Technology lesson 6th grade ” Sawing techniques with a hacksaw

We pay your attention that according to the Federal law N 273-FZ “About education in the Russian Federation” in the organizations which are carrying out educational activity, training and education of students with HIA both together with other students, and in separate classes or groups is organized.

Topic . Sawing techniques with a hacksaw

What is sheet and bar stock? Name the sections of long products.

What includes preparing a hacksaw for work?

How to choose a hacksaw blade according to hardness

Predictable learning outcomes:

What are the techniques of working with a locksmith’s hacksaw, about the features

cutting sheet metal and long products of various profiles with a metal cutting hacksaw.

Select the hacksaw blade depending on the material to be cut, attach it correctly, master the techniques of cutting bars and sheet metal with the hacksaw.

Equipment and teaching aids: various types of metal. hacksaw, blades, projector, computer.

Checking readiness for the lesson. Mobilizing Your Attention.

II. Stage of actualization of the students’ subjective experience

What activity did you do in the last class??

What activity will be covered in today’s lesson?

Name the main parts of a locksmith’s hacksaw.

What are the frames of a hacksaw?? Which frame do you think is the most versatile? Explain your answer.

What is the difference between a locksmith’s hacksaw and a wood hacksaw??

What parameters will you use to select your hacksaw blade??

Tell how to set the hacksaw blade correctly and how to check for proper setting.

In your opinion, why should the teeth of a hacksaw be pointed in the right direction?

Explain what can cause a hacksaw blade to break. How it can be

The teacher, together with the students, formulates the topic and learning

tasks, defines practical tasks.

III. Stage of learning new material

Remember! The place of the cut should be as close as possible to the workpiece

to the jaws of the locksmith’s vice (approx. 20 mm). This will help prevent vibration of the workpiece when cutting.

Pressure on the hacksaw blade depends on the hardness of the metal and the size of the workpiece. The softer the metal or alloy and the smaller the size of the workpiece, the less pressure should be applied; the harder the material and the larger the size of the workpiece, the stronger the pressure should be.

When selecting a hacksaw blade for your locksmith’s hacksaw, you should be guided by the material it is made of and the parameters of the teeth. Use the marks on the hacksaw blade to do this.

material of the blade: HCS. carbon steel (the least strong teeth, suitable for soft metal); HSS. high-speed steel (have more wear-resistant teeth, but are brittle); BIM (Bi-metal). bimetal blades (basis is carbon steel, over which a strip of high-speed steel is welded, which serves as a basis for the teeth), are highly wear-resistant and can be painted in different colors;

Tooth spacing: the number of teeth per inch (18, 24, or 32 teeth per inch. to be converted into centimeters, these are 7, 10, and 13 teeth per 1 cm, respectively). the bigger the number of teeth, the shallower the tooth, the better the blade will cut harder metal. Do not use blades with very fine tooth for soft material

metals, t. к. The saw blade will become clogged quickly with metal filings (making the work much slower and harder).

Cutting of rolled section: strip (left) square (center) and round (right)

Cutting rolled angle section (left) pipe (right)

Section Cutting Techniques . Do not use blades with a very fine tooth for soft material

begin cutting a square section by tilting the metalcutting saw forward

by about 10° to 15°. then the slope is gradually reduced to

Until the kerf reaches the closest rib of the workpiece. Next

Cut with hacksaw horizontally. Round Roll

Small cross-sections are cut in a vise, having previously performed not-

Make a deep cut with a three-edged file.

The tension on the hacksaw blade must not be too great. otherwise the cut will be uneven and the blade will break easily. A blade that is too taut may also break at the slightest twist. Tension of the blade is checked by light pressure on the side of the blade with a finger: if the blade doesn’t sag, it means there is enough tension.

When choosing a hacksaw blade for a locksmith’s hacksaw you can be guided by

the following tooth parameters. For cutting of small or medium sized workpieces of cast iron, brass are suitable blades with 8 teeth per 1 cm. For cutting hard metals, steel and cutting at a blunt angle. 10 teeth per 1 cm (this is the best choice for universal use of a hacksaw). Use blades with 12 teeth per 1 cm for cutting materials under 3 mm thickness, thin tubes, profiles and for cutting at sharp angles. To cut in hard-to-reach places, you can also use a locksmith’s hacksaws, the frame of which has a profile with a narrowed front part.

