The Ultimate Buying Guide for Cutting-Off Tools: How to Choose the Right Cutoff Tool for Your Machining Needs
This comprehensive buying guide covers everything you need to know about cutting-off tools, from material selection and geometry to coating options and cutting parameters. Includes detailed specification tables to help you make an informed purchase decision.
What Is a Cutting-Off Tool and Why Does It Matter?
A cutting-off tool (also known as a parting tool or cutoff tool) is a single-point cutting tool used to separate a finished workpiece from the remaining stock on a lathe or automatic screw machine. Unlike turning or grooving tools, the cutoff tool must withstand high axial forces and provide a clean, burr-free cut at the very end of the machining cycle. Selecting the right cutoff tool directly impacts part quality, cycle time, tool life, and overall cost per part.
Key Selection Criteria for Cutting-Off Tools
1. Tool Material
The substrate of the cutting edge determines its hardness, toughness, and heat resistance. Common materials include:
| Material | Hardness (HRA) | Key Characteristics | Best For |
|---|---|---|---|
| High-Speed Steel (HSS) | 60–65 | Tough, low cost, easy to re-grind | Low-volume, manual machines; small diameters |
| Uncoated Carbide | 89–93 | High hardness, good wear resistance | General-purpose steel and cast iron |
| Coated Carbide (PVD/CVD) | 89–93 | Enhanced wear resistance, lower friction | High-speed production, steels, stainless steels |
| Cermet | 90–94 | Excellent heat resistance, chemical stability | Finish cutting, hard steels, high surface finish |
| Polycrystalline Diamond (PCD) | 95+ | Extreme wear resistance, non-ferrous only | Aluminum, composites, high-volume production |
2. Coating Technology
Coatings extend tool life by reducing friction, heat buildup, and built-up edge. Popular coatings for cutoff tools include:
- TiN (Titanium Nitride) – Gold-colored, general-purpose, good for steel.
- TiCN (Titanium Carbonitride) – Dark gray, harder and more wear-resistant than TiN.
- AlTiN (Aluminum Titanium Nitride) – Blue-black, excellent for high-temperature operations (e.g., stainless steel, super alloys).
- TiAlN (Titanium Aluminum Nitride) – Similar to AlTiN, very high temperature stability.
- CVD Diamond – For non-ferrous materials; extremely hard, but brittle.
3. Insert Geometry and Chip Control
Cutoff tools are available in different geometries that influence cutting forces, chip formation, and surface quality:
| Geometry Type | Rake Angle | Relief Angle | Advantages |
|---|---|---|---|
| Standard flat top | 0°–6° | 6°–8° | Lowest cost, simple regrinding |
| Positive rake | 8°–15° | 6°–10° | Lower cutting forces, better for small diameters |
| Negative rake | −5° to −10° | 6°–8° | Stronger cutting edge, longer life on tough materials |
| Chip former / grooved | 0°–10° | 6°–12° | Excellent chip control, avoids bird-nesting |
4. Shank Design and Tool Holding
A stable clamping system is critical for chatter-free cutoff operations. Common shank types include:
- Square shank (blade-style) – For traditional turning centers; offers high rigidity.
- Dovetail or wedge-style – Prevents pull-out during heavy cuts.
- Quick-change tool posts – Reduce setup time on manual lathes.
- Tool block / holder for CNC – Must match turret or slide specifications.
Ensure the tool overhang is minimized (ratio of overhang to shank depth ≤ 1.5) to avoid vibration.
5. Cutting Parameters
Proper cutting speed, feed rate, and depth of cut are essential for tool life and part quality. The table below provides general starting recommendations for common workpiece materials using coated carbide inserts:
| Workpiece Material | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) |
|---|---|---|---|
| Low-carbon steel (e.g., 1018) | 180–250 | 0.05–0.15 | 2–6 |
| Alloy steel (e.g., 4140) | 140–200 | 0.04–0.12 | 2–5 |
| Stainless steel (304) | 100–160 | 0.03–0.10 | 1–4 |
| Cast iron (gray) | 150–220 | 0.06–0.18 | 2–7 |
| Aluminum (6061) | 400–800 | 0.08–0.25 | 3–8 |
| Brass / bronze | 250–400 | 0.07–0.20 | 2–6 |
Common Mistakes to Avoid When Buying Cutoff Tools
- Using a sub-size tool for large diameters – The tool must have sufficient blade width to handle the bar diameter. A good rule: blade width ≥ 0.10 × bar diameter.
- Ignoring chip evacuation – Without proper chip breaking, long stringy chips can wrap around the tool and cause breakage. Choose inserts with chip formers for ductile materials.
- Incorrect feed rate – Too low a feed may cause rubbing and work hardening; too high a feed can lead to tool breakage. Always start with the manufacturer’s recommended range.
- Overlooking coolant delivery – High-pressure coolant (40–70 bar) directed at the cutting zone dramatically improves tool life, especially in deep cuts.
Top Brands and What to Look For
While this guide focuses on selection criteria, it is helpful to know that reputable tool manufacturers such as Sandvik Coromant, Kennametal, Iscar, Walter, and Seco offer extensive cutoff product lines. When comparing options, look for:
- Modular tooling systems – Allow you to change inserts without removing the shank.
- Multi-edged inserts – Some vendors offer double-ended or even four-edged inserts for lower cost per edge.
- Corner radius options – A radius of 0.2–0.4 mm improves edge strength; sharper radii yield better finishes but are more fragile.
Final Checklist Before You Buy
- Determine the maximum workpiece diameter and material type.
- Select the tool material and coating based on material and cutting speed.
- Choose an insert geometry that matches chip control needs.
- Verify that the shank size and style fit your machine’s tool holder.
- Start with conservative cutting parameters and adjust based on results.
- Consider buying a small sample set first to test tool life and finish.
By following this guide, you can confidently select a cutting-off tool that delivers consistent performance, reduces downtime, and lowers your cost per cut. For further technical assistance, consult the manufacturer’s online databases or contact their application engineers.