A sawing machine is a machine tool designed to cut off bar stock, tubing, pipe, or any metal stock within its capacity, or to cut sheet stock to desired contours. The sawing machine functions by bringing a saw blade containing cutting teeth in contact with the workpiece to be cut, and drawing the cutting teeth through the workpiece. The sawing machine is much faster and easier than hand sawing, and is used principally to produce an accurate square or mitered cut on rectangular or cylindrical material.
One of the two common types of sawing machines used for metal cutting in the machine shop is the bandsaw machine. The bandsaw machine cuts by drawing a continuous metal band, called a bandsaw blade, across the workpiece. The bandsaw blade is supported and driven by a drive wheel and an idler wheel.
This course describes bandsaw operations and maintenance. This lesson introduces three common models of bandsaw machines and describes their use. In lesson two, the methods for maintaining, repairing, and troubleshooting these three bandsaw machines will be discussed.
Metal cutting bandsaw machines fall into two basic categories: horizontal machines and vertical machines. Vertical bandsaw machines are more commonly used. On vertical machines, the blade's cutting position is vertical and cuts into the side of the stock. The blade rotates on a fixed track between the idler wheel mounted above the worktable and the drive wheel mounted beneath the worktable. The stock is moved against the blade to make the cut. On the horizontal bandsaw machine, the cutting position of the bandsaw blade is horizontal and cuts downward into the stock. The drive and idler wheels are positioned lengthwise on the sawing machine frame, which pivots from a corner of the sawing machine bed. With the horizontal machine, the stock is fixed rigidly in a vise to the bed of the machine, and the blade is fed downward into the workpiece. The horizontal bandsaw machine is used primarily for cutting stock to length, either at right angles or to any desired miter angle. The vertical machine is more versatile and can be used for contour cutting, filing, and polishing, as well as for simple stock cutting.
a. Vertical Bandsaw. The vertical metal cutting bandsaw machine, being the more common of the two types of bandsaw machines, is usually identified as a "bandsaw machine" without using the word "vertical." A typical bandsaw machine ( figure 1) is driven by an electric motor through a belt transmission which permits adjustment of the blade speed through a range of speeds. The table may be tilted front-to-back or sideways to make mitered cuts. The metal cutting bandsaw machine does not require preformed bandsaw blades. An electric butt welder and grinding wheel are fastened to the sawing machine. The welder is used to weld a length of blade into a continuous band, and the grinding wheel is used to remove beads caused by the welding. Since the machine can weld its own blades, internal cutting is possible. When making internal cuts, the blade is inserted through a hole cut in the workpiece and is then welded into a band and mounted to the machine. After cutting the internal shape in the piece, the band is cut so that it can be removed.
An attachment for the metal cutting bandsaw twists the blade 30° or 90° so that stock which normally could not be cut because of insufficient clearance of the sawing machine column can be successfully cut. Other attachments permit the use of band files and polishing bands in place of the bandsaw blade. Adjustable guides for holding and feeding workpieces are also provided. The machine has a power feed mechanism operated by counterweights. Forced air for chip removal is supplied by an air pump in the base of the machine.
FIGURE 1. THE VERTICAL BANDSAW MACHINE.
b. Horizontal Bandsaw. The typical metal cutting horizontal bandsaw machine (figure 2) is a floor-mounted machine used for simple cutting of solid steel, tubing, and odd shaped material. The material to be cut is mounted in a vise attached to the bed of the machine. An electric motor drives the bandsaw blade through a belt and pulley arrangement from which three speeds may be obtained. The sawing machine frame, upon which the drive wheel, idler wheel, bandsaw blade, and motor are mounted, pivots from one corner of the sawing machine bed. The frame is counterbalanced by a tension spring between the frame and the bed. Feed is controlled by positioning a sliding weight along a bar fixed to the top side of the sawing machine frame. A dashpot is positioned between the frame and bed to stabilize the feed movement and prevent any quick movement of the frame that could cause damage to the bandsaw blade. The vise used to hold the material being cut is a quick-positioning type and can be adjusted easily to any angle. An adjustable workpiece stop is provided for rapid positioning of production work pieces.
FIGURE 2. A HORIZONTAL BANDSAW MACHINE.
Since the vertical bandsaw machine is more common than the horizontal type, three models of vertical bandsaw machines will be considered in this subcourse.
a. Model 1612-0. Model 1612-0 is a floor mounting, metal cutting, vertical bandsaw machine (figure 3). It has a 16 inch throat depth, and can accommodate a saw blade or a file band. The heavy, ribbed, cast iron table is 24 x 24 inches; it can be adjusted for a tilt of 10° to the left or 45° to the right. Precision insert guides are furnished with the machine to cover all sizes of saw band from 1/16 to 3/4 inch. The drive motor is a 208 volt, 60 cycle, 3 phase electric motor. Power is transmitted from the drive motor to a variable speed pulley, and then to the two-speed transmission which in turn drives the lower saw band wheel. A saw blade welder with grinder is mounted in the machine column.
FIGURE 3. FEATURES OF MODEL 1612-0.
b. Model 2612-1M. The model 2612-1M is a floor mounting, metal cutting, vertical bandsaw machine. It has a 24 inch throat depth and can accommodate a 1 inch maximum bandsaw blade and a 1/2 inch maximum band file. The worktable (figure 4) measures 26 x 26 inches; it can be manually titled up to 45° to the right and up to 5° to the left. Power is fed from the 220 volt, 60 cycle motor through a variable speed pulley to the three-speed transmission (figure 5). The model 2612-1M bandsaw machine has an integral butt welder and grinder.
c. Model 2614-1. Model 2614-1 is a floor mounted, metal cutting, vertical bandsaw machine (figure 6). It has a 26 inch throat depth. The heavy duty 30 x 30 inch table has a removable center disk. The table can be tilted manually to a maximum of 5° to the left and 45° to the right. The five horsepower motor drives a variable speed pulley which, in turn, drives the three-speed transmission. The bandsaw machine is equipped with a butt welder and grinder.
