PowerPoint Slideshow about ' Sawing – An Introduction' - beck-russell
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Sawing is a way of separating the material that is not needed from the material that is. The cut or gap that is produced by the saw is called the kerf. The kerf is usually wider than the saw blade so that the blade does not get stuck when it is cutting through the material. Bending alternative teeth from left to right produces this gap. This bending of the teeth is called the set.
Hacksaw blades are normally in the shape of a wavy cutting edge. It is important when cutting to always cut to the outside of the marked line. This side of the line is called the waste side. You must also leave enough room for filing and sanding.
The choice of saw depends upon the type of material to be cut. Always use the correct saw. Wood saws like tenon and panel saws are not hard enough to cut through metal. Metal-working saws like hacksaws will cut through wood, but not very effectively. Plastics like acrylic and polystyrene may be cut with coping saws, but it is best to use a craft knife to slice the plastic along a straight line and snap it over a hard edge.
Large panels or sheets of materials, for example plywood or MDF, require larger ripsaws in order to cut them by hand. Sheets that are small enough may be held in the vice, but larger sheets may need to be supported on special types of portable carpenter's supports called trestles.
Ripsaws are used to cut along the grain of large panels of real timber. Panel saws are shorter in length to ripsaws and have finer teeth, 10 teeth every 25mm. Ripsaws have 4-5 teeth every 25mm. Because of its finer teeth and shorter length, the panel saw is suited to thinner wood and sheets of manufactured boards.
Hacksaws and junior hacksaws produce straight cuts in metal. Both have replaceable blades held in tension in the saw frame. The teeth face away from the handle and cut on the forward stroke. This is the opposite effect to the coping saw, which cuts on the pull stroke.
The lengths of hacksaw blades are between 250mm and 300mm. The saw frames can be adjusted to cater for both sizes. Like the coping saw, the blades can be turned through 90 in the frame. This allows the hacksaw to cut larger sheets of metal.
Blades normally have 14, 18, 24 or 32 teeth every 25mm. This is called the pitch of the blade.This is more teeth per blade than the coping saw, tenon saw, panel saw and rip saw. Soft materials require a coarse pitch, less teeth, hard materials, a fine pitch, more teeth. Three teeth should be in contact with the materials at all times. A fine-pitched blade needs to be used for tubes and thin gauge materials.
Sheet saws are like panel saws but with a hacksaw blade attached. These types of saws are used to cut sheet metals and plastics. They also cut corrugated sheet.
The abrafile has a toothed, circular blade that fits into a frame. Abrafile blades can fit into a hacksaw frame using a pair of adaptors. Coarse, medium and fine grades are available. Abrafiles are used to cut out curves and rounded shapes from sheet metal. Abrafiles are very good at cutting wall tiles.
This image shows an abrafile blade in a junior hacksaw frame.
An electric fret saw has a reciprocating blade built into a frame. This means that the blade moves up and down and is pushed against the material. This type of machine is ideal for fine, detailed shapes and cuts small pieces of flat, sheet materials. It is very good for making jigsaw puzzles.
It does not cut thicker materials very well. It can be used to cut plastic; a useful tip is to cover the part to be cut with masking tape to stop the plastic's waste sticking in the cut behind the blade.
Mitre saws have a blade that can be adjusted to any angle. The saw has cramps that allow the material to be fixed to the frame while cutting. The mitre saw may be used to cut 45° corners for picture frames and mitre joints.
The blade cuts on the backward stroke. It is possible to buy electrical mitre saws. These are called chopsaws.