SAWING METAL

Various types of saws and blades are available to cover the range of metalworking jobs you are likely to tackle in the home. It is important to use the right type and to hold the work securely.

The all-purpose tool for cutting metal is the hacksaw. For good results you need to look after it and use the correct blade at the right tension. Insert the blade with the teeth pointing away from the handle. Take up the slack so the blade is just held without fore-and-aft movement: then turn the adjusting wing nut between one and a half arid two complete turns to get the right tension. Always cut work on the forward stroke only.

CHOOSING CORRECT BLADE

Sizes of hacksaw blades are available from 229 to 457mm. but the most commonly used are 254 and 305mm : some hacksaws adjust to take both these sizes, while others also take a 229mm blade. A junior hacksaw has a 152mm blade which is narrow and finer than the standard type and automatically tensioned by springingthe frame to grip pins set in the blade ends. The junior hacksaw is useful for small work. Hardness Blades come in different degrees of hardness. Flexible blades, with hard teeth but a flexible back, are ideal for an inexperienced worker and for awkward material which is likely to break a hard blade. All-hard blades are recommended only for experienced operators. Both types are available in high speed steel which cuts hard and soft material. There is also a low alloy flexible blade for use with soft material ONLY.

TEETH The number of teeth in a blade varies from 14 to 32 per 25mm. The 14-tooth blade is used for softer metals such as aluminium and copper. the 18 for general purposes and the finer 24 and 32 for thinner materials.

A good guide is to have at least three teeth in contact with the work at any one time. If you have less than this, you will get judder; if you have a lot more, such as a 32-tooth blade in a piece of 12mm thick iron, you will waste a lot of time and energy without getting any better results.

There is also a progressive tooth blade which has fine teeth at the front and progressively coarser teeth towards the rear. It gives smoothness at the start of the cut and a fast cut towards the end; it is suitable only for general purpose work.

For extra tough jobs there is a blade which will cut through most things – for example files, glass, alloy steels, ball bearings and ceramics. The blade action is abrading rather than cutting since it wears away the material rather like glasspaper wears away wood.

For cutting shapes, in particular curves around which an ordinary blade will not go, a tension file is suitable. This is a thin blade shaped like a knitting needle with teeth cut all round the circumference. It can be fitted to a standard hacksaw frame by means of a specially designed hacksaw link.

USING LUBRICANTS

Lubrication makes metals easier to cut. reduces blade wear and heat build-up, which could destroy the blade, and improves the finish of the cut. Cast iron does not need lubricant as it has sufficient free graphite in it to be self-lubricating, but lubricating oil should be used for other ferrous metals. For softer metals, such as copper and aluminium, paraffin is a good lubricant.

WORKING CORRECTLY

For ease of working, the position of the vice must be at such a height that your forearm, when positioned for sawing, is horizontal and in line with the jaws of the vice. It is also important that your body is comfortably placed. For right-handed sawing your left foot should be forward with the toe pointing forward and your right foot placed back at right-angles to the left one. For left-handed sawing, reverse the position of your feet.

Cutting metal

When cutting always use the full length of the blade; if you do not. the blade will become unevenly worn and will jam when you do use the full length. The only exception to this rule might be the progressive tooth blade if. on occasions, you want to avoid using the coarsest teeth.

When starting a cut. work from the side away from you or the saw may jam on the leading edge of the work. Always cut on the waste side of the cutting line and smooth off with a file. If you have to cut a piece of metal at an angle, turn the piece in the vice so the saw cutting action is always vertical. Awkward access When access to a piece of work is difficult, you need a hacksaw frame with at least one alternative mounting position for the blade. This allows the blade to be turned to either a 45 or 90 degree angle from its normal position so the cut can be made at an angle to the frame.

In some cases you may have to resort to a pad saw handle, a metal casting which clamps the hacksaw blade at one end only. This means the blade is not under tension so you have to take care not to bend it. It is advisable to use a short blade such as a junior hacksaw blade. When used with a pad saw handle, the blade should cut on the pull stroke rather than the push stroke, so insert the blade with the teeth pointing towards the handle. You can also use a mini hacksaw with an extendible blade. Wide slots To cut an extra wide slot, such as a screwdriver slot, mount two blades alongside each other in the hacksaw frame. Most frames have long enough mounting pegs to allow for two blades. Some metalworkers prefer to have the blades with their teeth in opposite directions so one cuts on the forward stroke and the other on the return.

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