Fig. 2295.
An excellent example of filing is to file up a hexagon nut or a bolt head. This is apparently a simple piece of work, but it is in fact a job that requires a good deal of care and precision to properly accomplish. The requirements are that the nut shall measure alike across the flats, that each flat shall be parallel to the axial line of the bolt, and at a proper and equal angle to both of its neighbors, and that the nut shall be of equal thickness all round. The method of accomplishing this result is as follows: Let [Fig. 2295] represent a bolt head, after it has been turned in the lathe. It will be observed that the end face of the bolt head is rounded. Now a bolt head of this form gives a very neat appearance, but it presents difficulties in the filing up, as we shall see presently.
Fig. 2296.
Fig. 2297.
Suppose that one flat (which we will call flat a) of a nut, is nearest to the bore, then to make the nut of equal thickness all around, the other flats must be so filed down as to approach the bore as nearly as a does, and it is assumed that there is metal enough to permit this. The flat a will then be the first one to be filed up, taking off just sufficient to make it true when tested by the nut gauge, applied as in [Fig. 2296], in which n is the nut, and g the gauge. The flat must also be filed true when tested by the gauge, as in [Figs. 2297] and [2298], the gauge g being tried rested on a and applied to b, and then rested on a and applied to c. a should be filed so that, if possible, it will be at the proper angle to both b and c, but if, from errors in the angles of b and c, this is impossible, the error should be divided between the two, as shown, for example, in [Figs. 2299] and [2300], where the gauge is shown in the two positions necessary to test each respective flat, b and c; the amount of error being equal at h and i.