Saw-Cut Burr Removal for Tube Bending Tooling Protection

Unchamfered tube edges and heavy saw-cut burrs on raw cut stock introduce immediate mechanical damage to internal bending components. When a tube with an inward-facing burr or ragged saw cut is loaded over a mandrel, the sharp steel protrusion acts as a cutting tool against the hardened surface of the mandrel nose and balls. Over repeated cycles, these burrs tear grooves into the mandrel body, alter the effective diameter of the support tooling, and strip protective lubrication films. Pre-processing the tube end with a dedicated beveling unit such as the Bora pipe chamfering machine removes both inner and outer burrs while establishing a true perpendicular face for consistent axial location against carriage stops.

Mechanisms of Mandrel and Wiper Wear from Heavy Cut Burrs

Cold saws and band saws leave distinct burr profiles depending on blade pitch, feed rate, and coolant condition. An internal burr curls inward into the tube lumen, reducing the effective inside diameter at the tube end. When the mandrel shaft advances into the tube, or when the tube is pushed over the mandrel during loading on a CNC bender like the Griffin, the internal burr strikes the leading edge of the mandrel nose. This impact forces localized high pressure on the mandrel material, stripping the oil film and creating axial gouges along the chrome or ampco bronze surface.

Outer burrs create a separate failure mode at the clamping and wiper die interfaces. An external ridge prevents the tube from seating flat against the pressure die or wiper die heel. As the clamp die closes, the burr concentrates the entire clamping load onto a tiny contact patch, creating indentations in the tool cavity. Furthermore, when the tube rotates during multi-plane bend sequences, an oversized external burr scrapes along the delicate tip of the wiper die, chipping the sharp knife edge required to prevent inside-radius wrinkles.

Measuring Chamfer Angles and Facing Depths Before Bending

Preventing tool damage requires a combined facing and chamfering operation rather than simple hand-deburring. Hand-deburring leaves an irregular edge profile that varies across operators, leading to inconsistent wall contact during the bending stroke. An engineered tube end requires three distinct geometric features: a flat face perpendicular to the tube centerline, an internal chamfer (ID chamfer), and an external chamfer (OD chamfer).

The inner chamfer angle must match or exceed the entry lead angle of the mandrel nose, typically 30 to 45 degrees. The depth of the internal chamfer must fully encompass the maximum expected wall thickness variation and saw burr height. If the burr height measures 0.5 mm, the internal chamfer depth should be set to at least 0.8 mm to ensure that the mandrel nose contacts smooth, clean parent metal rather than cut flash. Facing the tube end simultaneously eliminates blade wander errors, providing a precise stop face for carriage collets and axial positioning sensors.

Tooling Clearance and Chamfer Consistency on Bora Machines

Dural Machinery builds the Bora series specifically to handle simultaneous inside, outside, and face machining in a single clamping cycle. Using a rigid twin-blade cutter head, the machine clamps the tube in a hydraulic or pneumatic vice while the rotating cutter advances axially. This rigid clamping prevents the tube from rotating or chatter-marking during the cut, which is critical for thin-wall tubing where excessive clamping force can distort the cross-section.

Consistency in chamfer depth directly affects mandrel life and automated loading cycles. On automatic loading systems, variable tube lengths caused by rough saw cuts force the carriage axis to compensate or risk over-driving the mandrel into internal obstructions. By standardizing the tube end preparation on a double-ended machine like the Bora B2, both tube ends are faced to precise length tolerances while receiving identical inner and outer bevels. This uniform chamfer eliminates the sharp edges that cut wiper die tips and allows smooth, low-friction mandrel insertion on every cycle.

Field Inspection Steps for Burred Tube Ends

When investigating premature wear on mandrel balls, internal grooving on bronze mandrels, or chipped wiper die tips during service calls, tube end quality is one of the first parameters evaluated. A systematic check isolates cut quality issues before replacing expensive bending dies.

• Inspect raw tube ends using an optical comparator or depth micrometer to measure maximum burr height and cut non-perpendicularity across the diameter.
• Check the leading edge of the mandrel nose for axial scratches, metal pickup, or gouging that aligns with the tube loading axis.
• Verify that the internal chamfer depth completely removes the heat-affected zone and plastic deformation left by the saw blade.
• Inspect the clamping area of the wiper die tip for localized crushing or micro-chipping caused by external burr interference during loading.
• Confirm that tube facing tolerances maintain a true 90-degree angle to the tube axis to prevent angular misalignment inside the collet chuck.