WoodWorking

Woodworking Tutorial – Chapter 4

USING LEVELING INSTRUMENTS

Before construction of a foundation or slab a carpenter must know where the building is going to be on the building lot. There are certain set backs that must be observed and must meet the local zoning and building codes.
The local codes must be observed and checked for these requirements before layout begins.

ESTABLISHING   BUILDING  LINES

Building lines are the lines marking where the building will be. They are the lines that must conform to the code requirements on distance from the property lines.

USING   TAPES   TO  LOCATE  LINES

To use measuring tapes to locate a building line you must first find the boundry lines and then measure perpendicular to the line and set a stake. Then go to another point in the same line and set another stake.
Now to make sure that you are going to be square and  paralell to the boundry line, pull the tape out 8′ and swing an arc till it crosses the line you just established. then pull a tape back towards the boundry line 6′ and stick a pin temporarly and measure diagonally from the 8′ point to th 6′ point and it should read 10′. If not adjust the 6′ pin till it is at 6′ and 10′. Therefore the one corner will be established for your building. Now carry both lines the measured distance from that corner and check the lines for square by using the same 6 – 8- 10 ‘ measurements.

Now to square the foundation layout measure diagonally from corner to corner and make any adjustments that are neccessary to square the foundation. If the ground slopes in any way use a level to plumb in the stake as measuring down a slope will change the arch and make the measurement in accurate.

LAYING OUT WITH LEVELING INSTRUMENTS

In residential construction, especially in built up areas of a community, it is important that building lines be accurately established in relation to lot lines. It is also important that footings and foundation walls be:
1. Level
2. Square
3. The correct size
If the building is small the carpenters level, framing square, and a rule are accurate enough for laying out and checking the building lines. But, as size increases, special leveling instruments are needed for greater accuracy and effiency. They should be used for single family dwelling as well as for commercial structures and institutional buildings.

LEVELING INSTRUMENTS

 The builders level and level-transit are commonly used in laying out and checking construction work.These  instruments can also be used for surveying and other space and land-layout jobs. When the job is too big for the chalk line, straightedge, level, and square, leveling instruments should be used.

The instruments include an optical device which operates on the basic principle that a LINE OF SIGHT is a straight line that neither dips , sags , nor curves. Any point along the line of sight will be the same height as any other point. Through the use of these instruments, the line of sight replaces the chalk line and straightedge.

The builders level, also known as a dumpy level or an optical level . It consists of an accurate spirit level and a telescope assembly. These are attached to a circular base. Leveling scews are used to adjust the base after the instrument is mounted to a tripod. The telescope rotates on the base so that any angle in a horizontal plane can be laidout or measured. The level-transit works like the builders’ level. an additional feature permits the telescope  to be pivoted up or down  in a vertical plane.

Using this instrument it is possible to accurately measure vertical  angles or determine if a wall is  perfectly plumb.
Its vertical movement also simplifies the operation of aligning a row of stakes , especially when they vary in height.

These instruments are mounted on tripods the are adjustable so any leg can be shortened to set up on an uneven ground.

The leveling rod has graduations in feet and decimal parts of a foot or also in feet an inches as well as fractions of an inch. When sighting short distances (100 ft. or less) a regular folding rule can be held against  a wood strip and read through the instrument. This procedure will be satisfactory for jobs such as setting grade stakes  for a footer. Always be sure that the strip and rule are held verticaly plumb.

CARE OF LEVELING INSTRUMENTS

Leveling instruments are more delicate than most other tools and equipment. Special precautions must be followed in their use so they will continue to provide accurate readings over a long period of time. Some suggestions follow;
1. Keep the instrument clean and dry. Store it in its carrying case when not in use.
2. When the instrument is set up, have a plasticbag or cover handy to use in case of rain. should it become wet, dry it before storing.
3. It is best to grip the instrument by the base when moving it from the case to the tripod.
4. Never leave the instrument unattended when it is set up especially around moving equipment.
5. When moving a tripod mounted instrument, handle it with care. Hold it upright and never carry it in the horizontal position.
6. Never over tighten the leveling screws or any of the adjusting screws or clamps.
7. Always set the tripod on firm ground with the legs spread well apart. When set up on floors or pavement, take extra precautions to insure that the legs will not slip.
8. For precision work, permit the instrument to reach air temprature before making readings.
9. When the lense collect dust and dirt, clean them with a camel’s hair brush or special lens paper.
10. Never use force on any of the adjustments. They should turn easily by hand.
11. Have the instrument cleaned, oiled, and checked  yearly by a qualified repair station or by the manufacturer.

