HEIDENHAIN CNC Pilot 4290 V7.1 - Manual (Page 588)

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3 – Centric predrilling
Centric predrilling – Tool selection
For predrilling, a maximum of three drilling steps is used:
„ 1st predrilling step (limit diameter UBD1)
„ 2nd predrilling step (limit diameter UBD2)
„ Finish-drilling step
„ Finish-drilling is performed with: dimin <= UBD2
„ Tool selection: db = dimin
Designations in the figures at right:
„ db1, db2: Drill diameter
„ DB1max: Maximum inside diameter for 1st drilling step
„ DB2max: Maximum inside diameter for 2nd drilling step
„ dimin: Minimum inside diameter
„ BBG (drilling limitation elements): Contour elements intersected by
UBD1/UBD2
Tool selection
1. 1st drilling diameter limit [UBD1]
„ 1. 1st predrilling step: if UBD1 < DB1max
„ Tool selection: UBD1 <= db1 <= DB1max
2nd drilling diameter limit [UBD1]
„ 2nd predrilling step: if UBD2 < DB2max
„ Tool selection: UBD2 <= db2 <= DB2max
„ UBD1/UBD2 have no effect when “Centric predrilling”
has been defined as main machining operation followed
by “Finish-drilling” as submachining operation in the
machining sequence (see “Machining sequence –
Fundamentals” on page 535).
„ Prerequisite: UBD1 > UBD2
„ UBD2 must permit subsequent inside machining with
boring bars.