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A manufacturer of precision hydraulic spools (AISI 4140, 32 HRC, Ø6 mm × 400 mm deep, tolerance ±0.003 mm, Cpk > 1.67) used an offline optical presetter (HAIMER Microset, 20×, 0.001 mm resolution) to measure each gun drill before loading. The presetter measured tip concentricity, point angle (±0.5°), and step diameters (±0.002 mm). About 8% of resharpened drills failed the concentricity check (> 0.003 mm) from misaligned grinding. Tool presetting reduced the first-article rejection rate from 6% to 0.5%, and the $5/tool presetting cost was offset by eliminating scrapped spools at $85 each.
Tool Presetting Methods for Deep Hole Drilling
Comparison of Tool Presetting and Measurement Methods
| Method | Measurement Parameters | Accuracy | Measurement Time per Tool | Suitable for Gun Drills | Suitable for BTA Heads | Capital Cost ($) | Operator Skill Required | In-Machine or Off-Machine | Key Advantage | Key Limitation |
|---|---|---|---|---|---|---|---|---|---|---|
| Optical presetter (manual, CCD camera + image processing) | Tip geometry: point angle, step diameter, clearance angles, tip concentricity, overall length, chip flute condition | ±0.002–0.005 mm (length); ±0.5° (angles); ±0.003 mm (concentricity) | 2–5 minutes per tool (manual positioning and measurement) | Yes — standard method for gun drill presetting | Yes — but limited by BTA head size (max Ø200 mm for most presetters) | $20 000–60 000 | Moderate — operator must position the tool and interpret the image | Off-machine — tool is brought to the presetter | Most comprehensive measurement — captures all geometrical parameters in a single setup; image can be stored for quality records | Manual operation — operator skill affects measurement repeatability; slower than automated methods |
| Optical presetter (CNC, automated measurement cycle) | Same as manual optical, plus automated edge detection and measurement at multiple angular positions | ±0.001–0.002 mm (length); ±0.2° (angles); ±0.001 mm (concentricity) | 30 seconds–2 minutes (automated — operator loads, presetter measures and records) | Yes — preferred for high-volume presetting | Yes — automated measurement of insert positions and runout | $60 000–150 000 | Low — operator loads the tool and starts the measurement cycle | Off-machine | High throughput; consistent measurement (no operator-dependent variation); data automatically logged to tool database | Higher capital cost; less flexible for unusual tool geometries (may not recognise a non-standard gun drill) |
| Laser tool setter (in-machine, non-contact) | Tip position (length and diameter at the cutting edge), tool wear (change in tip position over time), broken tool detection | ±0.002–0.010 mm (length and diameter) | 5–20 seconds per tool (laser sweep while spindle rotates at 50–100 rpm) | Yes — in-machine laser setter is standard on most CNC gun drilling machines | Yes — measures the cutting edge position and detects insert breakage | $8000–20 000 | Low — automated cycle; operator initiates the measurement from the CNC | In-machine — tool is measured in the machine spindle | Measures the tool in its operating position (accounts for spindle runout and thermal expansion); fastest measurement method; broken tool detection | Does not measure all geometrical parameters (no point angle, clearance angle, or surface finish); limited to length and diameter measurement at the cutting edge |
| Contact probe (touch-trigger, in-machine) | Tip position (length and diameter at a single point at the cutting edge) | ±0.003–0.015 mm (length and diameter) | 10–30 seconds per tool (probe approaches and contacts the tool at 2–4 measurement points) | Limited — probe tip may not contact the small-diameter tip of a micro gun drill reliably | Yes — can measure the BTA head insert positions and the guide pad diameters | $3000–8000 | Low — automated cycle | In-machine | Low cost; can measure geometry parameters that laser cannot (clearance angle by touching two points on the clearance face) | Contact forces (0.1–0.5 N) may deflect a long, slender gun drill (0.01–0.05 mm deflection for a 400 mm long Ø6 mm drill); slower than laser |
| Runout measurement fixture (manual, dial indicator) | Tip concentricity (eccentricity of the carbide tip relative to the drill shank), measured at the drill tip and at 100 mm from the tip | ±0.001 mm (dial indicator resolution) | 30–60 seconds per tool | Yes — standard runout check for gun drills before loading | Yes — for BTA head OD runout relative to the drill tube OD | $500–2000 (V-block + dial indicator) | Low — operator places the drill in the V-block and rotates it manually | Off-machine (bench-top) | Simple, low-cost, provides direct measurement of tip concentricity — the most critical parameter for bore position accuracy | Measures only runout — no other geometrical parameters; operator may not detect a bent drill if the bend is at the mid-point (not at the tip) |
| 3D optical scanner (white light or structured light) | Full 3D model of the tool tip: all geometrical parameters, chip flute profile, guide pad wear, surface finish of clearance faces | ±0.002–0.005 mm (3D model accuracy) | 5–15 minutes per tool (scan + processing) | Yes — provides the most comprehensive measurement | Yes — full 3D model of the BTA head, including insert pocket wear | $50 000–120 000 | High — operator must set up the scan and interpret the 3D model | Off-machine | Full 3D representation of the tool — can detect wear patterns that are not visible in 2D optical images; can measure guide pad wear and chip flute condition | Slow; high cost; requires skill to interpret; not suitable for production presetting — used for first-article qualification and failure analysis |
FAQ
What is the most critical tool geometry parameter for gun drilling accuracy, and how should it be measured?
