By manufacture of rectilinear draughts as it was told above, directing straight lines rejki serve. And how to be, if it is necessary to execute draughts circular, polutsirkulnye, elliptic? Here other tool, other approach to work is necessary.
Draughts of a various kind of curvature are carried out by means of so-called voroby - a profile board with mobile radiusnoj rejkoj. Each kind of curvilinear draughts demands the tool corresponding to it. That it to make, it is necessary to define first of all the centre of curvature and length of radius of each given draught.
We Will begin with the most simple draught - polutsirkulnoj arches (fig. 75).
a Fig. 75. Draught polutsirkulnoj arches
Here to find the curvature centre easily: as the arch represents half of circle, its centre lies on the middle of width of an aperture. On diameter of the future arch place rejku with the probe in the centre. Voroba on the rejke has an aperture removed from the bottom profile side voroby on distance of radius of an arch. Having planted rejku voroby on the probe, working conducts a profile board on a circle, extending the necessary profile.
The Center in flat (or segment) an arch (fig. 76) lies on half of width of an aperture on crossing of lines of heels of an arch. In this point also put rejku with the probe, placing on it rejku voroby, and conduct a profile.
a Fig. 76. Draught of a flat arch :
1 - the centre; 2 - voroba; 3 - a heel
Can happen that draught has the big radius of curvature (an arch so bed curtains that the curvature centre settles down even somewhere under a floor) then draught carry out without voroby. For this purpose do curves - curvilinear directing (fig. 77) and on them conduct a template. Curves carry out from pine reek. That they did not break, them presoak in water. On one party rejki to half of its width through 5... 6 sm do prosaws and bend rejku that prosaws have converged.
a Fig. 77. Manufacturing curvilinear directing
Curvilinear directing it is possible to cut simply from a board.