Remember! If the hacksaw blade “moves” away from the line of scribing, it should not be straightened out, because this can cause breakage of the hacksaw blade. к. This can cause the blade to break. You must remove the hacksaw blade from the kerf, turn the workpiece over and continue cutting from the opposite side of the workpiece.

Sheet metal cutting techniques. Cut sheet metal into strips

Along the narrow edge if its thickness enables simultaneous operation of at least three teeth. When cutting wide surfaces, the hacksaw is consistently tilted away from and toward you. Thin-sheet blanks are clamped between wooden blocks and cut along with the blocks. You can also bundle all the workpieces together, clamp them in a bench vice, and cut at the same time.

During saw blade breakage and chipping of teeth, their fragments remain in the kerf. Before you start working with a new hacksaw blade, it is necessary to remove the remains of the broken blade from the kerf. Before installing a new blade, keep in mind that the old blade made thinner during operation, so the kerf width for the new blade will be less. In this case you need to turn the workpiece over and start cutting from the other edge. Also with slow movements you can widen the kerf with a new blade, and then already continue cutting

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The general theory of sawing with a metal hacksaw looks something like this:

Sawing theory with a hacksaw. Introductory Course

Therefore, we will not study the theory, but go straight to practice:

In this video the whole story about how to saw is actually presented, but now there will be a postscript, a number of additions and corrections (plus a brief retelling of the video content).

So, let’s start with the fact that it is necessary to saw horizontally with a metal saw grasping the tool with both hands. For which it would be good to use a hacksaw with a well-defined handle for gripping with the second hand.

Sawing horizontally is uncomfortable because it requires the workpiece to be secured at chest level, and sawing while standing up. However, workbenches are usually tables at which one must sit, or if one is sawing, standing and from top to bottom. That’s why hacksaws are more often made one-handed and cut with them at a 45° angle.

To regulate the pressure on the saw (the harder the metal, the harder you have to load the blade, to press it so that the teeth dig into the flesh; and vice versa. if the teeth dig too deep into, for example, aluminum, you need to reduce the pressure) you can: a) change the angle of the saw, b) put the hand on top for more weight, c) turn the blade with the teeth backwards.

The saw often gets stuck in the kerf when it reaches the end of the blade. This is because the blade has a wavy pattern of teeth (so that the kerf is wider than the blade and it does not get stuck in the kerf), but over time, the amplitude of this wave decreases in the center of the blade, and at the ends. almost none.

The teeth are ground more in the center of the blade

This misalignment is the result of not sawing with the full length of the blade before. It is no longer possible to correct (increase the separation in the center or decrease it at the ends) because the teeth are hardened. So the moral: since the beginning of a new band saw you must always cut all the length of the band saw.

Next problem: If you saw a thin sheet of metal that is less thick than the distance between the teeth, the saw jams:

Too thin workpiece gets stuck between the teeth

If metal is hard (iron). you can hardly move it, and if it is soft (aluminum). a huge piece of metal is torn out, ragged edges are formed, the edge is bent.

Saw a thin workpiece with a steep inclination

Saw at an angle to form a kerf of such length that at least two teeth are on the kerf at the same time (kerf length ≥ two tooth spacing).

Next topic: Sawing thin-walled aluminum pipe:

Torsion direction of the pipe

Set the blade with teeth backwards, twist the pipe in the direction of the teeth (otherwise the blade will get stuck on the near edge of the kerf, and when force is applied it will tear).

Well, and one more thing the metal hacksaw blade can be restored, sharpening the teeth, for example, in this way:

Originally this diamond disc was bigger in diameter and this drill with this disc, being pressed this way to the blade was strictly parallel to the blade’s tooth line and the disc, respectively, perpendicular. And that was right. the new hacksaw has the cutting edge-surfaces of the teeth orthogonal to the blade. Now a slight negative angle is formed. a little less better, but also ok.

Another note: this blade can be drilled with an ordinary metal drill bit (made of HSS steel). Because the whole blade is not hardened very much at production, for elasticity, but the teeth are hardened separately by induction heating with rapid cooling for hardness, so these teeth can be easily sawed backwards in the drill.

Model Classification

Today the market for hand tools offers the following types of hacksaws for working with metal and other solid compositions:

Traditional home model. Has a wooden handle like a file. Handle is flush with the cutting part.

However, this does not negate the addition of a threaded design and inserts for better blade retention and angular sawing, respectively.