The most critical tool geometry parameter for gun drilling accuracy is tip concentricity — the eccentricity (off-centre distance) between the carbide tip's rotational centre and the drill shank's rotational centre. Tip concentricity directly determines the bore position accuracy: a tip concentricity error of 0.003 mm causes the drill to rotate off-centre, producing a bore that is 0.006 mm oversize (the drill cuts at a radius that is 0.003 mm larger than its intended radius) and a sinusoidal path deviation with an amplitude equal to the concentricity error at the frequency of one cycle per revolution of the drill. The sinusoidal path deviation propagates over the bore length: for a gun drill with a 0.003 mm tip concentricity error drilling a 400 mm deep bore, the bore position at the far end can deviate by 0.10–0.30 mm from the intended position (the deviation is amplified by the drill's bending as it follows the sinusoidal path within the constraints of the drill bushings and the guide pads). The tip concentricity should be below 0.002 mm for precision gun drilling (bore position tolerance < ±0.05 mm at 500 mm depth) and below 0.005 mm for standard gun drilling (bore position tolerance < ±0.15 mm at 500 mm depth).
Tip concentricity is measured using an off-machine runout fixture: the drill is placed in a precision V-block (two V-blocks, one near the shank and one near the tip) and a dial indicator (0.001 mm resolution) is placed against the carbide tip at the outer diameter. The drill is rotated manually while the dial indicator reading is observed. The total indicated runout (TIR) is the difference between the maximum and minimum readings over one full rotation. The TIR measured at the drill tip should be less than 0.003 mm for precision gun drilling. The test must be performed with the drill at room temperature (20 ± 2°C) — a drill that has been heated by the resharpening grinding operation will cool and contract during the measurement, giving a false reading. The drill must be rotated at less than 10 rpm (manual rotation is acceptable) to avoid dynamic effects from out-of-balance. The measurement should be repeated at the 100 mm position behind the tip (to detect a bent drill — a drill that is bent at the mid-section will show 0.003 mm TIR at the tip but 0.01–0.02 mm TIR at 100 mm). The second most critical parameter is the step diameter tolerance — for a gun drill with a carbide tip diameter tolerance of h6 (0/−0.005 mm for Ø6 mm), the drill must be measured with a micrometer at two positions: at the carbide tip (to verify the diameter that cuts the bore) and at the steel shank (to verify the diameter that contacts the drill bushing). The tip diameter determines the bore diameter, and the shank diameter determines the bushing clearance and the centring accuracy. The tip diameter must be maintained within the specified tolerance across all regrinds (the diameter decreases by 0.001–0.002 mm per regrind as the carbide tip is ground to a fresh geometry, and the tool should be discarded when the tip diameter drops below the minimum).
When should an in-machine laser tool setter be used instead of an offline optical presetter, and what are the advantages of each approach for deep hole drilling?
The choice between an in-machine laser tool setter and an offline optical presetter depends on the primary measurement objective: if the objective is to verify that a resharpened or new tool has the correct geometry before it is used (quality assurance of the tool itself), an offline optical presetter is the correct choice. If the objective is to measure the tool's position and condition in the machine (compensation for spindle runout, thermal expansion, and tool wear during the production run), an in-machine laser tool setter is the correct choice. For production deep hole drilling, the recommended approach is to use both: an offline optical presetter for pre-load verification of every tool (ensuring that the tool geometry is correct before it is loaded into the machine), and an in-machine laser tool setter for periodic measurement of the tool in the spindle (compensating for thermal expansion and detecting tool wear during the run). The offline presetter provides the go/no-go decision for the tool before it enters production, preventing a defective tool (incorrect tip geometry, excessive runout, or chipped cutting edge) from causing a non-conforming bore. The in-machine laser setter provides the in-process compensation that ensures the bore diameter remains within tolerance as the tool heats up during the first 5–20 minutes of production (the drill expands thermally by 0.003–0.010 mm, which increases the bore diameter by the same amount). The laser setter measures the tip position and the CNC control compensates the tool offset in real time, maintaining the bore diameter within ±0.002 mm of the target throughout the production run.
The laser setter also detects tool breakage — each time the drill passes through the laser beam after a hole cycle, the laser sensor measures the tip position. If the tip position deviates by more than 0.05 mm from the previous reading (indicating that the tip has chipped or the drill has broken), the machine stops and alarms the operator. The breakage detection function prevents the machine from attempting the next bore with a broken drill (which would damage the workpiece and the bushing). The cost-benefit of adding a laser setter to a gun drilling machine ($8000–20 000) is typically recovered within 3–6 months through the reduction in scrapped components from tool wear and breakage. The offline presetter cost ($20 000–150 000) is recovered over 2–4 years through the reduction in first-article rejection caused by defective tools. For job shops that run a high variety of tool diameters and geometries, the offline presetter is essential because it allows a single operator to verify the geometry of 10–20 different gun drills in a single shift — a task that would require 2–4 hours of machine downtime if each tool were measured in the machine by the laser setter.
The information provided in this article is for general informational purposes only and does not constitute professional engineering advice. Always consult qualified metrology engineers, tooling suppliers, and equipment manufacturers for specific tool presetting applications. Data and recommendations are based on published research and industry experience as of 2026.