. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing . size and strength, isless liable to legs of the bow-pen compasses arejointed. Fig. 19 is afront elevation of aninstrument preciselysimilar to the last, ex-cept that it has a pen-cil instead of a compasses re-quire to be adjusted to any desired radius by the direct action ofthe hand. In work where great accuracy and minuteness is calledfor, it will often be found a very tedious matter to
. The practical draughtsman's book of industrial design, and machinist's and engineer's drawing companion: forming a complete course of mechanical, engineering, and architectural drawing . size and strength, isless liable to legs of the bow-pen compasses arejointed. Fig. 19 is afront elevation of aninstrument preciselysimilar to the last, ex-cept that it has a pen-cil instead of a compasses re-quire to be adjusted to any desired radius by the direct action ofthe hand. In work where great accuracy and minuteness is calledfor, it will often be found a very tedious matter to obtain a trueadjustment in this manner, particularly if the joints of the instru-ment are not in perfect working condition. This difficulty is gotover in what are termed spring, or screw bow compasses:. BOOK OF INDUSTRIAL DESIGN. 189 Fig. 20 is a side, and fig. 21 a front view of a pair of pen com-passes of this class. The use of such instruments is confined to. very small circles, of half or three quarters of an inch in radius atthe most. In the example we have selected for illustration, thecentre leg is of brass, or german silver, and is in one piece withthe milled handle. It is also providedwith a needle point. The pen is madewith a spring-tempered steel shank, k,which lies in a groove cut in the centreleg, or body, and which is fixed to thelatter, at its top, by a screw. A smallscrew spindle, L, is passed through anopening in the pen shank, and is jointedto the centre leg, and a button, or nut,is passed on to the screw spindle outsidethe shank. This pen shank is so fixedas to have a tendency to stand out fromthe centre leg to the full extent of theinstruments range, and by turning thebutton of the screw, L, it may be forcedin or allowed to open, so as to give thenecessary adjustment. Fig. 22 is a sideelevation of a pair of slightly modifiedspring-and-screw compasses; it is shownwith a socket, carrying an engraversburin. An ivory handle is
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Keywords: ., bookcentury1800, booksubjectdecorativearts, booksubjectdrawing
