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4.73

CHAPTER 4.7

PARTS PRODUCED BYPLANING, SHAPING,

AND SLOTTING

THE PROCESSES

Planing, shaping, and slotting are machining processes that provide a cutting action asa result of a straight-line reciprocating motion between the tool and the work.

Planing

This process is utilized for large components. The workpiece is fixed to a table thatmoves back and forth against single-point cutting tools. The tools are stationary exceptfor feeding between strokes of the machine. Tools can be fed across the workpiece in ahorizontal, vertical, or angular direction. As many as four tool holders, each of whichcan produce a separate machined surface, may be employed simultaneously.

Shaping

Shaping is a process similar to planing that is used for smaller workpieces or smallersurfaces. The workpiece is stationary (except for feeding between strokes), while thesingle-point cutting tool moves. The tool is supported by a ram that reciprocates with alinear motion. In the conventional shaper this motion is horizontal. Feeding of theworkpiece between strokes is normally automatic and is in the horizontal directionacross the stroke of the ram. However, the tool may be fed vertically, horizontally, orat an angle, as desired. Figure 4.7.1 illustrates a standard horizontal shaper.

Slotting

This process is identical to shaping except that the motion of the ram is verticalinstead of horizontal. This factor sometimes provides a more convenient means ofholding certain workpieces, most commonly those for which a rotary rather than linearfeed is used.

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4.74 MACHINED COMPONENTS

FIGURE 4.7.1 Standard horizontal shaper. (Courtesy General

Motors Engineering Standards.)

CHARACTERISTICS AND APPLICATIONS OF

PLANER-MACHINED PARTS

Planers are used most frequently to machine large, flat surfaces. Machinery bases,diesel engine blocks, and locomotive and ship parts commonly undergo planer opera-

tions. Large, rough castings and welded assemblies that require some afterweldmachining are candidates for planing. A typical planer will have a maximum work-piece capacity of 1 by 1 by 4 m (3 by 3 by 12 ft). However, machines have been builtwith part-length capacities as long as 15 m (50 ft) or more. Surfaces shorter than 300mm (12 in) usually are not practical to machine on a planer except as part of a gang-machining operation.



PARTS PRODUCED BY PLANING, SHAPING, AND SLOTTING


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PLANING, SHAPING, AND SLOTTING 4.75

Dovetail and V-groove machine-tool surfaces are frequently machined on a planer.(Planed surfaces lend themselves better than milled surfaces to subsequent hand-scraping operations.) Another common application is the machining of large die

blocks, since difficult-to-machine alloys and tool steels up to a hardness of about Rc46 can be processed.

Although primarily used for the production of flat surfaces, planing also can beemployed to produce contoured surfaces. This can be accomplished by hand manipula-tion of the tool height (usually in following a scribed line of the workpiece). It alsocan be accomplished through the use of a tracer attachment that automatically changesthe tool position from stroke to stroke of the machine. With a special work holder torotate the work during cutting, helical surfaces or slots can be machined. Form toolsalso will machine curved and irregular surfaces of limited size. Figure 4.7.2 illustratestypical parts and surfaces machined on a planer.

CHARACTERISTICS AND APPLICATIONS OF

SHAPER-MACHINED PARTS

Shaper parts are smaller than those run on planers. Usually, they are small enough tobe moved easily by hand and clamped in a vise-type work holder on the machinetable. Surfaces machined with shapers are usually, but not necessarily, flat and can bein the horizontal, vertical, or angular plane.

Shapers seldom have a stroke longer than 900 mm (36 in), which is therefore thelongest surface machinable. A minimum surface is less than 13 mm (12 in), with theusual case about 150 to 400 mm (6 to 16 in). The width capacity of a 36-in shaper nor-mally is about 20 in, and that of a 12-in shaper is about 10 in.

Although some shapers are equipped with tracer attachments that permit them toreproduce accurately surface contours both at right angles and parallel to the machine

FIGURE 4.7.2 Typical parts and surfaces machined on a planer.





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stroke, most such contours are made by manually controlling the height of the cuttingtool during each stroke. Such surfaces therefore are only roughly machined. A thirdmethod involves the use of a template mounted below the shaper table to raise andlower it during cross feeding and thereby to produce gentle contours at right angles tothe machine stroke.

