BTA Insert Chipbreaker: G vs HF Geometry Guide

An insert with the wrong chipbreaker will produce long stringy chips that pack the drill tube, a blocked coolant return, and a stalled spindle — in less time than it takes to read the feed rate readout. Chipbreaker selection is not a fine point of BTA drilling; it is the difference between a stable process and a jammed tube.

Why Chipbreaker Selection Matters ​

In BTA drilling, chips must travel the full length of the drill tube (often 1–15 metres) before exiting. Unlike open-face turning or milling, there is no room for error — a single uncut chip longer than the drill tube diameter can bridge the tube cross-section and block chip evacuation. The chipbreaker geometry on the insert determines:

Warning: The chipbreaker geometry on a BTA insert is not optional or interchangeable with turning inserts of the same size. BTA chipbreakers are specifically designed for the internal chip evacuation environment. Using a turning chipbreaker in a BTA head will produce chips that jam the tube within seconds.

Chipbreaker Types Overview ​

The ISCAR FINEBEAM BTA system — the most widely adopted indexable BTA tooling system — offers the following chipbreaker types:

The most commonly encountered types in production BTA drilling are G and HF, which are the focus of this guide. GF and DT are specialised geometries for specific machine or feed constraints.

Insert Position and Chipbreaker ​

Chipbreaker selection must account for insert position in the BTA head:

The peripheral insert (NPHT) does the majority of the cutting work and its chipbreaker selection has the greatest impact on process stability. Ground inserts (H type) are used at the periphery for tighter dimensional control.

G vs HF: Detailed Comparison ​

Chipbreaker Cross-Section ​

Feed Rate Capability by Material ​

The critical distinction between G and HF is the feed rate range they support. Data from the ISCAR HOLE MAKING catalog:

Metric equivalents:

Tip: The HF chipbreaker extends the upper feed limit by approximately 25–30% compared to G in most material groups. This is because the HF geometry is designed to break thicker chips at higher feed rates. However, the minimum feed remains similar — both types require a minimum chip load to activate the chipbreaking mechanism.

Material Group Recommendations ​

Other Chipbreaker Types ​

GF (Low Feed) Chipbreaker ​

The GF chipbreaker addresses a specific problem: BTA drilling at low feed rates (below 0.08 mm/rev) where standard G or HF geometries produce long, stringy chips. GF uses a positive rake with a unique chip gullet that forces chip curl even at minimal chip loads.

Test data (SUS304 at 0.04 mm/rev):

• GF chipbreaker: 4.5 m tool life per corner
• Standard geometry: 1.0 m tool life per corner

DT (Reduced Machine Load) Chipbreaker ​

The DT chipbreaker is designed for machines with limited spindle power. It reduces cutting forces by approximately 15–25% compared to G geometry through an open chip groove design. Use DT when:

• Machine power is marginal for the required diameter and depth
• Setup rigidity is compromised (older machines, long overhangs)
• Feed rate requirements are moderate to high

B and BG Chipbreakers ​

These are material-specific chipbreakers:

Insert Naming Convention ​

Understanding the insert code is essential for correct chipbreaker selection:

NPHT 060512R-HF IC908
││││  │││││ ││  │    │
││││  │││││ ││  │    └── Grade (IC908 = first choice for steel)
││││  │││││ ││  └── Chipbreaker (HF = High Feed)
││││  │││││ │└── Hand (R = Right, L = Left)
││││  │││││ └── Position (P = Peripheral, I = Intermediate, C = Center)
││││  ││││└── Corner radius (in 1/10 mm steps)
││││  │││└── Thickness (in 1/10 mm steps)
││││  ││└── Width/IC (in 1/10 mm steps)
││││  │└── Relief angle code
││││  └── Tolerance class
│││└── H = Ground insert (peripheral), M = Pressed (center/intermediate)
││└── P = Positive rake
│└── T = Tungsten carbide
└── N = Negative basic shape

Reading the Chipbreaker Code ​

For the position of the chipbreaker letter in the code:

• Position 8 in NPMT/NPHT codes: NPMT 050304_**R-G**-I
  • The dash separates the chipbreaker from the hand and position designator
  • G = General chipbreaker
  • HF = High Feed chipbreaker
  • Some codes place chipbreaker position differently — always verify with the manufacturer's catalog

