Bandsaw

File:Band saw.JPG

A bandsaw in use

File:Bandsaw at Lowes.jpg

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 small bandsaws have three wheels. The saw may be powered by wind, water, steam, electrical motor or animal power. 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 radius of a curve that can be cut on a particular saw is determined by the width of the band and its lateral flexibility.

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

File:John Henry Walker06.jpg

19th century wood bandsaw

Brushes or brushwheels are sometimes used to remove chips from the blade as it exits the material. Bandsaws are available in vertical and horizontal designs. Band speeds range from 40 feet per minute to 5000 feet per minute.

Horizontal bandsaws may employ a gravity-fed blade or the rate of descent may be controlled by a hydraulic cylinder bleeding through an adjustable valve. When the saw is set up for a cut, the operator raises the saw by hand and the material is clamped in place and the saw is turned on, the blade slowly descending 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.

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 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 against a hydraulic cylinder which has a control valve. Common in small saws.
• Hydraulic feed saws use a positive pressure hydraulic piston to advance the saw through the work. 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.

Gallery

• Boatshed-band-saw.jpg

  Small boatyard horizontal bandsaw, resaw, Hoi AN, Vietnam.

• Bandsaw-resaw.jpg

  Larger resaw, Mekong delta boatyard, note width of blades, about 150mm or 6".

See also

• Chainsaw
• Portable sawmill

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

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