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Tool presetting and measurement are critical quality gates in deep hole drilling operations. Unlike conventional cutting tools where diameter and length are the primary parameters, gun drills and BTA tools require measurement of tip geometry, guide pad condition, coolant hole position, and concentricity — each directly affecting hole quality and tool life. This article covers the measurement methods and equipment used for deep hole drilling tool setup.
Why Tool Presetting Matters for Deep Hole Drilling
Deep hole drilling tools differ fundamentally from conventional drills in their geometry and cutting mechanics. A gun drill has a single cutting edge offset from the centerline, supported by guide pads that ride along the bore wall. A BTA head has multiple cutting edges with a complex arrangement of guide pads and chip passages.
Incorrect tool setup or undetected wear can cause:
| Problem | Root Cause | Effect |
|---|---|---|
| Oversized hole | Excessive tip offset or worn guide pads | Scrap or rework |
| Undersized hole | Insufficient tip offset | Tool binding, breakage |
| Poor surface finish | Worn cutting edge or damaged guide pads | Secondary finishing required |
| Bore taper | Asymmetric guide pad wear | Non-uniform hole diameter |
| Short tool life | Incorrect runout or coolant hole blockage | Increased tooling cost |
| Broken tool | Excessive runout or chip packing | Machine downtime, part loss |
A systematic presetting process reduces these risks by verifying tool geometry before the tool reaches the workpiece.
Gun Drill Measurement Parameters
Gun drills require measurement of several geometry parameters that are unique to their asymmetric design.
Critical Gun Drill Parameters
| Parameter | Description | Typical Tolerance | Measurement Method |
|---|---|---|---|
| Tip offset (K) | Radial distance from centerline to cutting edge | ±0.02–0.05 mm | Vision system, microscope |
| Outer corner radius | Radius at the periphery of the cutting edge | ±0.05 mm | Vision system |
| Inner corner geometry | Shape of the cutting edge near center | ±0.05 mm | Vision system |
| Shank diameter | Diameter of the drill shank for collet clamping | h6 | Micrometer |
| Head diameter (D) | Cutting diameter at the guide pads | ±0.01–0.02 mm | Micrometer, vision |
| Coolant hole position | Location of coolant exit relative to cutting edge | ±0.1 mm | Visual inspection |
| Overall length | Length from tip to shank end | ±0.5 mm | Height gauge, presetter |
| Runout (TIR) | Radial deviation at the tip when rotated | ≤ 0.01–0.02 mm | Dial indicator, presetter |
| Guide pad width | Width of the wear pad surface | ±0.1 mm | Caliper, vision |
Tip Offset Measurement
The tip offset — the distance from the drill centerline to the cutting edge — is the most critical parameter for hole size control. It determines the effective cutting diameter:
Effective cutting diameter = 2 × (tip offset) + (guide pad wear allowance)
A tip offset that is too large produces oversized holes. Tip offset that is too small produces undersized holes and can cause the guide pads to rub excessively.
Measurement method using a tool presetter:
- Mount the gun drill in the presetter spindle with the appropriate collet
- Rotate the drill to find the cutting edge position using the vision system
- Measure the radial distance from centerline to the cutting edge
- Compare against the tool drawing specification
- Record and apply any required offset compensation in the CNC program
Runout Measurement
Runout (total indicated runout or TIR) measures the wobble of the drill tip when rotated in the spindle. For gun drills, runout is measured at two points:
| Measurement Point | Acceptable TIR | Effect of Excessive Runout |
|---|---|---|
| At the drill tip | ≤ 0.01 mm | Oversized hole, poor finish |
| 100 mm from the tip | ≤ 0.02 mm | Hole straightness deviation |
Measurement method:
- Mount the tool in the machine spindle (not a presetter — machine spindle conditions matter)
- Position a dial indicator or laser sensor at the measurement point
- Rotate the spindle manually
- Read the total indicator movement
- Adjust collet or holder if runout exceeds specification
TIP
A tool presetter measures the tool in a stationary spindle, which does not replicate the machine's spindle runout conditions. For final verification, always measure runout with the tool mounted in the machine spindle. Machine spindle runout and collet condition can add 0.005–0.015 mm of additional runout beyond what the presetter measures.
BTA Tool Measurement Parameters
BTA drilling heads have a more complex geometry than gun drills, requiring additional measurement parameters.
