Fig. 792.
To obviate this difficulty we have Boardman’s device, which is shown in [Fig. 792]. It consists of a threaded mandrel provided with a ring, with two rounded projections a, a and b, b, on each radial face, those on one side being at a right angle to those on the other. This ring adapts itself to the irregular surface of the nut and by equally distributing the pressure on each side of the nut destroys the tendency to cant over, hence the nut may be turned true, notwithstanding any irregularity of its radial faces, and independently of its fitting the arbor or mandrel thread tightly.
Fig. 793.
Another form of mandrel for the same purpose is shown in [Fig. 793], the mandrel being turned spherical, instead of having a square shoulder, and the washer w being cupped to fit, so that the washer will cant over and conform to the nut surface.
