Cycle Time in Deep Hole Drilling: Pecking, Retracts & Delay

Accurate cycle time estimation for deep hole drilling requires accounting for the cutting feed, peck retraction, rapid approach, coolant delay dwells, and chip evacuation time. In deep holes drilled with full-retract peck cycles, non-cutting motion and dwell time can account for more than 50% of the total cycle — making it essential to model all components, not just the feed distance divided by feed rate.

Overview ​

Cycle time estimation for deep hole drilling differs fundamentally from conventional drilling estimation. In conventional drilling (L/D < 3), the feed time dominates and retraction time is negligible. In deep hole drilling — particularly when G83-style full-retract pecking is used — the tool may retract and re-approach dozens or hundreds of times, and each peck may include dwell time for chip clearing.

The total cycle time for any drilling operation is the sum of four components:

T_total = T_feed + T_retract + T_approach + T_dwell

Where:

• T_feed — time spent cutting (tool engaged with workpiece)
• T_retract — time spent retracting the tool out of the hole
• T_approach — time spent advancing the tool back to the cutting depth
• T_dwell — programmed pauses for chip breaking, coolant flushing, or spindle orientation

This article provides formulas for each component, with specific attention to how drilling method (gun drilling, BTA, or conventional peck drilling) changes the relative importance of each term.

Core Formulas ​

Before calculating cycle time, the basic cutting parameters must be established.

Spindle Speed ​

n = (1000 × v_c) / (π × D)

Where:

• n = spindle speed (RPM)
• v_c = cutting speed (m/min)
• D = drill diameter (mm)

Feed Rate (Penetration Rate) ​

v_f = f × n

Where:

• v_f = feed rate (mm/min)
• f = feed per revolution (mm/rev)
• n = spindle speed (RPM)

Material Removal Rate ​

MRR = (π/4) × D² × f × n

Or the simplified form:

MRR = (D × f × v_c) / 4

Where MRR is in mm³/min when D is in mm and v_c is in m/min.

Basic Feed Time (No Pecking) ​

For continuous drilling without pecking (as in gun drilling or BTA):

T_feed = L / v_f

Where L is the total hole depth (mm).

This is the starting point. All additional cycle time components are penalties relative to this ideal.

Pecking Strategies and Cycle Time ​

The choice of pecking strategy is the single largest factor affecting total cycle time in deep hole drilling.

G83: Full Retract Pecking ​

G83 retracts the tool to the R-plane (clearance plane) after each peck. This provides maximum chip clearing but adds substantial non-cutting time.

Number of pecks:

N = ceil(L / Q)

Where:

• Q = peck depth (mm)
• L = total hole depth (mm)

Total feed distance:

L_feed = L + (N × C)

Where C is the clearance distance (typically 0.5–1.0 mm) that the tool feeds after rapiding down to just above the previous depth.

Feed time:

T_feed = L_feed / v_f

G73: Chip Break Pecking (Short Retract) ​

G73 retracts only a small distance (typically 0.5–1.0 mm) after each peck. This breaks chips without fully clearing them, and the non-cutting time is much lower.

T_retract_G73 = N × d / v_rapidT_approach_G73 = N × d / v_rapid

Where d is the short retract distance (mm) and v_rapid is the rapid traverse rate (mm/min).

The total non-cutting time for G73 is typically 5–10% of the cutting time, compared to 50–150% for G83.

Variable Peck Depth (Degressive Pecking) ​

Fanuc and Siemens controls support variable peck depth where the peck depth decreases with each pass:

P_i = P_1 - (i - 1) × DAM

Where:

• P_1 = first peck depth (mm)
• DAM = decrement per peck (mm)
• P_i = peck depth for peck i

The number of pecks is found by summing P_i until the total reaches L. This approach maintains a shorter peck depth as the hole gets deeper, balancing chip evacuation difficulty against cycle time.

Retraction Time Calculations ​

The retraction and approach time is the most commonly underestimated component in deep hole drilling cycle estimation.

G83 Full Retract Geometry ​

For G83 with full retract to the R-plane after each peck:

The retract distance for peck i is the cumulative depth at that peck plus the R-plane height:

D_ret,i = (i × Q) + R (for constant peck depth Q)

Where R is the R-plane height above the workpiece (mm).