Critical BTA Tool Parameters
| Parameter | Description | Typical Tolerance | Measurement Method |
|---|---|---|---|
| Cutting diameter | Diameter across all cutting edges | ±0.02–0.05 mm | Micrometer, setting gauge |
| Guide pad diameter | Diameter across guide pads | ±0.02 mm | Micrometer |
| Pad-to-pad concentricity | Concentricity between multiple guide pads | ≤ 0.01 mm | Dial indicator |
| Step height difference | Height variation between cutting edges | ±0.02 mm | Height gauge, vision |
| Chip breaker geometry | Width and depth of chip formers | ±0.1 mm | Visual, microscope |
| Coolant hole condition | Open passage, no blockage | Pass/fail | Visual, air flow test |
| Seat face condition | Condition of the seating surface on the drill tube | Pass/fail | Visual |
Guide Pad Measurement
Guide pads on BTA tools wear progressively and must be measured to determine when replacement is needed.
Measurement method:
- Clean the tool head thoroughly
- Measure guide pad width using a caliper or micrometer
- Measure guide pad height from the tool body using a depth micrometer
- Check for uneven wear (one pad worn more than the other)
- Compare remaining pad height against the minimum allowable dimension
Cutting Edge Inspection
BTA heads with indexable inserts require checking:
- Insert seating — no chips or debris under the insert
- Clamp torque — verified with a torque wrench
- Edge condition — checked with a magnifier or microscope
- Insert grade — verified against the specification
- Height consistency — all inserts at the same height within ±0.02 mm
Tool Presetting Equipment
Vision-Based Presetters
Modern vision presetters are the most versatile option for deep hole drilling tool measurement.
| Feature | Benefit for Deep Hole Drilling |
|---|---|
| Magnified view (20–200×) | See cutting edge condition, chip breakers, wear |
| Profile measurement | Measure tip offset, corner radius, angle |
| Rotating spindle with encoder | Runout measurement, edge position |
| Incident and transmitted light | Inspect cutting edges and coolant holes |
| Data output | Export measurements to tool management system |
| Image storage | Document tool condition for quality records |
Vision presetters suitable for gun drills include:
- Benchtop models (Zoller, BIG Kaiser Innotool, Kelch, Speroni) — Most common, good for tools up to 500 mm length
- Floor-standing models — For large BTA tools exceeding 500 mm length
- Horizontal presetters — For very long gun drills (2,000+ mm) where vertical mounting is impractical
Contact Measurement
For simple diameter and runout measurement of gun drills and BTA tools:
| Tool | Measures | Accuracy |
|---|---|---|
| Micrometer | Head diameter, shank diameter | ±0.002 mm |
| Dial indicator + V-block | Runout, concentricity | ±0.005 mm |
| Setting gauge + feeler gauge | Tip offset (gun drill) | ±0.02 mm |
| Tool presetter (contact) | Length, diameter | ±0.005 mm |
| Laser micrometer | Diameter (non-contact) | ±0.002 mm |
Dedicated Gun Drill Measurement Fixtures
Some manufacturers use dedicated fixtures with:
| Feature | Purpose |
|---|---|
| V-block support along the shank | Support long gun drills for measurement |
| Precision collet or chuck | Mount the shank with consistent positioning |
| Dial indicators at multiple positions | Measure runout along the drill length |
| Microscope or camera | Inspect the tip geometry |
| Reference surface | Establish consistent measurement datum |
Measurement Frequency
Recommended Inspection Schedule
| Check | Frequency | Method |
|---|---|---|
| New tool inspection | Every new or resharpened tool | Full geometry measurement |
| Tool tip offset | Every tool before first use | Vision presetter |
| Runout on machine | Every tool change | Dial indicator on machine spindle |
| Cutting edge condition | After each use | Visual or vision inspection |
| Guide pad condition | Every 10–50 holes (depending on material) | Direct measurement |
| Diameter check | Every tool change | Micrometer or presetter |
| Coolant hole patency | Every tool change | Air flow check |
| Tool length offset | Each tool change | Tool presetter or machine probe |
When to Reject or Replace a Tool
| Condition | Action |
|---|---|
| Tip offset outside ±0.05 mm of specification | Reject — cannot produce correct hole size |
| Runout > 0.02 mm at tip | Check collet, re-mount, if still high — reject |
| Guide pad worn below minimum dimension | Replace guide pads |
| Cutting edge chipped or fractured | Re-sharpen or replace insert |
| Coolant hole blocked | Clear blockage; if unsuccessful — reject |
| Shank damaged (nicks, scoring) | Reject — will cause mounting inaccuracies |
Presetting Process Procedure