Professional version. Product has a handle that runs across the plane of the frame and blade for a comfortable grip. Often the handle is rubber coated and almost always grooved.

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Miniature construction. If the area to be sawed is difficult to get to, and if the work itself is away from the tool room, craftsmen often use mini metal hacksaws.

The frame of such a tool is made of plastic, and sometimes even rubberized, and has holes for light weight. Some models allow the use of broken blades.

Unfortunately, you have to carry the latter separately from the frames, because the mini-saw cannot be folded.

Basic rules for cutting pipes with a pipe cutter

The cutting line for the trimmer should be marked all around the pipe with chalk.

Clamp the pipe firmly in a pipe clamp or vise. Clamp the pipe in a vise using a wood vise liner. The place of cutting should be not more than 80 100 mm from the clamping jaws or vice.

In the process of cutting it is necessary to comply with the following requirements:

Make sure the pipe cutter handle is perpendicular to the pipe axis;

Make sure that the blades are positioned true to line and not twisted;

Do not apply too much force when turning the screw of the pipe cutter handle to feed the cutting blades;

At the end of the cut, support the pipe cutter with both hands; make sure that the cut piece of pipe does not fall on your feet.

Execution of the lesson

Checking readiness for the lesson. Introducing the students into the workshop.

What are the main parts of a caliper??

How many measuring scales does a caliper have??

What measurements can be made with a caliper??

How many times the accuracy of a caliper is greater than that of a ruler??

List the rules for using a caliper.

How do you read off whole and tenths of a millimeter on a caliper??

Which feature of the nonius allows measurements to be made to an accuracy of 0.1 mm?

Giving a new program material.

When machining rolled metal products, it is often necessary to cut the material by hand. Thin sheet metal is cut with scissors, strip metal, thick sheet metal as well as bars, angles, etc. д.- With a locksmith’s hacksaw.

A hacksaw consists of two main parts: the hacksaw (frame) and the hacksaw blade. Figure 1, а A locksmith’s hacksaw with a one-piece hacksaw is shown. It can hold a hacksaw blade of a certain length. To mount hacksaw blades of different lengths into the hacksaw, the hacksaw frame is designed as a sliding frame (fig. 1, б).

The sliding angle machine consists of a front angle and a back angle connected to each other by a cage. the distance between the shank and the tensioning screw can be altered by the position of the back angle that is inserted into the cage. The deeper the angle piece is inserted into the frame, the shorter the distance. Shank with handle is inserted into the back bracket of the hacksaw. The shank has a slot and a hole for a pin. Front angle piece contains clamping screw with wing nut. The tension screw has the same slot and the same hole as the shank. The ends of the hacksaw blade are installed in the slots of the shank and the tensioning screw, which are secured by pins inserted in the holes. The hacksaw blade is tensioned by turning the wing nut.

Hacksaw blades are thin, narrow steel plates with teeth on one edge (see Pic. Fig. 1, а).

Fig.1. Hand Hacksaw: а. with a one-piece machine tool; б. main parts of the sliding machine.

The ends of the hacksaw blade have holes for attaching it to the hacksaw. Most common hacksaw blades are 250 mm long. 300 mm. Each tooth is shaped like a wedge and works like a chisel when cutting. When notching, the size of the teeth is selected so that the cuttings formed will fit between the teeth before they emerge from the kerf. So that the width of the kerf, made with a hacksaw, was slightly larger than the thickness of the blade, the teeth are bent. every 2-3 adjacent teeth are slightly bent in different directions. This setting is called corrugated.

Note that the teeth must point in the opposite direction from the hand, and the tension of the blade must be such as not to cause breakage of the blade.

The workpiece is firmly clamped in a vice and a file is notched at the place of the cut.

The place of the cut is at a distance of 10° from the blade. 15 mm from the edge of the jaws.

Fig. 2. Work with a hacksaw: a. housing position; b. hand position.

During the operating stroke of the hacksaw (forward) the hacksaw is moved with a light pressure, during the idle stroke (backward) the hacksaw is moved with a light pressure. without pushing.

If the thickness of the workpiece is 3 toes of the blade the workpiece is clamped between two wooden blocks.

If the workpiece is long and the frame rests against it, then the blade is clamped as shown in the sketch below. 3.

а. without turning the blade; b. with turning the blade.

Preparing the hacksaw for work involves installing the hacksaw blade in the machine and tensioning it.

