Learn Mechanical Engineering at Home Series – (Hand Tools)

In this article of the series we will be learning about various types of chisels. If you are familiar with the term, a chisel is a tool used to work on metal in their cold state, as against hot work such as blacksmith’s work. They are used to remove small pieces of metal from the work piece in order to reduce its size or give a rough shape after which it can be smoothened by using finer tools such as files. Because of the nature of the work, chisels are made of quite tough quality steel known as tool steel. Given below are the few basic types of chisels, their images and uses.

Flat Chisel

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As seen in the above figure it is one of the most commonly chisels and in shape is resembles that of a “minus” screw driver if you know what I mean, and the cross-section of the hand is normally hexagonal or round. This type of chisel can be mainly used to remove pieces of metal from flat surfaces by striking it repeatedly with a hammer and placing it on the workface at an inclined angle. It would be possible to give very detailed guidelines on its exact striking pattern since that is better learnt by observing an experienced fitter at work or some video of the same. The other end of the chisel become burred after a prolong used due to repetitive striking by hammer blows hence that needs to be taken care of at repeated intervals using grinding.

Side Cutting Chisel

Normally slots are cut in metals using machines but sometimes it might be necessary that for already installed systems, a slot might be required on site. In such cases the manual method consists of drilling two or more holes of appropriate diameters in close proximity and then removing the metal from them using specially shaped chisel known as side cutting chisel. You can see the shape of this kind of a chisel in the diagram shown below and see that it looks like the human foot. Basically the flat underside of the “foot” has a small tapered end and is used to cut the slot.

Cross Cut Chisel

This type of chisel has a parallel sided blade with a narrow pointed end as can be seen from the figure below. Due to this shape it is useful to chip square or rectangular shaped grooves.

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There are other types of chisels as well such as bull nosed chisels etc which are used for different purposes but this much discussion should suffice to give you an idea about chisels and their uses. In the next article we will take up screwdrivers for study.

A screw driver is one of the most common tools which is not only found in mechanical workshop, but literally in every home. Screw drivers come in various shapes and sizes and this article is dedicated to the study of screw drivers of different kinds.

Plain Screwdriver

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As the name suggests this is the most commonly found screwdriver and consists of a steel blade having a flattened end which is case-hardened to withstand twisting force when it is inserted and twisted inside the base of the slot of the screw. The handle is either made up of plastic or wood depending on its usage, the former being used for lighter works while wood being normally used for lengthier screwdrivers used for heavy duty uses.

A variation of this type of screwdriver is where the steel extends till the other end (handle end) and has portions of wood riveted to it for a better grip. This type of screwdrivers can be used to apply much greater torque without the fear of the screwdriver failing by relative slipping between the steel blade and the handle. The portion of the handle which is covered with wood gives a better grip as compared to if it were only a full steel handle.

The ends of the screwdriver normally are either plus shaped or minus shaped

Ratchet Type Screwdriver

If you are tightening or loosening a screw, then every time your hand reaches the rotation limit you have to pull out the screwdriver from the slot in the screw head, turn the screwdriver to the appropriate angle and reinsert it. This might seem to be a very minor task but for people doing repetitive works this consumes a lot of extra time. Hence a ratchet screwdriver is helpful in such a case and there is a button which can be used to fix the direction of rotation. Suppose the direction is set to such a position that it can be used to tighten a screw in the clockwise direction, then when the hand reaches its rotary limit, instead of pulling out the screwdriver you simply need to turn the handle of the ratchet screwdriver backwards. It rotates back freely without the blade rotating with it and then again ready for the next turn. The reverse can be done when the screw has to be loosened. The shape of a typical ratchet screwdriver is shown below

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Pump Screwdrivers

If you have ever ridden a bicycle then you certainly know about the air pump used to inflate the tyres of the bicycle. Similarly a pump screwdriver is used to tighten or loosen screws not by rotary motion but by pump type action which gets converted into rotary motion at the blade end through the appropriate mechanism while a ratchet arrangement ensures which direction the motion gets converted into rotation. All the parts are shown in the diagram below and are clearly labeled.

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We all know what a file means in the context of either office environment or a computer system but it has got a totally different meaning in context of mechanical engineering and has nothing to do with storing information or papers but is a simple yet equally effective hand tool used to remove the extra material from a work-piece by the act of scrubbing it over the latter. Learn about files, their types and uses in this article.

Files come in various types and are useful for different purposes and are usually manufactured out of very hard steel which is well-tempered. These properties ensure that they can remove the extra material with precision and do not get broken in the process. Some of the important files types are listed as follows.

Depending on the type of cut

Extra Rough Cut and Rough Cut Files

Both these types of files are used for the initial filing where the amount of material removed is quite a lot while precision is not a concern since it is normally carried out at the beginning of a filing operation.

Middle Cut, Bastard Cut and Second Cut Files

These types of files are used for intermediate operations after the heavy material removal is complete and before finishing the final smoothening out operation.

Smooth Cut and Dead Smooth Cut Files

These files are used for finishing the filing operation by smoothening out the irregularities which are left by the previous two operations.

In the above file classification is must be noted that the various types of cuts are made possible with the variation of teeth density of the file. A rough cut file and other coarse files have relatively less number of teeth per inch while the smoother files have the maximum number of teeth.

Depending on the shape of the shank

Flat Files

As the name itself suggests, these files have flat shank shape which have teeth on both sides and are mostly used for level filing work involving straight surfaces.

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Round Files

The blade or the shank of this type of files is round in shape and the teeth are formed on that round surface. The diameter of the whole shaft is uniform towards one end, while it slightly tapers at the outward end. These files are very useful in filing round shapes such as round holes or enlarging them.

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Square Files

These files are very similar in construction to the above mentioned round files with the only difference that the cross-section of the shaft is of square shape which is uniform towards the handle end but gets slightly tapered towards the outside end while maintaining its square shape.

There are still few other important file classifications which we will take up in the next article of the series.