The total retract distance for all N pecks:

D_ret,total = Σ(i × Q + R) for i = 1 to ND_ret,total = N × R + Q × N × (N + 1) / 2

The approach distance is nearly identical (rapid down to clearance above previous depth, then feed the last C mm), so:

D_approach,total ≈ D_ret,total

Total rapid distance:

D_rapid,total = 2 × [N × R + Q × N × (N + 1) / 2]

Total rapid time:

T_rapid = D_rapid,total / v_rapid

Simplified Approximation ​

For quick estimation, a commonly used simplification is:

Average retract distance per peck ≈ L / 2 + RTotal rapid time = 2 × N × (L/2 + R) / v_rapid

This approximation is accurate within 5% for most practical cases.

Example: The Impact of Peck Depth on Rapid Time ​

Consider a 500 mm deep hole drilled with a G83 cycle:

At 1 mm peck depth, the rapid time alone is 42 minutes — even before the cutting time is added. This illustrates why peck depth selection is critical for production cycle time.

Coolant Delay and Dwell Time ​

Coolant delay — the programmed dwell time that allows coolant to flush chips from the hole — is often overlooked in cycle time estimates but can be significant.

Sources of Dwell Time ​

Siemens CYCLE83 Parameters ​

The Siemens Sinumerik CYCLE83 cycle explicitly models both dwell components:

• DTB — dwell time at final drilling depth (for chip breaking)
• DTS — dwell time at starting point (for swarf removal)

These parameters directly map to the bottom dwell and top dwell in the table above.

Total Dwell Time Calculation ​

T_dwell = N × T_bottom + floor(N / K) × T_top + T_final

Where:

• T_bottom = dwell time per peck at hole bottom (min)
• K = number of pecks between full retract chip clearing cycles
• T_top = dwell time at retract position for chip clearing (min)
• T_final = final dwell at full depth (min)

Example: Coolant Delay Impact ​

For 200 pecks in a deep hole:

At 10+ minutes of accumulated dwell, the coolant delay is no longer negligible and must be included in production cycle time estimates.

BTA vs Gun Drilling: Cycle Time Comparison ​

The three main deep hole drilling methods have fundamentally different cycle time profiles.

Gun Drilling ​

Gun drilling typically operates without pecking. The single-lip gun drill cuts continuously from entry to exit, with high-pressure coolant (80–200 bar) flushing chips through the V-groove.

T_gun = L / (f × n) + T_entry + T_exit

Where T_entry and T_exit account for the reduced feed rate typically used at hole entry (to establish the guide bushing) and at hole exit (to prevent breakthrough burr).

Typical gun drilling parameters from production data:

Gun drilling cycle time is dominated by feed time. Non-cutting time is typically less than 5% of total.

BTA Drilling ​

BTA drilling also operates continuously, using high-pressure coolant (10–50 bar) to flush chips through the internal bore of the drill tube. The multi-edge BTA head achieves higher feed rates than gun drilling for a given diameter.

T_BTA = L / (f × n) + T_tool_change

Where T_tool_change accounts for the time to change BTA heads — relevant for long runs where tool wear requires replacement.

Typical BTA cycle time comparison from case study data:

The BTA cycle time is purely feed-driven. No pecking is required.

Conventional Peck Drilling (G83) ​

For deep holes drilled on conventional machining centres without gun drilling or BTA equipment, G83 peck drilling is the only option. The cycle time is dominated by rapid motion and dwell.

T_G83 = T_feed + T_rapid + T_dwell

Where T_rapid and T_dwell are calculated as shown in the preceding sections.

Comparison Summary ​

Worked Examples ​

Example 1: Gun Drilling ​

Parameters:

• Diameter: 10 mm
• Depth: 500 mm
• Cutting speed: 80 m/min
• Feed per rev: 0.05 mm/rev
• Entry feed reduction: 50% for first 5 mm
• Exit feed reduction: 50% for last 3 mm

Calculations:

n = (1000 × 80) / (π × 10) = 2,546 RPM

v_f = 0.05 × 2,546 = 127.3 mm/min

T_entry = 5 / (127.3 × 0.5) = 0.079 min (reduced feed) T_main = (500 - 5 - 3) / 127.3 = 3.865 min T_exit = 3 / (127.3 × 0.5) = 0.047 min (reduced feed)

T_total = 0.079 + 3.865 + 0.047 = 3.99 min

Non-cutting time: negligible (entry/exit accounts for 3.2% of total).