First, extend the front and rear corners of the machine by the length of the hacksaw blade and in this position secure the machine with a rim. Then insert the ends of the hacksaw blade into the slots of the tensioning screw and the shank and align their holes with the holes in the hacksaw blade. Take care that the teeth of the blade point in the opposite direction to the handle. Then insert the pins into the holes and turn the wing nut to tension the blade. The tension of the blade must not be too great, but just enough so it doesn’t bend while working. A high tension on the blade can cause it to break at the slightest misalignment during operation. If the tension on the blade is too weak, it will bend during cutting, which can cause the blade to break as well.

Cutting technique. To cut the workpiece clamp it firmly in the vice so that the place of the cut is near the edge of the vice jaws. In this position the workpiece will not vibrate while cutting. At the place of the cut, a risk is marked with a file. Then take the necessary working posture: stand half-turned to the vice the handle of the hacksaw embrace the fingers of the right hand: the end of the handle must rest in the middle of the palm

Fig. 4. Body and leg position at Fig. 5. Hands position when

Safety Precautions for Handling with a Hacksaw.

Work only with a properly adjusted and tensioned blade and a hacksaw in good condition. A blade that is not properly secured or loosely tensioned can jump or break during cutting, creating the risk of injury.

Hacksaw handle must be firmly seated and not cracked.

Do not fasten the hacksaw blade with nails or screws instead of pins.

Do not work with a hacksaw with broken teeth in the blade.

Sweep sawdust off the workbench using a brush. Do not blow off or remove with bare hands.

Support the part of the workpiece to be cut so it doesn’t fall off and cause damage to the legs.

Use the full length of the blade when working. This ensures even cutting edge wear and a longer blade life.

Cutting with a hacksaw. Area of application

Metal cutting is cutting (cutting up) metal into pieces. Cutting can be done manually and mechanically with a hacksaw, as well as with scissors. manual and mechanical, lever, parallel, circular ( circular ). For cutting heavy sections of metal (round bars, angles, I-beams, box sections, etc.) and flame cuts. п. ) drive hacksaws and circular saws are used, as well as fire cutting electric and gas.

Sheet metal is cut with hacksaw blades, both hand-operated and motor-driven. Manual cutting of pipes is performed with a hacksaw and pipe cutter; mechanical cutting of pipes is performed on special machines. Design and use of a hand hacksaw. Manual hacksaw. This tool consists of two main parts. a hacksaw blade and a special frame (holder). in which a hacksaw blade is placed; this frame is called a frame or machine. On one end of the frame has a shank with a manual and fixed head, and on the other end. a movable head and a tension screw with a wing nut for tensioning the hacksaw blade. There are slots and holes in the heads for securing the blade with a hacksaw. Hand-operated hacksaw (left. with sliding frame, right. with one-piece frame) 1. machine, 2. ratchet for tensioning screw, 3. hacksaw blade, 4. handle.

Blade for hand hacksaw blades are made of length from 150 to 400 mm, width from 10 to 25 mm and thickness from 0.6 to 1.25 mm. Hacksaw blades are made in lengths of 150 to 400 mm, widths of 10 to 25 mm and thicknesses of 0.6 to 1.25 mm thick. Work with a hacksaw. Before starting to cut with the hacksaw stand in front of the vice half-turn (in relation to the jaws of the vice or the axis of the workpiece). The left leg is slightly forward, approximately in line with the object to be cut, and the body is resting on it.

The hacksaw is taken in the right hand so that the handle rests in the palm of the hand, and the thumb is on top of the handle; the remaining four fingers support the handle from below, the left hand grasps the front end of the hacksaw frame. Work with the hacksaw at a speed of 30 to 60 strokes per minute (double strokes. forward and backward are meant). Hard metals are cut with a slower speed, soft metals are cut with a faster speed. Cutting round material with a hacksaw Cutting round material. Round material with a diameter of up to 100-115 mm can be cut with a hand hacksaw. In metalworkers’ practice it is allowed to cut metal manually only up to 60-70 mm; metal of larger diameters is transferred for cutting to cutting machines, and only in exceptional cases round material with a diameter of 70 mm can be cut with a hand saw.

If you do not want to get clean ends when cutting billets, it is allowed for the sake of saving time to cut the metal from several sides, not reaching the middle, and then break off the billet. Cutting pipe. First select a hacksaw blade with fine teeth, then make a template from a thin plate in the form of a rectangular plate curved along the tube. After that, from the end of the pipe measure off the required length of the workpiece and make a mark, then bring the template to the mark and on the edge of the template with a scribe draw a risk on the circumference of the pipe. Even more pipe cutters are used for cutting pipes, where the cutting tool is a steel disc.