The shaper is a very versatile machine, even more versatile than the planer. Someinaccessible surfaces that are not feasible to machine with other types of equipmentcan be produced by shaping. Examples are deep internal slots and contours in blindholes or inaccessible places.

Although single-point tools are normally used, shapers can cut with form tools,especially when a repeated form is required as, for example, in the machining of rackgears.

Shapers are frequently used for slot, keyway, and spline cutting. Such operationsmay require the use of a dividing head mounted on the shaper table. Figure 4.7.3 illus-trates typical shaper-machined parts.

ECONOMIC PRODUCTION QUANTITIES

With some exceptions, planing, shaping, and slotting are most suitable for unit or low-

FIGURE 4.7.3 Typical parts and surfaces machined on a shaper.





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quantity production. They are all very versatile processes with very low tool costs. Themachines frequently can be found in maintenance and model shops and toolrooms butseldom in quantity production. (The milling machine has supplemented the shaper andthe planer for production applications because of its faster metal-removal rate, which

is at least twice that of the latter machines.)Since only inexpensive single-point cutting tools and standard work holders and

clamps are required and setup times are usually short, planers, shapers, and slotters areespecially suited for one-of-a-kind or emergency production.

MATERIALS FOR PLANING, SHAPING, AND

SLOTTING

Although, as indicated above, planers, shapers, and slotters can machine difficultalloys and high hardnesses (to approximately R

c46), it still is advantageous, when

these machines are used, to specify as machinable a material as the functional require-ments of the workpiece will allow.

The machinability table in Chap. 4.1 provides general data on ferrous, nonferrous,and nonmetallic materials. These data are also applicable to planer, shaper, and slotteroperations. Table 4.7.1 also provides machinability information for the high-speedsteel-cutting-tool machining of materials commonly machined on shapers.

DESIGN RECOMMENDATIONS

Because of the flexible capability of planers, shapers, and slotters, there are very fewrestrictions on the design of parts to be machined with them. There are some rules,however, that should be adhered to, either for economy of the operation or for dimen-sional control. They are as follows:

1. Since the cutting forces in planing and shaping may be abrupt and rather large,design parts so that they can be easily clamped to the work table and are sturdyenough to withstand deflection during machining. (See Fig. 4.7.4.)

2. It is preferable to put machined surfaces in the same plane to reduce the number ofoperations required. (This stricture does not apply if a multitooled planer canmachine both surfaces simultaneously.)

3. Avoid multiple surfaces that are not parallel in the direction of reciprocatingmotion of the cutting tool because this would necessitate additional setups.

4. Avoid contoured surfaces unless a tracer attachment is available, and then specifygentle contours and generous radii as much as possible.

5. With shapers and slotters it is possible to cut to within 6 mm ( 14 in) of an obstruc-

tion or the end of a blind hole. (See Fig. 4.7.5.) If possible, allow a relieved portionat the end of the machined surface.

6. For thin, flat pieces that require surface machining, allow sufficient stock for astress-relieving operation between rough and finish machining, or, if possible,rough-machine equal amounts from both sides. Allow about 0.4 mm (0.015 in) for





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4.78

TABLE

4.7.1

Relativ

eMachinabilityofVariousMaterialsUsedonPlanersandShap

ers(BasedonRecommended

CuttingSpeedwithHig

h-Speed-SteelTools)

Material

Designation

Co

nditionandremarks

Brind

ellhardnessnumber

Rating

Steel

1212(G12120)

Col

d-drawn

150200

100*

Steel

1117(G11170)

Col

d-drawn

150200

85

Steel

1137(G11370)

Col

d-drawn

175225

80

Steel

12L13(G12134)

Col

d-drawn,leaded

100150

100

Steel

Plainlow-carbon

Col

d-drawn

85125

90

Steel

Plainmedium-carbon

Col

d-drawn

175225

70

Steel

Plainhigh-carbon

Col

d-drawn

175225

65

Steel

Alloy,medium-carbon

Col

d-drawn

175225

65

Stainlesssteel

430F(S43020)

Ferritic,annealed

135185

40

Stainlesssteel

304(S30400)

Austenitic,annealed

135185

30

Stainlesssteel

17-7PH(S17700)

Precipitation-hardened

150200

35

and

annealed

Caststeel

Plainlow-carbon

Annealedandnormalized

100150

80

Castiron

Gray

Ferritic,annealed

120150

100

Castiron

Gray

Pea

rlitic,ascast

190220

70

Castiron

Ductile

Ferritic,annealed

140190

100

Castiron

Malleable

Ferritic,malleabilized

110160

145

Castaluminumalloy

Ascastinsandor

40120

280

permanentmold

*Aratingof100isequ

ivalenttoacuttingspeedof30m(1

00ft)/min.Otherratingsareproportional.

