Bandsawing: As per the name of the process, the saw is formed as a band and is continuously cycled in one direction around pulley wheels. This enables a continuous cut to be made. The blade has to be sufficiently thin to bend around the pulley wheels. It is possible to make a contour cut, but the minimum curvature depends on the cross-section of the blade.
On some machines it is possible to adjust the table angle, creating tapered parts or parts with angled sides. Cutting fluids may be used for lubrication/cooling on some operations.
There are many variations on this basic set-up (see the Process variations section below).
Automated bandsaws have greater accuracy.
Typical Applications
- Stock cutting
- Profile cutting
Mechanical design guidelines
- Contours may be achieved, but the minimum radius depends on the width of the blade. Internal contours may also be achieved by welding the ends of the blade together after it has been passed through a hole in the workpiece.
- Convex radii of less than 1.6mm are possible in a single pass.
- Tolerances are limited to the ability of the operator. Close tolerances can be achieved by using an automated band saw or a skilled operator with a magnifying glass.
- The most satisfactory range of material hardness for sawing is about 180 to 250 HB, but steels up to 400 HB and some free-machining steels up to 450 HB can be sawed at reduced cutting rates.
Process variations
- Fixed-table machines: Manual feed.
- Power-table machines: Automatic workpiece feed.
- Contour band saws: (see above diagram) are oriented vertically. Radial arm machines are hinged and allow cutting over a crescent shape. This allows a larger operating envelope.
- Cut-off bandsaws: Stock cutting in a straight line only (horizontally or vertically).
- Tilt-frame universal bandsaws: Widely used for angle cutting operations.
- Plate band sawing machines: For cutting plate stock. Blades are very thin and create little waste.
- Friction Band Sawing: High band speeds (1800-4600m/min) cause friction which melt/soften the metal that is then removed by the teeth. This process is suitable for very hard metals or metals that work-harden very quickly. This process is also suitable for cutting thin materials without distortion.
Alternative names for bandsawing
- Contour band sawing.
Environmental implications
- Can be extremely noisy. Ear protection should be worn for extended operation.
Economics of bandsawing
- Wear is evenly distributed over the entire blade, making blade changes less frequent.
- Simple fixtures are required as the downward force of the blade holds the workpiece to the table.
Technical notes
- There are three main tooth forms for blades: regular (contour cutting), skip (deep cuts in soft metals) and hook (fast cutting rates). Pitch is defined as no. teeth/inch. There must be at least two teeth for the thickness of the workpiece (three is preferable).
- Thickness of saw blades (gauge) are standardised: 0.64mm, 0.81mm, 1.1mm, 1.3mm and 1.6mm.
- Saw teeth are intentionally offset to provide clearance for the back of the band.
- Bands are made of carbon steel or are bimetallic (high-speed steel) cutting edges electron beam welded to a steel back. Some are heat treated along the entire width to a spring temper (allowing the band to be tensioned), and some are heat treated at the teeth to increase hardness/wear resistance. Welded-edge high-speed steel bands are used for higher cutting rates. These have longer life, and may be coated with titanium nitride (TiN). These are used for materials that are more difficult to cut. Bands with tungsten carbide inserts are used for the most difficult to machine alloys or for ceramics. Diamond-edge and aluminium-oxide-edge blades are also used.
