Practical Carriage Building
Compiled by M.T. Richardson, Vol.1. 1891
Screwdrivers The correct form for a screwdriver is a matter of much importance, but no matter what the form, experience in its use is a great aid in keeping the lip from slipping. An amount of pressure must be brought to bear upon the driver equal to that expended in turning the screw, otherwise the power spent in turning being greater than the pressure, forces the lip from the slot. It is also necessary that the driver should be at all times held at right angles with the plane of the head of the screw.
The majority of screwdrivers are shaped like Fig. 38. The lip is wedge-shaped, while the two sides of the slot in the screw are parallel and at right angles with the plane of the screw head (Fig. 39), and when the screwdriver is inserted in the slot the appearance is similar to that of Fig. 40. It will be observed that this is wrong in principle, but is very convenient when one screwdriver answers for several sizes of screws. It is better—in fact, necessary—to have different sized screw drivers. I have at least a half dozen, having occasion to use screws ranging from three-eighths inch, No. 4, to five inches, No. 24.
I give to the lips of my screwdrivers the shape represented in Fig. 41. When the lip is inserted in the slot it appears as shown in Fig. 42; and if properly used a screwdriver of this shape will never slip from the slot. —Screwdrivers By JEFF. POTTER