Shows how to use a transit to locate a building correctly on the lot, plan proper grades with minimum excavation, find Building Layout Author, W.P. Jackson. Building Layout,WP Jackson. Shows how to use a transit, to locate a building correctly on the lot, plan grades with minimum excavation, find utility lines. : Building Layout () by W. P. Jackson and a great selection of similar New, Used and Collectible Books available now at great.
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Explains how to plan sewer connections, level a foundation that’s out of level, use a story pole and batterboards, work on steep sites, and minimize excavation costs. Chapter 1 The Transit A transit is used to measure horizontal and vertical angles. An engineer normally measures angles from the north-south meridian in surveying, so the engineer’s transit is equipped with a compass.
Building Layout – W. P. Jackson – Google Books
The builder’s or contractor’s transit, or transit-level, does not normally include a compass because buildings are laid out from an existing fixed point at or near the building site, such as the lot corner stake or monument.
A theodolite is essentially a more precise transit. Instead of a vernier scale, a theodolite is equipped with an optical micrometer scale. Figure shows the accuracy of these readings. The theodolite has an optical plummet, and the sensitivity of the level tube is usually 45″, or better.
Theodolites are used d.p.jackson precision work is essential. The operation of a builder’s transit or transit-level is not complicated. You don’t need an engineering degree or any technical knowledge to use one. More and more trades are using them to save time, cut costs, and insure accuracy in their work. There are three main parts layot any transit — the telescopethe leveling vialand the circle.
The degree of magnification of a telescope is called its power x. For example, a 20x telescope makes a distant object appear 20 times closer than if viewed with the naked eye. Crosshairs in the telescope permit the object sighted to be centered in the field of view. The power of the telescope can vary. The less expensive instruments have a lower power and are used for shorter range. An 18x instrument is usually used in work up to about feet. A 26x instrument may be used for work up to feet.
Telescopes come in one of two types: The fixed lens type has a fixed power, such as 18x or 26x. The variable powers of the zoom lens type depend on the model of the instrument; some adjust from 18x to 34x, others from 24x to 37x.
The advantage of the zoom lens is that it compensates for dim light and changes in distance. Leveling vials are available in various degrees of sensitivity. For precision work use a more sensitive vial. A level vial with a sensitivity of 90 seconds ” per 2 mm is more sensitive than one whose sensitivity is 14 minutes ‘ per 2 mm.
A vial with a sensitivity of 45 seconds ” per 2 mm is more sensitive than one with a 90 seconds ” per 2 mm sensitivity. Level tube sensitivity is explained later in the chapter.
It is marked in degrees and has a vernier scale that subdivides each degree in minutes on the better models. Instruments designed for still greater precision have a vernier that further subdivides each minute into seconds. Figure shows what different vernier readings mean in linear distance. The theodolite is recommended for work that requires greater precision than an instrument with a 20 second vernier reading. See Figures and These are extremely precise instruments. The optical plummet is a device for centering a transit over a point.
It replaces the plumb bob used in most transits. By sighting horizontally through a right angle prism, you see the point over which the transit is centered. When the instrument is properly set up it is directly over the mark.
The optical plummet serves the same purpose as a plumb bob, but is more accurate because it is not affected by the wind. Purchase the most precise transit you can afford. You may not need that degree of precision now, but you probably will need it later when your skills increase and you take on other types of jobs. Since you use a transit for its accuracy, there is no substitute for an accurate instrument regardless of the size of the job.
Figure shows a transit with a 20 second vernier reading.
The divisions on the circle and vernier are very fine. It takes practice to read a vernier with this precision.
Figure shows two theodolites, each with a micrometer scale. The TAT theodolite reads directly to 20 seconds on the optical micrometer. The TAT theodolite reads directly to 10 seconds on the optical micrometer.
As shown in the illustration, both horizontal H and vertical V circles are viewed simultaneously. This helps you make bbuilding readings. The right transit for you depends on your job requirements. The range of the work and the accuracy required are two factors you must consider before selecting any instrument. Be sure the transit you select has the power, the precision, and the versatility you need to meet all your requirements buildding the present and the bkilding.
The more sensitive the level tube, the greater the precision that may be obtained. Level tubes are ground to specific radii. If the radius is large, a small vertical movement on one end of the tube causes a large displacement of the bubble.
If the radius is small, the same vertical movement causes only a small displacement of the bubble. Thus the radius of the tube is a measure of its sensitivity. The more sensitive the level tube, the longer it takes to center the bubble. A bubble that byilding more with small movement takes longer to bilding with each w.p.jacksob of the leveling screw.
When the bubble moves even slightly on any transit, you will see a movement in the line of sight as indicated by the crosshairs in the field of vision.
Table shows the radii of level tubes of different sensitivities. The greater the precision of the transit, the more sensitive is the level tube built into it. An instrument whose vernier only reads to 15 minutes would probably have a level tube with a sensitivity of 8 to 14 minutes or “” per 2 mm. An instrument with a 5 minute vernier reading would probably have a level tube whose sensitivity would be from 90 to seconds per 2 mm, layojt an instrument with a 1 minute vernier reading would probably be in the 60 to 75 seconds per 2 mm sensitivity w.p.jsckson.
The more precise instruments whose vernier or optical micrometer scales read in the seconds would have level tubes in the 20 to 45 seconds sensitivity range.
Level tube sensitivity is normally given as the number of seconds of arc per 2 mm division on the tube. In most units, the markings on the level tubes are 2 mm apart. This means that for each w.p.jackkson mm the bubble moves in the tube, it forms an angle equal to the sensitivity of the arc given. So a level tube with a sensitivity of 45 seconds per 2 mm would form an angle of 45 seconds at a radius of 30 feet for each 2mm division the bubble moves in the tube.
A level tube with a sensitivity of 90 seconds per 2 mm would form an angle of 90 seconds at a radius of 15 feet for buipding 2 mm the bubble in the tube moves.
A tube with a sensitivity reading of 8 minutes seconds would form an angle of 08′ 00″ at a radius of 2 feet 10 inches 2′” with each 2 mm movement of the bubble. The transit is designed to produce precision work.
Building Layout – Surveying Guides – Books and Software – Craftsman Book Company
But if it is not set up and leveled properly, accurate work is impossible regardless of how accurate the instrument is. Make sure your instrument is in perfect adjustment before you follow the instructions below. The transit is usually set up w.p.jaackson a fixed point such as a tack in a stake, an iron pin or a crossmark in a concrete monument. The manual that comes with each transit gives step by step instructions for setting up and leveling the instrument.
They will not be covered here, but you should know the reason for some of the operations and how they can affect the accuracy lyout your work. Set the tripod on firm ground and make buildinv the tripod points are stuck well into the ground.
If you are setting up on a paved surface, be sure the points are secure. Position the tripod legs so the center of the tripod head is approximately over the centering point and the tripod head appears level.
If the center of the tripod head is not approximately over the point, centering the transit with the plumb bob or optical plummet isn’t possible. You must then reposition the tripod. If the tripod head is too far out of level, the transit can not be leveled with the leveling screws. Leveling layouy the most important operation you perform before you use your instrument.
The accuracy in all readings and surveying tasks requires a ,ayout instrument at all times.
Figure shows a serious w.p.jackaon due to an instrument out of level. Points A, B, and C have been located. Buipding instrument is set up over A to locate D. See Detail 1, Figure The instrument is set up over A, centered over the tack and properly leveled. But after setting up at A, say the instrument is not level. The vertical axis is not centered over A, even though the plumb bob might be.
Instead it will be centered over another point, a, resulting in an erroneous reading. This gives d instead of D.