This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The chisel in its simplest form constitutes a slice of an axe, but as the impact is not from the motion of the chisel, but from that of a swung mallet or hammer, the eye of the axe is replaced by a contrivance for receiving the blow. When the element of thrust enters, then the chisel is passing into the " plane iron." For applying the chisel, 2 contrivances are in general use. One is to put a tang on the metal of the chisel, and to let this be driven into a handle so shaped at the extremity as to receive the blow of a mallet. A very few blows would soon drive the handle forward, and so the tang end would then project through the handle and receive the blows. To avert this a shoulder is forged, where the tang is supposed to end, and the chisel proper to begin. When the blows have been repeated, so that the handle rests upon the tang shoulder, then the handle is " home," and the tool completed. In turners' chisels where mallets are not used, the shouldered tang is not required. A suitable handle being selected, a ferule is loosely put on it, and a hole is bored down the handle a little shallower than the length of the tang, and widened at the mouth so as to show a square, the sides of which are just shorter than those of the tang under the ferule - now, enter the chisel-tang, and let it be pressed in by the hand until it is so retained by friction, that by pointing the chisel edge downwards, the metal does not fall out.
The operation of fixing the handle may now be said to commence. The line of the handle and blade is then inclined at about an angle of 45° to the horizon. A blow with a mallet is struck at the end of the handle; the inclination remaining the same, the tool is turned round on its longitudinal axis, say, 1/4 rotation, another blow given; the operation of turning and striking being continued until the feruled end of the handle and tang meet. As to the effects of a blow upon the end of a handle, there being no apparent resistance, this takes place: The velocity of impact is communicated to the handle and chisel. Now the greatest effort is required to cause the first motion, so here a high velocity in the mallet has to be divided between a supported tool and itself. What is sometimes called "inertia" has to be overcome in the act of this transference of velocity through the length of the handle and chisel; that portion which offers the least resistance will be the first to move. No velocity can be communicated to a body at rest without what is usually called resistance.
The friction between the tang and the handle is so adjusted by the preliminary formation of the hole, that the resistance from friction is less than the resistance from inertia; hence the gradual approach of the ferule and the flange. Now as to the turning in the hand about the axial line. The wooden handle is held in the left hand, therefore the effect of gravity upon it is neutralized. Not so with the chisel; gravity produces its full effect upon this. Consequently some part or other of the hole becomes a fulcrum, the cutting end of the chisel is drawn downwards by gravity, and therefore the tang end is pointed upwards. Continued impact in this position would place the chisel oblique to the axis of the handle; the turning is to avert this. Again, it was said that the depth of the hole should be less than the length of the tang. The reason is this : the end of the hole is of greater diameter than the end of the tang; if, therefore, the tang does not enter and fix itself in the wood, there may be unsteadiness in the chisel.
Assuming the instrument to be under the operation of repeated blows, the effect of these will be first expended upon the end of the wooden handle, and then transmitted to the cutting edge Unless provision be made, the destruction of the end of the wooden handle will be assured. To diminish as much as possible liabilities to such a result, the end of the handle is formed as a portion of a sphere. Further, the impact blow is modified in the mallet, which is of wood, with a curvilinear face; thus these 2 wooden surfaces act and re-act upon each other. The yielding elasticity of the wood also gives to the blow and so transmits to the work a different effect to that which would take place if the handle and chisel were of iron. Another way of fixing the tool in the handle is to have a long tubular top to the tool, into which a wooden handle is driven. This is preferable for heavy work, as the repeated blows only tend to condense the fibre of the wooden handle and increase its firmness in the shank; but as it adds much to the weight of the complete tool, it is not adapted for ordinary cases. (Rigg.) Much annoyance is caused by the tendency of the butt end of the chisel handle to split under the effects of repeated blows from the mallet.
A remedy suggested for this is to saw off the round end, leaving it quite flat, and on this to nail 2 round discs of sole-leather to form a pad for receiving the blows. When the leather has expanded inconveniently it can be be trimmed round with a knife.