The choice of material affects the price of a turned part twice — once through the price of the bar and a second time through the machining time the part spends on the machine. In series production the second item usually weighs more: stainless steel can occupy the machine several times longer than free-cutting steel, and that shows in the unit price more than the difference in material price.
Machinability: what it means and why it matters
Machinability describes how a material behaves when cut — whether the chip breaks short or coils into a long spiral, how quickly it wears the tooling, and what cutting speed is possible.
On sliding-head automatics this is decisive. The machine runs long shifts unattended; a material that forms long chips wraps them around the workpiece and stops the run.
| Material | Machinability | Chip | Main limitation |
|---|---|---|---|
| Free-cutting steel | excellent | short, brittle | rusts without surface protection |
| Brass | excellent | short, crumbly | higher material price |
| Aluminium | good, fast | long, sticky | sticks to the cutting edge |
| Stainless steel | demanding | tough, breaks poorly | long machining time |
Free-cutting steel — the benchmark
Free-cutting steel has a raised sulphur content that markedly improves machinability. The chip breaks short, the tool lasts, cutting speed is high. For series parts with no particular corrosion requirement it is the cheapest choice.
Limits: it rusts and welds poorly. In a damp environment it needs surface treatment.
Brass — best machinability, higher entry price
Brass machines superbly: the chip crumbles, tooling lasts, achievable surface roughness is excellent. The material is also electrically conductive and corrosion resistant, which suits it for contact pins, connectors, valves and fittings.
Limits: the price per kilo is above steel, and brass is soft — unsuitable for highly loaded parts.
Aluminium — fast, but with catches
Aluminium takes high cutting speeds, so machining time is short; it is light and corrosion resistant.
Limits: it sticks to the cutting edge and forms long chips. Long unattended runs therefore need more attention. The price per kilo is usually above free-cutting steel.
Stainless steel — if it must be, then deliberately
Stainless steel is tough, the chip breaks less readily and cutting speeds are lower. The machine spends longer on the part and tooling wears faster.
There is, however, a compromise — free-machining stainless with added sulphur for better machinability. Its corrosion resistance is below that of standard stainless, but it is often sufficient for mildly corrosive environments and it shortens machining time considerably.
When a material change pays off
Three situations where it is most often worth reconsidering:
| On the drawing | When an alternative suffices | Alternative |
|---|---|---|
| Stainless steel | part sits inside equipment, low corrosion load | free-cutting steel + zinc plating |
| Stainless steel | corrosion protection needed, chemical resistance not | free-machining stainless |
| Aluminium | chosen for “lightness”, but weight is not critical | free-cutting steel |
The first row is by far the most common: steel with zinc plating comes out cheaper than stainless and lasts just as long in an ordinary environment. What plating does to dimensions, and what therefore belongs in the drawing, is covered in the article on surface treatment of turned parts.
⚠️ Never change the material without the designer’s approval. The point is not to push the cheaper option, but to ask whether the original choice still matches the function. A good supplier raises the question at quotation stage.
What belongs in the request
For a supplier to assess the material, they need more than the grade from the drawing:
- What the part does and in what environment it works
- Whether it will be welded (which rules out free-cutting steel)
- Whether surface treatment is required
- Whether the material is mandatory, or an alternative may be proposed
- Any sector requirements (food, medical, material certificate)
The last point is often decisive — if you need a material certificate or batch traceability, it has to be in the request from the start.
What Barluskat brings to this
On sliding-head automatics by Tsugami and Star Micronics we process free-cutting steel, stainless steel, aluminium, brass and steel tube in the range Ø 3–35 mm, in medium and large batches.
We source the material ourselves and it is included in the part price. We choose the specific grade according to the function of the part and the environment it works in — write us both in the request and we will propose the material. If we see the part could be made more cheaply without affecting function, we will say so.
We provide material certificates and batch traceability — on parts for automotive and medical, where we supply, that is usually a condition.
Choosing a material for a series part? Send us the drawing and tell us what the part is for. An overview of materials and machinery is on the Manufacturing page.