 | New
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 )
( How to Build a Standard Special Using Niagara Stock Cutters)
Product design changes require product versatility, and it is the tool engineer who must select tooling to build the desired multiplicity of products. Here's how standardization with building-block concepts can eliminate special milling cutters.
1) Workpiece dimensional requirements should be analyzed. A cross sectional view drawn to scale should be prepared showing the form to be milled in the workpiece. Tolerances and dimensions should be specified in this cross sectional sketch.
2) Check available milling equipment capacity to determine the amount of stock removal and maximum cutter diameters permissible for the application. A simple calculation can give us the quantity of metal which would be removed by any proposed cutter gang. As a general rule, one horsepower is required to remove one cubic inch of steel per minute. A simple analysis can be made to determine the cutter diameter, size of cuts, and the speed and feeds permissible - dependent upon available horsepower and equipment. Normally, the largest practical bore size is recommended. Larger bore sizes permit better drive to the cutter gang with less possibility of chatter.
3) Select , cutters from standard sizes available: for instance, Niagara Cutter has over 1600 stock sizes listed in Catalog MC 71. Included in the standard available cutters are straight tooth side mills, staggered tooth side mills, plain mills heavy duty, half side mills, saws, and angle cutters as shown in Fig. 47.
4) Alteration of off-size cutters, which can easily be made by grinding to the required diameters, widths, radii, chamfers, and angles to fulfill specific piece-part requirements.
5) Assembly of standard and altered cutters on an arbor. Use spacing collars where necessary to locate cutters in position. Final inspection checks out dimensions and tolerances.
Methods of Ganging
Cutters may be ganged on an arbor in various combinations and by various methods. The most common methods are described below:
• Mounted singly with spacing collars in between - Cutters may be mounted individually at various positions on an arbor. Spacing collars maybe ground to special widths to locate cutters on the arbor. This method is common and generally requires only minor, if any, grinding on the cutter.
• Butted adjacent to other cutters - The term "butting cutters together" refers to adjacent cutters contacting one another on the hubs. This method does not provide any overlapping of the cutting teeth. Butting of cutters may be satisfactory in cases where overlapping of cutting teeth between adjacent cutters is not required.
Setting-in of cutters (Nesting) - Whenever the number of teeth between adjacent cutters is different, or when cutter diameters vary appreciable, the "setting-in" method is often used. This simple procedure requires grinding the side of the larger cutter in the manner of a counterbore so that the smaller cutter can set in within the counterbore of the larger cutter. This condition is illustrated in Fig. 48, which shows the heavy duty plain mill located between the larger staggered-tooth cutters. This setting-in procedure provides over-lapping of cutting edges between the large and the smaller cutters, thereby preventing formation of burrs or ridges and other non-uniform surface on the workpiece.
• Interlocking staggered tooth cutters - Wherever possible, the interlocking of staggered tooth cutters is recommended in cutter gangs. This procedure offers the best possible chip removal and produces a smoother finish on the workpiece. Interlocking provides for a normal overlap of up to 3/32" between cutters. This interlocking feature permits greater cutter life because thin shims may later be mounted between the staggered cutters after sharpening, thereby maintaining the original width. Cutters having the same number of teeth are used for interlocking. In Fig. 50, interlocking of a 3-1/2" and a 4-1/2" dia. cutter is illustrated. Note that the teeth in the 3-1/2" dia. cutter actually overlap and intermesh with the 4-1/2" dia. cutter. Hubs between the interlocking cutters are ground lower than the side teeth, enabling intermeshing of the teeth. This procedure can be used when interlocking cutters of different diameters or the same diameter, provided the number of teeth are the same in both cutters.
Building Block Advantages
1) Preparation of special cutter gangs as proposed herein offers a cluick solution to delivery problems. Normally from 8 to 14 weeks are required for the Manufacture of special milling gangs from raw stock. But with the Building Block procedure, it is not uncommon to produce a special altered gang within one week - a big improvernent in delivery.
2) Tremendous cost economies are possible with the utilization of a wide range of standard cutters. This gives the milling cutter user the advantages of low cost standard cutters manufactured on a high volume basis.
3) Reuse of cutters after completion of a specilic job is very common. The cutters used within a gang are normally of standard proportions, and can later be used for day-to-day milling requirements.4) Damage to cutters within a gang can readily be repaired with minimum down time and at low cost. This is because replacement cutters can be drawn from stock and altered to suit.
5) Profit-style cutter gangs permit freer cutting and consequently more economical metal removal. Laboratory tests have proven that a profile-style cutter, similar to staggered tooth side mill or heavy duty plain mill, will out perform relieved cutters as much as two to one. Profile style milling cutter gangs are recommended for use wherever possible.6) Standard catalog cutters are designed with the optimum number of teeth, rake angles, clearances and other design features for most metal cutting applications. This eliminates the need for engineering specific design features for each individual cutter within a milling cutter gang
7) There are 1620 standard Niagara Cutters stocked in all configurations. The most common arbor used is 1-1/4". 679 Niagara Cutters are standard with 1-1/4" arbor hole, making it possible to build unlimited cutter gang combinations.
