1st year trade resource package -...
TRANSCRIPT
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Randwick Carpentry
1st Year Trade Resource Package
Book 6 – Set Out and Levelling
RANDWICK COLLEGE Carpentry & Joinery
Set-Out & Lev / 2016 / V1
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Publishing Details: These notes were prepared and compiled at Randwick TAFE College, to be used as a student workbook / learning recourse. Compiled of existing trade text as noted on topic pages Accompanying Text: Nil First Published February 2016 Copyright of this material is reserved to TAFE NSW. Reproduction or transmittal in whole or part, other than for the purposes and subject to the provision of the Copyright Act, is prohibited without the written authority of TAFE NSW.
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Contents Levelling ......................................................................................................................................... 4 Levelling Terms (Text from TAFE ‘Carp’ Set-out and levelling skills) ........................................ 9 Level Book Terminology ............................................................................................................ 12 Some Typical Level Run Diagram’s and booking sheets ............................................................. 16 Site Set Out ................................................................................................................................... 20 Additional Text ............................................................................................................................. 20
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Levelling Levelling is the measurement of geodetic height using a levelling instrument and a level staff. (Geodetic is ‐ a branch of applied mathematics, in this case used in land surveying). Levelling may also refer to in relation to Concrete, where we use the same or similar levelling instruments, to obtain the correct surface levels for the finished concrete surface. The term levelling in general can be used in relation to many building construction applications. Levelling equipment can be:
Spirit level
Plumb bob
Water level
Automatic levels
Staff
Theodolite
Laser Level
Tripod Spirit level ‐ a device consisting of a sealed glass tube partially filled with alcohol or other liquid, containing an air bubble whose position reveals whether a surface is perfectly level.
Image: http://www.a1-equipment.co.uk/category/spirit-levels/
Plumb bob - is a weight, usually with a pointed tip on the bottom, that is suspended from a string and used as a vertical reference line, or plumb‐line. It is essentially the vertical equivalent of a "water level".
Image: http://www.amazon.com/Stanley-47-973-8-Ounce-Brass-Plumb/dp/B00009OYGQ
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Water level ‐ is a device used for matching elevations of locations that are too far apart for a spirit level to span. The simplest water level is a section of clear tubing, often filled with a food colouring to make it easier to see.
Image: http://www.bateau2.com/howto/foam3.php
YouTube video on using a water level: Level Anything with Water
Automatic Levels – often called a dumpy level, or builder's auto level, leveling instrument, or automatic level. Which is is an optical instrument used to establish or check points in the same horizontal plane. This is an instrument that requires two people to operate it, and also requires the use of a staff.
Image: http://nikon.com/about/feelnikon/recollections/r27_e/index.htm
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Some good tutorial video’s are available via the following links: How to set up a level, (eg is a leica instrument) however the principle using the levelling screws is the same for all instruments. Leica set up
The next are a series of tutorial videos from TAFE oten, and provide very good basic information on the survey and levelling basics. Survey 1 – Introduction to levelling Survey 2 – Taking a level reading Survey 3 – Two peg test Survey 4 – Short level run Survey 5 – Making a contour plan Staff ‐ A level staff, also called levelling rod, is a graduated wooden or aluminum rod, used with a levelling instrument to determine the difference in height between points or heights of points above a datum surface.
Image: http://www.aliexpress.com/item/Leveling-staff-staff-rods-stadia-rods-5m-5m-staff-10-pcs-LR2-Aluminum-whole-sale-and/370287300.html
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Theodolite ‐ a surveying instrument with a rotating telescope for measuring horizontal and vertical angles.
Image: http://www.instrumentsmart.com/survey-instruments.html
The next are a series of tutorial videos from TAFE oten, and provide very good basic information on the instrument, however some of this work does go beyond your trade course, more a cert IV level instruction.
Theodolite 1 – intro and set up Theodolite 2 – collimation in altitude Theodolite 3 – collimation in azimuth Theodolite 4 – Vertical and Horizontal measurement
Laser Level ‐ a laser level or laser measuring tool is a hands‐free distance measurer, it can be operated by one person unlike the auto level. You first set up the instrument on a tripod, typically these are self‐levelling. Then the instrument produces a laser beam that is projected on a horizontal level plain, which is caught by a ‘receiver’ which is located on the staff. Once the instrument is set up, the same operator can leave the instrument and take readings themselves while holding the receiver on the staff. Image: http://www.shaughnessyrentals.com/equipment-rental/construction/self-leveling-laser-level
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Other forms of laser levels, used for simpler tasks, like installation of cabinetry, flooring and ceilings.
Image: http://www.blessthisstuff.com/stuff/technology/tools/pen-line-laser-level-by-bosch/
Cross line laser level, image: http://www.amerashop.it/it/livelli-laser/508-tracciatore-e-puntatore-laser-52xl-spektra.html
Image: http://www.directindustry.com/prod/flex/product-111921-1064803.html
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Tripod ‐ A surveyor's tripod is a device used to support any one of a number of surveying instruments, such as theodolites, auto levels and so on.
Image: http://www.archtools.eu/surveyors-archaeology-tripod.html
Levelling Terms (Text from TAFE ‘Carp’ Set‐out and levelling skills) Contour lines These are imaginary level lines on a plan, which represent the rise and fall or humps and hollows of the earth’s surface. These lines are like the water tide marks found on any beach, which are left in the sand when the tide goes out. When used on a site plan they give the designer information related to heights, which will enable drawings of a structure to be produced showing relative heights to ground level. Where these lines are close together on a plan it indicates a steep slope and when they are far apart it indicates a gentle slope. It also provides useful information for quantity surveyors, estimators, excavators and builders so they may calculate the amount of soil to be removed or the filling required to create a level area. Each contour line is given a reduced level which relates to the job datum or bench mark. Image: http://www.ownerbuilder.com/drawings.shtml
Contour interval This is the height difference between one contour line and the next contour line. Where the surface of the site has a gentle slope the contour lines are spaced far apart on plan but the contour intervals may only have a 100mm height difference, whereas to retain the same spacing of contour lines on plan for a steeply sloping site the contour intervals may be 1.000m or more. Contour lines have a reduced level measurement shown on them, and the difference in height between adjacent contour lines becomes known as the contour interval.
