Page 662 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 23.5 Drilling, Drills and Drilling Machines

23.5 Drilling, Drills, and Drilling Machines

When inspecting various large or small products, note that the vast majority have sev-
eral holes in them. Observe, for example, (a) the number of rivets on an airplane’s wings
and fuselage, (b) the bolts in engine blocks and heads, and (c) numerous consumer and
industrial products. Holes typically are used for assembly with fasteners (such as bolts,
screws, and rivets, each of which requires a hole), for design purposes (such as weight
reduction, ventilation, or access to the inside of parts), or for appearance.
Hole making is among the most important operations in manufacturing, and
drilling is a major and common hole-making process. Other processes for producing
holes are punching (as described in Section 16.2) and various advanced machining
processes (Chapter 27). The cost of hole making is among the highest machining
costs in automotive engine production.

23.5.l Drills
Drills typically have high length-to-diameter ratios (Fig. 23.19); hence, they are
capable of producing relatively deep holes. However, drills are somewhat flexible

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Point a"g|e
Tang Taper shank Chisel-edge drill
T Dfi" Body diameter
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Shank
Tang drive
diameter rrir e.,..... CNISGVGUDG f s? $1 Clearance
clearance
rrr. ---g g
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diameter
Flutes Helix angle
Lip-relief
if
if
if
Neck->| le `
angle
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Web
iicri,
Shank length->| Flute length Lip Margin \’ [ago Chisel edge
(3)
Body
Overall length
Crankshaft-point drill

(D)
FIGURE 23 I9 Two common types of drills: (a) Chisel-edge drill. The function of the pair of
margins is to provide a bearing surface for the drill against walls of the hole as it penetrates
into the workpiece. Drills with four margins (double-margin) are available for improved
guidance and accuracy. Drills with chip-breaker features also are available. (b) Crankshaft
drill. These drills have good centering ability, and because chips tend to break up easily,
crankshaft drills are suitable for producing deep holes.