Quality In The Cut

Longer saw blade life and quality cuts are achieved by utilizing specialized tools and following best practices

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Sawing requires quality control – this might not be your first thought when planning to make cuts, but it is nonetheless true. Saw blade quality starts with precision manufacturing to ensure that the blade begins sharp and remains sharp. In addition to being consistently sharp, fundamental requirements for the blade include being straight and flat. Also, the teeth need to be centered and set correctly and have a uniform height, unless for example, the tooth design is variable pitch.

At The L.S. Starrett Co., each tooth is precision-ground individually, going through several grinders to achieve the complex geometries necessary to imbue the blade with strength and efficiency. The weld between the carbide tooth and the steel band needs just the right amount of current, heating time and cooling time. Every tooth in any given blade must pass inspection; even one defective tooth can adversely affect all the teeth behind it.

Improper tension leads to bad cuts. Using a saw tension gauge for bandsaw blades allows operators to dial in the correct tension.

The geometric tolerances must be precise – the same way a micrometer is precise. This is because the amount of material each tooth removes is much smaller than that of a turning or milling tool. The chip load in saw cutting is measured on the order of 10-4 in. Depending on the material, each tooth may be removing half a millimeter or less. This means that if the grinding tolerance is off by more than that, some teeth will be cutting while others are not, resulting in decreased blade life.

Precision measurement

Starrett uses special Starrett-manufactured precision micrometers and dial gauges and other advanced Starrett-made metrology equipment to ensure the highest quality blade manufacture. This includes measuring the height of each tooth, the kerf, the bow of the band, the weld strength and other critical components while the blade is still in production. For every saw blade coil it produces, Starrett uses a force gauge to measure the strength of the carbide welds. A Starrett optical comparator is used to analyze the rake angle, clearance angle and other important features of the teeth that cannot be determined using a mechanical device.

Final product inspection after machining can identify any problems, but using precision measurement solutions together with knowledgeable expertise is critical at the start of the blade manufacturing process. State-of-the-art processes and dedicated employees churn out high quality bi-metal and carbide-tipped bandsaw blades with innovative tooth geometry designed for a range of materials including challenging alloys. From milling the gullet patterns into the raw material to inspecting every tooth of the final product, Starrett carefully controls the processes with precision.

A pocket laser tachometer measures blade speed so the user can quickly verify and adjust speed as needed.

To have the most productive sawing experience, consulting a blade manufacturer or supplier can be helpful. The following tips can also offer some help.

The break in

Using the right break-in procedures ensures longer blade life, faster cuts for a longer period of time and consistent performance. Conversely, blade life can be significantly compromised if the proper steps are not followed.

When a blade arrives from the factory, it may be brittle, resulting in the edge of the blade deforming or cracking as it goes into material, especially if running at full speed. This is why it is important to break in a blade prior to using it at full cutting speed. When breaking in a blade, reduce the feed rate and feed pressure so the blade does not have to work as hard and the teeth become honed, increasing blade strength. Again, a properly broken-in blade lasts longer.

The process to break in a bandsaw blade varies depending on the characteristics of the material being cut. While breaking in a blade, have the bandsaw running at the normal surface feet per minute (sfpm).

For softer materials, such as carbon steel and aluminum, adjust the feed pressure to 50 percent of the normal cutting rate for the first 50 to 100 sq. in. Then, gradually increase the feed pressure to 100 percent cutting rate.

For harder materials, such as nickel-based alloys including Inconel or other difficult materials such as hardened steels, tool steels and stainless steels, adjust the feed pressure to 75 percent of the normal cutting rate for 25 to 75 sq. in. Gradually increase the cutting rate to reach 100 percent after 50 sq. in. As the feed pressure is increased to the 100 percent cutting rate, be careful to avoid creating vibrations that can occur by increasing the rate too quickly.

Starrett uses its own precision gauges to quality control its bandsaw blades.

Check tension and alignment

For a straight and firm blade that will make accurate cuts, 30,000 psi is considered a normal tension. An improper tension leads to bad cuts and shortened blade life and may also negatively affect the bandsaw, resulting in wear and tear. Use a saw tension gauge for bandsaw blades to check for proper tension.

The blade should be running square to the cut. To check the blade, use a combination square and a bandsaw blade alignment gauge to measure the squareness of the cut. By fixing the alignment gauge to the bandsaw blade, you can accurately measure that the blade is perpendicular to the worktable. The gauge prevents misalignment that could cause uneven cuts, leading to workpiece scrap.

Measure blade speed

To check that the blade is running at its intended speed, a pocket laser tachometer is helpful. Maintaining the correct blade speed is crucial for achieving optimal cutting performance and prolonging the life of the blade. By using a pocket laser tachometer, you can quickly verify and adjust the blade speed if needed, improving cutting accuracy and efficiency. It is particularly important for adjusting the blade speed when switching between different types of materials or breaking in a new blade.

An optical comparator is used to check the quality of carbide blade teeth.

Note that determining the proper blade feeds and speeds is generally based on the type of material. In general, material can be broken into three groups – hard, medium and soft. While there are exceptions, you can group your material into one of these categories to estimate feed and speed.

Typically, the harder the material the slower the band speed. In the case of most structural materials, speeds and feeds are generally put in the soft category but there may be hard structural/tubing being cut. For quick estimates, soft materials may fall in the 300 sfpm range, while hard materials are in the 100 sfpm range with medium materials falling in between.

Most production bandsaws have a feed rate (traverse control) adjustment and a feed pressure adjustment. These two controls are very important and should change with the type (hardness) of the material. In essence, they work completely opposite from one another. Feed rate is the speed at which the head comes down or moves forward. Feed pressure is how much pressure is being applied to make the head move.

In general, the harder the material the more feed pressure is needed to penetrate the material. However, hard material cannot be cut fast, so typically the feed rate would be lowered. In soft material the opposite is true – lower feed pressure and higher feed rate.

Use coolant

Coolant removes heat and lubricate teeth to prevent chip welding. It is important to note that sawing processes generally need a heavier coolant mixture than coolants used for drilling, milling and tapping.

This optical comparator provides a magnified view of the blade teeth, easily identifying abnormalities.

Also, coolant designed for bandsaws works well in most other machinery, but the converse is likely not true, so it is best to follow the coolant specification recommendations from your bandsaw manufacturer. Sawing operations require an approximately 5:1 through 10:1 mix ratio for water and coolant, respectively. It is generally suggested to change the coolant at least once each year, based on how much cutting is being done – do not neglect this step.

Chip monitoring

Regularly brushing out chips is important for helping to avoid chips welding into the teeth gullets because once a chip is affixed to the blade, the blade design is changed. Most bandsaws utilize a steel wire or polymer (nylon) wheel brush.

Surely there are always additional considerations that factor into efficient sawing operations. Consulting with your bandsaw blade and machine manufacturer for best practices for your application is recommended.

The L.S. Starrett Co.

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