Bandsaw

A bandsaw in use

A bandsaw on display in a hardware store.

A bandsaw is a power tool which uses a blade consisting of a continuous band of metal with teeth along one edge to cut various workpieces. The band usually rides on two wheels rotating in the same plane, although some bandsaws may have three or four wheels. Bandsawing produces uniform cutting action as a result of an evenly distributed tooth load. Bandsaws are used for woodworking, metalworking, or for cutting a variety of other materials, and are particularly useful for cutting irregular or curved shapes, but can also be used to produce straight cuts. The minimum radius of a curve that can be cut on a particular saw is determined by the width of the band and its kerf.

Types

Meat cutting

Saws for cutting meat are typically of all stainless steel construction with easy to clean features. The blades either have fine teeth with heat treated tips, or have plain or scalloped knife edges.

Metal cutting

19th century wood bandsaw

Bandsaws for cutting metal are available in vertical and horizontal designs. Typical band speeds range from 40 feet (12 meters) per minute to 5,000 feet (1,500 meters) per minute, however specialized bandsaws are built for friction cutting of hard metals and run band speeds to 15,000 feet per minute. Metal-cutting bandsaws are usually equipped with brushes or brushwheels to prevent chips from becoming stuck in between the blade's teeth. Systems which cool the blade are also common equipment on metal-cutting bandsaws. The coolant washes away chips and keeps the blade cool and lubricated.

Horizontal bandsaws hold the workpiece stationary while the blade swings down through the cut. This configuration is used to cut long materials such as pipe or bar stock to length. Thus it is an important part of the facilities in most machine shops. The horizontal design is not useful for cutting curves or complicated shapes. Small horizontal bandsaws typically employ a gravity feed alone, retarded to an adjustable degree by a coil spring; on industrial models, the rate of descent is usually controlled by a hydraulic cylinder bleeding through an adjustable valve. When the saw is set up for a cut, the operator raises the saw, positions the material to be cut underneath the blade, and then turns on the saw. The blade slowly descends into the material, cutting it as the band blade moves. When the cut is complete, a switch is tripped and the saw automatically turns off. More sophisticated versions of this type of saw are partially or entirely automated (via PLC or CNC) for high-volume cutting of machining blanks. Such machines provide a stream of cutting fluid recirculated from a sump, in the same manner that a CNC machining center does.

A vertical bandsaw, also called a contour saw, The position of the moving blade is stationary while the workpiece is moved against the blade. This type of saw can be used to cut out complex shapes and angles. The part may be fed into the blade manually or with a power assist mechanism. This type of metal-cutting bandsaw is often equipped with a built-in blade welder. This not only allows the operator to repair broken blades or fabricate new blades quickly, but also allows for the blade to be purposely cut, routed through the center of a part, and re-welded in order to make interior cuts. These saws are often fitted with a built-in air blower to cool the blade and to blow chips away from the cut area giving the operator a clear view of the work. This type of saw is also built in a woodworking version. The woodworking type is generally of much lighter construction and does not incorporate a power feed mechanism, coolant, or welder.

Advancements have also been made in the bandsaw blades used to cut metals. The development of new tooth geometries and tooth pitches have produced increased production rates and greater blade life. New materials and processes such as M51 steel and the cryogenic treatment of blades have produced results that were thought impossible just a few years ago. New machines have been developed to automate the welding process of bandsaw blades as well. Ideal computerized welding machines, setting and cut to length machines and contributions from other manufacturers continue to increase productivity.

Timber cutting

Timber mills use very large bandsaws for ripping lumber; they are preferred over circular saws for ripping because they can accommodate large-diameter timber and because of their smaller kerf (cut size), resulting in less waste.

The blades range in size from about (4" wide x 19' long x 22 ga thickness) to (16" wide x 62' long x 11 ga thickness). The blades are mounted on wheels with a diameter large enough not to cause metal fatigue due to flexing when the blade repeatedly changes from a circular to a straight profile. It is stretched very tight (with fatigue strength of the saw metal being the limiting factor). Bandsaws of this size need to have a deformation worked into them that counteracts the forces and heating of operation. This is called benching. They also need to be removed and serviced at regular intervals. Sawfilers or sawdoctors are the craftsmen responsible for this work.