In the remainder of this course, the term "bandsaw machine" refers only to the vertical metal cutting bandsaw machine. Operations for the horizontal metal cutting bandsaw machine will not be discussed.
The bandsaw machine is used for external and internal sawing. With the use of attachments, the bandsaw machine can also serve a variety of other functions. Band files and polishing bands can be used in place of the bandsaw blade for filing and polishing operations. A disk cutting attachment permits the cutting of true circles. An angular blade guide attachment is furnished with most bandsaw machines. This attachment twists the bandsaw blade so that large or long workpieces that would not normally clear the bandsaw machine column can be cut. A miter guide attachment can be used to guide the workpiece at any convenient angle.
FIGURE 4. MODEL 2612-1M FEATURES -FRONT VIEW.
FIGURE 5. MODEL 2612-1M FEATURES -REAR VIEW.
FIGURE 6. MODEL 2614 FEATURES AND CONTROLS.
a. General Bandsawing Operations. The bandsaw machine can be used for making external straight-line, curved, or contoured cuts. When power sawing with the bandsaw machine, proper blade and guide selection are important.
(1) Blade Selection. Bandsaw blades are manufactured in two forms. They are supplied in rolls of 50 to 500 feet for use on machines that have butt welders for forming their own blade bands. Bandsaw blades are also supplied in continuous welded bands in standard sizes for machines having no provisions for welding blade bands. All three models discussed in this subcourse have provisions for welding blade bands.
(a) Characteristics of Blades. Bandsaw blades are made from special alloy steel. The blades are made flexible by annealing the body of the blade and hardening only the teeth. Metal cutting bandsaw blades have their teeth set to produce a kerf, or cut, slightly wider than the thickness of the blade to prevent the blade from being pinched by the stock. The setting of the teeth for most bandsaw blades is called the raker setting. Raker tooth blades have one tooth bent to the right, the next tooth bent to the left, and the third tooth set straight (figure 7). The pitch of bandsaw blade teeth is the number of teeth per linear inch of the blade (figure 8). For example, if a blade has 14 teeth per inch (tpi), it has a pitch of 14, or it may be referred to as a 14-pitch blade. Metal cutting bandsaw blades range from 6 to 32 teeth per inch. The finer tooth blades are used for sawing thin stock; the coarse tooth blades are used for sawing large stock and soft metal.
FIGURE 7. RAKER TOOTH SETTING.
FIGURE 8. PITCH OF TEETH.
(b) Selecting the Proper Blade. Bandsaw blades are selected according to the type of material to be cut, the thickness of the material to be cut, and the sawing operation to be performed.
1 Blade Pitch. Soft or gummy materials and thick stock require coarse tooth blades to provide adequate chip clearance. Hard materials generally require finer tooth blades. Fine tooth blades are also necessary if a good finish is desired. Since two or three teeth of the bandsaw blade must be in contact with the workpiece at all times to prevent chatter and shearing of teeth, fine tooth blades are used to cut sheet metal and tubing. If sheet metal is too thin to meet this requirement with the finest tooth blade available, the metal should first be mounted on plywood, fiber, or thicker metal to stiffen it. Table 1, may be used as a guide in selecting the proper pitch bandsaw blade for different metals and metal thicknesses. If the stock is exceptionally large, coarser tooth blades than those recommended for solid stock may be used. Remember, two or more teeth must contact the workpiece at all times to prevent shearing of the blade teeth. If the recommended pitch for solid stock fails to meet this requirement, a blade with finer pitch must be selected.
2 Blade Width. When straight sawing, the widest blade available of the proper pitch should be used. Thinner blades are required for contour sawing to prevent the body of the blade from rubbing the sides of the cut when cutting sharp curves. When curves or radii are to be cut on the bandsaw machine, the widest blade adaptable to the sharpest radius to be cut should be used. Narrow blades are more easily broken than wide blades and should be used only where necessary.
TABLE 1. SELECTION OF BLADE PITCH.
Table 2 lists the blade sizes which can be used for cutting different size radii. If the proper size blade for the radius to be cut is not available, the next size narrower should be used.
TABLE 2. BANDSAWING RADIUS GUIDE.
(c) Blade Wear. Bandsaw blades become dull from prolonged use, but some conditions promote greater than normal wear on the blades. Blades dull quickly if used at too high a speed for the material being cut. Also, if the material to be cut is too hard for the pitch of the blade, abnormal wear will result. This can be caused by hard spots in cast iron or welded metal, and usually can be anticipated so that the operator can reduce the feed. Rubber and some fibers or plastics contain abrasive material that will dull saw blades regardless of the sawing speed and feed. Premature blade dulling often occurs from using too fine a pitch blade and from feeding too quickly.
(d) Symptoms of Worn Blades. Several symptoms appear when a bandsaw blade is dull. If the bandsaw blade cuts slowly or not at all when the workpiece is fed by hand, the blade is probably dull. Blade teeth which are bright on the cutting edge also indicate a dull blade. Another sign of a dull blade is when it becomes difficult to follow a line or when the blade forces to one side or the other. A dull blade is also indicated when the chips from cutting metals are granular (except for cast iron which produces granular chips with both sharp and dull blades). With the machine stopped, or with the bandsaw blade removed from the machine, run a finger slowly over the teeth in the cutting direction. If sharp edges cannot be felt, the blade is dull and should be replaced.
(2) Guide Selection. Standard saw guides are furnished with the bandsaw machines and are designed to guide the saw blade to a constant location. The standard guides are installed directly on the post and keeper block. Adjustable saw guide inserts allow the guides to be adjusted to the size of the saw blade to be used. Two special attachments, the angular blade guide and the miter guide, provide added capabilities to the bandsaw machine.
