The hand screws, illustrated in Fig. 79, Part I, Pattern Making, enter so largely into all gluing for pattern work that some description of their construction and the manner of using is necessary here. The four parts of each hand screw consist of two jaws and two spindles. When using, the jaws must in every case be kept parallel. This is done by the adjustment of the middle or central spindle. The clamping is in all cases done by the outside or end spindle, the middle or adjusting spindle serving as a fulcrum for the jaws, and the leverage and pressure being obtained by the end spindle.
To open and close the hand screws for larger or smaller work, do not screw or unscrew one spindle at a time. Instead, grip the handle of the middle spindle in the left hand, and the handle of the end spindle in the right hand. Hold the hand screw at arms length and whirl it from or toward you as may be needed for closing or opening the jaws. In this way the spindles will each be kept in its proper relative position, and the jaws will, at all distances, remain parallel.
When clamping broad surfaces, care must be taken to see that the pressure of the jaws on the work being glued is the same at the points and at the back part of the applied portion of the jaws. This can be easily changed at will, by slightly loosening or tightening the middle spindle, which, as before stated, is the adjusting spindle and fulcrum, and not used for clamping. After adjusting the jaws parallel and to even pressure on all their length as applied to the work, screw up and tighten the end spindle to the utmost pressure which the jaws will bear, and again examine the clamp and the work to see if the jaws are parallel and the pressure even. If not, loosen the end spindle and readjust the middle spindle by opening or closing as the case may require.