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Image: http://www.cita.utoronto.ca/~murray/GLG130/Exercises/EXE2html.html Datum This is any fixed reference point where the height or elevation of that point is known. A position on a job site may be selected as a fixed reference point and is given an assumed height, eg. 100.0m, and all heights for the construction will be referred to that point for the duration of the job. The nominated fixed point may be set on a permanent local structure, tree, fence post, etc., and is then referred to as the job datum. It is shown on plan in the form of a symbol, as shown below:
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Bench mark This is a fixed point of reference which has a known height or elevation, and is formally recorded for use by qualified Surveyors. There is usually a permanent mark either chiselled into a concrete kerb, a metal plug set in a path or kerb, lines and arrows carved into the face of a mature tree, marked with paint on the retaining walls at railway stations, a stamp or metal plug on the plinth of a building or monument, etc. In Sydney all bench marks are given a height in relation to the average tide mark, which is set in a brass plate on the north wall of Fort Denison in Sydney harbour. Reduced Level (RL) This is a term given to the height or elevation of a point above or below a known point, such as the given datum. Example: The assumed height of the Datum has an RL of 50.000m, and a point some distance away is set 1.000m above this datum then this point would have an RL of 51.000m. If a point on the other side of this datum was say 2.000m below, it would have an RL of 48.000m, and so on. The assumed height of the datum is always given as a large measurement so that points lower than the datum will not be recorded as a negative measurement.
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Line of Collimation This is the line of sight taken through the eyepiece, centre of the cross hairs of the telescope and the centre of the object being viewed. It is important to note that the instrument should be set at a height to suit the viewer so it is not necessary to bend or stretch to take a reading as this may lead to ‘an error of parallax’ occurring, which means looking through the eyepiece at an angle above or below the cross hairs resulting in an incorrect reading. This imaginary line remains straight and level in all directions as the telescope is rotated to provide a constant common line from which to measure so an accurate picture of the surface being surveyed can be created. In other words, the surface is measured in relation to the height of the instrument, from the centre of the telescope. Once the reduced level of the datum or bench mark is known, all other sights may also be given a reduced level which is either above or below the datum or bench mark. This information can be used to create a contour map of the site or area being surveyed so builders and designers can use it to determine falls, cut and fill requirements, structural design requirements, etc.
Level Book Terminology Backsight This is the first sight taken and recorded after the levelling instrument is set up. It is usually taken from the Datum or Bench mark or Job Datum to establish a starting point and show the height of the instrument in relation to that point. Intermediate Sight These are all the sights taken at nominated positions, known as stations, to enable a running calculation of rises and falls, which are used to determine the reduced levels. Foresight This is the last sight taken before the instrument is moved to another location or when a traverse is complete. Change Station This is a point at which two readings are taken because the instrument has to be moved due to not being able to see the next intermediate sight from that set up position. The first sight taken at a change
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point will be recorded as a Foresight, because it is the last sight taken before the instrument is moved, and the second sight taken will be recorded as a Backsight, because it is the first sight taken once the instrument is set up again. This procedure allows the traverse to continue which in turn allows the reduced levels to continue in sequence, giving the impression that there was no obstacle or disruption in the levelling process. Rise This is a measurement calculated by subtracting the last two sights from one another, i.e. an intermediate sight from the backsight or an intermediate sight from an intermediate sight or a foresight from an intermediate sight, etc. If the height or elevation of the second sight is less than the first sight, then the difference in measurement will be recorded as a ‘rise’. Fall Same method of calculation as for the rise, but if the height or elevation of the second sight is greater than the first sight, then the difference will be recorded as a ‘fall’. Reduced Level These are the finished calculated heights or elevations in relation to the original reduced level, which was recorded as the identified Datum or Bench Mark. To calculate these levels it is necessary to add the rises and subtract the falls. Reading the staff: These come in different forms, look at the ones shown below.
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Some Typical Level Run Diagram’s and booking sheets
Image source: http://slideplayer.com/slide/4827474/
Image source above and following example calculations: http://www.boeingconsult.com/tafe/ss&so/survey1/level/notes-sur1.htm
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Procedure (for above diagram):
1. Set up the leveling instrument at Level position 1.
2. Hold the staff on the Datum (RL+50 m) and take a reading. This will be a backsight, because it is
the first staff reading after the leveling instrument has been set up.
3. Move the staff to A and take a reading. This will be an intermediate sight.
4. Move the staff to B and take a reading. This also will be an intermediate sight.
5. Move the staff to C and take a reading. This will be another intermediate sight.
6. Move the staff to D and take a reading. This will be a foresight; because after this reading the
level will be moved. (A changeplate should be placed on the ground to maintain the same level.)
7. The distance between the stations should be measured and recorded in the field book (see
Table 1)
8. Set up the level at Level position 2 and leave the staff at D on the changeplate. Turn the staff so
that it faces the level and take a reading. This will be a backsight.
9. Move the staff to E and take a reading. This will be an intermediate sight.
10. Move the staff to F and take a reading. This will be a foresight; because after taking this reading
the level will be moved.
11. Now move the level to Leveling position 3 and leave the staff at F on the changeplate.
Now repeat the steps describe 8 to 10 until you finished at point J. Field procedures for levelling All staff readings should be recorded in the field book. To eliminate errors resulting from any line of sight (or collimation) backsights and foresights should be equal in distance. Length of sight should be kept less than 100 metres. Always commence and finish a level run on a known datum or benchmark and close the level traverse; this enables the level run to be checked. Booking levels There are two main methods of booking levels: rise and fall method (on following page) and height of collimation method (last example)
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Table 1 Rise & Fall Method
Back- sight
Inter- mediate
Fore- sight
Rise Fall Reduced
levelDistance Remarks
2.554 50.00 0 Datum RL+50 m
1.783 0.771 50.771 14.990 A
0.926 0.857 51.628 29.105 B
1.963 1.037 50591 48.490 C
1.305 3.587 1.624 48.967 63.540 D / change point 1
1.432 0.127 48.840 87.665 E
3.250 0.573 0.859 49.699 102.050 F / change point 2
1.925 1.325 51.024 113.285 G
3.015 0.496 1.429 52.453 128.345 H / change point 3
0.780 2.235 54.688 150.460 J
10.124 5.436 7.476 2.788 54.688 Sum of B-sight & F-sight,Sum of Rise & Fall
-5.436 -2.788 -50.000 Take smaller from greater
4.688 4.688 4.688 Difference should be equal
The millimeter reading may be taken by estimation to an accuracy of 0.005 metres or even less.
1. Backsight, intermediate sight and forsight readings are entered in the appropriate columns on different lines. However, as shown in the table above backsights and foresights are place on the same line if you change the level instrument.