(a) Adjusting Saw Guide Inserts. Saw guide inserts are provided so that the guides can be adjusted for the size of saw blade to be used. The set of inserts marked for the width of saw band being used should be selected. The right hand insert (figure 9) is placed in the milled slot of the guide, and its adjusting screw is tightened lightly so that the insert is able to slide in the slot but will still hold its position when it is released. Using the proper insert gage to match the saw band being used, place the gage in the opposite slot and adjust the insert so that it meets the two gaging edges. Then tighten the insert securely in place. Place the left hand insert in the slot and tighten the screw lightly. Then place the gage edgewise between the two inserts. Bring the left hand insert down so that it rests against the gage. When the gage is removed, the gap left will be the proper thickness for the saw band.
FIGURE 9. SAW GUIDE INSERTS.
(b) Angular Blade Guide. The angular blade guide attachment is furnished with most metal cutting bandsaw machines. This attachment twists the bandsaw blade so that large or long workpieces that would not normally clear the bandsaw machine column can be cut. The blade is twisted 30° on some machines and 30° to 90° on others. The angular blade guide attachment consists of an upper bandsaw blade guide that attaches to the sawing machine post and a lower bandsaw blade guide that attaches to the frame beneath the table. Figure 10 shows 90° saw guide brackets (with guides and inserts installed on the bracket) as installed on the model 2612-1M bandsaw machine.
FIGURE 10. ANGULAR BLADE GUIDE ATTACHMENT.
(c) Miter Guide. The miter guide attachment is a device used to support and guide workpieces to the bandsaw blade so that the workpiece may be cut at a specific angle. The attachment can be swiveled and locked to guide the workpiece at any convenient angle. On the three bandsaw machine models discussed in this subcourse, the mitering attachment is side mounting. When not in use, the attachment is swung up to the right and around on the slide rod so that it hangs below the table. Figure 11 shows a typical side mounting mitering attachment.
FIGURE 11. THE MITER GUIDE.
(d) Rip Fence. The rip fence accessory helps in making even, straight cuts. A typical rip fence is shown in figure 12. In making a long cut with a rip fence as a guide, check to be sure that the saw band used is not worn on one side. This will cause the work to wander relative to the rip fence guide.
(e) Disk Cutting Attachment. The disk cutting attachment (figure 13) permits cutting true circles, either internally or externally, or any diameter from 2 1/2 to 30 inches. This attachment is bolted to the post with capscrews and washers.
(f) Screw Feed Attachment. The screw feed device (figure 14) is a machine tool attachment on some makes of bandsaw machines, and is a component part of other bandsaw machines. The screw feed accessory is used for precision contour sawing of heavy work. It is a hand-operated method of feeding the workpiece into the bandsaw blade or band file. The device is used with a work holding jaw to feed the workpiece into the blade at angles other than 90° to the blade.
FIGURE 12. A RIP FENCE.
(3) Band Tensioning. It is essential that the saw band be correctly tensioned in order to obtain a maximum accuracy and cutting rate. Band tension is applied by turning the removable handcrank (tension handle) located below the saw head.
The band should be tightened to the proper tension indicated on the band tension scale mounted on the machine. The figures on this scale are recommended tensions and are based on the most common gages and pitches used. When using bands with coarser pitch or lighter gage, the tension should be reduced. The tension should be increased when using heavier bands. A new band may stretch slightly as it is being used. It is important to check the tension of the band so that it does not become too slack. Table 3 gives the recommended tensions for all sizes of band tools.
(4) Tracking the Band. The upper wheel must be adjusted so that the band tracks correctly on both wheels. To accomplish this, the upper wheel can be tilted on its axis. Assuming that the saw band has been correctly installed and tensioned, the tracking adjustment can be made by opening the wheel doors, pressing the start button, and observing how the band tracks. The tilt controls (figure 15) can be used to adjust the upper wheel tilt until the band tracks properly. The band is tracking properly when the back edge of the band just touches the saw guide backup bearings. The band should ride near the center of the band wheel tire. When the band is tracking correctly, the tilt lock should be tightened.
FIGURE 13. DISK CUTTING ATTACHMENT.
FIGURE 14. SCREW FEED DEVICE.
TABLE 3. RECOMMENDED BAND TENSIONS.
Do not stand in front of bandsaw when operating machine or rotating upper wheel by hand to track blade.
(5) Band Installation. The procedures for installing a band differ slightly from model to model. The procedure for installing a band on model 2614-1 is considered typical and is described here. To install a band, the band wheel doors are opened. Then the bar which crosses the table saw slot just below the front edge of the table is unlocked and opened. The saw band guard is then removed from the post. Gloves are used when handling the band, as it is carefully placed over the wheels and between the saw guide inserts. The band guard is then replaced, and the bar is closed and locked over the table slot. Finally, the wheel doors must be closed. Blade tension should be set or adjusted. See TM 9-3419-227-10, page 10.
(6) Laying Out Workpieces. When laying out workpieces for bandsaw operations, the size of the stock must be considered in relation to the clearance of the bandsaw machine column. For straight-line sawing, the clearance is easy to judge; however, for contour sawing of large size stock, the directions of cut must be carefully planned to prevent the stock from hitting the column. If a small section is to be cut from a large sheet of metal, the section should be roughly cut oversize from the sheet, and then carefully cut to the exact outline.
FIGURE 15. TILT CONTROLS (MODEL 2612-1M).
(a) Laying Out Pieces for Circular Sawing. When a circle or disk is to be sawed using the disk cutting saw attachment, a compass or pair of dividers should be used to scribe a circle of the desired diameter on the stock. If possible, the circle should be scribed beginning at one edge of the stock so that the bandsaw blade may start the cut without preliminary sawing or notching. Next, a center hole should be drilled or center-punched into the disk to accept the center pin of the disk cutting attachment. The hole should be made only as deep and as large as needed for the center pin. Too large a hole will cause the center pin to fit loosely, which will result in an inaccurate cut.
