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Concepts in Milling Handbook A practical approach and illustrated guide to milling cutter selection and use <Table of Contents © 1973 Niagara Cutter Inc. |
| New
Concepts in Milling Handbook A practical approach and illustrated guide to milling cutter selection and use <Table of Contents © 1973 Niagara Cutter Inc. |
Basic Cutter Styles and Their Application - ( «Back )
( Which Cutter to Choose?) - screen [ 1 | 2 | 3 ]
PROFILE-GROUND AND FORM-RELIEVED MILLING CUTTERS DO DIFFER, BUT THEY'RE OFTEN CONFUSED. AND THE TOOL ENGINEER SHOULD KNOW WHICH JOB EACH DOES BEST.
Two much- misunderstood terms used in milling cutter nomenclature and selection are 'profile ground' style and 'form relieved' style. Yet it is important for tool engineers to be aware of the basic differences and general characteristics of these two cutter types, and to know the basic considerations involved in choosing one or the other for a specific task.
The basic differences in appearance are illustrated in Fig. 53 (profile-ground cutter) and Fig. 54 (form-relieved cutter) both of which will produce exactly the same form. The profile-ground style of cutter has narrow lands on the cutting edges, with abrupt secondary clearance angles. The form-relieved style of cutter, in contrast, has a long curved primary clearance with narrow gashes. With these details in mind, recognition of the specific style is not difficult.
Each style has advantages in different applications, but it rests with the tool engineer to make the most efficient selection.
Profile-ground Style
Most general-purpose milling cutters are profile-ground style. Such cutters as side mills, plain mills, half side mills, etc, are good examples of profile-ground cutters. This style is sharpened by grinding the outer periphery and sides with desired cutting clearances (Fig. 55). Each time the cutter is sharpened, the clearance angles can be maintained or changed to obtain the optimum cutting conditions. Actually the method of sharpening is one of the primary factors in determining which style of cutter to use. Profile-ground cutters can generally be supplied with more teeth and give superior cutting action particularly on straight-sided cuts (cuts at 90 degrees from axis of arbor) such as slots and grooves, because of the side cutting clearances, which can be readily ground. Tooth geometry can be greatly varied when manufactured, particularly with regard to axial and radial rake.Profile-ground cutters can usually be sharpened more times and can frequently be salvaged after excessive dulling. If there are changes in the part specifications, profile-ground cutters can usually be altered to new dimensions by simple grinding and sharpening. Chip space in a profile-ground cutter is at a maximum when the cutter is new. This space is reduced after repeated sharpenings, but the cutter may be regashed to provide ample chip space after many sharpenings. Due to sharpening the teeth on the outer periphery the cutter teeth actually become stronger as the cutter is sharpened.
Fast delivery requests can usually be met most readily by profile-ground cutters. These cutters are stocked in many diameters, widths and hole sizes, thereby making off-the-shelf selection simple, and standard cutters can often be modified to meet specialized requirements in a few days. On specially manufactured profile-ground cutters, delivery can be made in a few weeks.
Form-relieved Style
When the workpiece requires milling of an intricate form, this is the time to use a form-relieved cutter. Such shapes as gear tooth forms, spline cutters and forms with blending radii and angles are common applications for form-relieved style cutters. Due to the method of manufacturing, the form on the cutter will not change as the cutter is sharpened by face grinding (Fig. 56). This quality insures that the first piece cut and the last piece cut after many sharpenings will have identical shape. The sharpening of form-relieved cutters is a simple job on manually operated machines and automatic sharpening machines are available to make sharpening a low cost operation.High speed steel is the most common material used for form-relieved cutters, but for some limited applications in nonferrous metals, graphite and plastics, the use of carbide-tipped form-relieved cutters is well suited. The most common jobs are thread milling and serration cutters when the shapes to be cut consist of straight lines and relatively small radii.The primary limitation of carbide form-relieved cutters is the extreme cost in manufacturing because a diamond wheel must be shaped and dressed several times with the desired form to be ground. This operation is time consuming and expends a considerable amount of the diamond wheel for each cutter ground. Complex shapes with large radii or irregular forms are generally not economical.
Some shapes to be milled lend themselves best to form-relieved cutters even though they are not especially complex. Concave cutter forms are invariably made in form-relieved style since it is almost impossible to do profile sharpening on these forms because of grinding wheel interference (Fig. 5 7 ). Another cutter application that is always made in form-relieved style is multiple type thread and serration milling cutters. The small projections on these make profile sharpening almost impossible.
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