2. The first reduced level is the height of the datum, benchmark or R.L. 3. If an intermediate sight or foresight is smaller than the immediately preceding staff reading then
the difference between the two readings is place in the rise column. 4. If an intermediate sight or foresight is larger than the immediately preceding staff reading then
the difference between the two readings is place in the fall column. 5. A rise is added to the preceding reduced level (RL) and a fall is subtracted from the preceding RL
Arithmetic checks While all arithmetic calculations can be checked there is no assurance that errors in the field procedure will be picked up. The arithmetic check proves only that the rise and fall is correctly recorded in the appropriate rise & fall columns. To check the field procedure for errors the level traverse must be closed. It is prudent to let another student check your reading to avoid a repetition of the level run. If the arithmetic calculation are correct, the the difference between the sum of the backsights and the sum of the foresights will equal:
the difference between the sum of the rises and the sum of the falls, and
the difference between the first and the final R.L. or vice versa. (there are no arithmetic checks made on the intermediate sight calculations. Make sure you read them carefully)
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Table 2 Height of collimation method (height of instrument)
Back- sight
Inter- mediate
Fore- sight
Height ofcollimation
Reducedlevel
Distance Remarks
2.554 52.554 50.00 0 Datum RL+50 m
1.783 50.771 14.990 A
0.926 51.628 29.105 B
1.963 50591 48.490 C
1.305 3.587 50.272 48.967 63.540 D / change point 1
1.432 48.840 87.665 E
3.250 0.573 52.949 49.699 102.050 F / change point 2
1.925 51.024 113.285 G
3.015 0.496 55.468 52.453 128.345 H / change point 3
0.780 54.688 150.460 J
10.124 5.436 54.688 Sum of B-sight & F-sight, Difference between RL's
-5.436 -50.000 Take smaller from greater
4.688 4.688 Difference should be equal
1. Booking is the same as the rise and fall method for back‐, intermediate‐ and foresights. There
are no rise or fall columns, but instead a height of collimation column.
2. The first backsight reading (staff on datum, benchmark or RL) is added to the first RL giving the
height of collimation.
3. The next staff reading is entered in the appropriate column but on a new line. The RL for the
station is found by subtracting the staff reading from the height of collimation
4. The height of collimation changes only when the level is moved to a new position. The new
height of collimation is found by adding the backsight to the RL at the change point.
5. Please note there is no check on the accuracy of intermediate RL's and errors could go
undetected.
The rise and fall method may take a bit longer to complete, but a check on entries in all columns is carried out. The RL's are easier to calculate with the height of collimation method, but errors of intermediate RL's can go undetected. For this reason students should use the rise and fall method for all leveling exercises.
The site the above examples came from http://www.boeingconsult.com/tafe/ss&so/survey1/level/notes‐sur1.htm have other good examples of relative calculations, if you wish to further your knowledge.
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Site Set Out
Additional Text The following text is an extract from the Carpentry and Joinery Book by C Porter ad K Tooke, it is an English based text, so some icons may seem a little different, however the overall information is the same in any set out activity. If you come across a term that is different, ASK your teacher to explain it, and correct it in your notes.
Setting-out involves different processes; one or more of which willbe necessary before starting any constructional work. They includethe following:
● linear measurement,● working to a straight line,● setting out angles,● setting out concentric curves,● establishing a datum,● levelling,● vertical setting-out.
The accuracy with which these are carried out will determine thefinal outcome of the work.
Measuring distances greater than 1 m generally means using aretractable tape measure.
Available in a variety of lengths, made of steel or fibreglass coatedwith polyvinyl chloride (PVC) (linen tapes are now obsolete becauseof their tendency to stretch, they have been superseded by PVC-coated fibreglass types). Tapes under 10 m in length have a built-inlockable automatic retractable rewind mechanism (see Volume 1,Section 5.1.3), longer tapes are rewound manually.
Digital measuring tapes are available like the one shown in Fig. 1.1.Its liquid crystal display (LCD) panel is battery operated with auto-matic cut-off – measuring accuracies of �1 mm can be expected upto 5 m.
In use, the accuracy of a measuring tape will depend on:
● the clarity of its graduations;● whether it is held in the correct plane (Fig. 1.2);
1.1.1 Measuring tapes
Site setting-out1
1.1 Linearmeasurement
● the amount of, or lack of, tension being applied to the tape – veryimportant when measuring long distances;
● readings being correctly taken from left to right.
Measurement errors frequently occur when measurements are trans-ferred from drawing to site. An example of how errors can bereduced is shown in Fig. 1.3.
Figure 1.3(a) represents a plan view of individually dimensioned wallrecesses. If, on transfer, one of these distances was wrongly meas-ured it would not only affect the overall length of the wall, but alsohave a cumulative effect on all those measurements which followed.
Fig. 1.2 Using a tape measure
2 Site setting-out
DMBS
Metric & imperialtape measure
Memory/add button
‘Add’ casing length button
Measuring unit(m/mm or ft/in) button
BO
SC
H
Cancel button
Retrieve total button (display)
‘On’ button
Rewind button LCD – display
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4
DISPLAY
C
MODE
ON
�
M�
Fig. 1.1 Bosch digitalmeasuring tape
Keep tape taut and in the correct measuring plane
Possible inaccuracy when not measuring parallelto the required plane
Measuring plane
For example, an error between points B and C would result in pointsD, E, F, and G being wrongly positioned.
Figure 1.3(b) shows how measurements can be transferred by using‘running measurements’. The tape is run once from A to G (totallength), all intermediate measurements are referred back to A asshown in the build-up of the running total.
These instruments are intended to measure distances (lengths, heights),a typical example of use is shown in Fig. 1.5. When required theinstalment can also calculate areas and volumes.
They operate by projecting an intensive beam of light (laser beam)onto a wall or object. When switched on to the required programme(Fig. 1.4) the length of the beam is automatically measured, theresulting distance, area, or volume is then automatically portrayedonto the LCD panel.
Safety (also see section 1.7.8)
As with any instrument or tool using an exposed laser beam asdescribed in Fig. 1.4, special safety precautions must be taken beforeand during their use; for example:
● Operating manual (operational safety instructions) must be readcompletely, understood, and strictly followed before the instru-ment or tool is used.
● Operatives must be informed of the operating dangers and pro-tective measures.
● Never remove warning signs from the unit.● Never look into a laser beam, especially not with optical aids
such as glasses or binoculars, etc.● Laser-viewing glasses are not protective glasses against laser
beams.
1.1.2 Laser digitaldistance metres (Fig. 1.4)
Linear measurement 3
Fig. 1.3 Transferringmeasurements from a drawing to site
● Never direct a laser beam at persons or animals.● Before using for the first time a practical demonstration of safe
use must be given by a competent person.