The shape of the tooth gullet is highly optimized and designed by the sawyer and sawfiler. It varies according to the mill, as well as the type and condition of the wood. Frozen logs often require a frost notch ground into the gullet to break the chips. The shape of the tooth gullet is created when the blade is manufactured and its shape is automatically maintained with each sharpening. The sawfiler will need to maintain the grinding wheel's profile with periodic dressing of the wheel.

Head saws

Main article: Head saw

Head saws are large bandsaws that make the initial cuts in a log. They generally have a 2 to 3 in (51 to 76 mm) tooth space on the cutting edge and sliver teeth on the back. Sliver teeth are non-cutting teeth designed to wipe slivers out of the way when the blade needs to back out of a cut.

Resaws

Main article: Resaw

A resaw is a large bandsaw optimized for cutting timber along the grain to reduce larger sections into smaller sections or veneers. Resawing veneers requires a wide blade - commonly 2 to 3 in (51 to 76 mm) - with a small kerf to minimize waste. Resaw blades of up to 1 in (25 mm) may be fitted to a standard bandsaw.

Double cut saws

Double cut saws have cutting teeth on both sides. They are generally very large, similar in size to a head saw.

Construction

Feed mechanisms

• Gravity feed saws fall under their own weight. Sometimes the saw has a movable weight which allows the cutting force to be adjusted. Oftentimes this type of saw is equipped with a hydraulic speed control valve. This does not force the blade downwards, but rather limits the speed at which the saw can cut preventing excessive feed on thin or soft parts. This design is common in small saws.
• Hydraulic feed saws use a positive pressure hydraulic piston to advance the saw through the work at variable pressure and rate. Common in production saws.
• Screw feed employ a leadscrew to move the saw.

Fall mechanisms

• Pivot saws hinge in an arc as they advance through the work.
• Single column saws have a large diameter column that the entire saw rides up and down on, very similar to a drill press.
• Dual column saws have a pair of large columns, one on either side of the work, for very high rigidity and precision. The dual column setup is unable to make use of a miter base due to inherent design. Dual column saws are the largest variety of machine bandsaws encountered, to the point where some make use of a rotary table and X axis to perform complex cutting.

Automated saws

Automatic bandsaws feature preset feed rate, return, fall, part feeding, and part clamping. These are used in production environments where having a machine operator per saw is not practical. One operator can feed and unload many automatic saws.

Some automatic saws rely on numerical control to not only cut faster, but to be more precise and perform more complex miter cuts.

Common tooth forms

• Precision blade gives accurate cuts with a smooth finish.
• Buttress blade provides faster cutting and large chip loads.
• Claw tooth blade gives additional clearance for fast cuts and soft material.

At least two teeth must be in contact with the workpiece at all times to avoid stripping off the teeth. Blade Characteristics Blade must be checked before each cut. The blade must be secured to saws requirements. Slight flexing of the blade is normal, however a flexing blade is more prone to breaking.This can be very hazardous to the operator or anything surrounding the working environment. The blade stop is what protects the blade. Loosening the adjustment knob will raise or lower the stop until specifications are meet. Distance between work piece and stop may vary.

Gallery

• 
  Small boatyard horizontal bandsaw, resaw, Hoi AN, Vietnam.
• 
  Larger resaw, Mekong delta boatyard, note width of blades, about 150mm or 6".
• 
  Historical bandsaw from 1911.

See also

• Chainsaw
• Bandsaw box
• Portable sawmill
• Band knife

References

Bibliography

• Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes Reference Guide, Industrial Press Inc., ISBN 0-8311-3049-0.

Further reading

• Mark Duginske (1989). The Bandsaw Handbook. Sterling Publishing. ISBN 0-8069-6398-0