The basics of circular saws and saw blades
June 13, 2006
Experience and education are allowing metal fabricators to become more familiar with circular saw blades and the saw designed to run them. Choosing and applying the correct blade, along with proper maintenance, can provide an efficient method for a metal cutting operation.
Increasing knowledge and on-the-job experience regarding the uses of a circular saw blade has changed the way metal fabricators view the tool as well as uncovered expanding efficiencies gained through its use.
Metal cutting circular saw blades are designed to boost productivity for professionals who cut common materials such as angle iron, sheet metal, pipe, and steel plate found at almost every job site. Dedicated saws engineered to run these blades are relatively new to the industry, so some contractors may be unaware of the technology and use less efficient tools. Using a tool that is not specifically designed for a job can result in a loss of both time and money. For optimal performance, it is recommended that a saw made specifically for metal cutting be used.
For special fabrication, cutting, and custom fitting, job site sawing is a necessity.
A hand-held circular saw allows an operator to make a cut on the spot, or in other words, where the operation is taking place and where the raw material is stored. This can help lead to a high level of accuracy and less wasted materials caused by mistakes. For example, when using a circular saw in the fabrication of metal framing systems, the operator can eliminate travel time back and forth to the saw.
The precision of a metal cutting circular saw allows the blades to make a smooth, clean cut with low sparks and dust, making obsolete the need for secondary grinding operations. For example, when a circular saw cuts threaded rod without a cleanup operation, the nut can be threaded directly after the cut is made. Also, when cutting plate or angle iron, a circular saw leaves little burr. Cooling time is eliminated because parts are cool enough to touch, allowing the operator to continue working.
|The blade does not transfer heat to the workpiece.|
Saws specific to metal cutting are available in cordless hand-held, corded hand-held, and benchtop models. A good metal cutting saw will have a shield and collection bin that prevent the metal chips from getting into the machine, which reduces cleaning and maintenance time.
There are several things to consider when purchasing a circular saw blade, the first of which is the application. Blades are designed for a specific material, such as aluminum, steel, or copper. The size of the work determines blade pitch and design, which are specific to the material thickness. This information is specified on the packaging, and tech support can be contacted for more detailed information. In the case of a 7-1/4-in. blade, a wood cutting saw could be used, but the machine is not designed to capture chips like a metal cutting saw can, and the motor housing is open. However, if a wood cutting saw is used, it is recommended that a worm drive be used for the added torque it provides.
Buildup of materials on the cutting edge eventually leads to the premature attrition of the blade edge material and machine wear. A good metal cutting blade will resist this buildup. For optimal performance of both the saw and the blade, the revolutions per minute (RPM) need to be set specifically for metal cutting. Torque requirements for metal cutting are higher than those for wood cutting, and a slower speed is more conducive to producing a clean, smooth cut. A too-high RPM can lead to premature attrition and increased burring.
|Portable metal cutting saws come in corded or cordless hand held models, which can help make the cutting process more efficient.|
Although a circular saw blade is fairly versatile for many applications, it is highly recommended that a saw-specific metal cutting blade be used. These blades can cut through many structurals and solids, and they can be used on all shapes that fit within the specified size range for a given blade. As with many other blades, they do have their limitations, and there are a number of applications for which a metal cutting circular saw is unsuitable. These limitations are listed on the packaging.
On most saws the blade should be installed so that the label is visible. One exception to this rule is a worm-drive saw blade, which mounts on the opposite side of the machine. An arrow on the label indicates the direction of rotation. As mentioned previously, metal cutting circular saw blades should not be mounted on typical wood cutting saws (other than the 7-1/4-in. blade) or abrasive saws, because the amount of torque developed during metal cutting could cause machine failure or result in operator injury or tool damage. For this reason, metal cutting saws are built with high-torque motors. The blade should be allowed to "spin up," or get to full speed, before engaging the work. This allows the blade to work more efficiently and prevent tool damage.
Users shouldn't worry if the supplier does not have the exact blade the saw came with. Blade and tool manufacturers both say that excellent performance can be achieved with blades not sold specifically for a given saw. In this case, the fabricator should focus on buying a blade with the correct attributes for the work and saw, such as the right diameter and arbor size. High tooth counts are best for thin material, and low tooth counts are best for thick material.
Ken Hall is a senior research and development engineer/program manager at LENOX®, 301 Chestnut St., East Longmeadow, MA 01028, 413-525-3961.