Band saw
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A band saw is a saw that can be used for woodworking, metal working, and a variety of other materials. It gets its name from its blade, consisting of a narrow band of toothed metal. This band rides on two wheels in the same vertical plane with a space between them. Band saws are particularly useful for cutting irregular shapes. The radius of a curve that can be cut on a particular saw is determined by the width of the band.
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[edit] Metal Cutting Band Saws
When cutting metals, special band saws are required that include coolant pumps which provide a constant flow of liquid coolant over the blade. The coolant keeps blades cool, adding blade life. They also include a powered wire brushwheel to remove chips and buildup from the blade as it exits the material. Metal cutting band saws are available in vertical and horizontal designs. These units range from manual to semi-automatic and even automatic controls.
Machine shop bandsaws are horizontal, vertically cutting saws. Small, manual shop saws are usually employ a gravity-fed blade that falls in an arc around a pivot point. The rate of descent is controlled by a shock absorber that has an adjustable rate. When a manual saw is set up for another cut, the operator raises the saw by hand and leaves it in a 45 degree position. The material is unclamped, moved up to hit the part stop (which is then moved out of the way), material reclamped, and the operator hits the rapid advance switch to lower the saw just before the cut begins. The saw's piston is then set to cut advance, and another cut is made.
Additional common equipment on machine shop saws include
- A part stop for repeatable billet production, allowing long rods or bars to be cut into the correct billet size
- A long roller bed to assist long and heavy stock feeding
- Vices along the roller bed to ensure setup rigidity
- Miter base that allows angled cuts
- Saw braces that are adjusted to present just enough exposed saw to cut through the work. This increases rigidity and life of the blade.
[edit] Feed Mechanisms
Machine shop saws
- Gravity feed saws fall under their own weight against a shock abosrber in the saw base. 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.
[edit] 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 radial drill.
- 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.
[edit] 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 NC/CNC control to not only cut faster, but to be more precise and perform more complex miter cuts.
[edit] Large band saws
Timber mills use very large band saws for ripping lumber; they are preferred over circular saws for ripping 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 after every four hours of use. 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 with a grinding wheel. The sawfiler will need to maintain the grinding wheel's profile with periodic dressing of the wheel.
[edit] 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.
In the earlier years of wood production, Head Saws would be used to cut all log diameters generally up to approximately 72". Today, the Head saws may be more so used for cutting log diameters of 16" to 72" in diameter depending upon the type of Band Mill the saws are mounted on. More optimized machines now cut the smaller diameters since they are far more efficient and can provide greater production.
Dependent upon the log diameter, Head Saws can cut a log at speeds ranging from 1 to 300 feet per minute. Generally, Log Carriage speeds are adjustable for optimal performance.
[edit] Resaws
A resaw is a large bandsaw optimized for resawing. This involves 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 bandsaw.
Timber mills use larger resaws to rip large planks into smaller sizes. A typical mill sized resaw is eight inches wide and made with 16 gauge steel. Resaws can be identified by their flat back, as opposed to headsaws and doublecuts which don't have a flat back.
[edit] Double cut saws
Double cut saws have cutting teeth on both sides (see sawfiler for a picture of a very small double cut). They are generally very large, similar in size to a head saw.
[edit] See also
[edit] References
- Mark Duginske (1989). The Bandsaw Handbook. Sterling Publishing. ISBN 0-8069-6398-0