Chip Control Principles ​

Chip Formation in BTA Drilling ​

The chipbreaker controls chip formation through three mechanisms:

1. Deflector height — The raised ridge in the chip groove forces the chip to bend sharply, creating a stress concentration that initiates fracture
2. Groove width — Determines the chip curl radius; narrower groove = tighter curl = easier breaking
3. Rake angle — Influences chip flow direction and cutting forces; more positive = easier curl

Target Chip Forms ​

Warning: Long ribbon chips in BTA drilling will bridge the drill tube in seconds. The first sign is a coolant return flow drop — within 5 seconds the tube will pack solid, and the resulting torque spike can twist the drill tube or damage the machine spindle. If chip form monitoring is not automated, assign an operator to check chip form at the return port every 2–3 holes.

Application Guide ​

Troubleshooting Chipbreaker Issues ​

FAQ ​

What is the difference between G and HF chipbreakers in BTA drilling? ​

G (General) is for standard feed rates across all material groups. HF (High Feed) has a more aggressive deflector profile that breaks thicker chips at feed rates 25–30% higher than G. HF is preferred for stainless steel, titanium, and hardened steels.

When should I use the HF chipbreaker? ​

Use HF when: running feed rates above 0.25 mm/rev, machining difficult materials (stainless, titanium, superalloys), or when the G chipbreaker produces long stringy chips. HF provides better chip control and process stability at elevated feeds.

When should I use the G chipbreaker? ​

Use G as the default choice for: carbon and alloy steels at standard feeds (0.10–0.30 mm/rev), cast iron (where graphite provides natural chip breaking), aluminium alloys, and where machine power is limited.

What is the GF chipbreaker for? ​

GF (Low Feed) is for applications where feed rate must be kept low — below 0.08 mm/rev — due to machine limitations or small diameter constraints. It produces short chips at feeds where G or HF would produce stringy chips.

What insert grade should I use with each chipbreaker? ​

IC908 is the first choice for most steel and stainless applications with both G and HF chipbreakers. Switch to IC806 with HF chipbreaker for titanium and superalloys where fracture toughness matters. IC9025 with G chipbreaker for high-speed finishing in cast iron.

Why does chipbreaker selection matter for the centre insert? ​

The centre insert operates at the lowest cutting speed (nearest to zero radius) and has the least chip load. Its chipbreaker must be capable of breaking chips at the lowest feed per tooth in the head. The peripheral insert has the highest load and the longest chip travel distance.

How can I tell what chipbreaker an insert has? ​

Read the insert code: for ISCAR FINEBEAM, the chipbreaker letter appears after the hand designator (e.g., NPMT 050304R-G-I). G = General, HF = High Feed, GF = Low Feed. Verify against the manufacturer catalog, as code placement varies between systems.

Can I mix chipbreaker types in one BTA head? ​

Yes — and this is common practice. For example, peripheral position with HF chipbreaker (high feed, needs aggressive breaking) and centre with G or GF (lower chip load). The peripheral insert does the most work and typically benefits most from HF geometry.

What does DT chipbreaker mean? ​

DT (Reduce Machine Load) is a chipbreaker designed for low-power machines. Its open geometry reduces cutting forces by 15–25% compared to G at the same feed rate. Use DT when machine power is the process bottleneck.

How does material group affect chipbreaker selection? ​

ISO-P (steel): G or HF both work. ISO-M (stainless): HF preferred. ISO-K (cast iron): G sufficient. ISO-S (superalloys): HF or B required. ISO-H (hardened): HF for stability. ISO-N (non-ferrous): G standard.

Conclusion ​

Chipbreaker selection is the most frequently overlooked parameter in BTA drilling setup, yet it determines whether the process produces stable C-type chips or jams the drill tube. The ISCAR FINEBEAM system offers G (General) for standard feeds across all material groups and HF (High Feed) for elevated productivity in difficult materials, plus specialised GF, DT, B, and BG geometries for specific constraints. The general rule: start with G for cast iron and soft materials, switch to HF for stainless steel and titanium at higher feeds, use GF when feed rates must be kept low, and select DT when machine power is limited. Within a single BTA head, chipbreaker type can be mixed by position — peripheral inserts benefit most from HF geometry, while centre inserts may use G or GF.