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t:tympan [2018/03/30 02:07] (current)
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 +<< [[contents:​index| Dictionary Index]] << [[contents:​t|Definitions under T]]
  
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 +====== Tympan ======
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 +A [[f:​frame|frame]] covered with [[p:​parchment|parchment]],​ on which the sheet of paper to be printed is placed. This is the outer tympan; the [[i:​inner-tympan|inner tympan]] fits into it, and between the parchments of the two the [[b:​blankets|blankets]] are placed, all which being run in receive the pressure of the [[p:​platen|platen]],​ which produces the impression on the paper. ​
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 +Mr. T. C. Hansard took out a patent, for "​Improvements on, and Additions to, Printing Presses, and various Processes relative to Printing;"​ in his description of them he says, — "My first Improvement is the Dividing- Tympans, which are capable of being added to any Printing Press, for the purpose of printing double-sized sheets of paper, and then dividing or cutting such double-sized paper to the ordinary size of single sheets of paper. These Tympans consist of, first, the outer Tympan, of dimensions according to the size of the Press or Work required: the additions to which are, a plate of Iron, Steel, Brass, or other sufficient substance, about seven eighths of an inch in width; the back side of which is level, but the front side is raised in the middle, the centre part being about one fourth of an inch in thickness, and the two sides about one eighth of an inch only; along the middle or thicker part are cuts or openings, for the purpose of admitting the knife hereinafter described, leaving small parts of the plate uncut.
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 +"On each side of the same, along the centre of the thinner part, is a row of small holes, at about half inch distances. This plate is fixed across the middle of the outer Tympan, to each side, being countersunk into the same 2ndly. The inner Tympans are formed of two parts, having each part three sides, and moving on pivots attached to the outer Tympan; these inner Tympans, when shut down, are fastened in the common manner by [[h:​hooks-tympan|hooks]] and eyes or[[b:​button-tympan| buttons]], each part when opened to adjust the blankets will incline back on the pivots. These Tympans I cover with black Linen of the most fine and even texture, rolled and hot calendered: taking a sufficient length in one piece to cover the one half of both Tympans, then folding it in the middle, and laying each fold along the side-rebate of the Plate over the holes, I then firmly attach it thereto by strong sewing through the holes; I then turn one part of the fold of the linen over the outer, and the other part over the inner Tympans, and sew, or otherwise fasten, the same around the iron work, or sides and ends of the Tympans, in the closest and neatest manner, letting the hooks, eyes, or buttons, and pivots, through the linen, and keeping clear the openings for the point screws by carrying the linen on the inside, in the same manner as in putting on common parchment; the same operation then takes place for the other half of the Tympans.
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 +"I then take pieces of Velvet, Velveteen, or other uniform soft substance, which I attach, with the pile or softest side outwards, to the linen already described as being fastened to the Tympans, by sewing or pasting it to the outside of the outer Tympan, to receive the Tympan-sheet,​ and by this means to give a beautiful and regular impression of the Type: which mode of covering Tympans I also apply to common Presses. ​
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 +"The Divider or Knife is made of a plate of Iron or Steel, about three-fourths of an inch wide, turned down at a right angle on one side, about one-fourth of an inch in width, and in length sufficient for the width of the sheet of paper intended to be cut, and this must be fixed so as to be exactly corresponding to the openings in the Plate before described; the part so turned down is cut into angular teeth, about a quarter of an inch from point to point, each tooth having two chisel-like edges, formed by being filed and dressed on the outside of the part so turned down; on the inside of the angle the teeth are to be finished all along fair and smooth. One or more of the teeth are then to be filed out at intervals, corresponding with the parts of the Plate left uncut. The Pivots or Joints of the Tympans and [[f:​frisket|Frisket]] being accurately adjusted, the Knife is then fixed to the Frisket (at each end by screw or other connection) so that when the Frisket is turned down on the Tympans the Knife shall freely enter the Plate at the openings before described. ​
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 +"The Plate and Knife now occupying the usual place of [[p:​point-screws|Point Screws]] and [[p:​points|Points]],​ those necessary articles are removed to the centre of each half of the Tympans above and below the Plate. If wished, the positions of the Plate and Knife may be reversed, by fixing the Plate to the Frisket, and Knife to the Tympan, or a Plate both on Frisket and Tympan, and Knife to the Forme, or Table of the Press, but not with equal certainty of operation. All these parts being properly adjusted, the mode of application is as follows: — For making ready a Forme or Sheet, the [[t:​tympan-sheet|Tympan-sheet]] is drawn on the Tympan, as in the ordinary mode, and the Frisket pasted and cut out; but for working the first side of the Paper, the Knife must be displaced (or, which is sometimes preferable, two Friskets used, to be exchanged, one having the Knife, and one without).
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 +"The whole of the paper being worked on one side without the Knife, the Knife is then replaced, or the Friskets exchanged, and the [[r:​reiteration|Reiteration]] proceeded with; the sheet will then be divided exactly along the centre, excepting at the parts where the portions of the Plate have been left uncut, and the teeth filed out of the Knife, as before described; which uncut parts answer the important purpose of keeping the double-sheet adhering as one, for the Pressman who may be //​pulling//,​ to draw it off the Tympans over to the [[b:​bank|Bank]],​ where it is finally parted by the other man who is //​beating//,​ while looking over his [[h:​heap|heap]],​ when six or seven sheets are accumulated,​ by means of a gentle pressure with each hand at each end of the heap. The [[w:​white-paper|white paper]], or first side, is worked with four points, placed opposite to each other in the middle fold of each half of the double sheet, but for the Reiteration the two lower points are taken off, and the sheet kept in register by the two upper ones only. For cutting the sheet into more parts than two, I extend the same principle by placing knives and plates in various positions, or at right angles with each other." ​
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