The cauls should be left on till cold, and even then there need be no hurry in taking them off, as they cause no damage by being left on. When several pieces of the same size, such as drawer fronts, are being veneered, two of them may be laid back to back and a caul applied to each veneered surface, or they may be laid together with a caul between them.
When taken out of the caul the work should be laid on one side for a time to allow the glue to thoroughly harden before cleaning up. It is best to keep the veneered sides from the air either by placing them next a wall or by putting them together in pairs when there is more than one piece. To work on the veneers, or as it would be said in the workshop, to clean them up before the glue is thoroughly hard, would be to weaken the hold, and very likely cause blisters. These will be more fully referred to in due course. It must be noted that the heat caused by the use of the scraper and papering up is often sufficient to soften the glue so long as this retains any moisture, and if this is done the veneer is almost sure to rise. It may almost be said that to clean up veneers too soon is to ruin the work and render previous care futile. How long the veneers should remain untouched before cleaning up must depend on circumstances, and any cabinet-maker's advice would probably be to leave them alone as long as possible. There is no chance of justice being done to the work if they are cleaned up within two or three days, and if they are left for as many weeks it will not suffer.
If the veneer is thick enough the smoothing plane may be used if necessary, but it should, of course, be set as finely as possible, and very little be taken off with it, otherwise the scraper and glass paper alone must be used. When veneers are laid with the hammer cauls are not used, the contact being effected by simply passing over the work with pressure. Some cabinetmakers are of opinion that this method is as good as the other, or at any rate sufficiently so, but as a matter of fact the work is seldom so reliable unless for small pieces, and even then the caul is better when it can be used with convenience. In this respect, a good deal depends on the discretion of the worker, and there is no doubt that many are very successful in veneering even large panels with the hammer. The novice, however, cannot be recommended to use this for the purpose. All that can be said is that he may do so, and he must not be surprised if, occasionally, the work does not stand. With knife-cut veneer, the difficulty of doing the work properly with the hammer is less than with the thicker saw-cut. If I may venture to do so without being understood to fix arbitrary limits, I would say that the caul should be used with saw-cut, and that the hammer should be kept for knife-cut veneers, especially when large pieces are being laid. There is, however, nothing but experience to show when it is a matter of indifference whether caul or hammer be employed. The latter is often the easier and quicker for small work, such as rails and stiles of door frames, but it is really impossible to say exactly, and much must be left to the judgment of the worker. The broad end of the ordinary hammer may be used for narrow strips, but for general purposes a special veneering hammer is advisable, and will be more convenient. It can easily be made by or for the user, and is not generally on sale at tool-shops.
Its construction will be understood from the accompanying illustration, Fig. 165, and the following description - The head consists of a piece of strong wood say 1 in. thick; into the lower edge of this a piece of iron or steel about 1/8 in. thick is firmly secured, with, say, an inch projecting below. A wooden handle completes the contrivance, which is really more of a squeegee than a hammer. The size is comparatively unimportant, and depends more on the fancy of the user than on anything else, but to give some general idea of good useful dimensions the following may be stated: - Length of handle from 12 to 18 ins., head 6 to 9 ins. long and 4 to 6 ins. wide. The iron must be of such a thickness that it does not bend under the pressure, and should be straight across, with a slightly rounded edge and corners to prevent the veneer being scraped or scratched, instead of being merely rubbed. From these remarks it will be seen that the tool need only be a rough one. Indeed, fine finish would be thrown away, as it soon gets dirty with use.
When veneering with the hammer, the wood is not swelled on the back and the glue is simply rubbed on the face side. When this has been done, the veneer should be laid and pressed down as quickly as possible, so that the glue may not have cooled more than can be helped. As this is of importance when laying with the hammer, everything required should be at hand. A rag or sponge, some clean hot water (that from the outer glue-pot ought to do very well), and a heated flat iron such as used for laundry purposes should be ready. When the veneer has been hastily pressed down with the hands, the hammer will come into use to complete the work by forcing out the air and surplus glue. First go over the veneer with the sponge or rag moderately wrung out with the hot water as quickly as possible. Then take the hammer with the handle in the right hand, the left pressing down on the head, and with the iron on the veneer go over the whole surface by means of a series of zigzag movements as suggested by Fig. 166.
Fig. 165. - Veneering Hammer.
Naturally the centre of the panel should be treated first, so as to gradually work the air and glue towards the edges. In order to let the hammer work freely, the veneer should be kept tolerably wet, as mere dampness would not do; on the other hand, sloppiness should be avoided, and the water should be hot. It is not a bad plan to have a little glue in the water, though by wiping the edges with the sponge or rag enough will be got, and it is by no means necessary to mix glue and water specially. Before the veneer can be properly laid, especially if the panel is a large one, the glue will in all probability have become so set that it does not flow freely. To remelt where necessary go over the veneer with the warmed flat iron, which, be it noted, should not be too hot, and then continue rubbing with the hammer. As the work progresses blisters, which are really formed by air bubbles under the veneer, should be watched for. If removed at once, that is, by working them out to the edge of the wood while the glue is hot, there is not much difficulty with them, but if left till the glue has become hard it is often troublesome to get rid of them. To leave them in finished work would never do. When the veneer seems, so far as can be seen, properly laid, go over it carefully for the express purpose of discovering any blisters. These are often difficult to discover with the eye alone, but may easily be detected by lightly tapping on the veneer with the hammer handle; the hollow sound will betray them. It may be possible to lay the veneer at such places by simply reheating the glue and using pressure, but to allow the air to escape it will be necessary to prick a hole or make a short cut with a sharp chisel. If done with the grain of the wood the mark will not be noticeable. To heat the glue locally a warm hammer head may be large enough or the bottom of the inner glue pot answers very well. In some cases the blisters will be found to be caused not so much by air bubbles alone as by the glue having been all run out. It is then necessary to put some more under the unstuck parts of the veneer, and it may generally be managed by cutting through sufficiently to get a little in. If this cannot be done by a simple plain cut it may be necessary to cut so that a portion of the veneer can be partially raised. With some woods this is easy, but with others great care must be taken in order that the marks may not show afterwards. Blisters, it may be remarked, are not so likely to occur when the caul is used as with the hammer, but whenever they are found they may be laid as suggested. If there are many it is an evidence that the work has been badly managed, for with a fair amount of skill and ordinary care they will seldom occur. When a very soft or porous wood forms the ground it is sometimes considered advisable to prepare it by sizing over with weak glue, but if attention is paid to the consistency of the glue used to stick the veneer down with this is very rarely necessary.