(b) Laying Out Pieces for Contour Sawing. When an outline is to be cut that consists of more than two intersecting lines, the exact shape required should be scribed on the stock. When laying out the piece, save unnecessary cuts by taking advantage of straight, clean edges on the uncut stock. The bandsaw blade size should be selected according to the size needed to cut the smallest radius laid out on the workpiece. Then a twist drill equal to or greater in diameter than the width of the bandsaw blade must be selected. Using this drill, drill a hole in the solid stock in each corner of the pattern (figure 16), making sure the holes fall completely within the section of material that will be removed. These holes are needed when sawing to permit the change of direction of the bandsaw blade from one cut to the other.
If an internal section is to be removed from the stock, and the edge must remain unbroken, lay out and drill a starting hole, using a drill larger in diameter than the width of the bandsaw blade. The bandsaw blade will be inserted through this hole before being welded into a band and installed on the bandsaw machine.
(7) Bandsaw Speeds and Speed Controls. The cutting speed of a bandsaw machine is the speed of the bandsaw blade as it passes the table, measured in feet per minute (fpm). Proper bandsaw speeds are important in conserving bandsaw blades. Too great a speed for the material being cut will cause abnormally rapid blade wear. Too slow a speed will result in inefficient production. In general, the harder the material, the slower the speed that should be selected. Conversely, the softer the material, the faster the speed that should be selected. It is also true that the faster the speed, the finer the finish produced on the cut surface. This principle applies to light feeds in conjunction with fast speeds. Table 4 shows the recommended sawing speeds for different materials. In general, the faster speeds should be used to saw thin materials, and the slower speeds should be used for thick materials.
FIGURE 16. HOLE LAYOUTS FOR CONTOUR SAWING.
TABLE 4. BANDSAWING SPEEDS.
TABLE 4. BANDSAWING SPEEDS (CONTINUED).
All metal cutting bandsaw machines have several cutting speeds which can be selected. Since the diameter of the drive wheel of the bandsaw machine establishes a fixed ratio between the motor or transmission speed in revolutions per minute to the blade speed in feet per minute, it is not necessary to convert revolutions per minute into feet per minute as with most other machine tool operations. The speeds are identified in feet per minute on the bandsaw machine speed selector controls. Some machines have a speed indicator with which a careful check of sawing speeds may be made when the machine is operating with or without a load.
(8) Bandsaw Feeds. The feed of a vertical bandsaw machine is the pressure applied to the bandsaw blade by the material being cut. With vertical bandsaw machines, the feed is applied to the workpiece instead of the saw blade. The workpiece may be hand fed or power fed, depending upon the operation to be performed. Cutting curves or special contours requires that the workpiece be fed into the bandsaw blade by hand.
(a) Power Feeding. The power feed on a bandsaw machine is operated by adjustable weights in the machine pedestal. The weights are connected by cables to one of the work holding attachments of the sawing machine to pull the workpiece against the bandsaw blade. To operate the power feed, the weights are raised by depressing a pedal and the cables are then fixed to the work holding attachment. When the pedal is released, the weights pull the piece into the blade.
(b) General Rules for Feeding Workpieces. A number of general rules apply to feeding workpieces on bandsaw machines. The feed should be light when starting a cut. The pressure can be increased after the cut is established. Also, hard materials require lighter feeds than softer materials. It is generally true that wider bandsaw blades will withstand greater pressures than narrow blades and can therefore be used with heavier feeds. When hard spots in the material being cut are encountered, the feed should be reduced until the spots are cut through. A light feed should be used when cutting curves; a heavier feed can be used for straight line cutting.
(9) Coolants. Most sawing machines used in military operations are dry-cutting machines; that is, they are not intended for use with liquid coolants. These bandsaw machines contain air pumps and hoses through which a jet of air is directed against the bandsaw blade and workpiece. The air acts as both a coolant and as a means of removing chips from the cutting area. The nozzle of the air hose should always be directed at the contact area of the blade and workpiece. The model 2614-1 bandsaw machine uses a mist coolant, designed to direct a fine mist stream of liquid coolant on the blade teeth and workpiece.
(10) Safety Precautions. When using or servicing the bandsaw machine, it is important to make safety a habit. Be sure to close the doors and replace all covers and safety guards before operating the machine. Wear safety glasses and wear gloves when handling the saw band. DO NOT, however, wear gloves when operating the machine. Set the saw guides as close to the work as possible. Close the band wheel cover before tensioning the band or starting the machine. Disconnect the electrical supply before removing panels or drive covers. Keep hands away from the moving saw band or blade. Before working on the machine, always check for these and other safety precautions in the technical manual (TM) appropriate to the bandsaw machine being operated or serviced.
b. External Sawing. External sawing is the process of using the bandsaw machine to make saw cuts that begin at the outer edge of the workpiece. These cuts may be straight-line, curved, or contoured.
(1) Straight-Line Sawing. In a typical example of straight-line sawing, a bandsaw blade of the desired pitch for the material to be cut is selected. The blade should be as wide as possible for straight-line sawing. Then the desired speed is set on the bandsaw machine. The workpiece is positioned at the desired angle in one of the bandsaw machine attachments. Then the cable is connected to the power feed mechanism (if the power feed is to be used). The bandsaw machine is then started. The workpiece is lightly fed into the blade to start the cut. Once the cut has been started, the feed can be increased. If the feed is being done by hand, the pressure applied to the workpiece by the operator can be varied to find the best cutting conditions.
Straight-line sawing is performed on the bandsaw machine by using one or a combination of several mechanisms or attachments: the miter guide attachment, with or without a power feed; the screw feed device, with or without the work holding jaw device; and the work holding jaw device with power feed and the angular blade guide attachment.
