HEIDENHAIN CNC Pilot 4290 V7.1 - Manual (Page 590)

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Centric predrilling – Safety clearances
Centric predrilling – Machining
Safety Clearances
Safety clearance on blank part [SAB]
Internal safety clearance [SIB]
Retraction distance for deep-hole drilling (“B” for G74).
Machining
Drilling depth ratio [BTV]
TURN PLUS checks the 1st and 2nd drilling steps. The
predrilling step is performed with:
BTV <= BT / dmax
Drilling depth factor [BTF]
1. Reduction for deep-hole drilling cycle (G74):
bt1 = BTF * db
Depth reduction [BTR]
Reduction for deep-hole drilling cycle (G74):
bt2 = bt1 – BTR
Overhang length – Predrilling [ULB]
Through-drilling length