How to Buy Saws

Saws and filing machines execute the most basic of all metalworking procedures, the cutting of bar stock to proper lengths for machining. It is done in the simplest of ways, substituting mechanically or hydraulically powered motion for hand or arm motion. Saws used on powered sawing machines are made as thin as possible in order to be consistent with tool strength and rigidness. The width of a cut will be close to the width of the saw, this allows the individual teeth of the saw to deepen the cut made by each preceding tooth as it moves through what’s being cut. Straight or curved cuts can be achieved by controlling the direction of feed.

The principal parts on a circular saw machine are:

• Bed - The foundation of the machine, provides strength.
• Speed change hand wheel - Performs speed changes through selective gearing, pickoff gears or sheave changes.
• Power vertical & Power horizontal clamp - Saw blade to be fed into the work.
• Automatic bar feed - Feeds work in and out of the machine, smaller-sized machines furnished with auto bar feeds.
• Feed control - May be mechanical or hydraulic or a combination of both.
• Stock stop - Provides for positive positioning of the work.
• Saw head unit - The main drive mechanism. Wideface, closely fitted, ruggedly supported spiral or herringbone gearing is generally used for the final drive to worms and wormgears may also be used for the input drive to eliminate chatter.

The principal parts on a vertical band saw are:

• Base - A box-like casting housing the main drive unit, speed control mechanism and gear shift.
• Head Assembly - Accommodates the upper band wheel assembly, job selector mechanism, speed indicator gauge and the band tension indicator.
• Tension adjustment - Changes the distance between the two wheels carrying the band. Tension on the band makes it more rigid comparable to the more heavier tools.
• Table - Supports the work as it’s fed into the blade.
• Chip blower - An air system that removes chips from the cutting areas.
• Blade shear, welder & grinder - These are provided so the machine can perform internal cutting of shapes.

There are 3 basic types of sawing machines: the power hack saw, the circular saw & the continuous blade band saw.

The power hack saws are depicted by the reciprocating motion of the blade as it cuts. The cutting takes place in only one direction and the saw becomes idle on the return stroke. Hack saws basically follow the same setup: a base and table support the work which is held stationary while sawing, and a C-frame that runs the saw blade. Hydraulic or mechanical drives with speed selection are employed, and three different types of feeds are used.The weight of the C-frame itself maintains pressure that feeds the saw into the cut in gravity feeding. In mechanical friction or hydraulic pressure feeding, the saw is forced into the cut for faster cutting. In a ratchet mechanism, feed may be executed by means of a screw or pawl. Since the stroke is intermittent, hack saws do not have a very fast method of cutting off stock. Their advantage, though, is they are simple in design, easily interchangeable from job to job, and relatively inexpensive to operate and maintain. Hack saws are also available in a wide range of models and sizes, ranging anywhere from manual clamping of a single cut to the more complex automated machines.

The circular sawing machine functions on a milling principle, however unlike conventional milling machines, the diameter of the spindle gear will be smaller than that of the saw blade. This requires careful design characteristics implemented into the machine to guarantee a smooth, powerful drive to the blade without hardly any backlash. That is why wide-face, closely fitted spiral or herringbone gears are used for the final drive, and hourglass worms and wormgears are often used for the input drive to eliminate chatter. Circular sawing machines are distinguished by a round or circular saw blade that is mounted on a power-driven arbor and rotated through the cut. These machines are divided into 3 types: the cold saw, abrasive cutoff machine and the friction saw. Cold saws are the most sturdy and powerful of the saws. Their direct geared drive allows the application of increased cutting speeds, lending itself well to automation and to combine with other machining units. Friction saws operate at high speeds and develop intense frictional heat when coupled with heavy feed pressures and actually melt or burn the metal away as it touches the blade. Teeth, if supplied, serve mainly to carry oxygen into the cut.