(a) The Miter Guide Attachment. The miter guide attachment on some machines can be connected to the power feed mechanism. On other machines, feeding must be done by hand when using the miter guide. The workpiece is clamped or hand-held against the miter guide attachment, and the workpiece and attachment are moved against the bandsaw blade. The miter guide assembly moves on a track parallel to the blade, thereby assuring a straight-line cut.
(b) The Screw Feed Device. The screw feed device is used to push the workpiece against the bandsaw blade in a direction parallel to the blade. The feed screw may be applied directly to the workpiece, or may be used to push the work holding jaw device in which the workpiece can be positioned at various angles.
(c) The Work Holding Jaw Device. The work holding jaw device (figure 17) can be connected, on some machines, to the power feed to produce straight-line cuts.
(d) The Angular Blade Guide Attachment. The angular blade guide attachment is used for straight-line sawing when the workpiece cannot be cut in the normal manner because it is too large or too long to clear the column of the bandsaw machine frame.
(2) Curve Sawing. Curve sawing is performed either by using the disk cutting saw attachment or by hand guiding the workpiece.
FIGURE 17. WORK HOLDING JAW DEVICE.
(a) Selecting the Blade. Care must be taken to select a bandsaw blade of the proper width for the radius or curve to be cut. If a blade is too wide for the radius, the heel of the blade will press against the outer edge of the kerf (figure 18). When the heel contacts this edge, any further twisting of the workpiece in an attempt to cut a sharper radius will twist the bandsaw blade without cutting a sharper radius.
(b) Cutting the Curve. On curve cutting, less pressure must be applied to the workpiece than on straight-line cutting. The smaller the curve, the more care must be exercised. It should be understood that when any material is cut with a flexible bandsaw blade, the blade deflects to the rear in proportion to the amount of pressure applied to the workpiece. This deflection, referred to as "drag," will not affect a straight-line cut because the sides of the blade remain parallel to the cut. However, when curves are cut on the bandsaw machine, the drag will cause a "belly" in the cut section. To reduce the belly to a minimum, the drag must be reduced to a minimum, and this can only be done by reducing the pressure applied in feeding the workpiece into the blade.
FIGURE 18. CURVE LIMITATIONS.
(c) Curve Sawing at an Angle. When sawing at an angle with the table tilted, a curve or radius will be shaped like a cone section, with a larger radius on one workpiece surface, and a smaller radius on the other workpiece surface. It is very important when cutting at angles that the smaller of the two radii be used to determine the bandsaw blade size. Figure 19 shows a chart of recommended bandsaw widths for minimum radii to be cut. The recommendations on this radii chart are based on sawing relatively thin stock. Use a narrower blade than recommended when sawing stock more than one inch thick.
FIGURE 19. MINIMUM RADII CHART.
(3) Contour Sawing. Contour sawing is the process of cutting shapes in which the direction of the cut must be changed at intervals. Holes larger in diameter than the width of the saw blade must be drilled at each corner where a change of direction of the bandsaw blade will occur. After the shape is cut either by sawing away from the hole or sawing toward the hole, and the slug or waste material has been removed, the corners should be finished by filing or notching. The bandsaw blade should not be used for these operations because the blade will bow and cut unevenly.
(a) Sawing Away From the Hole. To saw away from the hole on a line next to the hole, the bandsaw blade must cut away from the center of the hole, or the blade will bow and cause a belly in the cut. Two methods can be used to accomplish this. In the first method, to start the cut, a curve is cut outward from the hole to meet the layout line, leaving a piece of excess metal which can be removed later by filing (figure 20). In the second method, a section of metal is notched out with a saw blade by several short cuts to give the blade clearance for starting the cut along the layout line (figure 21).
FIGURE 20. SAWING AWAY FROM THE HOLE - METHOD 1.
FIGURE 21. SAWING AWAY FROM THE HOLE - METHOD 2.
FIGURE 22. SAWING TOWARD THE HOLE - FIRST CUT.
FIGURE 23. SAWING TOWARD THE HOLE - SECOND CUT.
c. Internal Sawing. Internal sawing is performed in the same way as contour sawing, except that the bandsaw blade cannot start cutting from the edge of the workpiece but must start cutting from a drilled hole in the workpiece (refer to figure 16). With the pattern laid out on the workpiece and with the starting hole drilled, an unwelded bandsaw blade of the proper length is inserted through the starting hole. Then the two ends of the blade are brought together at the butt welder of the bandsaw machine. The blade is then welded into a continuous band. The bandsaw blade is then installed onto the bandsaw machine. When the sawing operation is completed, the bandsaw blade is cut so that it can be removed from the workpiece.
d. Cutting and Welding the Band. When installing a bandsaw blade, or when cutting and rewelding the blade for internal sawing operations, the blade and the welder must first be properly prepared; then the blade can be welded. Follow this procedure to cut and weld a bandsaw blade.
In the description that follows, the model 2612-1M bandsaw machine with integral welder is used as an example. The procedures for welding a bandsaw blade are similar for all models.
(1) General. The butt welder on the model 2612-1M bandsaw machine is capable of welding 3/4 inch wide by .032 gage carbon or Dart saw bands. The two clamping jaws of the welder hold the butted band ends together. When the welding switch lever is pressed, an electric current is induced through the butted ends of the blade, creating enough heat to soften the metal and join the ends. Pressing the welding lever (figure 24) also releases a spring which causes the jaws to force the band ends together. When the movable jaw has moved .065 inches toward the stationary jaw, the electric current is automatically cut off. The spring force on the jaws is released when the welding lever is released.
FIGURE 24. WELDER CONTROLS.
