General purpose fine toothed: Used for cutting fine wood and man-made boards-such as blockboard.
General purpose medium toothed:
For plywoods and particle boards.
General purpose rough toothed:
For rough cut wood.
Tungsten carbide tipped: Specially designed for cutting chipboard.
Special purpose blades: These are designed for cutting materials other than wood, such as metal, stainless steel and plastic.
Flush blade: This sticks out from the front of the jig saw so that you can cut right up to obstructions.
Scroll blade: Used for cutting tight curves and intricate shapes.
The same straightedge can be clamped to the workpiece to cut at various angles. Once the straightedge has been secured and the cramps adjusted so that they do not restrict the motor, the cut can be made by running the edge of the sole-plate along the straightedge. Angled cuts: Bevelled or angled cuts are easily made using the angle adjustment knob mounted on the saw. This is calibrated to allow cuts to be made with the saw positioned anywhere between upright and 45°, but this is a fairly inaccurate guide so you should make a number of test cuts first and adjust the saw as necessary.
Once you have found the true angle of cut by trial and error either secure a straightedge to the workpiece or use the fence as a guide. Then carefully run the saw across the workpiece keeping the soleplate held flat at all times to ensure a neat, bevelled cut. Cutting slots: A power saw can be used to cut long slots in wood. This is particularly useful when making joints in shelving or when constructing simple furniture, for instance.
Carefully mark the position of the slot on to the surface of the wood and adjust the blade to cut only partway through the board. Use the rip fence or clamp a long straightedge to the workpiece to act as a guide and cut carefully along each marked-out line in turn. Use a chisel to chop out the waste and clean up the bottom and sides of the slot.
Making slots in the middle of a piece of wood-often known as pocket cutting- can also be made easier with the help of a circular power saw. First mark out the position of the proposed slot on the face of the workpiece. Then move the saw into position above the marked-out slot and carefully start the motor. With care you should be able to slowly lower the saw, starting with the front of the soleplate, until the blade starts to bite into the wood. Move the saw backwards and forwards until one side of the slot has been cut then switch it off, remove it, and cut out the other side of the slot in the. same way.
This technique ‘may require a little practice before it is mastered. Begin by making a number of trial slots on a piece of waste wood before you cut the slot itself. You may find that you have to help the blade to make contact by carefully raising the saw guard by hand-this should be done with great care since it is potentially dangerous. Make sure also that the body of the machine is held steady during the moment that the saw blade first comes into contact with the wood: it often jumps and.kicks back at this important stage. Wobble washers: These are a means of using the circular power saw to cut out neat slots in one pass without the need for chiselling afterwards. Special washers, fitted on each side of the saw blade, set it at an angle to the shaft so that it moves from side to side as it rotates. This makes a cut wider than the normal blade and in a number of runs you can cut out slots of practically any size.
However, wobble washers should be used with care and preferably only in saws mounted on a saw bench- since they can unbalance the saw, making it more difficult to control.
Choosing a jig saw
Like circular saws, jig saws are available both as integrals-with their own motor-or as attachments to electric drills. It is worth spending time deciding which of these is best suited to your needs.
As with circular saws, a good guide to the quality of a jig saw is its depth of cut: it should be capable of making a cut 50mm deep in softwood and a 25mm cut in hardwood or particle boards.
Some saws have variable speed controls and bases which tilt allowing you to make angled cuts. However, one of the most important things to check is whether the saw cuts with a straight ‘up and down’ or an orbital action; the orbital action is to be preferred since it produces a cleaner cut with less blade wear.
Like the circular saw, you should make sure that the jig saw you choose is comfortable to hold and use. Check also the blades are readily available and easy to change. Some jig saws can be fitted to a saw bench, so if necessary ensure that the model you buy has this facility.
Parts of a jig saw
At its centre is a motor driving a blade. The saw is controlled by a handle mounted above the motor which contains the on/off switch.
Power to the blade is provided by a series of gears within the main housing which drive the blade up and down. The blade is held in place by a small collar with a locking screw.
Again, like the circul-.. saw, the jig saw has a soleplate which rests on top of the workpiece and a detachable rip fence used as a cutting guide.
Fitting a new blade
A number of different blades are available for use with the jig saw, enabling you to cut quite a wide range of materials. It is important to ensure that they are fitted correctly.
Insert the blade into the holder mounted on the base of the main housing and push it firmly upwards to ensure that it is firmly seated; the blade should then be impossible to move if twisted from side to side. Tighten the blade locking screw with a screwdriver or Allen key (hex key wrench) and ensure the blade is secured by giving it a sharp tug.
Using the jig saw
Although the jig saw can be used for straight cuts, it comes into its own on curves and intricate shapes. In this case it can either be used freehand or else in conjunction with the rip fence.
When cutting with the jig saw, always secure the workpiece face downwards so that the ragged edges formed by the exit of the blade will not show. The saw should be held down firmly against the item you are cutting to counteract the natural action of the saw-which cuts on the upstroke of the blade.
Never force the pace of the blade but let it work its own way through the work-piece. This will avoid strain on the motor as well as broken blades.
Also never attempt to cut curves which are too sharp: a circle with a radius of 13mm should be the maximum. If you need to make a tighter curve than this a special, narrow-back scrolling blade should be fitted.
Freehand cutting: This is a fairly common method of cutting curves or shapes in wood using a jig saw.
Carefully mark the proposed position of the curve across the face of the workpiece. Lay the front of the soleplate on the board and line it up with the start of the curve. Start the motor and begin the cut, keeping slightly to the waste side of the cutting line. As you come to the end of the cut, support the two boards carefully to avoid splintering as they begin to separate.
Often you need to start a cut in the middle of a board. To do this, tilt the saw on its front end with the blade well clear of the work. Switch on and slowly lower the blade on to the point where the proposed cut starts. Do not force the blade but keep it pressed down against the surface until it finds its way through. The cut can then be continued for as long as you like and the blade removed once you get to the end. Circle cuts: If you need to cut a perfect circle, fit the rip fence on to the machine so that the fence is inverted and facing directly upwards. Then fix a nail in the surface of the wood at the exact centre of the proposed circle.
The end of the rip fence can now be slipped over the nail so that the saw pivots around it to make the cut. Most fences already have a small hole in the end designed for this purpose but otherwise one can easily be made with a twist drill.
Power saws can be dangerous tools if used in the wrong way-safety should always be your first consideration.
– All the safety precautions which apply to power drills should be adhered to.
– Never adjust the saw or change blades without switching off beforehand.
– If you are using an attachment, never use the trigger locking button on the drill.
– Never use any saw without an adequate guard. Make regular checks that they are securely fitted and in perfect working order.
– Eye protection is essential to protect you from loose flying material when cutting. With very noisy machines, ear muffs should also be worn.
– When cutting, hang the flex over your shoulder. Check occasionally that the flex is undamaged and replace it if necessary.
– Always use a sharp blade-this makes cutting safer and more accurate. Circular saw blades should be sharpened regularly-most manufacturers provide this service on request. Jig saw blades cannot be sharpened and should be thrown away once they become blunt.