Page 52 - machining_titanium_05_2019

DRILLING TITANIUM Center Drilling

MULTI-MASTER replaceable MM ECS heads (Fig. 33), produced from solid carbide, are intended
for drilling 60° center holes in accordance with DIN 332 and ANSI B94.11M (metric and inch products
correspondingly). There are two types of heads that ensure drilling the center holes of form A
(without protective chamfer, “plain type”) and form B (with conical protective chamfer, “bell type”).
Table 36 specifies the application range for ISCAR's standard line of these heads.

Fig. 33 MM ECS head for drilling center holes

Table 36 - Applicabillity Of MM ECS Center Drilling Heads
Size acc. to ANSI
Designation acc. to DIN 332
Center hole B94.11M
Type
1×2.12 1.6×3.35 2×4.25 3.15×6.7 4×8.5 5×10.6 6.3×13.2 4 5 6

A (“plain”)
B (“bell”)

Drill or countersink?
A center drill is needed for forming a conical hole in workpieces. This hole is used for
supporting the workpieces by the centers of machine tools. One of the methods for forming
conical holes is countersinking - machining by a specially designed cutter, a countersink. In
fact, the center drill performs a combination of two operations simultaneously: drilling and
countersinking. Therefore, the center drill is often referenced as a “combined countersink”.
Other names of the center drill – “Slocombe drill” and “Slocomb drill” – are rarely used.
Sometimes, the center drill is considered as a spot drill; however this specification is not
strictly correct. A spot drill only drills but a center drill performs two operations: drilling
and countersinking, therefore “spot a hole” and “drill a center hole” are not the same.

50 ISCAR