Figure 1.6 shows how horizontal measurements over sloping orobstructed ground are carried out. Pegs or posts are positioned on or
1.1.3 Sloping sites
4 Site setting-out
Before using for the first time a practical demonstration of safe use must begiven by a competent person.
Operational safety instruction manual must be read completely and strictlyfollowed.
Laser beam – laser class 2 (EN 60825-1:1997)
Never look into a laser beam, especially not with optical aids such asglasses or binoculars, etc.Never direct a laser beam at persons or animals.
Measure – function buttonLCD display
2
LASER
On/off button
Continuous measurement
Laser beam
Guide groove for multi-function box(optical extra for use with tripod –also serves as a case with a belt clip)
Aligning aid
BOSCH
BOSCH
DLI 30 laser plus
88.888 m
88.888 m
88.888 m
88.8.8.8 m
No. 1
BOSCH
Protective soft case
Indirect length measurement
Volume measurement
Area measurementLength measurement
Display lighting button
Fig. 1.4 Bosch Laser ‘Rangefinder’
driven into the ground to act as intermediate measuring stations, eachdistance is registered separately to produce a final running total.
Simple measuring aids like those shown in Fig. 1.7 are very accurateand useful. Probably the simplest method as shown in Fig. 1.7(a)involves the use of a small-sectioned length of timber as a ‘rod’. Inthis case the actual brick reveal distances are transferred directly tothe rod with a pencil or marker. Measurement transfers of this natureare often made from site to workshop where an item of joinery has tofit over or into a specific space or opening.
1.1.4 Transferringmeasurements
Linear measurement 5
BOSCH
BOSCH
BOSCH
BOSCH
10 m
Note: The instrument is also capable of measuring lengths by taking indirect readings
1220
0500
1225
1490
42857850
10000
0.5
m
2.45
m
As the ‘Rangefinder’ is moved horizontally or verticallyfrom a solid object or surface – distances areregistered on the LCD panel
2450
Fig. 1.5 Measuring distances using a Bosch Laser ‘Rangefinder’
Posts (temporary) acting as measuring stations
Staff held vertical
Horizontal lines
Staff held vertical
Sloping ground
Sloping and uneven ground
Fig. 1.6 Measuring slopingsites
A ‘pinch rod’ (Fig. 1.7(b)), on the other hand, consists of two shortlengths of timber, one of which slides on the other to enable its totallength to be varied. This is ideal for measuring between openings –once set, the pieces are held in that position with nails or a cramp, etc.
As shown in Fig. 1.8 a more sophisticated method of taking either vertical or horizontal internal measurements is by using a Rabone‘Digi-rod’. The rod is fabricated from steel, and consists of a bodywhich houses a battery-operated LCD panel, level and plumb vials to ensure accurate readings, and telescopic sections which are manu-ally extended. As the rod is extended the reading is simultaneouslyregistered on the LCD.
6 Site setting-out
Plan of brickwork
Length of timberTransfer lines
Note: Left-hand (LH) side and right-hand (RH) side market on timber face
Plan of opening
Bolt with wing nut
Slide close
Sliding ‘Pinch rod’ – can be used to establishand retain measured distances betweenreveals or surfaces.
Slide open
LH RH
(a)
(b)
Fig. 1.7 Useful devices fortransferring measurements
Fig. 1.8 Using a digital measuring rod to measure the distance between two vertical surfaces
Most work carried out by the carpenter and joiner relates to or froma straight line. Straight lines are easily established without the helpof optical or other devices, by using the following methods:
● a length of string, cord, or wire held taut;● a predetermined flat surface such as a straight-edge;● visual judgement – sighting.
As shown in Fig. 1.9(a), the line can be held or left temporarily inplace whilst operations are carried out, Figure 1.9(b) shows howsmall obstacles can (particularly over long distances) interfere withthe line.
The line is first coated with chalk (blackboard chalk) – either manu-ally, or by using a proprietary device that automatically coats the linewith powdered chalk as it is withdrawn from the case. The line isthen stretched tight as shown at 1.9(c), then lifted just off the floormidway between its span and let go. On removing the line, it will be found that the chalk has left a clear impression of the line on thesurface.
A length of timber or other similar material of a sectional size cap-able of resisting deflection when only supported at either end. Figure1.10 shows one example of where a straight edge could be used –testing for misaligned posts or joists, etc. can quickly be recognised.
Fig. 1.9 Using a builder’s line to leave a straight chalk lineimpression on a flat surface
Straight lines 7
1.2 Straight lines
1.2.1 Builder’s line
1.2.2 Chalk line
(a)
(b)
(c)
1.2.3 Straight edges
Sighting a straight line
Neither the line nor the straight edge would be suitable for coveringlong distances – the line would sag and the straight edge for obviousreasons be impracticable. Without resorting to optical devices orother devices, sighting over long distances is possible by a methodknown as ‘boning’. Figure 1.11 shows how boning is carried out byusing a minimum of three ‘boning rods’, usually tee shaped. The rodsare held or stood above the required line. The middle one is pos-itioned at a predetermined point until its adjustment is such that it isin line with the line of sight – at which point the tops and bottoms ofall the boning rods are in a straight line with each other.
Let us first consider right angles (90° angles), and three simple meth-ods of forming them:
(i) by measurement – using the principle of a 3:4:5 ratio;(ii) by using a builder’s square;(iii) by using an optical site square.
1.3 Right angles
8 Site setting-out
Fig. 1.11 Sighting or lining along a straight line over a long distance
Note: A straight line is not necessarily a level line.
Fig. 1.10 Testing formisalignment with a wood straight edge
That is to say that, if the lengths of the sides of a triangle are in a ratioof 3:4:5 (no matter what size of unit is used), and are measured usingthe same unit, the resulting triangle will be right angled.
This principal stems from the theorem of Pythagoras, which statesthat in a right-angled triangle the square of the hypotenuse (thelongest side) is equal to the sum of the squares of the other two sides.
Consider the triangle in Fig. 1.12, where side ‘a’ is 3 units long, side‘b’ is 4 units long, and side ‘c’ (the longest side) is 5 units long:
a 2� 32
� 9
b2� 42
� 16
c2� 52
� 25
That is a2� b2
� c2
In other words, in a triangle with sides in the ratio 3:4:5, the squareof the longest side is equal to the sum of the squares of the other twosides; therefore, such a triangle must be right angled.
Figure 1.13 shows three ways of applying this principle to practicalsituations; for example:
(a) Positioning a timber sole plate for a screen or partition at rightangles to an abutting wall.
(b) Pegging out ground work to form a right-angled comer.(c) Positioning a corner brace to temporary hold a timber frame
square.
