Just say no to rework

The "3, 6-12, 24" rule is good to know when you're selecting tooth pitch for a particular application. No fewer than 3 teeth should be in the work at any given time, but never more than 24.

Reducing the time and cost associated with band sawing rework operations is key to increasing productivity and improving weld quality. A recent American Welding Society (AWS) survey of shipyard welders concluded that companies can save more than $3,200 a year per welder by reducing rework and scrap metal.

As a whole, the welding industry has invested millions of dollars in training programs designed to reduce rework. The band saw department often is a source for many defects that require rework. Poor control over sawing variables can cause defects such as burrs, uneven cuts, poor finish, and excessive fluid residue. Defects can lead to faulty welding and, ultimately, lost time, so taking time to make accurate cuts can save companies thousands of dollars each year.

You can avoid most of these imperfections by following proper band sawing techniques and strategies. Following are a few techniques that will help you make a smoother, straighter cut, which will help reduce the need for rework and provide productivity gains.

Make Time for Preventive Maintenance

The band saw machine must run properly to make quality cuts. Performing scheduled preventive maintenance tasks can maximize productivity by minimizing machine downtime and the need for outside contractors to finish jobs. You can reduce costs by increasing machine and blade life and decreasing the need for overtime emergency maintenance repairs. Well-maintained machines make quality cuts at maximum efficiency and are safer to operate.

It's especially important for those involved with fabricating or welding to use machines that cut as efficiently and precisely as possible, simply because of the nature of the work. Cuts should be straight and smooth, because the pieces ultimately will be welded together.

Critical checkpoints in a preventive maintenance schedule include the following:

Daily:

• Clean chips from vise jaws, band wheels, blade guides and wipers, chip brush and pans, and machine surfaces.
• Inspect blade, blade guides, and chip brush for wear.
• Replace worn parts.
• Check sawing fluid and lubricants.

Every Three Months:

• Clean sawing fluid/lubricant reservoir and screen.

Every Six Months:

• Change hydraulic fluid filters.
• Clean hydraulic fluid reservoir magnetic plug.
• Lubricate saw column pivot point.
• Inspect and adjust blade guides.

Once a Year:

• Drain hydraulic fluid tank and change fluid.
• Clean hydraulic fluid strainer and fluid filter.
• Change transmission oil.

To perform proper and thorough preventive maintenance, you must know the machine's specific checkpoints. Refer to the machine's manual to ensure that you haven't overlooked a checkpoint that needs regular maintenance.

Choose the Right Blade for the Application

Choosing the right blade style to suit a specific application is an important step toward preventing rework. Always select a blade designed specifically for the material being cut and the machine being used.

The band saw machine often dictates the type of blade that should be used. Common blade categories are:

• Carbon
• Bimetal
• Carbide

Selecting the wrong blade style can cause crooked cutting, inefficient cut times, and unnecessary rework. Manufacturers now offer a variety of blades that ensure optimal performance based on specific cutting applications.

Selecting the appropriate tooth pitch for the application also is essential. If your goal is to cut materials with a smooth finish and no burrs, then the proper tooth pitch will put as many teeth into the work as possible without overloading the gullets. To select the right tooth pitch, a good rule of thumb is the "3, 6-12, 24" rule, which states that at any time there must never be fewer than 3 in the work, but never more than 24. In most cases, 6 to 12 teeth in the work is preferred. For a finer finish, move closer to 24 teeth per inch (TPI), and for faster, rough cuts, move toward 3 TPI. Blade manufacturers often provide blade TPI selection charts in product catalogs and on their Web sites.

Quality and consistency of the teeth in the blade also are important when you're choosing a band saw blade. The quality of a blade literally can determine the overall accuracy and smoothness of the cut over a period of time.

Use Less Fluid

While fluids help increase the smoothness of a cut by keeping the blade lubricated, the major drawback to using fluids is the residue left on the materials being cut. The more fluid used, the more residue typically is left behind on the cut surface. Residue must be removed after a cut because it later causes paint to come off, leaving the product appearance substandard. Removing fluid residue is a common example of rework.

Spray fluid systems apply small amounts of high-lubricity oil precisely at the entry point of the cut, distributing just enough to lubricate the blade before evaporating. Virtually no fluid residue is left, leaving nothing to be cleaned before welding.

Advanced second-generation blade coatings such as aluminum titanium nitride (AlTiN) and titanium nitride (TiN) provide additional lubricity and help reduce friction, but the technology has not yet advanced to the point at which you can omit fluids entirely. However, it's likely that band saw blade coating technology eventually will advance so that fluids will not be necessary in many—if not all—cutting applications.

Chuck Wahr is the director of marketing for band saw blades and sawing fluids at LENOX®, 301 Chestnut St., East Longmeadow, MA 01028, 413-525-3961, www.lenoxsaw.com.