Example 2: BTA Drilling ​

Parameters:

• Diameter: 40 mm
• Depth: 2,000 mm
• Cutting speed: 80 m/min
• Feed per rev: 0.15 mm/rev

Calculations:

n = (1000 × 80) / (π × 40) = 637 RPM

v_f = 0.15 × 637 = 95.5 mm/min

T_feed = 2000 / 95.5 = 20.94 min

T_total = 20.94 min

No pecking, no dwell. Approximately 21 minutes per hole.

Example 3: G83 Peck Drilling (Full Retract) ​

Parameters:

• Diameter: 10 mm
• Depth: 100 mm
• Cutting speed: 50 m/min
• Feed per rev: 0.10 mm/rev
• Peck depth (Q): 10 mm
• R-plane: 5 mm
• Clearance (C): 0.5 mm
• Rapid traverse rate: 15,000 mm/min
• Bottom dwell: 0.3 s per peck
• Top dwell: 2.0 s every 5 pecks

Calculations:

n = (1000 × 50) / (π × 10) = 1,592 RPM

v_f = 0.10 × 1,592 = 159.2 mm/min

N = ceil(100 / 10) = 10 pecks

L_feed = 100 + (10 × 0.5) = 105 mm T_feed = 105 / 159.2 = 0.66 min

D_ret,total = 10 × 5 + 10 × 10 × 11 / 2 = 50 + 550 = 600 mm D_rapid,total = 2 × 600 = 1,200 mm T_rapid = 1200 / 15000 = 0.08 min

T_dwell = 10 × 0.3 + floor(10/5) × 2.0 + 0.5 = 3.0 + 4.0 + 0.5 = 7.5 s = 0.13 min

T_total = 0.66 + 0.08 + 0.13 = 0.87 min

In this case, non-cutting time (0.21 min) is 24% of the total — even at a modest 10:1 L/D ratio.

Example 4: G83 with Very Deep Hole (Shallow Peck) ​

Parameters:

• Diameter: 5 mm
• Depth: 250 mm (L/D = 50:1)
• Cutting speed: 40 m/min
• Feed per rev: 0.03 mm/rev
• Peck depth (Q): 2 mm
• R-plane: 3 mm
• Rapid traverse: 12,000 mm/min
• Bottom dwell: 0.5 s per peck

Calculations:

n = (1000 × 40) / (π × 5) = 2,546 RPM

v_f = 0.03 × 2,546 = 76.4 mm/min

N = ceil(250 / 2) = 125 pecks

L_feed = 250 + (125 × 0.5) = 312.5 mm T_feed = 312.5 / 76.4 = 4.09 min

D_ret,total = 125 × 3 + 2 × 125 × 126 / 2 = 375 + 15,750 = 16,125 mm D_rapid,total = 2 × 16,125 = 32,250 mm T_rapid = 32,250 / 12,000 = 2.69 min

T_dwell = 125 × 0.5 = 62.5 s = 1.04 min

T_total = 4.09 + 2.69 + 1.04 = 7.82 min

In this case, non-cutting time (3.73 min) is 48% of the total. The cutting time alone would suggest 3.27 minutes, but the actual cycle is 2.4× longer.

Cycle Time Optimisation ​

Reduce Peck Retraction ​

The single largest lever for reducing cycle time in peck drilling is to minimise the number of full retracts:

• Use G73 instead of G83 where chip evacuation allows — short retract cycles reduce rapid time by 80–90%
• Use variable peck depth to increase peck depth at shallow depths where chip evacuation is easier
• Use periodic full retract (every 3–5 pecks) instead of full retract every peck — this combines chip clearance with efficiency

Optimise Dwell Parameters ​

Dwell time accumulates quickly over many pecks:

Increase Coolant Pressure ​

Higher coolant pressure improves chip evacuation, allowing deeper pecks and fewer retracts. The relationship is not linear — doubling coolant pressure may allow 1.5–2× deeper peck depths in many materials.

Note: Coolant pressure above 70 bar (1,000 PSI) typically requires through-spindle coolant delivery and appropriate machine specifications.

Use the Right Drilling Method ​

The most effective optimisation is to use a method that eliminates pecking entirely:

Summary ​

The total cycle time for deep hole drilling is the sum of feed time, rapid retraction and approach time, and dwell time. The relative contribution of each component depends critically on the drilling method and pecking strategy.

Spreadsheet-Ready Calculation Template ​

FAQ ​

What is the most common mistake in estimating deep hole drilling cycle time? ​

The most common mistake is omitting the retraction and approach time for G83 peck cycles. Many estimators simply divide the hole depth by the feed rate and use that as the cycle time, ignoring that the tool may retract 50–100 times. This can underestimate the actual cycle time by 50–100%.

