DRAWING INSTRUMENTS. 



Drawing 

 bawd. 



PLATE 

 rcxxxvn 

 Vtf. 19. 



Rg.4. 



Kig. 18. 



Kig. 19. 



Wiih a 

 WvcL 



This invention i-. letter in theory than practice ; tin- 

 rollers being liable to be diverted in their motion by 

 tlu 1 least irregularity on the paper, and it therefore re- 

 quires to be used with the greatest cure, otherwise it 

 will not be so accurate a> thr common instrument-. 



(>(' ;ill iiu-thinls of drawing parallel lines, the draw- 

 ing board and T square is undoubtedly the best. This, 

 inionly used, is t<x> well known to require any 

 description ; Imt in 1 ig. lit. a square and draw ing hoard 

 is shewn. ha\ing si-mc improvements. The edges have 

 slips (if box, or other h;ird light-coloured wood, inlaid; 

 and these lx-ing divided into tlw*e .scales which are 

 most frequently re(|uired, will be found extremely con- 

 < i nii-iit to work from, without requiring com panel. 

 The divisions on the adjacent sides of the board are of 

 the same scale ; but those upon the sides which arc op- 

 jwi-ite to each other are of different values. This ren- 

 i!er- the use of the board more extensive, because it is 

 the two adjacent sides only which are used for the 

 same drawing ; one being used for the measurements of 

 lengths upon it, and the other for heights of elevation. 

 The paper on this drawing board is represented to be 

 fixed down at the angles by pins with a large flat head, 

 such as is shewn in its full size at Fig. 4. The point is 

 sharp, and is pressed down into the board. Another me- 

 thod of holding the paper, is shewn in half its full .sine in 

 Fig. 18. a is a steel screw, passing through the board 

 with a thin, flat, conical head, which is very exactly 

 fitted into a brass cell i, fixed fast into the wood of the 

 drawing board. The screw is tapped beneath, and has 

 a nut c upon it, to draw it down. The shank of the 

 screw is made square, that it may not turn round in the 

 cell 6. The edge of the sheet of paper being introdu- 

 ced under one side of this conical head, and the nut c 

 turned, it draws the head a down upon tRe paper, and 

 pinches it tight into the cell, so as to hold it fast ; and 

 at the same time makes no elevation above the surfaces 

 of the paper, which can obstruct the passage of the 

 square or other rulers over it. The stock A of the 

 square AB, Fig. 19, is as usual made of three times the 

 thickness of the blade or ruler B ; so that when either 

 side is turned upwards, the stock presents an edge pro- 

 jecting beneath the plane of the blade B, which being 

 applied to slide against the edge of the drawing board, 

 keeps the ruler in all situations perpendicular to it. 

 The upper of the three projecting edges, which is seen 

 in Fig. ip. at A, is not formed of the same piece as the 

 other part of the stock, but is a thin ruler fitted upon it 

 by a centre-screw a, and has another screw 6 passing 

 through a curved slit to fasten it. By relieving this 

 screw, the inside edge of this ruler can be made to in- 

 cline, at any required angle, with the edge of the stock 

 on which it is fixed, and with which it is now represent- 

 ed as coincident. There is a semicircular part at b, 

 which is divided into degrees, and reads against a 

 vernier, divided UJKHI the lower part of the stock; 

 and by this the angle is im-a-tired. The use of this 

 moveable side to the stock is to draw lines inclined to 

 others at any required angle, or indeed to answer 

 all the purposes of a protractor. Thus having with the 

 edge of the ruler B of the square, as it stands in the 

 Figure, drawn any line, set the moveable part of the 

 stock to the required angle, by the divisions at li ; then 

 turning the square the other side upwards, and apply- 

 ing it to the edge of the board, the ruler 15 will make 

 the required angle with the former line, and also with 

 the edge of the drawing board; and by applying the 

 aquarc to the adjacent side of the drawing, a line may- 

 be drawn at right angles to the inclined line. 



