Fig. 2581.
[Fig. 2581] is an end view of the device in position on a lathe tail stock, and [Fig. 2582] is an enlarged view (being half full size) of the devices at the lower end of arms or rods e, e.
Fig. 2582.
At the lower ends of e, e are provided two pieces g, g, which are capable of adjustment to fit the Vs h, h of the lathe, as follows:—
The middle pins i are fast in the arms j, but are pivoted in g, the end pins, as k, are pivoted in g, are flat where they pass through j, and threaded to receive the nuts, l, of which there are four, two to each piece g. By operating these nuts, g may be adjusted to bed fair on the angles on the lathe Vs h. At m are two fixed pins which afford a fulcrum, at n and o respectively, to four index needle arms. Two of these index arms only are seen in the cut, marked respectively p and q, which are pivoted at n. Two similar pointer or needle arms are on the other side of m, being behind p and q, these two being pivoted respectively at o. At the lower end of p is a point resting in the centre of the nut, and similarly the end of q rests in the centre of the nut on that side. Similarly the two needles not seen have pointed ends resting in the centre of the nuts marked respectively l. Between g and j are two springs placed back to back, which act to hold g away from j. But it will be seen that if either end of g be forced towards j, as by passing over a projection on the V h, then the pin k, will push nut l, and this will raise the end of the pointer or needle to a corresponding degree, and the pointer being pivoted (as at n), its upper end will move and denote on the graduated index r that there is an error in the lathe V, the amount of the error being shown multiplied on account of the leverage of the needle arms from the pivots.
The pieces g being adjusted to bed fairly on the lathe Vs, the heads of the lathe are moved along the lathe shears, and if the Vs are true to angle the upper ends of the needles will remain stationary, a projecting part of a V will, however, cause the needle point to move toward e, while a depression on a V would cause the springs k to move g in, keeping it in contact with the V, while the needle point would move away from e. To maintain the needle arms in contact with the nut heads l, springs s are employed. Variations in the widths apart of the Vs on either side of the shears would obviously be shown in the same manner, the defect being located by the needle movement. The corrections are made from the contact marks of the heads, caused by moving the heads along the Vs and by careful scraping.