The automotive brake drum is a key component of a drum brake system, widely used in commercial vehicles, light trucks, and older passenger cars. It works in conjunction with brake shoes to provide friction for deceleration and stopping.
Over time, due to friction and heat, brake drums can become worn, scored, or out of round. Proper machining of brake drums — whether during manufacturing or resurfacing in repair — is critical to restoring precise geometry, surface finish, and braking performance.
PCBN (Polycrystalline Cubic Boron Nitride) inserts possess extremely high wear resistance, thermal stability, and red hardness at high temperatures. These properties make them particularly suitable for high-speed machining of gray cast iron brake drums.
Copared with traditional cutting tools, PCBN inserts can achieve higher machining efficiency and better surface quality.
A brake drum is a cylindrical component attached to the wheel hub. When the brake pedal is pressed, brake shoes with friction linings expand outward to press against the inner surface of the rotating drum, generating frictional torque that slows or stops the wheel.
Typical brake drums include:
Drum body (working surface) – The inner cylindrical surface where friction occurs.
Mounting flange – Connects the drum to the wheel hub or axle.
Cooling fins or ribs – Enhance heat dissipation and structural rigidity.
Pilot hole and bolt holes – Ensure accurate installation alignment.
Brake drums are usually made from gray cast iron (HT250–HT300) due to its excellent wear resistance, damping capacity, and thermal conductivity. For heavy-duty applications, nodular cast iron (ductile iron) or aluminum alloy with cast iron liner may be used to reduce weight.
Brake drum machining involves turning, boring, drilling, balancing, and finishing. Depending on the production stage (new part or repair), the process differs slightly.
Manufacturing of New Brake Drums
For new brake drums, machining operations are performed on cast blanks using CNC or specialized drum lathes. The process flow generally includes:
Casting inspection and cleaning
Rough turning of outer surface and flange
Machining mounting holes and pilot hole
Semi-finishing inner friction surface
Heat treatment and stress relief
Finish turning of inner surface and outer diameter
Drilling bolt holes
Dynamic balancing and inspection
Resurfacing (Repair) Machining
In brake maintenance, resurfacing or refacing is done to remove scoring or taper wear on the inner surface. Specialized brake drum lathes are used to restore the cylindrical geometry.
Resurfacing steps:
Inspection and measurement – check drum diameter and thickness.
Mounting on drum lathe – align the drum accurately on arbor or hub.
Rough cutting – remove damaged or uneven material.
Finish cutting – achieve smooth surface and correct diameter.
Chamfering and deburring
Cleaning and balancing check
Tool Materials
Brake drum machining involves cutting cast iron, which is brittle but abrasive. Therefore, tool materials must have high wear resistance and thermal stability.
Common tool types include:
-PCD (Polycrystalline Diamond) Tools – for aluminum alloy drums or composite drums.
-CBN (Cubic Boron Nitride) Tools – for hardened iron or high-speed finishing.
-Carbide Inserts (CVD-coated) – economical and suitable for most gray iron machining.
Tool Geometry
For internal turning of brake drums:
Rake angle: 0°–10°
Clearance angle: 6°–8°
Nose radius: 0.4–0.8 mm for finishing
Tool Bonding and Edge Preparation
When machining gray cast iron, sharp edges are unnecessary — a slight hone (0.02–0.05 mm) improves tool life. For aluminum drums, polished cutting edges prevent material sticking.
Let’s go step-by-step through new brake drum machining and resurfacing.
* Clean casting with compressed air and remove any burrs or sand.
* Check for cracks, porosity, or casting defects.
* Verify dimensions according to the design drawing.
Mount the drum casting on a CNC or manual lathe using a 3-jaw chuck or special fixture.
Operations:
Turn the outer cylindrical surface.
Face the mounting flange.
Rough-turn the inner friction surface (leave machining allowance).
Parameters (typical for cast iron):
Cutting speed: 120–180 m/min
Feed rate: 0.3–0.5 mm/rev
Depth of cut: 1.5–3 mm
-Drill pilot holes and bolt holes on the flange. Bore the central hole for mounting.
Tools used:
-Carbide-tipped drill
-Reamer or boring tool for precision diameter
After stress relief or heat treatment, the drum is remounted for semi-finishing.
This ensures dimensional stability and minimizes distortion.
Parameters:
-Cutting speed: 150–200 m/min
-Feed: 0.2–0.3 mm/rev
-Depth of cut: 0.5–1 mm
Final finishing defines the precise geometry and surface quality of the friction surface.
Requirements:
Roundness ≤ 0.02 mm
Surface roughness Ra 1.6–3.2 µm
Parallelism of flange ≤ 0.02 mm
Tool choice:
CBN insert for gray cast iron finishing
PCD insert for aluminum composite drums
Parameters:
Cutting speed: 200–350 m/min
Feed rate: 0.1–0.2 mm/rev
Depth of cut: 0.1–0.3 mm
Smooth all edges to remove burrs and sharp corners. This prevents assembly interference and cracking.
Dynamic balancing is critical for brake drum performance. Unbalanced drums can cause vibration, uneven braking, or bearing wear.
Inspection includes:
Runout test (≤ 0.05 mm)
Roundness check (≤ 0.02 mm)
Balance test (ISO 1940 grade G16 or better)
Surface roughness measurement
After machining, the brake drum is thoroughly cleaned to remove chips and oil, then coated with anti-rust oil before packaging or assembly.
As an enterprise specializing in the R&D and manufacturing of PCBN cutting tools, we have been committed to the R&D and production of superhard cutting tools over the past 10 years.
In the field of brake drum machining, our PCBN inserts demonstrate significant technological advantages. The fully sintered PCBN inserts we produce feature ultra-high wear resistance and impact resistance, which can effectively help customers reduce the frequency of tool changes, improve machining efficiency, and lower production costs. The multi-edge indexable PCBN inserts launched this time possess extremely high hardness and wear resistance, greatly enhancing production efficiency and serving as an ideal choice for cutting gray cast iron.
Other ceramic inserts | More Super Hard | |
Workpiece and material | brake drums HT250 | |
Part | Brake surface | |
Inserts model | CNGN120412 | CNGN120412 MBN2800 |
Ap(mm) | 1~2 | |
V(m/mim) | 800~1000 | |
F(mm/rev) | 0.3~0.4 | |
Tool life | 40~60 | 160~180 |
In terms of machining accuracy, our PCBN inserts reduce friction between the tool flank and the workpiece through a unique cutting edge design, which alleviates tool wear while enhancing cutting edge strength and cutting stability. This design ensures that the machined products have high precision and surface finish, good dimensional consistency, and small shape errors.
Our PCBN inserts also support high-speed cutting, which can significantly improve machining efficiency. In brake drum machining, high efficiency means being able to complete production tasks faster and meet market demands.
---EDITOR: Doris Hu,Miya Ma
--POST: Doris Hu
Semiconductor Industry Solutions
PCD & PCBN Tools Grinding Industry
Diamond Cutting Bruting Polishing
Add: No.171 Zhongyuan Rd, Zhongyuan District, Zhengzhou, 450001, Henan, China
Tel: +86-371-86545906
Phone / Whats App: +86 18339903057
E-mail: [email protected]
