The travelling part is one with the two racks, while the double gearing and the arrangement for reversing by shifting the strap from the middle pulley - which is idle - to the right or (eft, forward motion, will be obiions to anyone who has given attention to machinery. The sluw heavy cut, with a cutter at right angles to the plate, is essentially wring, and tends to drug the plate out of shape, and, unless care is taken will sometimes lift it from the bed of the machine. A machine tool for cutting stereotype metal will not work eifficiently at a much lew speed than 12 ft, per second between it aud the metal. In ordinary cases, the est is clean and easy with such a speed, and an angle of 60° on the approaching aide, and 15° Is a good angle for cutting edge, leaving an angle of relief of 15°. When a cutting tool rapidly removes small shavings of stereotype metal - as in the case of a circular saw or rotary cntter __there is a tendency for the clean particle of metal to weld together, and also for some of them to weld upon the clean surface of the work, thus making it rough, but a minute film of thin mineral lubricating oil prevents the tendency to welding, and it is generally sufficient to allow a brush charged with the oil to very lightly play against the cutler or the work, according to circumstances.
The free use of oil on stereotypes is objectionable for obvioas reasons. For heavy work, water con-Winint; a little soap is more efficient, but it most be used freely. The above remarks as to the relation of stereo-type metal to cutting tools apply more especially to the ordinary and rather soft alloys. It is a matter of surprise to me that a planing machine with a revolving cutter like that used for thicknessing floor boards is not always used for the backs of stereotypes when planing is required.
Draw bench for striping back of plates.
In most cases - at any rate for jobbing work - the stereotype plates are brought up to type height by being nailed or screwed down on mahogany boards, these being, roughly speaking, 3/4 in. high; and, from the printer's point of view, it is very desirable that the thickness of the whole should exactly equal the height of the type, a matter which may very well be gauged by a sort of bridge (Fig. 308), under which the mounted stereotype can be just passed if it is the right height. Wood blocks expand when exposed to damp, and contract when they dry, and consequently they vary from time to time; so printers, when using wood-mounted stereotypes, would save time by passing them one at a time, and face downwards, under such a bridge set to type height. The low places can then be readily brought up with paper patches in far less time than when made up in the chase. As a matter of fact, stereotypers very seldom send out the blocks too high, as the printer finds it much easier to pack up than to plane off.
Printing from stereotypes becomes much more easy and certain if, instead of being mounted upon material which, like wood, varies in thickness with difference in the degree of dryness, the stereotypes are either cast type-high in the first instance, or are mounted upon some firm foundation not subject to considerable variations of thickness.
Casting the plates type-high is a common practice for ephemeral work, as in that case the plates can be melted as soon as done with; but it is the usual practice not to cast the plate quite solid, a number of hollow spaces at the bottom, generally arched or domed, serving to lighten the plate. Any person with elementary notions of handicraft can devise for himself ready means of making cores for placing in the casting-box so as to produce the required cavities, and several ingenious forms of adjustable core are now made, among which may be specially mentioned that in which a set of core-bars of graduated sizes enables one to readily cast type-high blocks to any required width. For very small blocks, it is more convenient to cast solid, and if reasonable care is taken, the blocks may be cast so accurately to type-height, that planing at the back becomes quite unnecessary, and the sides may readily be squared up with the hand plane (Fig. 306), or sometimes it is more convenient to cast small metal mounting-blocks, and to solder the thin stereotypes upon these.
Metal mounting-blocks, upon which bevel-edged stereotype plates are held by catches placed round the edges, are on the market in various forms, much cleverness being sometimes noticeable in the devices for enabling the printer to build up any required size of mounting-block out of stock sizes. In the case of an ingenious device by Harvey Dalziel, the loose clips are avoided, and by dividing the mounting-block diagonally, variations in size are very readily provided for by the inseition of suitable distance pieces. Fig. 309 illustrates the arrangement. The small diagram at the west side is a sectional view showing the clips, which arc one with the blocks, and it also shows the coring of the blocks, while the diagram under it shows a pair of twin blocks in plan. Next we have the same adapted for a larger plate by the insertion of one of the various distance pieces, a series of which ii shown an the outer tide of the group. Fine adjustments can be made by inserting an ordinary lead, and it is obvious that these adjustments con be made to take effect either across or along the pace, or may be apportioned between the two.
Gauge for height.
A very firm and satisfactory blocking up of the stereo piste is a method due to Brightler. A few short pieces of wire are soldered to the back of the plate, and it is laid on its face and aurrounded with a type-high border. A mixture of calcareous cement and water is filled in level with the top of the border, and a flat plate, slightly oiled, is laid over and weighted. Brightley used Roman cement, but in the present day Portland cement is more convenient. This method is unsuitable when the plates are wanted for immediate use, as in ordinary cases the mould should not be removed for about 12 hours, and 2 days should elapse before tho mounted stereotypes are used for printing.