Machine Shop Tools and operations - Power Hacksaws, Power Band Saws, and Circular Saws

 

 

Power hacksaws, power band saws, and circular saws are very important to machine shop operations. A large number of power hacksaws and power band saws are in use in the metalworking industry.

 

Power Hacksaws

A power hacksaw is an essential machine in most machine shop operations. For many years a hand-operated hacksaw was the only means for sawing off metal. Power-driven machines for driving metal-cutting saw blades have been developed to make the task easier. The power hacksaw can do the work much more rapidly and accurately. The machinist should be familiar with these machines, the blades used on the machines, and the operations performed on them. One type of power hacksaw commonly found in machine shops is shown in Figure – 1.

 

Fig -1 Power Hacksaws

 

Basic Construction

Power hacksaws are designed to make the sawing of metal a mechanical operation. The stock is usually held in a vise mounted on the base of the machine. An electric motor is used to supply power for the machine.

 

 

Drive Mechanism

The drive shaft is connected by a V-belt and gears to the electric motor mounted on the machine. The drive mechanism is shielded by guards for safety in operation.

 

Frame

A U-shaped frame is used on the smaller power hacksaws to support the two ends of the saw blade, which is under tension. The heavier machines use a four-sided frame and a thin backing plate for the blade of the saw.

 

Worktable and Vise

Most worktables are equipped with a vise that can be mounted either straight or angular to the blade. The worktable is usually mounted on a ruggedly constructed base. Many worktables are provided with T-slots for the purpose of supporting special clamping devices.

 

Special Features

Nearly all power hacksaws raise the blade on the return stroke. This feature prevents dulling of the blade by dragging it over the work as the blade is returned to the starting position. Another important feature is a blade safety switch that automatically stops the machine if the blade should break during operation of the saw. The safety switch prevents any damage that could result if the machine continued operation with a broken blade.

 

Coolant System

Some power hacksaws are equipped with a coolant system that delivers a coolant to the hacksaw blade. The coolant passes from a receiving tank to a pump and then to the work. The machine is equipped with a trough to catch the coolant, which may be screened to remove any chips of metal.

 

Saw Capacity

Small power hacksaws can be used on square or round stock ranging from % inch to 3 inches. The larger machines have a capacity ranging to 12 inches (square or round), or even larger. The capacity of a machine for angular cuts is different from its capacity for straight cuts. The cutting surface is longer for angular cutting. Thus, the saw must be equipped not only with a swivel vise but also with a long enough stroke to make the angular cut. Blades High-speed tungsten steel and high-speed molybdenum steel are the most commonly used materials in power saw blades. If only the teeth are hardened, the blades are called flexible blades.

 

Power hacksaw blades are ordered by specifying length and width, thickness, and teeth per inch. For example, they are available in 12" x 1" length and width at 0.050-inch thickness. The teeth per inch (TPI) would be either 10 or 14. The 14 x 1" x 0.050" blade is available in only 14 TPI. Blades also come in 17" X 1" with a thickness of 0.050 inch and either 10 or 14 TPI. Blades with a thickness of 62 thousandths of an inch (0.062 inch) are usually 1% inches wide. High-speed, shatterproof blades are designed to meet safety and performance requirements. The high-speed molybdenum blades are longer wearing and give the best results for general use. They, too, come in 12-inch, 14-inch, and 17-inch lengths with a 1-inch or 11/4- inch width. These blades are made in both 10 and 14 TPI sizes. Thickness of the metal being cut determines the number of teeth per inch chosen to do the job. There should be no fewer than two or three teeth touching the metal being cut. Figure - 2 shows the power hacksaw blade end with a hole for mounting in the machine and the pointed nature of the teeth.

 

Fig – 2 hacksaw blade

 

 

Hacksaw Operation

Straight cuts are made easily on power hacksaws. The vise is stationary, and the cut is made at a right angle to the sides of the stock. Most machines are equipped with an adjustable vise. Angular cuts at any desired angle up to 45 degrees can be made by swiveling the vise. To operate the power saw properly, the work should be fastened securely in the vise so that the blade will saw in the proper place. The blade will break if the work loosens in the vise. The saw blade should be lowered onto the work carefully to start the cut. On some machines this is done by hand, but it can be done automatically on some saws. In either method, the points of the teeth will be broken or damaged if the blade is permitted to strike the work suddenly. The machine should be watched carefully to make certain that the saw blade lifts about '/s inch on the return stroke.

 

Fig – 3 Hacksaw Operation

 

If the blade fails to lift, adjustments should be made immediately, as the blade will be damaged if operation is continued. When making angular cuts with the work turned at an angle in the vise, another precaution is to be certain that the saw blade can make both the backward and the forward strokes without the saw frame making contact with either the work or the vise. Serious damage to the machine can result from failure to observe this precaution. When a saw blade is replaced, or a new blade is started in an old cut, it should be remembered that the set of the new blade is wider. The new blade will stick in the old cut unless the work is rotated in the vise a quarter turn. If the work cannot be rotated, the new blade should be guided into the old cut. The cutting speed of a power hacksaw, of course, varies with the material being cut. Suggested cutting speeds are as follows: for mild steel, 130; for tool steel (annealed), 90; and for tool steel (unannealed), 60. For example, on a machine with a 6-inch stroke, the revolutions per minute of the driving crank should be 130. All steels should be cut with a cutting compound. Bronze should be cut with a suitable compound at the same speed as mild steel. The saw blade will heat rapidly if an attempt is made to cut brass without a cutting compound adapted to brass. Brass may be cut at the same speed as steel if a suitable compound is used.