How do I estimate cycle time for gun drilling? ​

For gun drilling, the cycle time is approximately the hole depth divided by the penetration rate (feed rate in mm/min), plus a small allowance for reduced feed at entry and exit. Gun drilling rarely uses pecking, so rapid motion and dwell are negligible. A 5 mm × 100 mm hole in 42CrMo4 steel at 800 mm/min feed has a cycle time of approximately 0.13 minutes (8 seconds).

Does BTA drilling require pecking? ​

No. BTA drilling is a continuous-feed process. The high-pressure coolant (10–50 bar) flushes chips through the internal bore of the drill tube, eliminating the need for peck retraction. This is one of the primary advantages of BTA over conventional peck drilling for deep holes.

How does peck depth affect cycle time? ​

Peck depth has a non-linear effect on cycle time because it determines both the number of retractions and the total rapid travel distance. Halving the peck depth doubles the number of pecks, but the rapid travel distance increases quadratically (the retract distance grows with cumulative hole depth for each peck). A shallow peck depth (1–2 mm) for a deep hole can result in rapid time exceeding feed time.

What is the difference between G73 and G83 cycle time? ​

G73 (chip break cycle) retracts only a small distance (typically 0.5–1.0 mm) after each peck, so the total rapid travel distance is N × d × 2 — a small fraction of the hole depth. G83 (deep hole peck cycle) retracts to the R-plane after each peck, so the total rapid travel distance is approximately 2 × N × (L/2 + R) — proportional to N × L. For a 100 mm deep hole with 5 mm peck depth, G73 rapid time is negligible while G83 rapid time can be several minutes.

How much dwell time should I include for coolant flushing? ​

A reasonable starting point is 0.2–0.5 seconds bottom dwell per peck and 2–3 seconds top dwell every 3–5 pecks. These values should be confirmed experimentally for the specific material, hole geometry, and coolant delivery system. Higher coolant pressure generally allows shorter dwell times.

Can variable peck depth reduce cycle time? ​

Yes. Variable peck depth (starting with deeper pecks and reducing depth as the hole gets deeper) can reduce the total number of pecks by 20–40% compared to constant shallow pecking. This is supported by Fanuc G83 with I/J/K parameters and Siemens CYCLE83 with degression (DAM). The deeper initial pecks occur when chip evacuation is easiest (shortest chip travel distance).

How do I estimate cycle time for a deep hole on a conventional CNC machine? ​

Use the spreadsheet template above with your specific parameters. The key inputs are: hole depth, peck depth, cutting speed, feed per revolution, rapid traverse rate, R-plane height, clearance, and dwell parameters. For a conservative estimate, assume G83 full retract and add 0.3–0.5 seconds dwell per peck.

What penetration rates are achievable with modern gun drills? ​

Modern single-lip solid carbide gun drills (e.g., Botek Typ 113-HP) can achieve penetration rates of 800–1,700 mm/min depending on material, diameter, and coolant pressure. For example, 950 mm/min in 50CrMo4 steel with a 3 mm diameter at 140 bar coolant pressure, and 1,700 mm/min in aluminium with a 7 mm diameter at 80 bar.

Does coolant pressure affect cycle time? ​

Yes, indirectly. Higher coolant pressure improves chip evacuation, which can allow deeper peck depths (fewer retracts) or, in the case of gun drilling, higher feed rates. The relationship is material-dependent, but increasing coolant pressure from 40 bar to 100 bar often allows 20–40% higher penetration rates in difficult-to-machine materials. The cycle time benefit is realised through reduced pecking (conventional drilling) or increased feed rate (gun drilling).

When should I use G73 instead of G83 for deep holes? ​

Use G73 (chip break) when chips can be effectively cleared without full retraction — typically in materials that produce small, well-broken chips at L/D ratios under 5:1. Use G83 (full retract) when chip evacuation is critical, such as in materials that produce long stringy chips, at L/D ratios above 5:1, or when hole surface finish requires consistent chip clearing.

How accurate are these cycle time estimates? ​

These formulas typically produce estimates within ±10% of actual cycle time for well-characterised operations. The main sources of error are: unmodelled acceleration/deceleration of rapid axes (adds 0.05–0.2 s per direction change), coolant pressure variation affecting chip evacuation efficiency, and operator-adjusted feed rate overrides. For quoting purposes, add a 15–20% contingency factor.