A turning or milling insert ends in a small corner called the nose radius. Pick the right radius and you get mirror finish, longer tool life, and lower cycle time. Pick it wrong and chatter, burrs, or extra passes ruin your quote. This guide explains, in plain language, how to match insert radius to feed, depth, and material so your finishing cuts shine.
目次
- Why insert radius choice impacts finish
- Key terms for radius and feed
- Surface roughness vs feed and radius
- Recommended radius by material
- Depth of cut and chatter risk
- Tool life and edge strength
- Radius selection for turning vs milling
- CNC parameter cheat sheet
- Optimize cost with correct radius
- Need precision machined surfaces?
- Quick recap before running finish pass
Why Insert Radius Choice Impacts Finish
The nose radius forms the final scallop on the part. A larger radius blends peaks but also pushes more metal, which can vibrate thin walls. A smaller radius cuts lightly yet leaves deeper feed marks. Balancing these effects is the art of finishing.
Key Terms For Radius And Feed
Review four short definitions before looking at numbers.
| Term | Symbol | Typical range | Meaning |
|---|---|---|---|
| Nose radius | R | 0.1–1.2 mm | Corner arc on insert |
| Feed per rev | f | 0.02–0.4 mm | Tool advance in one turn |
| Scallop height | h | 1–10 µm | Peak-to-valley left on part |
| Depth of cut | ap | 0.05–0.3 mm (finish) | Radial engagement |
These four drive finish and tool load in every NC block.
Surface Roughness Vs Feed And Radius
The next chart links theoretical Ra to feed and radius; smaller values read smoother.
Feed mm/rev | Ra µm @ R=0.2 | Ra µm @ R=0.4 | Ra µm @ R=0.8 ------------------------------------------------------------ 0.04 | 0.6 | 0.3 | 0.15 0.08 | 2.2 | 1.1 | 0.55 0.12 | 5.0 | 2.5 | 1.2 0.20 | 11 | 5.5 | 2.8
Rule of thumb: Keep feed less than one-third of radius to hit a Ra below 1 µm.
Recommended Radius By Material
Chip support and surface requirements differ among metals. The table offers practical starting points.
| 素材 | Finish goal Ra µm | Suggested radius mm | Typical feed mm/rev | Reason |
|---|---|---|---|---|
| アルミニウム6061 | <0.8 | 0.4 | 0.05 | Soft chip, low cutting force |
| Mild steel 1018 | <1.0 | 0.8 | 0.08 | Stiffer chip, needs support |
| Stainless 304 | <1.2 | 0.4 | 0.06 | Work-hardens, avoid heat |
| Titanium 6-4 | <0.9 | 0.2 | 0.04 | High force, chatter prone |
| 真鍮 C360 | <0.6 | 0.8 | 0.10 | Brittle chip, low burr |
If the part wall is thin, drop the radius one size to cut radial load.
Depth Of Cut And Chatter Risk
Finish passes often use ap between 0.05 and 0.15 mm. A large radius may plow instead of cut. The bar graph shows chatter tendency on a 50 mm steel bar at 0.1 mm depth.
Radius mm | Chatter index* 0.2 | █ 0.4 | ██ 0.8 | ████ 1.2 | ██████
*Higher bar means more chatter. Keep radius to 0.4 mm or less when tool overhang exceeds four times its diameter.
Tool Life And Edge Strength
Smaller radius edges chip sooner. The next table compares tool life at equal feeds.
| Radius mm | Turning 1045 life min | Milling 7075 life min |
|---|---|---|
| 0.2 | 11 | 9 |
| 0.4 | 19 | 15 |
| 0.8 | 28 | 22 |
Choose a coated 0.8 mm radius for long runs if the part tolerates the slightly higher scallop.
Radius Selection For Turning Vs Milling
Turning inserts hold one radius, while milling uses cutter corners. For face mills, a 0.8 mm corner lowers notch wear on interrupted cuts. For ball-nose finishing, radius equals the ball itself; keep feed per tooth below 0.02 mm to reach Ra under 0.6 µm.
CNC Parameter Cheat Sheet
Match radius, feed, and speed for a predictable finish.
| Radius mm | Max feed mm/rev | Surface speed m/min (steel) | Depth of cut mm |
|---|---|---|---|
| 0.2 | 0.05 | 120 | 0.05 |
| 0.4 | 0.08 | 150 | 0.10 |
| 0.8 | 0.12 | 180 | 0.15 |
Increase cutting speed by 20 % when machining aluminum or brass with the same radius.
Optimize Cost With Correct Radius
The curve below links cycle time and insert consumption. A mid-range radius usually pays off.
Radius mm | Cycle time sec | Inserts per 1000 parts 0.2 | 40 | 5 0.4 | 32 | 4 0.8 | 30 | 3
Radius 0.4 mm often wins: shorter cycle, good life, acceptable finish.
Need Precision Machined Surfaces?
Our team picks the right radius, grind, and coating for every job, then machines metal or plastic parts in one stop. Upload your drawing for a swift, all-in-quote.
Quick Recap Before Running Finish Pass
- Keep feed ≤ one-third of radius for Ra below 1 µm.
- Use 0.4 mm radius for general steel, 0.2 mm for thin walls, 0.8 mm for long life.
- Lower radius when chatter shows, raise when edge chips.
- For plastics, use sharp 0.2 mm un-coated inserts and light feeds.
- Log roughness data and adjust on the next run.
Follow these rules and your finishing passes will sparkle—without extra polishing or wasted inserts.
