Technical Guidance Basics of Drilling, Drilling Edition
■ Parts of Drill
Height of point
Leading edge
Margin width
Back Taper
Lead
Margin
Neck
Flank
Body clearance
Taper shank
Flute
Poiintt anglle
Heel
Shank Length
Helix Angle
Cutting edge
Body clearance
Cutting edge
Outer corner
Rake Face
N
Flute Length
Overall Length
Chisel edge Depth of body clearance
Chisel edge corner
Diameter of body clearance
Chisel edge length
Relief Angle
B
A
Web thinning
A:B or A/B = Groove width ratio
● Minimum requirement relief angle for drilling
● Relation between edge treatment and cutting force
● Point angle and force
f : Feed rate ( mm / rev )
8,000
θ x
T
T
6,000
f
P
4,000
Md
Md
X DX
2,000
X· DC
0
.0079 .0118 .0156
P x=tan -1 f π· DX * A large relief angle is needed at the centre of the drill.
Point angle (small)
Point angle (large)
Feed Rate (IPR)
When point angle is large, thrust increases but torque decreases.
60
● Effects of web thinning
40
● Point angle and burr
20
0
.0079 .0118 .0156 Feed Rate (IPR)
.0315
118° 140° 150°
.0236
Drill
: MultiDrill KDS215MAK
Edge treatment width: ● .0059” → .0091” Part material : Carbon Steel (230HB) Cutting conditions : v c = 165 SFM, wet
.0157
.0079
0
.002 .004 .006 Feed Rate (IPR)
.008 .010
Removed
When point angle is large, burr height becomes low. Part material: Structural Carbon Steel Cutting speed: v c = 165 SFM
Web thinning decreases the thrust concentrated at the chisel edge, makes the drill edge sharp, and improves chip control.
● Chisel width decreased by thinning
Typical types of thinning
S Type
N Type
X Type
S Type: Standard type used for general purposes. N Type: Suitable for thin web drills. X Type: For hard-to-cut materials or deep hole drilling. Entry easier.
N60
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