# Sinumerik 840D CYCLE81 Drilling Centering Cycle Programming

For CNC machinists who work on Siemens Sinumerik 840D (and related) cnc controls, here is brief article about Sinumerik 840D CYCLE81 Drilling Cycle (Centering Cycle).

Here is cnc programming example Sinumerik 840D Drilling Cycle CYCLE81 CNC Programming Example Code

No-doubt drilling cycles are one of the most used cycles in cnc machine workshops.

For cnc machinists who work on Fanuc and Haas cnc controls there is an equivalent G81 Drilling Cycle read G81 Drilling Canned Cycle – CNC Mill Programming.

## Sinumerik CYCLE81 Drilling Centering Cycle Format

Sinumerik 840D CYCLE81

`CYCLE81 (RTP, RFP, SDIS, DP, DPR)`

RTP  – Return plane or Retraction plane (absolute)
RFP  – Reference plane (absolute)
SDIS – Safety distance (enter without sign)
DP    – Final drilling depth (absolute)
DPR – Final drilling depth relative to reference plane (enter without sign)

With CYCLE81 the tool drills at the programmed spindle speed and feed-rate to the specified final drilling
depth.

As the above figure shows
1: the drill will rapidly reach the start point (RFP + SDIS).
2: with given feed-rate will complete final drilling depth or hole depth (DP).
3: after completing the depth the tool will retract rapidly to Return plane (RTP)

## Drilling Depth Calculation (DP or DPR) for CYCLE81

Here is a crucial point , final drilling depth can be given in two ways
Absolute depth (DP) or Relative to reference plane depth (DPR).

If you use absolute final drilling depth (DP) then this is the absolute value from workpiece-zero-point.

But if you use relative to reference plane depth (DPR) then final drilling depth will be calculated as below
DPR = Distance from Reference plane (RFP) to Final depth.