1.3.1 Right anglesusing a 3:4:5 ratio
Right angles 9
Note: The same principle will alsowork with sides in the ratio5:12:13 or 6:8:10.
52 � 25
42 � 16
32 � 9Note: This symbolsignifies aright angle
Applying the theoremof Pythagoras to aright-angled triangle
c5
3
a
4b
Fig. 1.12 Using a ratio of 3:4:5to form a right-angled triangle
As can be seen from Fig. 1.14 this is a purpose-made timber setsquare. Its size will depend upon where and for what it is used. Auseful size could be built around a triangle with sides 900, 1200, and1500 mm, which fulfils the 3:4:5 rule; for example:
Side ‘a’ � 3 � 300 � 900 side ‘b’ � 4 � 300 � 1200 side ‘c’ � 5 � 300 � 1500
Its application is shown in Fig. 1.14.
As shown in Fig. 1.15 optical site square consists of two fixed-focustelescopes permanently set at right angles to one another, each beingcapable of independent movement within a limited vertical arc. Onceattached to its tripod, a circular spirit level set into the head enablesthe datum rod, which is suspended below the tripod, to be positionedplumb over a fixed point or peg.
Figure 1.16 show the stages in using an optical site square to set outa right angle.
Fig. 1.14 Traditional builder’ssquare
10 Site setting-out
Proposed screen/partition etc.
Marks on wall
Peg
5 m
3 m 4 m
4
35
(b) Pegging out a right angle
(c) Temporary brace for large open frames
Building line
Move untilmarks coincide
5
43
(a) Setting for floor positions
Fig. 1.13 Using the ratio of 3:4:5 to form right angles on site
1500 mm
900 mm 1200 mm
Diagonal brace set at 45°
Using a ratio of 3:4:5
Dovetail halving
Dovetail halving
Half lap90°
45°
5
3
(c)
(b)(a)
4
1.3.2 Builder’s square
1.3.3 Optical sitesquare
1. Measure the length of one side of the rectangle and mark the ends ‘A’ and ‘B’ with a ‘cross’ or ‘peg’. A nail should bepartly driven into the top of each peg as a sight marker (see Fig. 1.16).
2. Set up the square at position ‘A’, then after positioning the datumrod over the cross or nail. Plumb the datum rod using the spiritlevel and by adjusting the tripod legs.
Fig. 1.16 Setting out a rightangle with an optical square
Right angles 11
Telescopeeyepiece
Telescopeeyepiece
360° spirit bubble
Fine traverseadjustment
Tripodmounting
Point Hollow
Datum rod
Adjustabletripod
Head
Traverse lock
Sight lines
90°
Plan view of sitesquare head
Note: Telescopes are set at right angles to one another – both move vertically
Floor mark Peg with nail(alternative ends ofdatum rod)
Site square head
Fig. 1.15 Optical site square
Move peg to right or left until in-lineC
Off Off
View through telescope
Fixed line or building line
Peg with nail
B
On
Site square set-up overnail or mark
A
3. From position ‘A’, rotate the head and lock it when the telescopeis in line with ‘B’ (Fig. 1.17(a)). Use the fine-adjustment knob tobring the cross-hairs (viewed through the telescope) exactly overthe cross, or nail head (see Fig 1.15), or floor mark (1.16).
4. Keeping the head in the same position, move round 90° to lookthrough the other telescope (Fig. 1.17(b)). Place a mark, or pos-ition a peg ‘C’, in line with the cross-hairs of the telescope andthe correct distance from ‘A’. The two sides ‘AB’ and ‘AC’ arenow at right angles.
5. Repeat the process from ‘B’ or ‘C’, or measure two lines paral-lel with those right-angled sides formed.
6. Diagonals must always be checked as shown in Fig. 1.18.
As an added bonus, this instrument can also be used to set workplumb (vertical), by raising or lowering the telescope about a hori-zontal axis so that its line of sight will follow a vertical path.
Fig. 1.17 An optical site squarein use
12 Site setting-out
As shown in Fig. 1.18 no matter which method of setting out is cho-sen, the perimeter or framework of a square or rectangle must haveboth opposite sides parallel and diagonals of equal length, as shownin Fig. 1.19(a).
Where corner squaring pegs interfere with constructional work, linesare extended outside the perimeter and repositioned onto nails or set into saw kerfs cut into the top of pegs or boards as shown inFig. 1.19(b). The corners are now located where the lines cross eachother, and the lines may now be removed or replaced at will.
Figure 1.20 shows how a rectangular building plot can be set outfrom a known ‘Building-line’. A ‘Building-line’ is a hypotheticalline, usually set down by the Local Authority to determine thefrontage of the proposed building. It may relate to existing buildingsor a fixed distance from a roadway.
Fig. 1.19 Setting out a rectangular area
Right angles 13
1.3.4 Application ofsquaring methods
Diagonals same length –frame not square
Opposite sides parallel –frame not square
A A
B
B
Opposite sides AA and BBmust be parallel andcorner-to-cornerdiagonal same length
(a)
Profile boards
Corner pegsremoved – linesextended toprofile boards
(b)
Fig. 1.18 Squaring techniques
1.4 Angles otherthan right angles
Once the building-line is established via pegs 1 and 2, the followingprocedures can be followed:
● Frontage distance can be determined with pegs 3 and 4.● Left-hand side line is set square from the building-line pegs 3 to 5.● Right-hand side line is set square from the building-line pegs 4 to 6.● Depth of building is marked with pegs 7 and 8.● Check for square as previously stated in Fig. 1.19(a).
These, with the aid of a builder’s line, indicate where corners, junc-tions or changes of direction occur. Figure 1.21 shows how theseboards are assembled and positioned in line with the proposed wallsand/or foundations, etc.
Timber stakes are driven into the ground and rails nailed to them;rails are positioned behind the stakes to resist the pull of the lines.
These angles are set out by using on-site geometry or by mechanicalmeans with the aid of either a Stanley or Smallwood Roofing Square(the roofing square, and its application in pitch roof construction is fea-tured in Chapter 8), or an angle measuring device as featured at 1.4.2.
Figure 1.22 shows a means of fabricating templates based on an equi-lateral triangle.