 

 

Power Band Saws

In the past few years the power band saw has become very important in machine shop operations. In some instances it is used in production operations prior to final machining operations.

 

Basic Construction

Power band saws are also designed to make the sawing of metal a mechanical operation (Figure - 3). The stock can be held in a vise mounted on the machine or it can be supported by the operator's hand. Electric motors are used to supply the power for the band saws.

 

Drive Mechanism

Wheels on the power band saw can be adjusted to apply tension to the band saw blade, which is a flexible, thin, narrow ribbon of steel. One of these wheels is powered by the electric motor mounted on the machine. These wheels are enclosed by guards for safety in operation. Frame Many variations of power band saws are available. However, band saws can be grouped into three classifications: horizontal machines for cut-off sawing, vertical machines for straight and profile sawing. at conventional speeds, and vertical machines for nonferrous cutting and friction cutting.

 

Worktable and Vise

Power band saws have either a worktable or vise to hold the metal that is to be cut. The worktable is usually part of the band saw. The vise, if there is one, is usually designed to fit the worktable. Many worktables also have T-slots for the purpose of supporting special clamping devices to hold the work to be cut.

 

Special Features

Some power band saws have automatic tensioning devices so that the proper amount of tension is applied to the band saw at all times. This type of device reduces excessive wear and damage to the blade.

 

Coolant System

Coolant systems are common on power band saws designed for high-speed production work. These systems deliver coolant to the band saw blade and the work. After the coolant has been used, it is recycled through a screen and filter to remove any chips.

 

Capacity of Power Band Saws

The maximum capacity of power band saws varies according to the size of the band saw. Some of the larger machines can accommodate work that is 18" x 18" and larger. Band saws also have the capacity to do a wide variety of operations that include cut-off, straight sawing, and contour, or profile, sawing. Rough shaping and semi finishing can be accomplished on almost all types of ferrous and nonferrous materials.

 
Band Saw Operation

When operating a band saw, there are some general principles that should be followed so that you will be able to select the blade with the proper pitch:

• Small and thin-wall sections of metal require fine teeth.
• Large metal sections require the use of blades with coarse teeth so that adequate chip clearance is provided.
• Two teeth should be engaged in the metal to be cut at all times.
• Soft, easily machined metals require slightly coarser teeth to provide chip clearance. Hard metals of low machinability require finer teeth so that there are more cutting edges per inch.
• Stainless steel should be sawed with a coarse (NQ) tooth saw blade for best results.

 

 

Circular Saws

 

Circular saws have some advantages. They produce a burr-free mill finish when slow-speed cold sawing is used. This eliminates secondary operations on tubing, channels, angles, and solid stock of most steels and other ferrous materials, as well as most nonferrous metals. The rigidity of the blade produces cuts of extreme accuracy and close tolerances. The cutting operation is safe, clean, and quiet because of the slower speed. Figure -4 shows a manually operated saw. Semiautomatic types with an air-operated vise are available. Special vise insets for holding thin-walled pipe or tubing to prevent distortion.

Other special shapes can be made to fit in the vises, or they can be purchased from the saw manufacturer. The semiautomatic machines have heavy-duty feed mechanisms to feed the metal to the saw. The saw can do straight cutting, miter cutting, slot (or longitudinal) cutting, or any number of other arrangements that will fit within the limits of the machine.

 

 

Summary

Power hacksaws, power band saws, and circular saws are very important to machine shop operations. A large number of power hacksaws are in use in the metalworking industry. A power hacksaw is an essential machine in most machine shop operations. It is designed to make the sawing of metal a mechanical operation. High-speed tungsten steel and high-speed molybdenum steel are the most commonly used materials in power saw blades. High-speed, shatterproof blades are designed to meet safety and performance requirements. These blades are designed with 12-inch, 14-inch, and 17-inch lengths with a 1-inch or 1%-inch width. In the past few years, the power band saw has become very important in machine shop operations. In some instances it is used in production operations prior to final machining operations. There are three types of saw blades: the regular tooth, skip tooth, and hook tooth. Small and thin-wall sections of metal require a fine[1]tooth blade. Large metal sections require the use of blades with coarse teeth so that adequate chip clearance is provided. Two teeth should be engaged in the metal to be cut at all times. Soft, easily machined materials require slightly coarser teeth to provide chip clearance. Hard metals of low machinability require finer teeth so that there are more cutting edges per inch. Stainless steel should be sawed with a coarse-tooth saw blade for best results. Cast iron is always cut dry. Almost all the commercially available soluble oils or light cutting oils will give good results when cutting ferrous metals. When aluminum is cut, paraffin and beeswax are commonly used lubricants. Cutting oil mineral base with fatty oils added is one of four types of cutting fluids. Cutting oil with light viscosity fatty oils is another, as well as synthetic water-soluble cutting agent and soluble oil cutting agent with fatty oils and sulfu- rized for extreme pressure with ant weldment properties.