(2) Preparing the Blade. First, the saw blade must be cut to length. Using a blade shear will ensure that the blade ends are flat, square, and smooth. If snips have been used to cut the blade, the ends must be squared before welding. This is done by grinding the ends of the blade. Both ends of the saw blade should be ground in one operation. Holding the ends so that the teeth point in opposite directions during grinding will ensure that the two ends will match perfectly when turned over, regardless of the angle of grinding. Then blade ends must then be carefully cleaned. The part of each blade that comes into contact with the welder jaws must be free of all dirt or oil. Any dirt or oil on the blade or welder jaws will prevent good electrical contact.
(3) Preparing the Welder. First, clean the welder jaws. On the model 2612-1M bandsaw machine, the integral butt welder has a jaw upset force selector (refer to figure 24), located directly above the stationary jaw. The jaw upset force selector provides a variable control since wider saw bands need greater upsetting force between the jaws than narrow bands, and since too much force on small bands will cause climbing or overlapping. In preparing to make a weld, the jaw upsetting force selector control should be set to the correct position for the width of the saw blade being welded.
(4) Saw Blade Alignment Before Welding. Before making the weld, the saw blade ends must be aligned so that the blade will be straight after welding. If internal sawing is to be done, the blade is inserted through the starting hole in the work. Then the ends of the saw blade are brought to the welder to be clamped into the jaws. Align the blade using these steps:
(a) Insert the saw blade between the jaws with the back of the blade against the back of the jaws, lining up the blade so that it will be straight after welding.
(b) The blade ends should meet in the center of the jaw gap without any offset either in thickness or across the width (figure 25). If the ends are clamped in an offset manner, an overlapping weld will result. This type of weld will have to be ground too much, resulting in a weak weld.
FIGURE 25. SAW BLADE ALIGNMENT.
(c) If the contact across the width is not complete when the ends are clamped in the jaws, remove one end and recut it. A misaligned joint will cause an incomplete weld.
(d) After the blade ends are lined up, clamp them securely, but not so tightly as to harm the set, between the welder jaws.
(5) Making the Weld. After the blade ends have been aligned, press and hold down the weld lever (refer to figure 24) to make the weld. The lever should be held down until the weld has cooled. The stationary jaw clamp should be released before the weld lever is released. This will prevent scoring the welder jaw surface. Then release the weld lever. When the lever is released, the butt welder mechanism and electrical switches will be automatically recocked, and the band will be ready to be annealed. Remove the welded saw band. Two general statements about welding the band should be noted:
(a) Cut out the old weld as each new weld is made. Since only one weld is recommended in a saw band, use the blade shear to cut away small portions of the ends of the old weld. Since the welding operation uses up no more than 1/16 inch of the band, it will not shorten the band appreciably, even after several welds have been made. Starting with a full size saw band, approximately three to four inches of band can be used in making welds before the band will be too short to fit over the machine wheels.
(b) If it is found, after making the weld, that the teeth of the band point in the wrong direction, it can be reversed by turning the band inside out. However, this cannot be done when the band is welded through a piece of material for internal sawing. In this case, the saw band must be cut and welded.
(6) Cleaning Up After Welding. It is important that the welder jaws be kept clean at all times. The jaws and inserts must be wiped and/or scraped clean after every weld. Doing this will maintain the strength and fatigue characteristics of the band by holding proper alignment, preventing flash from becoming embedded in the band, and preventing shorts or poor electrical contact.
(7) Inspecting the Weld. When the band is removed from the welder, it should be inspected carefully. The color of the upset material around the weld should be blue-gray, and of equal intensity throughout. The spacing of the teeth should be uniform, and the weld should be located in the center of the gullet. Major jaw misalignment is easily noted at this time from the weld appearance. Figure 26 shows several types of defective welds. If a weld is imperfect, some of the possible causes can be found, if needed, in TM 9-3419-228-10, beginning on page 46 (or in the troubleshooting section of the TM for the welder being used).
FIGURE 26. DEFECTIVE WELDS.
(8) Grinding the Welded Band. After welding, the band must be dressed to remove excess metal or flash from the weld. Grind the welded area down to the same thickness as the rest of the band. The weld should be ground with the teeth facing out (figure 27). Care must be taken during grinding so as not to hit the teeth, not to grind deeper than the thickness of the band, and not to burn or overheat the weld area. The weld should pass freely through the gage above the grinding wheel.
Use care in handling the band; the weld is brittle because it has not yet been annealed.
FIGURE 27. GRINDING THE WELD.
(9) Annealing the Welded Band. Directly above the grinding wheel is the annealing pushbutton. When the band is heated up in the welding and grinding process, the steel at the point of the weld air-hardens and is brittle. Therefore, it is necessary to anneal the weld by reheating it and allowing it to cool slowly. This returns the band to an approximation of its original temper. Use these steps to anneal the weld:
(a) Clean the welder jaws.
(b) Press the spring clip behind the weld lever, and move the lever up all the way.
(c) Clamp the band just back of the teeth.
(d) Set the ANNEAL HEAT selector switch (refer to figure 24) at either the 1/16 inch to 1/2 inch or the 5/8 inch to 3/4 inch position, according to the width of the blade being annealed.
(e) The next step in the annealing process depends on the type of blade being annealed. It is very important that this step be performed carefully:
1 Carbon Blades. If a carbon blade is being annealed, press and jog the anneal switch pushbutton until the weld is a dull cherry to cherry red in color. Then allow the blade to cool slowly by decreasing the jogging frequency.
2 Dart Blades. For a Dart blade, heat the blade slowly until the weld becomes a deep blue color. Continue to heat by jogging the anneal switch pushbutton until the width of the blue color is one-half the length of the band exposed between the jaws. Do not overheat or the temper of the band adjacent to the weld will be damaged. Cool quickly by releasing the button.
e. General Filing Operations. Filing operations are performed on the bandsaw machine using a band file and the band file attachment. As with sawing operations, the quality of filing and the economical wear of the band file depend upon proper selection of files and filing speeds for different materials and conditions.