1.3.5 Profile boards
14 Site setting-out
Fig. 1.20 Setting out a rectangular building plot
Fig. 1.21 Using profile boardsto line out the position of a walland/or foundation
Angles other than right angles 15
Nail or saw kerfProfile boards
Profile boards used on open groundLines indicate corner position of astrip foundation or wall
Lines removedLines
All cross lines in positionBuilding line
Builder’s line
60°
Equilateraltriangle
Right-angledtriangle
Timber templatesconstructed
f to suit
f to suit
90°
30°120°
Other angles
Fig. 1.22 Fabricating angle templates
16 Site setting-out
4567
Hexagon –outside angle60°
Octagon –outside angle45°
8C
A B
C
Rad
Internal angles
60° 45°
Nailed jointsPlywood gusset plates
Rostrum, dais,display unit, or plinth
Semi-octagonalbay window, alcove,or partition
(a) Regular polygon geometry
(b) Semi-hexagonal and octagonal templates
(c) Typical applications
Fig. 1.23 Regular and semi-regular polygons andexamples of use
Figure 1.23 shows examples of where and how angles are applied tosimple regular and semi-regular polygon shapes.
These are figures of more than four sides, all of which are equal inlength.
1.4.1 Regular polygons
Figure 1.23(a) shows one geometrical method of setting out regularpolygons of five, six, and eight-sided figures; for example:
● Draw side AB.● Bisect AB to produce the centre line.● Erect the perpendicular BC.● Using radius AB, scribe arc AC from B across the centre line to
produce point 6.● Join AC to produce point 4.● Point 5 is midway between points 4 and 6.● Points 4, 5, 6, 7, 8, etc. are the same distance apart.
The numbered circle centre points are used to circumscribe theequivalent number of sides AB of the polygon.
Figure 1.23(b) shows how a semi-regular hexagonal and octagonaltemplate can be fabricated by using nailed plywood gusset platesover both sides where members intersect. Figure 1.23(c) shows howregular polygon shapes can be applied in practical situations.
There are many different proprietary devices on the market to helpthe carpenter and joiner measure and transfer angles. Those used inconstructing and assembling items of joinery were dealt with inVolume 1.
One worth mentioning here is the ‘Bosch digital angle measurer’ asshown in Fig. 1.24. it has an accuracy of � 0.1° with a measuringrange of 0° to 220°. Whether you are measuring a corner angle,mitre, or simply determining a bevel. By pressing the appropriatebutton the resulting angles are stored in its memory and displayed onthe LCD panel. Standard or rechargeable batteries power it.
Figure 1.25 shows a few examples of where this device can beemployed.
Angles other than right angles 17
Note: There are other methods ofconstructing Regular Polygons –see Chapter 4.
Number of sides Name
5 Pentagon6 Hexagon7 Heptagon8 Octagon9 Nonagon
10 Decagon
1.4.2 Angle measuringdevices
Each polygon has a specific name in relation to its number of sides;for example:
Figure 1.26(a) shows how a large circles, semicircles, and arcs can beformed by using a trammel board, pin and marker (in this case a pen-cil). We came across a trammel in Volume 1, Fig. 5.6 where it wasshown how proprietary trammel heads fitted over hardwood trammelbar were used to circumscribe small- to medium-sized circles and arcs.
Figure 1.26(b) shows a practical site method using a triangular tim-ber templates with differing apex(x) angles. Using this method, it isthen possible to scribe large segmental arcs between the two fixedpoints. Note that the greater the rise from the chord to the apex(x) thegreater the chord length (span).
A datum is a fixed point or horizontal line to which a height or depthcan be referred.
Before any levels can be taken on a building site, a fixed datum pointmust be established as shown in Fig. 1.27. This point is known as a
1.5 Circles, arcs,and segments
18 Site setting-out
Window for vertical alignment bubble
Window for LCD paneland controls
Extension arm (leg)
BOSCH
Hinge joint cover
LCD panel
Vial – containing bubble for horizontal alignment
Main body
Vial – containing bubble for vertical alignment
‘U’ shaped foldingarm (leg)fits over themain body
Adjustablearm (leg)movement
Batterycompartment
BOSCH
Fig. 1.24 Bosch angle measurer
1.6 Datums
Datums 19
Marking a cutting angle With extension arm checkinga rafter angle
Using the extension armwhere the folding would
be too long
Checking or taking a readingof an internal angle
Checking or taking a reading of theintersections of the exterior of
a bay window
Using the extension arm tomeasure the angle of an
inclined window cill or bracket
Checking or taking a reading of theintersections of the interior of a bay window
Using the extension arm to measurethe angle between a stair
tread and riser
Fig. 1.25 Examples of applying the ‘Bosch’ angle measurer
20 Site setting-out
Marker
Trammel
Springing line
Using a trammel
Marker
Trammel
Circle or semicircle
(a) Using a trammel
Semi-circular arc
Segmental arc
(b) Using a framed template
Marker
Template frame pushed againstboth pegs as it is moved
Chord
x
x
Segment – centre determinedgeometrically
PegPeg
Angle ‘a’ will determine rise ‘R’
xR
R
R
Note: Both sides of the template must be longer than the chord (span)
Datum point
Plus
Level datum line
Minus
Temporary bench mark (TBM)on site – timber or steelset in concrete
Ordnancesurvey
bench mark (BM)Fig. 1.27 Benchmarks
temporary benchmark (TBM) to which all other site levels can bereferred. It should however relate to a true ordnance benchmark(OBM). OBMs can be found cut into surfaces’ permanent structuressuch as public buildings, or other landmarks which are not liable toany earth movement. They can be recognised by an arrow pointingup to a line – the line is the datum point signifying its position (height)as recorded on Ordnance Survey maps. The origin of this height istaken from the ‘mean’ sea level (middle distance between high andlow tides) at Newlyn in Cornwall.
Fig. 1.26 Setting out large circles segments and arcs
Datum lines shown in Fig. 1.28 need only relate to the work in hand.These are temporary horizontal lines, which have been struck at aconvenient height so that floor and/or ceiling slopes can be measuredand their dimensions be recorded.
Levelling is the act of producing a line or surface which is horizontal(level). Any one of the following aids can be used to establish a levelline:
● Traditional spirit level● Digital spirit level● Water level● ‘Cowley’ automatic level● Laser level.
It consists of a metal body (rule) with parallel edges into which areinset one or more plastic tubes containing a spirit and a bubble of air.The position of the air bubble indicates whether the spirit level ishorizontal (Fig. 1.29(a)).
The accuracy of the level will depend on:
● how true the bubble tube is set,● the level’s effective length,● the skill of the operative.
