In this article we will learn about hack-saw used in mechanical works, its construction and uses. Basically a hack-saw is a type of hand-saw which is used by carpenters. Take a look at the adjacent figure which shows the various parts clearly labeled. Most hack-saws have adjustable frames which can be used to insert a blade of different size than the one fitted earlier. This is necessary since sometimes the length of the blade varies with the type of work to be done by that blade. Hence the same frame can be used instead of using separate frames for different sized blades.
The frame of the hack-saw is made out of metal while handle is usually wooden. The blade is made out of hard but brittle steel. Hence the necessity of providing the wing nut as shown in the figure to keep the blade as taut as possible because if it is loose it will simply break off during the cutting operation. The main cutting operation is performed with the help of tiny teeth on the underside of the blade which are either fine or coarse depending on the nature of work to be carried out. The shape of the teeth is in such a direction that they cut during the forward stroke and not during the backward stroke.
The exact operation of sawing can only be learnt by experience as in the case of filing which we learnt in a previous article. Broadly speaking you should keep the hack saw cut as straight as possible to prevent snapping of the blade. Very little pressure should be applied towards the beginning of the sawing operation and this pressure should be increased gradually. Coarse blades should be used for harder materials while softer materials can be sawed using fine sized blade teeth as well.
The two main variants of the hack saw in common use are the tubular type hack saws and the hack saws used mainly for sheet metal cutting work. The latter is unique in that it has a narrow sectioned frame made out of sheet steel plate which acts as a guide by going through the slot while the cut is being made thus helping to maintain the straight direction of the cut which would otherwise be difficult to maintain considering the depth of cut.
Apart from the manual hacksaws mentioned here, there are also electrical hacksaws and hydraulic hacksaws which are used for heavy duty work but since we are only dealing with hand tools in this article we wont go into the details of these types but you can still satisfy your curiosity by observing a picture of a hydraulic hacksaw which will give you an idea about its usage and cutting capacity.