(1) Band File Attachment. Most bandsaw machines have a band file attachment (figure 28) to permit the use of band files on the machine. A typical band file attachment consists of a band file guide and upper and lower guide supports. These supports attach to the frame and post of the bandsaw machine to provide a rigid track upon which the band file can ride. A special filing filler plate is provided to adapt the table slot to the extra width and depth required for the band file and the file band guide. Most band file attachments have either adjustable guides and guide supports, or two or more file band guides, so that different width file bands can be accommodated.
FIGURE 28. BAND FILE ATTACHMENT.
(2) File Bands. The bandsaw machine is adapted for filing by use of the band file attachment. A band file is fitted over the drive and idler wheels in place of the bandsaw blade. Band files (figure 29 ) consist of many interlocking file segments that are riveted to flexible steel bands. These bands are attached to each other, end to end, to form a continuous band. The file segments are attached to the steel bands in such a way that they will form a continuous filing surface when held in a straight line, but will separate from each other as they move around the idler and drive wheels. The band file attachment provides a support behind the file above the table, so that the band file cannot be forced backward by the pressure of the workpiece as it is filed.
FIGURE 29. A TYPICAL BAND FILE.
(a) Cut of File Teeth. Most files are classed as single-cut or double-cut files according to the kind of teeth. Single-cut files have rows of parallel teeth extending across the face of the file at an angle. Double-cut files have two rows of parallel teeth which cross each other. The first row, usually cut at about a 45° angle, is coarser and deeper than the second row which is generally cut at an angle of from 70° to 80°. Band files are always of the double-cut type. Double cut files of medium pitch are called bastard-cut files. These files usually have between 12 and 24 teeth per inch. Bastard-cut band files are commonly used for filing steel and other hard metals on the bandsaw machine. Short angle-cut files are double-cut files in which the two rows of teeth have been cut at shorter angles than those of the bastard-cut file. Short angle-cut files are usually coarse pitch, having 10 or 11 teeth per inch. Short angle-cut band files are commonly used for filing soft metals on the bandsaw machine.
(b) Band File Shapes. Band files are manufactured in flat and oval shapes. Flat band files are used for most filing jobs. Oval band files have a curved face, and are used for filing inside curves and contours. Band files are made in 1/4, 3/8, and 1/2 inch widths.
(c) Selection of Band Files. Band files should be chosen on the basis of workpiece thickness and the kind of material to be filed. In general, as the workpiece becomes thicker, the file should be coarser. This is because larger total chip accumulation from thick pieces requires additional space for the chips between the teeth. On thin sheet metal, a fine pitch file is required to prevent chatter. Narrower pitch files are used for tough carbon and alloy steels; wider and coarser pitch files are used for softer, more free-cutting materials such as cast iron and nonferrous metals. Table 5 provides a guide for selecting the proper file for specific materials. If sheet metal is to be filed, a finer tooth file should be used, if necessary, to reduce chatter and produce a better finish on the workpiece.
TABLE 5. SELECTION OF BAND FILES.
(d) Care and Cleaning of Band Files. The particles of metal removed by the file often lodge in the file teeth, reducing the cutting efficiency of the file and affecting the quality of the finish. If hard metal particles are lodged in the file teeth, they may scratch the workpiece. When steel is to be filed, chalk can be rubbed into the file before filing; the chalk will reduce the tendency for hard particles to adhere to the file. The file should be cleaned often, using a stiff brush or a file card. The brush should be moved in the direction of each cut of the file to dislodge all particles hidden between the teeth.
(3) Band Filing Speed. Band files should be run at relatively slow speeds as compared to speeds used for bandsawing. In general, the best filing speeds are between 80 and 150 feet per minute (fpm). Table 6 lists the recommended filing speeds for band filing. Note that, in general, the slower speeds are used for filing harder metals, and the faster speeds are used for filing softer metals.
TABLE 6. BAND FILING SPEEDS.
(4) Band Filing Feeds. Work pressure on the band file should not be excessive. Medium pressure applied against the band file moving at the proper speed will produce curled chips which will not clog the file. Heavy pressure will cause clogging and can cause the file to break or the machine to stall. A light pressure should be used for finish filing, with a slow, sideways motion that will not leave vertical file marks on the workpiece.
The procedures used for band filing using bandsaw machine model 2612-1M are presented here as an example of band filing procedures. Band filing procedures are similar for all bandsaw machine models.
(5) Setting Up the Machine for Filing. To set up the model 2612-1M bandsaw machine for either internal or external filing, perform these steps:
(a) If the machine is set up for sawing, remove the saw band.
(b) Remove the table center disk and post saw band guard.
(c) Remove the saw guides from the machine.
(d) Mount the file guide support on the lower keeper block, making sure the proper width of slot for the file band is being used.
(e) Lower the upper post to the proper work thickness. This thickness should not exceed two inches for a 1/4 inch file band and four inches for 3/8 and 1/2 inch bands.
(f) Install the upper file guide (figure 30), locking it firmly to the post with the knurled thumb screws.
(g) Install the special table center disk for filing.
(6) Joining the File Band. To join the file band, take one end of the file band in each hand, with the yellow painted end (figure 31) in the left hand. Hold the file ends at right angles with the filing surface up. Depress the tip of the spring steel band held in the right hand with the lock rivet of the yellow segment held in the left hand. Allow the rivet head to slip into the slotted hole. Slide the rivet head into the small end of the slot. Straighten the file band, allowing the spring steel end to snap over the dowel. Make sure that the ends of the band are flush before running the band on the machine.
FIGURE 30. SETTING UP FOR FILING.
FIGURE 31. JOINING THE FILE BAND.