Fig. 1.28 Datum lines
Levelling 21
Theatre
Temporary datum line
Paneldimensionlines
Panel
Porter’s
Shopfront
Datum line
Slope of pavement
Stage
Plumbline
Level
� w
�
�
� w� h � h
1.7.1 Traditional spiritlevel (see also 1.8.3)
1.7 Levelling
Figure 1.29(b) shows how effective the length of the level is. With theaid of a straight edge, its efficiency can be increased for lengths up to 3 m; Greater distances can be covered by moving both level andstraight edge together progressively forward. There is however, adanger of minor errors accumulating. This can as shown in Fig. 1.29(c)be avoided if, at each stage of movement, both level and straight-edgeare turned through 180°. For example, end ‘A’ is rotated about end‘B’ then end ‘B’ is rotated about end ‘A’ and so on. In this way anyminor inaccuracies will be equalled out over the whole distance.
Similar to the traditional spirit level but includes a digital read-outand audio sound when the required angle or level has been estab-lished (Fig. 1.30).
This works on the principle that ‘water always finds its own level’which is true when it is contained in an open system.
Consider Fig. 1.31(a) – water is contained in a U-tube and, no matterwhich way the tube is tilted, the water level remains in a horizontal
22 Site setting-out
(a)
(b)
(c)
A B A
AB
Bubble position
LevelOff-level
Boat level Short level
Long level
Fixed point datum
Extend use – multiples of not more than 3 m
Level and straight-edge (3 m maximum length)
Off-level
Fig. 1.29 Levelling with a spiritlevel
Note: To test the level for accuracy(see 1.8.3).
1.7.2 Digital spirit level
1.7.3 Water level
plane. In Fig. 1.31(b) the tube has been divided and base connectionshave been made with a flexible hose. Again, provided the hose isunobstructed, the water level will be the same at both ends. This isthe basic principle on which the modern water level is founded.However, as can be seen from this model (Fig. 1.31(c)), if one end israised or lowered too far, water will spill out – a problem that in themain has been overcome with the modern water levels.
A modern two-man-operated water level (Fig. 1.32) consists of twotransparent (and in some cases graduated) plastic sight tubes. Eachtube has in this case a brass sealable cap with vent holes. Attached toeach cap is a brass rod (plunger) with a rubber stopper which acts asa valve by preventing air entering the hose when the cap is shut downand the level is not in use.
Fig. 1.30 Bosch digital spirit level
Levelling 23
Fig. 1.31 Basic principles of awater level
Fig. 1.33 The ‘Comp-Mark’electronic level
The long rubber or plastic hose makes this level particularly usefulfor levelling floors, ceilings, formwork, etc. especially around cornersor obstacles.
As shown in Fig. 1.33 all the components of this one-man-operatedelectronic level are housed within a durable carrying case, theyinclude:
● a detachable winding drum with two-way winding handle;● heavy-duty plastic hose (wound around a drum reservoir);● hand-held digital level indicator;● leveling accessories compartment to hold or contain;● marker pencil;● extendable staff (made up of short screw aluminium rod sections)
which fits into the base of the hand-held digital indicator – an ideal attachment for taking existing floor levels, or belowground, etc.
● staff end stops (a small plain disc and a larger magnetic one);● operating manual.
Fig. 1.32 Two-man-operatedwater level
24 Site setting-out
Two-wayWinding handle
Operatingmanual
Hand-heldDigital levelindicator
Windingdrum
Accessories
Screw forzero setting
1.7.4 The ‘Comp-Mark’electronic level
The centre of the winding drum is fitted with a sealed unit (reservoir)containing an oil-based liquid. Also included is an adjusting screwfor zero setting prior to use.
Inside the hand-held level indicator unit is a high-performance meas-uring device with a numeric digital readout that works in conjunctionwith the liquid within the drum. Levels are detected by means of thepressure difference between the fluid level in the drum and that at thehand-held device.
Levels are transferred to different areas or points by repositioning thehand-held device above or below the datum line as shown in Fig. 1.34until a satisfactory level is achieved as indicated by the light-emittingdiode (LED with its plus or minus (�) readout) within the device.
Practical uses include:
● suspended ceilings,● floor construction,● kitchen fitting,● formwork.
Also see Figs 1.34–1.36.
Other uses include Horizontal and vertical operating in addition totransferring levels from a recess, i.e. trenches, etc. (Fig. 1.35).
Figure 1.36 shows how the level can be used for measuring inclined(sloping) surfaces or members, for example when constructing form-work (see Chapter 3, Formwork) for paths or driveways, etc.
Levelling 25
Fig. 1.34 Positioning the hand-held device
Table 1.1 gives the angle obtained for every one horizontal metre andvertical measurement. For example, a height of 105 mm over a dis-tance of 1 m will give an incline of 6°.
Fig. 1.35 Horizontal andvertical range
26 Site setting-out
(d)
(b) Maximum distance .... 2.5 m
(c) Maximum distance .... 2.5 m
(a) Maximum distance .... 45 m
(a)
(b)
(c)
Hand-held level indicator
Table 1.1 Inclination conversion table
Angle * Millimetres per metre (mm/m)
1° 17.52° 353° 52.54° 706° 1058° 141
* Figures listed have been taken to the nearest millimetre.
Angle in degrees°
mm/m ratio
Fig. 1.36 Positioning the hand-held device to inclined surfaces
This provides a simple means of levelling distances of up to 50 mwith an accuracy of 6 mm in every 30 m. It requires no setting-up or alignment. The levelling mechanism (Fig. 1.37) consists of a dualset of mirrors arranged inside a metal case in such a way that areflected ‘target’ as viewed through the eyepiece will appear to besplit (Fig. 1.38(a)) unless the top of the target is in line with the ‘sightline’ – in which case the split images will join together, as shown inFig. 1.38(b).
The metal case need not be level – variations will automatically becompensated for by the pendulum movement of one of the mirrors,which comes into operation as soon as the tripod pin is inserted intothe base of the metal case.
Figure 1.39 shows some of the accessories. The tripod (Fig. 1.39(a)),staff and its target (Fig. 1.39(d)) are supplied with the level. Thebricklayer’s stand (Fig. 1.39(b)) can be used in place of a tripod.
Levelling 27
Fig. 1.37 Cowley level andmirror arrangement
1.7.5 ‘Cowley’automatic level
Note: Never carry the level whilstattached to a tripod or stand – themirror mechanism could be damaged. Once the level isdetached from the tripod pin, the mechanism becomes lockedand is therefore safe to travel.
Fig. 1.38 Level application
28 Site setting-out
Fig. 1.39 Cowley level accessories
Using the level
The procedure for using the Cowley level is as follows:
(i) Set the tripod, pin uppermost, on a secure footing – a baseboard may be necessary on smooth flat surfaces (Fig. 1.39(c)).
(ii) Position the level on the tripod and see that it is free to rotate –the levelling mechanism is now unlocked.
