like carbide. Cutters in this group are confined mainly to large diameter cutters known as face mills.