Medium-diameter pipes are cut with pipe cutters with one and three cutting wheels. Large diameter pipes are cut with a chain or clamp-type pipe cutter. These pipe cutters are multi-disc cutters and are operated by rocking the handle with a small swing. When cutting pipes with the pipe cutter a special pipe clamp is used. a device consisting of a frame with a hinged upper part, in which a bump is placed with ledges allowing to clamp pipes of different diameters.

Sawing and application

Sawing off metal is the simplest metal working operation.

Sawing is a metalworking operation. which involves removing material from the surface of the workpiece with a file. A file is a tool that is used for metalwork. consists of multi-blade cutting elements, it provides high accuracy of work done, as well as not considerable roughness of the processed surface of the part. Metal cutting itself. is performed qualitatively and with a small tolerance.

Using filing, the parts are given the required size and shape, the parts are adjusted to each other and many other operations are carried out. Files are used to work on different shaped metals: curved surfaces, planes, grooves, holes of different shapes, grooves, various types of surfaces, etc.д. the allowance during filing is left small, from 0.55 to 0.015 mm. And the error after the work carried out can be from 0.1 to 0.05, and in some cases even less, down to 0.005 mm., which ensures quality metalwork.

The tool file is a bar made of steel of a certain length and profile, which has a notch on its surface. The cutting (notch) forms small and sharp teeth, which determine the wedge shape in the cross-section. The sectional angle of a file with a sectional tooth is usually 65-70 degrees, the posterior angle is 35 to 50 degrees, and the anterior angle is 16 degrees. Single-cut tools remove wide chips from the metal, all over the notch. They are used for metalworking of soft metals. Double-cut files are used when filing cast iron, steel, and other hard metals because the cross-cutting cuts crush the chips, making them easier to handle.

The notch with the rasp is made by pressing the metal through special prongs consisting of a triangle. Rasping is used for metal only on soft metals and non-metals. Another type of notch can also be obtained by milling. It has an arched shape and large notches between the teeth. this ensures good surface quality and high productivity in metalworking. The files are made from U13A and U13 steel, and also from chrome steel ShKh 15. When the notching of the teeth is finished, the files are heat-treated. Handles of files are made of wood (maple, birch and others).

Files are divided into the following groups according to their metal cutting purpose:

Cutting round, square and sheet metal with a hacksaw

Hacksaws are commonly used for cutting thick sheets, strips, round and shaped metal, cutting grooves, slots in screw heads, contour trimming, etc. п. It consists of a hacksaw / (fig. 59, a), tensioning screw with wing nut 2, handle 6 and hacksaw blade 4, which is inserted into the head slots 3 and secured with pins 5.

Hacksaw machines are of two types. one-piece

(figs. 59, (a) and sliding, which allow hacksaw blades of different lengths.

The size (length) of the handheld hacksaw blade is determined by the distance between the centers of the holes for the pins. Most commonly used hacksaw blades with a length of 250. 300 mm,

13 and 16 mm high, 0.65 and 0.8 mm thick.

The tension of the hacksaw blade in the machine should be adjusted. A blade that is too taut tends to twist during cutting, which can cause the teeth to break and then the blade to break. A blade that is too taut can also break during cutting if it tilts slightly when the saw is in motion.

Hacksaw blades are divided into manual and machine-made blades, depending on their purpose. Hand saw blades are made of steel grades U10, U10A, U12, U12A, and machine tools are made of steel grades R9 and ShKh15. There are teeth cut on the lower edge of the blade along the whole length. Each tooth of the hacksaw blade has the shape of a cutting wedge. The following angles are distinguished on the tooth of a hacksaw blade, just like on the tooth of a chisel (Fig. 59, b): back angle a, sharpening angle p, front angle y and cutting angle 5.

The working conditions of a hacksaw differ from those of a chisel and cutter, so different angle values must be taken here.

when cutting materials of large width, you get a significant length of cuts, in which each individual tooth of the blade removes chips, which have the form of a comma. These chips should be placed between two adjacent teeth in the chip space until the tooth tip leaves the slot.

The size of the chip space depends on the value of the posterior angle a, the anterior angle u and the tooth pitch £.