SETTING UP THE INSTRUMENT

Set up the tripod so it will be a firm and stable base for the instrument. Make sure the points are well into the ground. On hard surfaces make sure the points won’t slip.
Check the wing nuts on the legs if the tripod has them and make sure they are tight, and that the adjustable legs won’t slip. Tighten the hex nuts holding the legs to the head to the tension desired.
The legs should be spread about 3 1/2’ft. apart and adjust them so the head appears to be level. Now attach the instrument to the head. If it is to be located over an exact spot or point, such as a bench mark, attach the plumb bob and move the instrument directly over the spot. Do this before the final leveling.

LEVELING THE INSTRUMENT

Leveling the instrument is a very important operation in preparing it for use. None of the readings will be accurate unless the instrument is level throughout the work.
First, releasee the horizintal screw or clamp and line the up over a pair of leveling screws. Bring them to a rough level, then swing the instrument over the other two leveling scews and repeat, turn the instrument again to the first two screws clockwise, and relevel. continue this method till the instrument is level 360 degrees or all the way around turning clockwise.Caution, do not over tighten the leveling screws.

SIGHTING

The telescope will magnify or enlarge the image (object being sighted). Most builders levels have a telescope with a power of about 20X. This means that the object will appear to be only one twentieth of its actual distance.
First line up the telescope by sighting along the barrel and then sight through the eyepiece and adjust the focusing knob till the image is clea an sharp. When the cross hairs are in the aproximate position on the object, tighten the horizontal-motion clamp. then make the final adjustment with the tangent screw. this is the screw that allows you to pin point the exat location of the cross hairs.

USING THE INSTRUMENT

Leveling instruments can be used by the carpenter to prepare the building site for excavation and /or leveling. Jobs that can be done with them include;
1. Locating the building lines and laying out horizontal angles (square corners).
2. Finding grade levels and elevations.
3. Determine plumb (vertical) lines.
     For , layout the builders level or level-transit must start from a reference point. this can be a stone marker in the ground or a point on a manhole cover or on a permanent structure nearby.
The point where the instrument is located is called the STATION MARK. The location of the point of origination of determining the given level is call the  BENCH MARK.

Everything pertaining to the building site, surrounding terrain, and the building elevation is determined from the Bench Mark and is commonly marked as the BM. on a set of prints.

The builders level is mainly used for determining horizontal levels, where the transit is used to determine horizontal levels, verticle lines and is also used to locate the building lines and any row of stakes in the line of sight in a straight line.

To establish a square building lay out, first layout one line of the structure to be. Stake the corners at the proper measurement, then turn the instrument ninety degrees left or right of the original building line and measure the distance and drive a stake. Then turn the transit back 45 degrees and sight to a point where two tapes cross at the given measurements and locate the final stake. Note this work must be done on a level plain as running up hill or down hill will change the measurement or length of the building layout.

 THE HORIZONTAL GRADUATED CIRCLE

Laying out corners with the transit requires an understanding of how the horizontal graduated circle is marked.
It is divided into spaces of 1 degree of a circle as indicated below;
A circle is 360 degrees around and if yo quarter it you will see 90 degrees 180 degrees and 270 degrees, with 360 or 0 being at twelve oclock if using the clock method. 90 degrees then becomes 3 oclock , 180 is six oclock, with 270 being 9 oclock. A complete circle as we have already stated is 360 degrees which is then divided by single degrees. One degree = 1 minute, and one minute = 60 seconds, and one quadrant = 1/4 of a circle or 90 degrees.

