How to use hand saws and precautions
1. Relevant process knowledge
Use a hand saw to cut the workpiece material or saw a groove on the workpiece The operation is called sawing. 1 Hand saw structure A hand saw consists of a saw bow and a saw blade. The saw bow is used to install the saw blade. It has two types: adjustable and fixed. The fixed saw bow can only install saw blades of one length, while the adjustable saw bow can be installed with saw blades of several lengths through adjustment. Moreover, the shape of the saw handle of the adjustable saw bow makes it easier to use force. So it is now widely used.
2. The correct selection of saw blades depends on the pitch of the saw teeth, including fine teeth (1.1mm), medium teeth (1.4mm), and coarse teeth (1.8mm). When using, it should be selected according to the softness, hardness and thickness of the material being sawed. When cutting soft materials (such as copper, bronze, etc.) and thick materials, coarse-tooth saw blades should be used; when cutting hard materials or thin materials (such as tool steel, alloy steel, etc.), fine-tooth saw blades should be used. Generally speaking, when cutting thin materials, there should be at least three gears on the sawing section that can participate in sawing at the same time, so as to avoid the saw teeth from being hooked and cracked.
2. Hand saw grip, sawing posture, pressure speed
(1) Grip: Hold the saw handle fully with your right hand, and lightly hold the front end of the saw bow with your left hand.
(2) Posture: The standing position and body swing posture when sawing are basically similar to those when filing, and the swing should be natural.
(3) Pressure During the sawing movement, the thrust and pressure are controlled by the right hand. The left hand mainly cooperates with the right hand to straighten the saw bow and the pressure should not be too high. When the hand saw is pushed out, it applies pressure to the cutting stroke, and when the return stroke does not cut or apply pressure, it pulls back naturally. The pressure should be small when the workpiece is about to break.
(4) Movement and speed Sawing movement generally adopts a small up and down swing movement. That is, when the hand saw is pushed forward, the body leans slightly forward, and while pressing the hands toward the hand saw, the left hand is raised and the right hand is pressed down; when returning, the right hand is raised and the left hand follows naturally. The bottom surface of the saw kerf is required to be cut straight, and linear motion must be used. The speed of sawing movement is generally about 44 times/min. Hard materials are cut slower and soft materials are faster. At the same time, the sawing stroke should be kept even and the return stroke should be relatively fast.
3. Sawing operation method
(1) Clamping of the workpiece The workpiece should generally be clamped on the left side of the Taiwan tiger lead to facilitate operation; the workpiece should not protrude too long from the jaws to allow the saw kerf to leave About 20mm from the side of the jaw floor to prevent the workpiece from vibrating during sawing; the saw seam line should be kept parallel to the side of the jaw (making the saw seam line consistent with the direction of the plumb line) so that the saw seam does not deviate from the scribed line; clamp It should be firm and at the same time avoid deforming the workpiece clamp and damaging the processed surface.
(2) Installation of the saw blade. The hand saw only has a cutting effect when pushed forward. Therefore, the saw blade should be installed with the tooth tip facing forward. If it is installed backwards, the rake angle of the saw tooth will be negative. It cannot be sawed normally. When adjusting the tightness of the saw blade, the butterfly nut should not be tightened too tightly or too loosely. If it is too tight, the force on the saw blade will be too great. If the force is slightly improper during sawing, it will break; if it is too loose, the saw blade will be easily twisted during sawing. , it is also easy to break into sections, and the saw kerf is easily skewed. The tightness can be adjusted by using a hand to move the saw blade until it feels firm. After the saw blade is installed, make sure that the plane of the saw blade is parallel to the center plane of the saw bow and must not be tilted or twisted. Otherwise, the saw kerf will easily become skewed during sawing.
(3) Sawing starting method Sawing starting is the beginning of sawing work. The quality of sawing will directly affect the quality of sawing. If the sawing is not started correctly, the saw blade will jump out of the saw gap, roughen the workpiece, or cause the saw teeth to break. There are two types of sawing: far sawing and near sawing. When starting the saw, place your left thumb against the saw blade so that the saw blade can be cut correctly at the required position. The stroke should be short, the pressure should be small, and the speed should be slow. The starting angle θ is about 15°. If the starting angle is too small, it will be difficult to start the saw smoothly. Especially when starting the saw, the saw teeth will be caught by the edge of the workpiece and cause cracking.) However, the starting angle should not be too small, otherwise, the number of teeth in contact with the workpiece at the same time will be too large. It is not suitable to cut into the material. Repeated sawing operations are often prone to deviation, causing many saw marks on the surface of the workpiece and affecting the surface quality.
