The general method pursued in glueing the angles of the frame for a panel, is somewhat similar, although modified, to meet the different structure of the joints. The tenons are made quite parallel both ways, but the mortises are a little bevelled or made longer outside, to admit the small wedges by which the tenons are fastened: and the stiles are made somewhat longer than when finished, to prevent the mortises from being broken out in driving the wedges, which are mostly cut out of the waste pieces sawn off from the tenons in forming their shoulders or haunches. These details are seen in fig. 22, p. 56.
In glueing the frame for a single panel which is fitted into a groove, the whole of the frame is put together before commencing the glueing, and the stiles are knocked off one at a time, by which the misplacement of the pieces is avoided. The tenons are glued, and a little glue is thrust into the two mortises with a thin piece of wood; when the stiles have been driven down close, the joint is completed by the insertion of a wedge on each side of the tenon; their points are dipped in the glue, and they are driven in like nails, so as to fill out the mortises, after which the tenons cannot be withdrawn: sometimes the wedges are driven into saw-kerfs, previously made near the sides of the tenons; the other stile is then knocked off, glued, and fixed in the same manner. Occasionally all four tenons are glued at the same time, and the two stiles are pressed together by screw-clamps, stertching across the frame just within the tenous; the wedges are lastly driven in, before the removal of the clamps, and the door if square and true is left to dry.
In ninny other cases also, the respective pieces are pressed together by screws variously contrived; the boards employed to save the work from being disfigured by the screws arc planed flat, and are warmed before the fire, to supply heat to keep the glue fluid until the work is screwed up, and the warmth afterwards assists in drying the glue: such heated boards are named cauls, and they arc particularly needed in laying down large veneers, which process is thus accomplished.
The surfaces of the table or panel, and both sides of the veneer are scratched over with a tool called a toothing-plane, which has a perpendicular iron full of small grooves, so that it always retains a notched or serrated edge; this makes the roughness on the respective pieces, called the tooth or key, for the hold of the glue. A caul of the size of the table is made ready; and several pairs of clamps, each consisting of two strong wooden bars, placed edgeways and planed a little convex or rounding on their inner edges, and connected at their extremities with iron screw-bolts and nuts, arc adjusted to the proper opening; the table is warmed on its face, and the veneer and caul are both made very hot.*
All being ready, the table is brushed over quickly with thin glue or size, the veneer is glued and laid on the table, then the hot caul, and lastly the clamping bars, which are screwed down as quickly as possible, at distances of three or four inches asunder, until they lie exactly flat. The slender veneer is thereby made to touch the table at every point, and almost the whole of the glue is squeezed out, as the heat of the caul is readily com-municated through the thin veneer to the glue and retains it in estate of fluidity for the short space of time required for screwing down, when several active men are engaged in the process. The table is kept under restraint until entirely cold, generally for the whole night at least, and the drying is not considered complete under two or three days.*
* If the clamps were straight, their pressure would bo only exerted at the sides of the table, but being curved to the extent of one inch in three or four feet, their pressure is first exerted in the center, and gradually extends over their entire length, when they are so far strained as to make the rounded edge bear flat upon the table and caul respectively.
When the objects to be glued are curved, the cauls, or moulds, must be made of the counterpart curve, so as to fit them; for example, in glueing the sounding board upon the body of a harp, which may be compared to the half of a cone, a trough or caul is used of a corresponding curvature, and furnished all along the edge with a series of screws to bring the work into the closest possible contact.
In glueing the veneers of maple, oak, and other woods upon curved mouldings, such as those for picture frames, the cauls or counterpart moulds, are made to fit the work exactly. The moulding is usually made in long pieces and polished, previously to being mitred or joined together to the sizes required.
In works that are curved in their length, as the circular fronts of drawers, and many of the foundry patterns that are worked to a long sweep, the pieces that receive the pressure of the screws used in fixing the work together " whilst it is under glue," are made in narrow slips, and pierced with a small hole at each end; they are then strung together like a necklace, but with two strings. This flexible caul can be used for all curves; the strings prevent the derangement of the pieces whilst they are being fixed, or their loss when they are not in use.
I have mentioned these cases to explain the general methods, and to urge the necessity of thin glue, of a proper degree of warmth to prevent it from being chilled, and of a pressure that may cause the greatest possible exclusion of glue from the joint. But for the comparatively small purposes of the amateur, four or six hand-screws, or ordinary clamps, or the screw-chaps of the bench, aided by a string to bind around many of the curvilinear and other works, will generally suffice.
As however the amateur may occasionally require to glue down a piece of veneer, I will, in conclusion, describe the method of "laying it with the hammer," which requires none of the