The sharpening angle P must be large enough to overcome the cutting resistance of the material without fracturing. The normal value of this angle is 60°; in harder materials the angle is slightly larger. The rake angle y has a decisive influence on chip formation. For knife teeth-

The blade angle of the saw blade is usually from 0 (for hard metals) to 12° (for ductile metals). Tooth pitch for soft and ductile metals (copper, brass) 1 mm, for materials (steel, cast iron) 1.3 mm; for mild steel 1.6 mm. In practice, handheld metal cutting is mainly used with a hacksaw blade with a pitch of 1.3-1.6 mm, which on a length of 25 mm has 17-20 teeth. The thicker the workpiece to be cut, the coarser the teeth must be, and vice versa, the thinner the workpiece, the finer the teeth of the hacksaw blade must be.

When cutting with a hand hacksaw, at least 2-3 teeth must be involved in the operation (simultaneously cutting the metal).

To reduce friction of the hacksaw blade on the walls of the cut metal, its teeth are bred in different directions. Depending on the pitch size £ (fig. 59, a) the teeth are made in different ways. Teeth with a large pitch bend one by one to the right and left (Fig. 59, c); the medium pitch teeth are bent one at a time to the right and one to the left, and the third one is not bent. Tines with small pitch bend two by two. three to the left and two or three to the right, thus forming a wavy trimmer line, or the so-called corrugated branching (Fig. 59, г).

Hacksaw blade bending should end at the distance of not more than 30 mm from the end face.

Hacksaw blades with corrugated lines are less productive and wear out faster. The degree of separation per side should exceed the thickness of the blade by 0,2-0,5 mm.

Blades for handheld hacksaws are manufactured in different lengths 1, width 12-15 mm and thickness from 0,6 to 0,8 mm. The most popular should be considered blades with a length of 250-300 mm.

Metal cutting techniques with a hand hacksaw

Before you start cutting metal, you need to choose a hacksaw blade, taking into account the hardness, shape and size of the material to be cut.

it is necessary to clamp the blade in the hacksaw so that the edge of teeth faces forward in the course of the hacksaw; tensioning of the blade in the hacksaw must be adjusted. Getting down to work with the hacksaw, the material to be cut should be firmly secured in a vise. Metal clamping level in the vice should correspond to the height of the user. Then stand half-turned in front of the vice, i.e. е. at an angle of 45° to the axis line of the vice (the distance between the vice and the working body must be 150-200 mm). leaning on the left leg slightly forward, the right leg should be 60-70° to the left. The hacksaw should be held with the right hand as shown in fig.1 and fig.2, and the hacksaw should be held with the right hand as shown in fig.3. 60, and with the left hand by the front end of the hacksaw in order to balance it and obtain a steady movement while cutting (Fig. 60, б). Hold the hacksaw horizontally while cutting. Move the hacksaw smoothly, without jerking, slightly pressing it down with both hands when moving forward. It is considered, that the pressure force should correspond to about 1 kg per 0,1 mm of the blade thickness. At the end of the cut the tension must be released.

The normal stroke of the hacksaw should be such that about 2/z of its length works, not just the middle section of the blade.

Hacksaw speed depends on the hardness of the material to be cut and averages between 30 and 60 double strokes per minute. To reduce friction on the walls of the workpiece to be cut, periodically lubricate the blade with thick lard or mineral oil.

In the process of work the hacksaw blade sometimes “moves” away from the marking; do not straighten it out as breakage or chipping of blade teeth is possible. In this case it is best to start cutting from the opposite side of the workpiece.

Cutting with a hand hacksaw

Cutting rules.Securely clamp the workpiece to be cut in a vise, because if it slips when cutting, the blade could break.

The hacksaw blade is clamped in the frame so that the tooth cuts when it moves forward and is well tensioned. If the tension is too low, the hacksaw will deflect to the sides and may cause the blade to break. If there is a lot of tension the slightest misalignment of the hacksaw can cause a breakage.

Fig. 2. Hacksaw grip and worker’s stand when cutting

Holding the hacksaw with the right and left hand and the worker’s handstand when cutting is shown in Fig. 2. During forward travel. stroke. both hands press the hacksaw, with the left hand concentrating most of the force on pressing, and the right hand on the forward motion of the hacksaw. Reverse motion of the hacksaw is idle, without pressure.