Recommended Presetting Workflow
- Clean the tool — Remove all chips, coolant residue, and debris
- Visual inspection — Check for damage, wear, or abnormalities
- Mount in presetter — Use the correct collet, clean the collet bore first
- Measure overall length — Set the length offset
- Measure diameter — Record head diameter at the guide pads
- Measure tip offset (gun drill) — Verify cutting geometry
- Measure runout — Rotate tool, record TIR
- Inspect coolant hole — Verify clear passage
- Document results — Record all measurements in tool log
- Tag the tool — Mark as inspected and ready for use
Data Recording
Tool measurement data should be recorded for:
- Tool life tracking — Predict remaining tool life from wear trends
- Quality traceability — Link hole measurements to tool geometry at time of production
- Process optimization — Identify correlations between setup parameters and hole quality
- Supplier quality monitoring — Track consistency of resharpened tools
Common Setup Errors
| Error | Symptom | Correction |
|---|---|---|
| Tool not fully seated in collet | Length offset incorrect, runout | Re-mount with proper seating |
| Dirty collet or holder | Runout, tool vibration | Clean all mating surfaces |
| Wrong tip offset compensation | Oversized or undersized holes | Verify tip offset, adjust CNC offset |
| Inconsistent guide pad measurement | Unexpected diameter variation | Use consistent measurement procedure |
| Coolant hole misalignment | Poor chip evacuation | Rotate tool to align coolant hole with chip opening |
| Worn collet | Progressive runout increase | Replace collet at regular intervals |
FAQ
Q: What is the most critical parameter to measure on a gun drill? Tip offset is the most critical parameter. It directly determines the hole diameter, which is the primary quality characteristic for most deep hole drilling operations. A 0.01 mm error in tip offset produces a 0.02 mm error in hole diameter.
Q: How often should gun drill runout be checked? Runout should be checked at every tool change — meaning every time a new or resharpened tool is mounted in the machine spindle. Machine spindle runout should be checked quarterly or whenever a crash occurs.
Q: Can a standard tool presetter measure gun drills? Yes, most vision-based tool presetters can measure gun drills. However, very long gun drills (over 1,000 mm) may require a horizontal presetter or special fixturing. The presetter must have a rotating spindle for runout measurement and a sharp, clear vision system for tip geometry measurement.
Q: How is a BTA drill head measured? BTA heads are measured primarily for cutting diameter (across all cutting edges) and guide pad diameter. Indexable insert height is checked with a height gauge or dial indicator. The seating face where the head attaches to the drill tube is inspected for damage.
Q: What is the acceptable runout for a gun drill? Total indicated runout (TIR) at the drill tip should be ≤ 0.01 mm for precision work and ≤ 0.02 mm for general applications. Runout measured 100 mm from the tip should not exceed 0.02 mm.
Q: How do you measure guide pad wear on a gun drill? Guide pad wear is measured by the reduction in pad width and the increase in clearance between the pad surface and the nominal drill diameter. A worn pad will have reduced contact area and visible scoring marks. Micrometer measurement across the pads compared to the original specification quantifies the wear.
Q: What equipment is needed for a deep hole drilling tool presetting station? Minimum: a vision tool presetter with rotating spindle, micrometers, a clean workspace with good lighting, tool holders and collets, and a data recording system. Recommended addition: a microscope for detailed edge inspection.
Q: How does tool presetting differ between gun drilling and BTA drilling? Gun drill presetting focuses on tip offset and single-edge geometry. BTA presetting focuses on cutting diameter consistency across multiple cutting edges, guide pad condition, and insert seating quality. Both require runout measurement and coolant hole verification.
Q: Should tool presetting data be recorded for every tool change? Yes. Recording tool measurement data enables trend analysis (wear rate prediction), quality traceability (linking part measurements to tool condition), and process optimization (identifying the best setup parameters).
Q: What is the typical time required to preset a gun drill? A thorough presetting procedure — including cleaning, mounting, length/diameter/runout measurement, tip offset verification, coolant hole check, and documentation — takes 3–8 minutes per tool, depending on experience and equipment capability.