(7) Tracking and Tensioning the File Band. The file bands are aligned on the wheels in the same way as is used in tracking the saw bands, described in paragraph 4a(4). The band can be made to run on the crown of the wheel by tilting the upper wheel with the tilt control. When properly tracked, the file band should run freely in the file guide channel. The tension of the file band should be adjusted to the same tension as that used for a 1/8 inch wide carbon saw band. Too much tension will cause the file segment rivets to break when heavy filing pressure is applied. While it might seem, at first, that better filing results are obtained with excess tightening of the file band, this will not be the case in the long run. Most accurate filing can be obtained with the light band tension.
Check the file band to see that it is in alignment and will pass freely over the channel in the file guide. Then shift the machine into low gear and start the drive motor. Observe the file band (figure 32) to be sure that it is tracking properly.
FIGURE 32. TRACKING THE FILE BAND.
File segment must travel with the riveted section down; if not, injury to operator and damage to file band and bandsaw will occur.
(8) The Filing Operation. During the filing operation, the correct combination of speed and pressure will produce curled chips. The best filing speeds are between 80 and 150 fpm. For internal filing, unlock the band and run it through the opening in the workpiece; then reassemble the band. Keep the files clean. Do not file when the teeth are loaded. Loaded files cause bumpy filing and scratch the workpiece. Excessive filing pressures when the file segments are clogged with chips will cause the file teeth to strip out. Use a file card or brush to clean the band before returning any file band to the storage cabinet.
(9) Removing the File Band. To remove the file band, release the tension by lowering the upper wheel, and slip the band off the wheels. To separate the band after it has been removed from the wheels, perform these steps:
(a) Hold the band at the joint with both hands, with the yellow segment in the left hand.
(b) Bend the joint to not more than a 12 inch radius, exposing the joint slot.
(c) Using the forefinger of the left hand, depress the front end of the yellow file band. With the thumb and forefinger of the right hand, disengage the dowel.
(d) Slide the lock rivet to the open end of the slot and lift off.
(e) For storage after removal, the file band should not be coiled into more than three loops.
f. General Polishing Operations. Polishing bands and a polishing attachment are provided with the bandsaw machine so that light polishing operations can be performed. The polishing bands are intended primarily for removing saw marks on the cut edges of workpieces.
(1) Polishing Attachment. A polishing attachment (figure 33) is provided with most bandsaw machines to allow the machine to be used for polishing. The attachment, similar to the band file attachment, provides support for the polishing band, together with the polishing band plate which is supported between the post and frame of the bandsaw machine. The polishing band plate acts as a solid backing for the polishing band to prevent stretching and distorting the polishing band when the workpiece is held against it. A polishing band filler plate is used to fill the table slot so the workpiece can be supported close to the polishing band.
(2) Polishing Bands. When the polishing attachment has been installed on the bandsaw machine and the bandsaw blade has been replaced by the polishing band, polishing operations can be performed on the bandsaw machine. The polishing band is usually one inch wide, and has a heavy fabric backing. Polishing bands are manufactured to withstand high finishing and polishing temperatures. Abrasive bands are mounted over the wheels in the same manner as saw bands; however, a rigid backup support which has a graphite impregnated facing is used. This polishing guide support (figure 34) is mounted to the post in place of the saw guides.
FIGURE 33. POLISHING ATTACHMENT.
(a) Types of Polishing Bands. Polishing bands for bandsaw machines are usually supplied in three grain sizes of aluminum oxide or silicone carbide abrasive. Number 50 grain (coarse-medium) is used for light grinding operations, soft materials, and heavy stock removal with the bandsaw machine. Number 80 grain (medium-fine) is used for coarse polishing operations and general surface finishing. Number 120 (or number 150) grain (fine) should be used for fine polishing operations. The bands are preformed in continuous bands in appropriate sizes to fit the bandsaw machine.
FIGURE 34. BAND POLISHING GUIDE.
(b) Selection of Polishing Bands. Polishing bands should be selected according to the particular job to be performed. For general removal of tool marks and for smoothing edges, the number 50 grain polishing band should be used. This band will remove small amounts of metal by grinding, and is not, in the true sense of the word, a polishing band. When finer-grain polishing bands are used on the bandsaw machine, soft metals like aluminum or cast iron should not be polished, or the band will quickly fill with metal particles, reducing the cutting action of the polishing band.
(3) Polishing Speeds. Polishing bands should be moved at speeds between 75 and 260 feet per minute (fpm), the faster speeds being used for softer materials and the slower speeds being used for harder materials. The band speed for polishing is determined by the application. For grinding, a 50 grain polishing band should be used at speeds between 50 and 300 fpm. For general/coarse polishing, a 80 grain polishing band should be used at speeds between 850 and 1000 fpm. For fine polishing, a 120 (or 150) grain polishing band can be used at speeds between 850 and 1500 fpm.
(4) Polishing Feeds. Feeds should be light for polishing operations. Use a slow, sideways motion so that the polishing band will leave no marks on the workpiece. If the band does not remove the tool marks quickly, a coarser polishing band should be used.
The procedures used for polishing using bandsaw machine model 2612-1M are presented here as an example of band polishing procedures. Band polishing procedures are similar for all bandsaw machine models.
(5) Setting Up for Band Polishing. Set up for band polishing with the model 2612-1M bandsaw machine using these steps:
(a) Remove the table center disk.
(b) Mount the polishing band guide backup support to the lower adapter as for filing.
(c) Lower the post to four inches from the table. Then mount the band polishing guide on the post and secure it with the two thumb screws.
(d) Occasionally, graphite powder should be rubbed into the guide fabric to lubricate and to increase the life of the polishing bands.
(e) Mount polishing band to travel in direction of arrow printed on the back side of polishing band. The correct polishing band tension is the same as that used for a 1/16 inch wide carbon saw blade.
(f) Install the special center adapter plate in the table.
(g) Do not use coolant with the polishing band.