CNC Turned vs Milled Parts
— Which Process Do You Need?

When you need a precision machined component manufactured — whether a replacement part, prototype or production batch — the most fundamental question is: should this be CNC turned or CNC milled? Getting this right affects cost, lead time and quality. This guide explains clearly when to use each process and what information you need to provide to get an accurate quotation.

CNC Turning — What It Is and What It Makes

In CNC turning, the workpiece rotates while a cutting tool removes material. This is fundamentally a process for making cylindrical and rotational components. If the part is round in cross-section — or mostly round — it is almost certainly a turned part.

When You Need Both — Combined Operations

Many precision components require both turning and milling. A shaft with keyways needs turning first, then milling for the keyway. A housing with a bored cylindrical seat needs milling for the outer shape and turning/boring for the internal bore. At Bajrang Engineering Works we manufacture combined-operation components as a single order — you receive a finished part, not separate operations to assemble.

Tolerances: What Can Each Process Achieve?

For components requiring bearing-fit tolerances (h6/H7) — such as shafts running in bearings or housings with press-fit bearings — grinding after turning or boring is essential. Always specify the fit class you need (h6, H7, f7, etc.) rather than a numeric tolerance if you know the bearing you are fitting to.

How to Specify a CNC Machined Part Correctly

To get an accurate quotation quickly, provide as many of these as possible:

For a Turned Part (Shaft, Roller, Bush):

• Overall length and maximum diameter
• Diameter and length of each step or section
• All bore diameters (if hollow)
• Thread specifications if any (M30x2, G1/2 BSP, etc.)
• Keyway dimensions if required
• Fit class on critical diameters (h6, f7, etc.) or tolerance (±0.02mm)
• Material required (EN8, EN36, SS304, phosphor bronze, etc.)
• Surface finish requirement on critical surfaces
• Any heat treatment required (case harden, induction harden)

For a Milled Part (Housing, Flange, Bracket):

• Overall envelope dimensions (length x width x height)
• Drawing or sketch (even hand-drawn is helpful)
• All hole positions, diameters and depths
• Any bored or reamed holes with fit class
• Thread positions and specifications
• Material and finish required

When Grinding is Required

Grinding is necessary when a turned or milled surface needs to meet bearing-fit tolerances or a very fine surface finish. Common situations requiring grinding:

• Shaft journals that run in plain or rolling element bearings
• Housing bores that accept press-fit bearings
• Gear tooth profiles for DIN class 5 or 6 quality
• Hydraulic cylinder bores and pistons
• Any surface requiring Ra 0.4 to 0.8 micron finish
• Precision lead screws for CNC machines

If you are unsure whether your component needs grinding, tell us the application and we will advise on the appropriate process.