(iii) Position the staff and target on the ‘datum’ or starting point.The staff must be held as near to vertical as possible.
(iv) Direct the level towards the yellow face of the target.(v) Sight on to the target. An assistant moves the target up or down
until the ‘on-target’ position appears through the eyepiece asshown in Fig. 1.38(b).
(vi) As soon as the ‘on-target’ position is achieved, the target isclamped to the staff ready to be transferred to other pointsrequiring the same level as shown in Fig. 1.40.
Figure 1.41 shows that, by taking a reading of the graduated staff,different levels can be measured.
Levelling situations
A Cowley level is ideal for pegging-out groundwork; levelling form-work, wallplates, floor joists, etc.; and establishing a datum line onthe wall of a building (Fig. 1.40).
These types of levels are being used more and more within the con-struction industry as an alternative to the more traditional methods ofsetting datum lines.
Consisting of a metal body containing electronics to produce a thinlaser light, the unit can be placed on a tripod (Fig. 1.42(a)) and rotatedthrough 360° to provide markings on walls or surfaces at differentpositions within an area. It can also be placed on a sturdy base (Fig.1.42(b)) and leveled with the adjustment screw. Once levelled, thebeam is activated and where it strikes the wall or surface a mark isplaced. By using the dual beam prism, the unit can be set to providetwo beams set at 90° lines horizontally and vertically (Fig. 1.42(b)and (c)) which is ideal for constructing stud partitioning. Anotherattachment is the beam spreader lens (Fig. 1.42(d)) which will provide a line, again both horizontally and vertically, for situationsincluding fitting and levelling cupboard units, etc.
Applications (Fig. 1.43)
The laser level can be used for a variety of situations including estab-lishing a level line around the wall or surface (Fig. 1.43(a)), where
Levelling 29
1.7.6 Laser levels
Fig. 1.41 Measuring differentheights
30 Site setting-out
Difference between position ‘A’ andposition ‘B’ is ‘h’, therefore h � a � b
Fig. 1.40 Levelling situations
Levelling 31
Line of laser
Line of laser
Line of laser
Line of laser
Leveling plate
(a) Leveling (with optional tripod)
Level adjustmentscrew
Level bubble
(b) Split beam (level supported off floor or object)
Floor supporting foot
(d) Beam spreader (level supported off floor or object)
(c) 90 degree prism (level supported off floor or object)
Line of laser
Level rotation
the level is placed on a tripod, or for setting out 90° angles in pre-paration for the sole plate for stud partitioning (Fig. 1.43(b)). Figure1.43(c) illustrates a method of vertical setting-out for positioning onthe ceiling. Finally, using the beam spreader (Fig. 1.43(d)) for levellingcupboard units, etc.
A more sophisticated compact piece of equipment which has similaruses. A rotating laser level with variable speed provides a continuousbeam of light both horizontal and vertical on walls or surfaces. Examples of use include suspended ceilings, datum points and align-ing partitioning. A hand remote control device is available with some models.
1.7.7 Auto rotatinglaser level (Fig. 1.44)
Fig. 1.42 Laser levels
Fig. 1.44 Auto rotating laser level
32 Site setting-out
(a)
(b)
(c)
(d)
Fig. 1.43 Applications: (a) Making a ‘datum’ level (perimeter of a horizontal plain); (b) Marking theperimeter of a vertical plain; (c) Transferring a ground point vertically; (d) Marking a straight line
It must be stressed at this point to mention the dangers from mis-use of laser levels. The laser beam that is created is classified as laser class 2 (EN 60825-1:1997) and the following points must beobserved:
● Do not look directly into the beam, not even at a great distancedue to the narrow focus of the beam. Also not with optical aidssuch as binoculars or glasses.
● Do not point at people or animals, particularly at head height.● Wear the laser-viewing glasses to improve visibility in areas of
poor light. Do not use as sunglasses or while driving. Laser-viewingglasses are not protective glasses against laser beams.
● Never tamper with the unit unless qualified to do so.
It is essential that all constructional work is carried out with plumb-ness in mind – not just for the sake of appearance, but as an assuranceof structural balance and stability.
Plumbness can be achieved with the aid of:
● a suspended plumb-bob,● a plumb-bob and rule,● a spirit level,● a site square (as already mentioned, see optical site square,
1.3.3).
A plumb-bob is a metal weight which, when freely suspended by acord or wire, produces a true vertical line. It is ideal for indicatingvertical drop positions (Fig. 1.45(a)) or as a vertical margin line fromwhich parallels can be measured or referred such as a wall (Fig.1.45(b)) or a column box.
The size of the weight will largely depend on the type of work andthe conditions under which they will be used. A very long plumb linemay have to have its bob submerged in a container of water to helpreduce the amount of swing.
A plumb-bob and rule (Fig. 1.46) allows the plumb line to make con-tact with the item being tested for plumb. The rule is made from astraight parallel-sided board – a hole is cut through one end toaccommodate the bob and allow the line to make contact with the
Vertical setting-out 33
1.8 Vertical setting-out
Note: The more specialised opticalinstruments in this field are knownas theodolites, used by profes-sional surveyors in industry.
1.8.1 Plumb-bob
1.8.2 Plumb-bob and rule
1.7.8 Laser level safety
Fig. 1.46 Plumb-bob and rule
34 Site setting-out
Fig. 1.45 Plumb-bob and line
face of the rule, and saw kerfs cut in the top grip the line. A centralvertical gauge line is used as the plumb indicator.
With the exception of the very short level, all spirit levels can be usedto test plumbness (Fig. 1.47). Accuracy will depend greatly on thelevel’s length and bubble setting – most are factory sealed; others areprovided with means of adjustment.
Testing a bubble for accuracy
The following steps can be followed:
(i) Position the level against a firm straight vertical object. Notethe position of the bubble in relation to the central margin onthe tube (vial).
(ii) Keeping the level in a vertical plane, turn it through 180°. Thebubble has now been turned about (end for end).
(iii) Reposition the level against the vertical object. The bubbleshould take up exactly the same position in the tube as before-even the smallest variation is unacceptable.
Fig. 1.47 Testing for plumbwith a spirit level
Vertical setting-out 35
1.8.3 Spirit level (Plumb stick)
(iv) If adjustment is necessary, the level should be returned to themaker or their agent; in the case of adjustable levels, the maker’sinstructions should be carefully followed.
Inaccuracies usually only occur as a result of accidental damage ormisuse.
36 Site setting-out
Note: By substituting the horizontalplane for the vertical plane, thesame testing principles can beapplied to levelling.
Reference
BS EN 60825-1: 1997.