Band saw
A band saw uses a blade consisting of a continuous band of metal with teeth along one edge. Workpieces are fed into the cutting edge on vertical machines. The saw may be powered by wind, water, steam, electrical motor or animal power. The band rides on two wheels rotating in the same plane. Band sawing produces uniform cutting action as a result of an evenly distributed tooth load. Band saws can be 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
Metal cutting band saws
When cutting metals, a constant flow of liquid over the blade facilitates cutting by lubricating to keep the blade cool as well as preventing encrustation or smearing on the blade, prolonging blade life and making for greater cutting accuracy. Brushes or brushwheels are sometimes used to remove chips and encrustation from the blade as it exits the material. Band saws are available in vertical and horizontal designs. These units range from manually operated machines to fully automatic machines. Band speeds range from 40 feet per minute to 5000 feet per minute.
Machine shop band saws may also be horizontal or vertical. Small band saws 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.
Cutting metals with a band saw is an art form in and of itself. It requires a considerable amount of knowledge and experience to be a profitable operation. There are several variables to consider when cutting metals with a band saw. The selection of the appropriate band saw blade, type of cutting fluid, type and condition of the band saw machine and level of machine operator experience are but a few.
Many technological advancements have made their way to metal cutting band saw machines in the past few years such as computer controls. A significant breakthrough in feed rate controls has been made by Hem Saw Inc of Pryor, OK. Hem saw has pioneered computerized cutting feed and pressure controls with their CCT system that greatly enhances production rates and increases blade life. Another advancement has been the transition from variable pulleys to frequency inverters to control band speed. Berhinger and Lexas band saw machines are among those that employ this new process for controlling band speed.
Advancements have also been made in the band saw 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 material 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 band saw blades as well. Ideal computerized welding machines, Also setting and cut to length machines and contributions from other manufacturers continues to increase productivity.
Stone cutting band saws
Common in mining industries band saws are used to cut hard stone into large blocks that can then be shipped to processing plants to be further refined. These saws use the same mechanical principals as other band saws but with one major difference. The major difference is that instead of a thin flat blade these use a thick cable. The cable is coated in diamond allowing it to cut through the hard rock.
Meat band saws
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. The heat treated blades designed for meat saws are also used for cutting hard plastics and laminates.
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 band saws encountered, to the point where some make use of a rotary table and X axis to perform complex cutting.
Automated saws
Automatic band saws 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 NC/CNC 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.
Note: At least two teeth must be in contact with the workpiece at all times to avoid stripping off the teeth.
Large band saws
Timber mills use very large band saws 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). Band saws 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
Head saws are large band saws that make the initial cuts in a log. They generally have a two to three inch 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
A resaw is a large band saw 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" (52 - 78 mm) - with a small kerf to minimize waste. Resaw blades of up to 1" (26 mm) may be fitted to a standard band saw.
Double cut saws
Double cut saws have cutting teeth on both sides. They are generally very large, similar in size to a head saw.
Extra Information
Band saws range in throat capacity from 8" to 36", with either two or three wheels for the blade. Blades for the home shop range from 1/8" to 1" wide, the narrow blades are used to cut small radius curves, the wide blades are used for straight cuts such as resawing.
Translation of "Band saw"
Czech: Pásová pila, Danish: Båndsav, German: Bandsäge, Estonian: Lintsaag, Spanish: Sierra de cinta, French: Scie à ruban, Icelandic: Bandsög, Italian: Sega a nastro, Luxembourgish: Bandsee, Dutch: Lintzaag, Japanese: コンターマシン, Serbian: Трачна пила, Finnish: Vannesaha, Swedish: Bandsåg.
|
