Handscrews are used to secure the work to the bench, and to hold several pieces of work fast while a drawing is being made or while glue is drying. The bench itself, when not otherwise engaged, may be used with advantage in the case last named.
Handscrews are made of wood or of iron, and are of various sizes.
Wooden handscrews (Figs. 13, 14), consist of three straight pieces of wood, two of which are joined to the third on the same side, and at right angles to it. Horn-beam or tough birch is the best wood for the purpose. A strong wooden screw passes through one of the parallel arms and gives the necessary pressure.
As the handscrew is sometimes subjected to a greater strain than the construction just described can bear, it is often strengthened by an iron rod. (See Fig. 14.)
Fig. 13. Handscrew. 1/8.
Fig. 14. Handscrew. 1/8.
Fig. 15. Adjustable Handscrew. 1/16.
When the screw is applied, one hand only should grasp the handle, and the other should take hold of the screw either above or below the nut. Otherwise, if the pressure is great, the screw may break. If the screw should go off the straight during the process, a light blow from the mallet on the lower part will put it right. A piece of wood should always be laid under the point of the screw, to prevent marks on the work.
[The English hand-screw (Fig. 16) differs from the Swedish handscrew in having two screws a a instead of one. These screws work in opposite directions,through two square wooden cheeks, 6 6. - Trs.]
Fig. 16. English Handscrew. a a screws, 6 b cheeks.
Thumbscrew cramps are now made of wrought iron. This gives strength without weight or clumsiness. These screws are very useful, and easily managed. (See Fig. 17).
When broad pieces of wood have to be glued together, and the handscrews already described are not large enough, and the bench is not available, use is made of a screw in which a movable block is substituted for one of the parallel arms. Such screws are called adjustable handscrews (see Fig. 15).