430 -^'^y Machine for ruling engraved Plates, 



gularly tapped part when (hut, or leave it at liberty when open. Fig. 3. fhews the face of 

 this cock with the clip, of which P is the joint, Q^Q__tapped part, R a pin to infure their 

 coming up fairly, and S a c';iw, which, when drawn upwards, ferves to clofe them ; or, 

 if thrown back, leaves them at liberty to open by the action of a fmall fpiral fpring, let 

 into oppofite holes near the joint. ED, fig. 1, reprefents the other cock, which is fixed 

 to the Aiding piece. Jt carries the llcel ruler E F, which, though fuihciently ftrong, is 

 tJbin enough to adapt itfelf to ilight variations of thicknefs of the plate beneath it. In my 

 inflrument I have made it adjuftable to much greater variations of thicknefs, by means of 

 an horizontal axis \ but as this contrivance adds to the expence, and diminiflies the fim- 

 plicity of the inflrument, I would rather recommend that great variations fliould be al- 

 lowed for by putting paper or thin flips of metal underneath the plate A A, as may be 

 required. The end C of the fcrew is turned down, and fixed in the cock ED by means 

 of a nut and waflier ; or in any other of the methods which are familiar to inftrument- 

 makers. The upper part of the cock ED is filed round, and cut into teeth, of which 

 £fty would complete the whole circle. The centre of this external circular part corre- 

 fponds with the axis of the fcrew (fee fig. 4 ). L, M reprefent two fhort cyhndrical pieces 

 which are hollow, and apply to each other fo as to form a kind of box. Within, and fixed 

 to the part M, which is fixed to the fcrew itfelf, there is a ratchet wheel divided into 

 fifty teeth ; and within the part L, which is merely fupported by the cylindrical part or ftem 

 of the fcrewj there is a ratchet, which holds when the part L is moved by its handle N 

 from right to left, but efcapes when that handle is moved in the contrary dire<3ion. O 

 is a lever, or arm, likewife fupported by the flem of the fcrew, and occupying the re- 

 maining fpace between the handle N and the cock D. At the outer extremity of this 

 lever there is a fmall (leel blade, which, by means of a back fpring exactly refembling that of 

 a pocket knife, may be made to form a continuation of the lever itfelf, or, by being placed 

 at right angles to the lever, m*y be made to refl in any of the divifions between the teeth 

 of the circumference of the cock -, and confequentlyMvill, by that means, confine the 

 lever to the pofition in which it is placed. The handle N cannot pafs the lever O, be- 

 caufe this lafl is too thick, and there is a flud or pin T, fig. 4, upon the face of the cock 

 D, which prevents the handle from being moved beyond a certain determinate ftation to 

 the left hand. And, laftly, the ruler I K, which is reprefented as broken off at K, but 

 (like E F) may be of any required length, ferves, by means of a thumb fcrew at I, 

 and another at the oppofite end, to fecure the copper-plate againft the drawing-board ia 

 the ufual manner. 



After this defcription the uie of the apparatus may be eafily underftood. By drawing 

 back the claw S, fig. 3. the fcrew is fet at liberty, and the ruler E F may be brought to any 

 required diflance from I K by hand. The plate may then be duly placed and fecured to 

 the board, and the clip drawn gently together by the claw S. In this fituation, fuppofe the 

 lever O to be placed at a confiderable difl:ance from the handle N, that handle may be 

 moved to the right, during which the click will gather upon the ratchet wheel j and then 

 being returned to the left, it will carry the fcrew round. The gentle prefTure, exerted by 

 means of the claw, will tend to clofe the clip upon the fcrew, as foon as it comes into a fair 

 pofition by its rotation ; at which inflant the claw will fuddenly fall into its place, and the 

 machine \% ready for work, excepting that the adjuflmcnt for the finenefa or coarfenefs of 



the 



