Bandsaw blades naturally play a vital role in the sawing process, but maintaining the saw machine and paying attention to the cutting essentials are critical factors, as well. Therefore, the road to successful sawing can be easily traveled by heeding the following advice.
First and foremost, use heavy-duty, rigid bandsaw machines that can withstand the rigors of cutting and deliver accurate results. Next, select the proper saw blade for the material being cut and the machine being used. When selecting a blade, pay attention to important factors such as blade pitch, blade width, tooth design and the hardness of the material being cut. To assist in the selection process, saw blade manufacturers such as The L.S. Starrett Co. offer free slide charts and selection programs.
Once the initial selections have been made, be sure to run the proper feed and speed rate per the bandsaw machine manufacturer’s recommendations. Quality coolant is also key, but be sure it’s properly mixed at the ratio required for the job.
Follow saw blade installation guidelines, including the bandsaw machine manufacturer’s instructions and recommendations for blade changes and the safe operation for the machine. A few general tips for proper blade installation to achieve more efficient blade performance and employee safety, include:
- Wearing gloves when handling bandsaw blades
- Wearing eye and hearing protection and safety shoes
- Following all of the safety instructions in the machine operator’s manual and on the machine labels
- Recognizing and reading safety and warning signs
- Following the blade installation instructions for the make and model of the machine
Also, have well-trained operators who can effectively use their “eyes and ears to saw.” A good operator notices clues that indicate whether or not they are running at optimal performance. It’s key to be attentive to issues such as whether good chips are being made or whether they are too fine or too stringy. Other issues to be aware of include excessive chatter, vibration or squealing while the cut is being made.
In addition to proper equipment selection and use, preventive maintenance is paramount. Although it’s difficult to place a direct value on this, when preventive maintenance is at an optimal level, cutting and saw blade performance tend to mirror that similar high level.
There are several helpful steps to follow for preventive maintenance. The top five considerations include:
- Condition and adjustment of band guides. If the guides are worn or loose, the result will be misaligned cuts and blade failure.
- Band wheel and bearing conditions. Worn flanges and out-of-round wheels can cause blade stress, which in turn, creates blade failure and poor cuts.
- Blade tension. Low tension increases blade wear while excessive tension can not only cause blade failure but can also damage the bandsaw machine. Always tension a blade within the manufacturer’s specifications.
- Blade alignment. Improper alignment to the vise or bed leads to out-of-spec, crooked cuts and blade fatigue.
- Feed and speed calibration. Once the blade is properly guided, it is imperative that the feed and speed of the blade and machine are calculated to the machine manufacturer’s recommendations. This will optimize the blade and, ultimately, the machine performance.
More often than not, it’s best to consult with the saw blade manufacturer or supplier to determine the optimal blade for the application. However, here are some general guidelines to follow:
1. Material to be cut: Bi-metal bandsaw blades are often the right choice for a range of steels, while typically carbide-tipped blades are optimal for harder materials, such as nickel and titanium alloys. Carbon blades offer advantages for cutting non-ferrous materials, including aluminum, copper alloys and composites.
2. Tooth set: Tooth set is the side-to-side bending of the teeth, left and right. This produces a kerf that provides adequate clearance for the blade to move through the cut by helping to clear chips. In addition, the tooth set can affect how efficiently the blade cuts and the quality of the resulting surface finish.
Different set considerations include raker, alternate, wavy and trapezoid. Raker is a recurring sequence of teeth set left and right, followed by one tooth unset. The frequency of unset teeth on variable-pitch blades varies depending on the tooth configuration. The raker set is most common, and is used for cutting thicker materials, and provides a smooth surface finish.
Alternate refers to a recurring sequence of teeth set alternately, left and right. An alternate set can cut faster, although the surface finish may not be as smooth. A wavy configuration has groups of teeth set to each side of the blade with varying amounts of set in a controlled pattern. A wavy set is used on blades with a fine tooth pitch, when cutting thin sheets, tubes and thin sections. A trapezoid configuration has a special carbide cylinder welded to an alloy backer that is precision ground with a high/low tooth form.
3. Blade width: Consult the bandsaw machine manufacturer for the optimal blade width, except for contour cutting in vertical machines when a chart, as shown in Figure 1, can be referenced.
4. Blade pitch: Blade pitch, defined as the number of teeth per inch, needs to be properly selected. The number of teeth that come in contact with the workpiece can affect blade performance and durability. Too few teeth in contact with the workpiece can lead to early tooth strippage. Contrastingly, too many teeth in contact can greatly reduce cutting rates and, ultimately, make the material impossible to cut. At lower cutting rates, there is less penetration per tooth, causing more rubbing than cutting, which can result in substantial work hardening of the material.
A constant-pitch blade, which is a uniform distance from one tooth tip to the next tip, can increase harmonic vibrations, which can lead to excessive noise, undesirable blade or machine vibrations and, in severe cases, bad cuts. A variable-pitch blade can greatly reduce harmonic vibrations. By varying the tooth spacing, sawing rhythms are interrupted, chip evacuation is improved and vibration is reduced, resulting in less noise and a better overall cut.
With constant pitch, all teeth on the blade have uniform spacing, gullet depth and rake angle throughout the full length and it is typically for general-purpose cutting. Variable-pitch teeth have varying tooth sizes and depth of gullets to substantially reduce noise levels and vibrations. The latter cuts all structurals, tubing and solids smoothly and quickly. See Figure 2 for helpful guidelines.
5. Blade length: Blade length varies according to the bandsaw machine type and specifications. The correct blade length should be referenced in the user manual.
Before initiating any production cuts, be sure to break in the saw blade, which contributes to overall sawing success and an increase in the blade’s service life. Remember, however, that the process will vary depending on the characteristics of the material being cut. While breaking in a blade, run the bandsaw machine at a normal surface feet per minute rate.
For softer materials, such as carbon steel and aluminum, adjust the feed rate to 50 percent of the normal cutting rate for the first 50 to 100 sq. in. Then, gradually increase the feed rate to 100 percent.
For harder materials, such as nickel-based alloys including Inconel or other difficult-to-cut materials such as hardened steels, tool steels and stainless steels, adjust the feed rate to 75 percent of the normal cutting rate for 25 to 75 sq. in. Gradually increase the feed rate to reach 100 percent after 50 sq. in. As the feed rate is increased to 100 percent, be careful to avoid creating vibrations that can occur by increasing the rate too quickly.