![]() If each window on each floor will be in the same position, this plumb line aligns several windows at once. Imagine someone standing on top of a tall building and lowering a line straight down. Where a plumb bob truly shines is when several objects need alignment over long vertical distances. While levels might be better for horizontal alignment, they require drawing a line out to match large components or multiple components over long distances. Without proper alignment from a plumb bob or level, you might accidentally build a house with crooked doors or windows.īoth a level or surveying plumb bob can be used for aligning components on the jobsite. Plumb bobs are often used to align components of a housing project or building. This weight, precisely machined for accuracy, is usually made from brass, steel, or plastic. It is used to determine a true vertical line.Ī plumb bob reel is often made from twisted threads of nylon or cotton with a pointed weight affixed to one end. If you aren't too familiar with construction or mathematics, you might be asking yourself, “What is a plumb bob?” A plumb bob is a simple tool, basically just a string with a carefully balanced weight tied to it. If necessary, plastic sheet should be carried to cover the drawing sheet from rain and dust.Plumb Bobs for Accurate Vertical Alignment Sharp hard pencil, good quality eraser, pencil cutter and sand paper to keep pencil point sharp are other accessories required for the drawing work. For important works fibre glass sheets or paper backed with thin aluminium sheets are used.Ĭlips clamps, adhesive tapes may be used for fixing drawing sheet to the plane table. The drawing sheet may be rolled when not in use, but should never is folded. Drawing Sheet and Accessories for DrawingĪ good quality, seasoned drawing sheet should be used for plane table surveying. Hence marking on the edges in this state indicates magnetic north–south direction.įig. When needle is centred (reading 0–0), the line of needle is parallel to the edge of the box. ![]() The box is provided with glass top to prevent oscillation of the needle by wind. At the ends of the needle graduations are marked on the box to indicate zero to five degrees on either side of the centre. use surveying equipment thats accurate to within a thousandth of a degree to orient their robots on startup, Coordinated often relies on a plumb bob. It consists of a 80 to 150 mm long and 30 mm wide box carrying a freely suspended needle at its centre (Ref. To get perfect level, spirit level should show central position for bubble tube when checked with its positions in any two mutually perpendicular directions. Spirit LevelĪ flat based spirit level is used to level the plane table during surveying (Fig.5). The plumb bob helps in transferring the ground point to the drawing sheet and vice versa also.įig. When the plumbing fork is kept on the plane table the vertical line (line of plumb bob) passes through the pointed edge of upper arm. The upper arm is provided with a pointer at the end while the lower arm is provided with a hook to suspend plumb bob. Plumbing fork is a U-shaped metal frame with a upper horizontal arm and a lower inclined arm. Plumbing Fork and Plumb Bobįigure 4 shows a typical plumbing fork with a plum bob. By providing telescope the range and the accuracy of line of sight is increased.įig. It is typically made of stone, wood, or lead but can also be made of other metals. It is a precursor to the spirit level and used to establish a vertical datum. If inclined sights are required vertical graduation helps in noting the inclination of the line of sight. According to Wikipedia, A plumb bob, or plummet, is a weight, usually with a pointed tip on the bottom, suspended from a string and used as a vertical reference line, or plumb-line. If horizontal sight is required bubble in the level tube is kept at the centre. The telescope is provided with a level tube and vertical graduation arc. The line of sight through the telescope is kept parallel to the bevelled edge of the ruler. It consists of a telescope mounted on a column fixed to the ruler. Plain alidade is not suitable in surveying hilly areas as the inclination of line of sight in this case is limited.įig: 2 – Plane Alidade Telescopic Alidade: ![]() ![]() The two vanes are provided with hinges at the ends of ruler so that when not in use they can be folded on the ruler. The vane with narrow slit serves as eye vane and the other with wide slit and having a thin wire at its centre serves as object vane. A sight vane is provided at each end of the ruler. Depending on the type of line of sight there are two types of alidade:įigure 2 shows a typical plain alidade. Always this edge is used for drawing line of sight. One edge of the ruler is bevelled and is graduated. It is a straight edge ruler having some form of sighting device.
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