This is tailed a square with a bevel, and is very use- 



Drawiig 



Inslru- 



ful tor drawing long lines inclined to the side* of 

 the Ikxird. But for short lines, the instrument. 1 i 

 is more useful. This is a small l>cvcl or ruler, jointed 

 like a sector, with two limbs moving on a tight joint : Small*"" 

 the edges are bevelled towards the inside, fir ruling bcveL 

 against. In u-t 1 , it is laid against tin- 1 dge of the square. ,,, ATE 

 as at M. l-'jg. 1!). and max benpened to any angle; then ,, XXXVI[ 

 by eliding it along the edge of the ruler B, or moving };\g. 19. 

 the ruler up or down aero the width of the board. the 

 edge of the bevel may be brought to draw in any part 

 of t he paper ; and having drawn a line in one "place, 

 will draw another parallel to it at any distance. It will 

 also draw lines anti-parallel, that is, rcxcr-cd, or making 

 the sam<- angle in an opposite direction. This is done 

 by reversing the bevel, as shewn In the dotted line- ; 

 and will be found extremely useful for draw. ing the op- 

 posite sides of the roofs of buildings, or any other in- 

 clined lines. The same bexcl when applied against the 

 edge of a ruler, as at Fig. 17, will divide a line into any Fig. 17. 

 required number of equal parts. Thus, for instance, 

 suppose the space Ix-twecn the jx>ints 11 and It is to be 

 divided into seven equal jwirts. To do this by the be- 

 vel, lay the inside edge of one leg D, to cross the line 

 at one of the points, vi/. n ; then place the edge of the 

 long ruler 15, behind it, and hold it fast down, that the 

 bevel may slide freely against its edge, but without de- 

 viation from its direction. Now open the bevel to such 

 an extent, that when the division numbered 7. on the 

 inside of its limb E, is brought, by sliding the bevel 

 against the ruler, to intersect the line which is to be di- 

 vided, the intersection shall be at the other extreme 

 point of the space to be divided, viz. at b. The instru- 

 ment is now prepared ; and to nuirk the divisions, slide 

 the bevel against the ruler, till the division No. (i. inter- 

 sects the line. There draw a mark by the edge of the 

 bevel, cutting the line a l>, as at 6 ; next bring the divi- 

 sion 5. to cut the line, and mark No. ;> ; and so of all 

 the rest, and the line will be divided into seven, as re- 

 quired. It is plain, that if it had been required to di- 

 vide it into seven and one-third, instead of seven, the 

 same process would have effected it, by only preparing 

 the instrument, by opening the bevel so much more as 

 to bring the division seven and one-third to cut the line 

 at the point li, instead of seven. It is for these frac- 

 tional numbers the instrument is chiefly useful, because 

 it is so difficult to do them by the compasses. 



Dividers, or measuring compasses, are shewn in Fig. Dividing 

 5. They have nothing particular in their construction m PJ*** 

 which is not apparent from inspection, except the ad- 

 dition of a clamp and adjusting screw, to adjust and 

 preserve the opening of die compasses. This consists 

 of a piece of steel Afl, which is formed to a screw a at 

 one end; and the other has a slit or opening made through 

 it, for the reception of the milled-head screw d, which 

 screws into the leg of the compasses, and thus with a 

 clam)) binds the stivl A a last against it. B is a milled- 

 head nut, into whicb the screw n is received. This nut 

 has a shoulder and a neck, or small part, which is fit- 

 ted into the socket c, formed of a piece of brass fasten- 

 ed to the other leg of the compasses by a round pin, 

 which is adapted to a hole through the leg, ami secured 

 by a nut, or screw, on the other side, from either draw- 

 ing out or shaking ; and the nut B is so fitted to its 

 socket r, that it will not draw out, though it turns frcc- 

 1\. The utility of this clamp is very great, for measu- 

 ring accurately, or dividing lines or circles into a great 

 number of parts. When the screw d is loose, the com- 

 pass joint can be opened or shut on their common joint, 

 as easily as any common pair ; but clamping the screw 

 d fixes them quite fast. Still they admit of a delicate 



