Manufacturing processesReading time 12 min
Choose the Cutter—and Know When to Replace It
Tool choice affects cycle time, finish and scrap risk. Match geometry and grade to the material and cut, then use wear and process signals to decide when the tool is done.
01Tool material and toughness
| Material | Hardness | Toughness | Typical use |
|---|---|---|---|
| High-speed steel | Low | High | Low speed, interrupted cuts, form tools |
| Powder metallurgy HSS | Medium-low | High | Broaches, hobs |
| Carbide | High | Medium | The vast majority of milling and turning |
| Cermet | High | Medium-low | Finish turning steel, excellent surface |
| Ceramic | Very high | Low | High-speed turning of cast iron and heat-resistant alloys |
| CBN | Very high | Low | Hardened steel above HRC 45 |
| PCD | Very high | Low | Aluminium, copper, composites (never steel) |
02What coatings do
| Coating | Colour | Temperature | Good at |
|---|---|---|---|
| TiN | Gold | About 600 °C | General purpose, cheap |
| TiCN | Blue-grey | About 400 °C | Wear resistant; suits stainless and cast iron |
| TiAlN / AlTiN | Purple-black | Above 800 °C | High-speed dry cutting, hard materials |
| AlCrN | Grey-blue | Above 1000 °C | Heat-resistant alloys, stable at temperature |
| DLC | Black | Low | Aluminium, copper and other gummy materials; prevents built-up edge |
| Uncoated (polished flute) | — | — | Aluminium alloys; a sharp edge that does not load up |
03Flutes and chip evacuation
- Two flutes. The most chip room; suits aluminium, deep slots and full-engagement slotting.
- Three flutes. The usual compromise for high-speed aluminium work.
- Four flutes. The general choice for steel; balanced rigidity and productivity.
- Five or more. Finishing and high-speed machining at light radial depth: faster feed at the same speed, but little chip room and no deep slotting.
Flute count affects feed because table feed is Vf = fz × z × n: feed per tooth, flute count and spindle speed. Adding flutes can raise feed at the same chip load, but only if the chips have room to escape and the machine has enough power.
04Making accurate holes
| Method | Achievable accuracy | Depth | Notes |
|---|---|---|---|
| Drill | IT11 ～ IT13 | 3 to 5 D typically | Poor positional accuracy; needs a spot drill or centre drill |
| Gun drill / deep-hole drill | IT9 ～ IT10 | Beyond 10 D | Through coolant, excellent straightness |
| Reamer | IT7 ～ IT8 | Shallow holes | Corrects size only, never position |
| Boring bar | IT6 ～ IT7 | Depends on the bar | Corrects position and roundness; single-point and adjustable |
| Helical interpolation | IT8 ～ IT9 | Depends on tool length | One tool covers many diameters; suits low-volume, high-mix |
05When to replace a tool
Wear does not have one pattern. Flank wear, built-up edge, chipping and crater wear point to different combinations of material, speed, feed and coolant. Identify the pattern before deciding whether to change the tool or the cutting conditions.
| Wear pattern | Appearance | Cause | What to do |
|---|---|---|---|
| Flank wear VB | A flat worn below the edge | Normal wear | Change at a set VB, usually 0.2 to 0.3 mm |
| Crater wear | A hollow in the rake face | Chip friction, diffusion wear | Reduce Vc, change coating |
| Chipping | A piece missing from the edge | Impact, chip packing | Reduce fz, improve chip evacuation, choose a tougher grade |
| Built-up edge | Material welded to the edge | Speed too low, gummy material | Raise Vc, use DLC or a sharper edge |
| Thermal cracking | Cracks perpendicular to the edge | Alternating heating and cooling in interrupted cuts | Cut dry or supply coolant steadily, never intermittently |