Band saws apply a very thin continuous steel loop with hundreds of cutting teeth on one edge. The band is carried on the rims of two or three wheels, one of which is powered by the drive. Friction is created between the band and the wheel prevents slippage. Adjusting of the tension on the band is possible, it gives the band saw a rigidness comparable to that of much heavier tools. There are two basic types of band saw: vertical and horizontal. The vertical saw has one wheel located above the other and a horizontal work table where the band passes. It is commonly recommended for contour sawing, notching, slotting, splitting, serrating and other cutoff operations. The horizontal saw has both wheels in line, so not much additional machining, if any, is required.

While demand for standard controlled bandsaws holds steady, demand for CNC production bandsaws are on the rise. For CNC bandsaws, operators are able to enter the number and length of parts into the CNC and go to other work as the saw cuts the material unattended. This increase in sawing time is also causing a shift in blade requirements. Operators now need blades that last longer to make unattended sawing more productive. Although a blade on modern saws only require two or three minutes to change, the cost of the blade and time to change it add up. Any prolonging of the chipmaking time in between blade changing lowers the cost per cut.

When selecting a saw it is important to consider the proper size and capacity for efficient production. For example, selecting the right cutoff machine can result in significant cost reductions by eliminating waste, and reducing machining time and labor costs. The capacity of hack or band saws is designated by the maximum square section that can be accommodated by the machine. Standard cutoff saw capacities range from anywhere from 6”x6” up until 24”x24”. Band saw size is designated by throat clearance, the distance between the cutting blade and the rear column which supports the upper band wheel. Standard sizes range from 16” to 60”. The size of a circular saw machine is made by the diameter of the circular blade for which the machine is designed. Sizes range from 10” to 120”.

When selecting a vertical or horizontal band saw, you must consider the specific advantages of each machine. User production requirements will then determine which of the two machines is more suitable for your needs. The vertical band saw is recommended for shaping work, simply because it can remove unwanted material both inside and outside. Since the cutting force is uniform on the vertical band machine, clamps and other fixtures are usually not required. However, machining time is low, the downward cutting force is a slicing action, therefore is best used when soft, spongy or honeycomb materials need to be cut without distortion. Vertical band saws come in a range of sizes from small toolroom machines to large production models. Throat depths range from 16” to 60” with band speeds from 35 to 15,000 sfpm and the horsepower from 1 to 15. The horizontal band saw is recommended when speed, high accuracy, low scrap losses and versatility are special priorities in the cutoff operation.

INSPECTION

NON-POWER

1. Check machine’s bed and structure support components for cracks, breaks or welded repairs. Breaks, even if repaired, can affect the machine’s ability to turn out precision work.
2. Look in gear boxes and confirm the gears are not chipped or worn down. Worn or faulty gears can cause slippage in the drive and feed mechanisms.
3. Check all ways and slides for signs of excessive wear. Also, check the machine’s table and saw arm.

UNDER POWER

1. Listen carefully to all gear boxes while machine is running. Proper coordinating of gears is important for chatter-free work.
2. Look for backlash in the saw blade, minimum back lash is evident that the drive blade is Smooth and rigid.
3. Check the clamping mechanism, make sure it works properly for accurate cutting.
4. Make sure the stock stops operate as they should.
5. Verify the lift roller mechanism is working properly so that work may be easily moved in and out of the machine.
6. Check the automatic bar feeder.
7. Examine the chip clearance system and see that it functions properly.
8. On a power hack saw, see that the force feed and quick return mechanism are properly working.
9. For hydraulic equipment, look for leaks, noisy valves and pumps.
10. Run the machine through its complete cycle. See that all feed and speed controls and electrical controls function properly.
11. Make sure the variable speed adjustment on hydraulic machines are working and that the speeds are adjusted correctly.
12. After running some work, check the smoothness and uniformity of the finished workpiece and determine if the machine fits your needs.

This is one article in a series of    How to Buy Metalworking Equipment.   Each article showcases and explains a particular type of metalworking machine. They were originally published in the Metalworking Machinery Mailer published by the Tade Publishing Group.

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