(4) Under normal circumstances, long-range starting is used (the saw teeth are not easy to get stuck and it is convenient to start the saw). If you use a close-up saw but do not control it well, the saw teeth will be stuck by the edge of the workpiece. At this time, you can also use the hand saw to pull back to perform a reverse saw.
Start the saw to a depth of 2 to 3 mm. During normal sawing, all effective teeth of the saw blade should be involved in sawing during each stroke.
4. Sawing methods of various materials
(1) Sawing of bars
If the sawing section is required to be flat, it should be continuous from the beginning Saw to the end. If the requirements are not high, it can be sawed in several directions.
(2) Sawing of pipes
Before sawing the pipe, you can draw a sawing line perpendicular to the axis. Since the precision of the marking is not high during sawing, The simplest method is to use a rectangular paper strip (the scribing edge must be straight) to wrap around the outer circle of the workpiece according to the saw cutting size and then use talc to mark it out. The pipe must be clamped straight when sawing.
Thin pipes and finished pipes should be sandwiched between two wooden liners with V-row grooves. When sawing thin-walled pipes, do not continuously saw from the beginning to the end in one direction.
(3) Sawing of thin materials
When sawing, try to cut off the wide surface as much as possible. But when it can only be sawed on the narrow side of the board, it can be clamped by two wooden boards and cut together with the wood block to avoid hooking of the saw teeth. It also increases the stiffness of the board so that it will not vibrate when sawing. . You can also clamp the thin sheet directly on the vise and use a hand saw as a transverse diagonal push saw to increase the number of teeth in contact with the thin sheet and avoid saw teeth from cracking.
(4) Deep seam sawing
When the depth of the saw kerf exceeds the height of the saw bow, the saw blade should be turned 90° and reinstalled so that the saw bow is turned to the side of the workpiece. When the saw bow is lowered horizontally and the height is not enough, the saw blade can also be Installed into saw teeth for sawing inside the saw.
5. Reasons for saw blade breaking
(1) The workpiece is not clamped and the workpiece is loose during sawing.
(2) The saw blade is installed too tight or too loose.
(3) The cutting pressure is too high or the cutting force suddenly deviates from the direction of the saw kerf.
(4) After forcibly correcting the skewed saw kerf or replacing the new saw blade, the saw blade is still cut too hard in the original saw kerf (5) The saw blade is partially worn in the middle during sawing, and gets stuck when the saw is lengthened. Causes breakage. (6) When the hand saw was stopped in use, the hand saw was broken without being taken out from the workpiece.
6. Reasons for saw tooth cracking
(1) Improper selection of saw blades, such as using coarse teeth when sawing thin materials and pipes.
(2) The starting angle of the saw is too large when starting the saw.
(3) The sawing movement suddenly swings too large and the saw teeth hit too hard.
(4) When several teeth of the saw blade are partially broken, it should be trimmed on the grinder, and the adjacent 2-3 teeth should be ground into a concave arc. And polish the broken teeth. If not dealt with immediately, the teeth behind the cracked tooth will crack one after another.
7. Reasons for the skew of the saw seam
(1) When the workpiece is installed, the saw seam line fails to be in the same direction as the plumb line. (2) The saw blade is installed too loosely or is twisted with the saw bow plane.
(3) Use a saw blade with uneven wear on both sides of the saw teeth.
(4) When the saw bow is straightened or tilted with force, the back of the saw blade deviates from the center plane of the saw kerf and leans against one side of the saw section.
8. Safety knowledge
(1) The saw blade should be installed with appropriate tightness, and do not use excessive force suddenly when sawing to prevent the saw blade from breaking and the bow of the saw to collapse during work and injure people.
(2) When the workpiece is about to be sawed off, the pressure should be small to avoid excessive pressure that may cause the workpiece to break suddenly and cause an accident by rushing forward. Generally, when the workpiece is about to be sawed off, hold the workpiece with your left hand. Open the part to avoid falling and injuring your legs.