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FOLDING.
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the other, as the paper at back retains sufficient glue to cause them to stick together if laid across one another; the whole must then be left to dry. When dry the groove should be knocked down on a flat surface, and for this the knocking-down iron screwed up in the lying press is perhaps the best thing to use. The groove is the projecting part of the
![Line drawing of Martini's Folding Machine.](http://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Art_of_Bookbinding_p039_Martini%27s_Folding_Machine.png/300px-Art_of_Bookbinding_p039_Martini%27s_Folding_Machine.png)
Martini's Folding Machine.
book close to the back, caused by the backing, and is the groove for the back edge of the mill-board to work in by a hinge; this hinge is technically called the "joint."
Machines.—There are many folding machines made by the various machinists; the working of them, however, is in nearly all cases identical. The machine is generally