The hacksaw can be tilted toward the back edge of the workpiece to facilitate plunge cuts. When the blade has plunged in, the hacksaw is moved horizontally and along the full length of the blade. This gives it a longer service life. Work with the hacksaw smoothly and evenly at a rate of 40 double strokes per minute on hard materials, and 60 strokes per minute on soft materials.

Pressing force depends on the material to be cut: more for hard materials and less for soft materials and when cutting thin metals such as strips, pipes. If great force is applied when cutting soft materials the blade will cut deep into the material and the teeth will shatter. When cutting thin metals, very few teeth are involved. Great pressure is applied to each tooth. Too much pressure will cause the teeth to break. Before finishing cutting in all cases the pressure on the hacksaw must be reduced and the material to be cut must be supported with the left hand.

With a new hacksaw blade it is recommended to first cut soft materials, and after some blunting to hard materials.

Handheld metal cutting is usually done without cooling. Hacksaw blades can be lubricated with mineral oil to reduce friction.

If the blade should drift sideways and not cut along the mark, do not try to straighten it by twisting the hacksaw. it could break the blade. Rotate the workpiece and start cutting in a new location. If the blade has chipped teeth, it must be replaced. Since a worn blade produces a narrower kerf, start cutting with a new blade in a new location.

Very thin material is clamped between two 15″ thick wooden blocks. 30mm and cut along with them with a fine-pitch blade, pressing lightly, using the full width of the blade in slow strokes.

Slots in screws are cut with hand hacksaws (Fig. 55, в) with narrow blade. Wide cuts are made with two blades stacked on top of each other.

Material cutting.Strip material is cut on a narrow plane if its thickness ensures simultaneous work of at least three teeth. If this condition is not maintained, when plunge cutting, the pressure on the teeth will be unequal and they may break. That is why thin strip material is cut on the broad side.

Round, square, hexagonal bars are cut with the hacksaw horizontally, but so that the blade does not meet during the movement of the sharp corners. If the ends of the workpiece to be cut are machined, it is permissible to notch on two or four sides and break.

Items with wide surfaces are cut by tilting the hacksaw towards the back and front edge in sequence. This does not cut across the entire width at once and makes the job easier.

To cut a strip from a sheet of metal the hacksaw blade is turned through 90° and cut with the hacksaw in a horizontal position (Pic. 3, а).

Fig. 3. Methods of cutting with a hand hacksaw

To process shaped holes in sheet metal, first a small hole is drilled, the blade is inserted into the hole, the hacksaw is assembled and the metal is cut out. Slots and shaped pieces are cut with a blade rebated to width of 8 mm using a hand saw. 10 mm thick (fig. 3, б).

Slots in screws are cut with hand hacksaws (fig. 3, c) with a narrow blade. Wide slits are made with two blades folded in thickness.

The main type of scrap cutting with the hacksaw is an oblique cut caused by blade retraction. Incorrect marking, cutting not according to the drawings do not maintain the size of the part. Damage can also occur to the outside of the workpiece if clamped in a vice without jaws.

Metal cutting with scissors is very productive, allows to cut parts of any shape without removing chips, but requires considerable effort for cutting. That is why sheet metal is usually cut with scissors. Mechanical shears for cutting bar and profile material are also available.

Hand scissors are used to cut thin sheet material: steel with thickness of 0.5. 0,7 mm, roofing iron, non-ferrous metals up to 1,5 mm thick. They have short blades and long handles and are produced in lengths of 200, 250, 320, 360 and 400 mm from steel grades 65, 70. The cutting part of the scissors is hardened up to HRC 52. 58.

Fig. 4. Hand scissors

A distinction is made between scissors right (Fig. 4, a) and left-handed scissors (Fig. 4, б). Mainly right scissors are used with the bevel of the lower blade on the right side during cutting. Curved details are cut with left-handed scissors. Shears with curved blades (fig. 4, c) are used for making shaped holes in sheet metal and pipes.

Cutting part of the scissors has a wedge shape with sharpening angle (β= 70°). A relatively large angle of sharpening is taken so that the blades do not chip out when cutting. To reduce friction, a back angle of α = 1. 2° (see “2°”). Fig. 4). The scissor blades should be straight, sharpened and fit together over the entire length with a small gap (no more than 0.2 mm). If there is no gap, the blades blunt quickly, with large gaps they do not cut, but crumple the metal.

Fig. 5. Types of scissors: a. straight: 1. left lever; 2. right lever; 3. joint axis assembly; b. curves; c. finger
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