Source:

Thistableiscompiledfrom

dataintheMachin

ingDataHandbook,3ded.,bypermissionoftheMachinabilityData

Center;1980byMetcut

ResearchAssociates,Inc.





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FIGURE 4.7.4 Design planer- and shaper-machined parts to be sturdyenough to withstand cutting-tool forces and to be solidly clamped.

FIGURE 4.7.5 Avoid machined surfaces too close to an obstruc-tion at the end of the cut.





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FIGURE 4.7.6 The minimum-size hole in which a key-way, slot, or other contour can be shaper-machined isabout 1 in. Slots and contours should not be longer than 4

times the largest dimension of the opening or the holediameter.

finish machining. Then finish-machine on both sides.

7. The minimum size of holes in which a keyway or a slot can be machined with aslotter or shaper is about 1 in. (See Fig. 4.7.6.)

8. Because of a lack of rigidity of long cutting-tool extensions, it is not normally fea-sible to machine a slot longer than 4 times the hole diameter (or the largest dimen-

sion of the opening). (See Fig. 4.7.6.)

DIMENSIONAL FACTORS

Planers, shapers, and slotters are rugged, precision machines. If they are maintained inproper operating condition, any major dimensional variations will occur from humanfactors, the design and condition of the part itself, and the clamping method.

The squareness and flatness of the clamping surface of the workpiece are of para-

mount importance. A piece that is distorted in clamping will spring back after machin-ing and will not have a true surface. This is especially true of parts machined on plan-ers when the cutting forces are very large and when particularly strong clamping isrequired.

The solidity of clamps, supports, and stops is quite important, especially in planers.Movement of the workpiece can cause tool and equipment damage as well as dimen-sional errors. Similarly, deflection of the part as a result of cutting forces can causesignificant dimensional variations. Workpieces must be rigidly designed and well sup-ported if accuracy requirements are high. Warpage also can occur as a result of therelease of internal stresses in the material during machining. Flat pieces are particular-ly susceptible to this condition.

Tool rigidity is another factor of importance, especially in slotting operations or inthe shaping of internal surfaces when there is substantial overhang of the tool or tool-holder.

Slower cutting speeds, lighter cuts with finer feeds, and the use of lubricants alltend to improve accuracy when tool or workpiece deflection factors are operating.





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TABLE 4.7.2 Recommended Dimensional Tolerances for Parts Produced by Planing, Shaping, and

Slotting

Preferred tolerance for Average tolerance, Closest tolerance,

manufacturing, mm (in) mm (in) mm (in)

Flatness

In 0.5 m2 (5 ft2) (planers) 0.13 (0.005) 0.05 (0.002) 0.013 (0.0005)

In 0.1 m2 (1 ft2) (planers 0.08 (0.003) 0.025 (0.001) 0.013 (0.0005)

or shapers)

In 65 cm2 (10 in2) 0.05 (0.002) 0.025 (0.001) 0.013 (0.0005)

(shapers)

Surface finish

Cast iron 3 m (125 in) 1.5 m (60 in) 0.8 m (32 in)

Steel 6 m (250 in) 3 m (125 in) 0.8 m (32 in)

Surface location

Small surfaces 0.25 (0.010) 0.13 (0.005) 0.025 (0.001)

Large surfaces, over 0.1 0.4 (0.015) 0.2 (0.008) 0.05 (0.002)

m2 (1 ft2)

Contour to specified position

Manual feed 1.0 (0.040) 0.7 (0.028) 0.4 (0.015)

Tracer feed 0.13 (0.005) 0.05 (0.002) 0.025 (0.001)

Similarly, sharp tools, correctly ground, and fine feeds facilitate smooth surface finish-es.

Table 4.7.2 presents recommended tolerances for dimensions and surfaces pro-duced on planers, shapers, and slotters.




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