When you swing the transit the graduated circle remains stationary but, another scale called the “vernier scale” moves.The verier scale is marked off in 15 minute intervals.
When laying out or measuringangles where there are fractions of degrees involved you will use the vernier scale.
Lets look at the vernier scale; In your mind , visuallize the scale of plastic mounted on the side of the transit body.
The scale as you look down on it will look like a scale with a 0 in the middle and minutes and seconds in 15 minute intervals on each side of the 0. On the left of the 0 you will see a 15 mark, 30 mark, 45 mark and 60 mark which are minutes. On the right you will see 15 seconds mark, 30 seconds mark, 45 seconds mark and 60 seconds mark. Now visuallize if the 0 of the vernier scale is over the 75 degrees mark then the transit will be sighting 75 degrees from magnetic North. Now if the 0 mark is off the 75, but not quite on the 76 degree mark, you will look on the left of the 0 on the vernier scale and see that the 45 is directly over a circle mark . The reading then becomes 75 degrees and 45 minutes.
Vernier scales will not be the same on all instruments. You should study the operator’s manual for instructions about the particular model you are using.

Most transits have a movable degree ring, so when you set the scope on magnetic North, you slide the degree ring till the 0/360 mark is under the 0 on the vernier scale. This is known as zeroing in the instrument. Then when you turn the instrument to the locations in the description of the survey and you are directly over the starting point of the survey, the instrument should be correctly set up. The survey example is as follows, N 45 degrees 14 minutes and 30 seconds W. This is telling you that from the zero point that the transit is set up on, you will turn the instrument 45 degrees 14 minutes and 30 seconds West or in this case, to the left. the 0 point scale will be a little past the 45 degrees mark on the ring, and the 14 minutes will be a little past the 14 on the ring and the 30 seconds will be directly over a mark on the adjustable ring. Therefore you will be looking from the North to the West by 45 degrees 14 minutes and 30 seconds on the degree ring.

LAYING OUT AND STAKING A HOUSE

Staking out usually proceeds after one building line has been established using the property line as reference and measuring in the proper distance. Drive a stake and insert a nail in the center of that stake. The next step is to attach a plumb bob to the center screw or hook on the under side of the instrument. Shift the tripod until the point of the plumb bob is directly over the nail in the stake marking the first corner of the building. This stake may be a 2 x 2 driven into the ground with your nail in the center.
Level the instrument before proceeding further. Check the plumb bob then the scope so the verticle cross hair is directly in line with the edge of the rod at the measured point from the property line and establish the second stake by measuring from the nail on the stake under the transit, and in line with the vertical cross hair and drive a second nail. Check to verify if the nail is on line, if it is then you may turn the transit 90 degrees to the left or right to establish the third stake in the layout. Again measure from the nail under the instrument the proper distance and line the vertical cross hair on the edge of the rod and drive the third stake and nail. Again check to assur the nail is on line. Now to establish the forth stake will require two tapes and by turning the instrument 45 degrees to the left or right and sight in on the tapes the are pulled from the other two corner stakes toward the forth stake point and where they cross is where you place the forth stake.
To check to assur that the layout is correct measure diagonally from corner to corner and you should have the same measurement by 1/16″ + or-.
Note that for all the above to work correctly the work area should be reasonably level, as if you are trying to layout on the slope the measurements will not work out because if you hold the tape on the ground and it is running up hill or down hill it woill be off by a few inches to as much as one foot, depending on how much slope is involved.

FINDING A GRADE LEVEL

Finding the difference in the grade level between several points or transferring the same level from one point to another is called grade leveling. With the instrument level, the line of sight will also be level and the readings can be used to calculate the difference in elevation. When there is a great amount of slope on the building site, the instrument can be set up between the points. The reading is taken with the rod on one of the points or position and by turning the instrument 180 degrees you can establish a reading at the second position.
When setting grade stakes for a footer or erecting batter boards, the instrument should be set up in a central location.
The distance will be about equal from one corner to another  and it will reduce the need to focas the instrument on each corner. An elevation can be established at one corner and transferred to the other corners  or points between.

SETTING FOOTER STAKES

Grade stakes for footings are usually set to the approximate level by ” eye ” juddgment. They are then carefully checked with the rod and level as they are driven deeper. The top of each stake should be at the required elevation.
Some times reference lines are drawn on the construction members or stakes near the work. Then the carpenters’ level and rule. If wooden stakes are used in the footer they must be pulled after the concrete is poured and can not be left into the concrete. One might want to use rebar rods instead of wood.

There may be situations where the existing grade will not permit the setting of a stake or refeence mark at the actual level of the grade. In such cases a mark is made on the stake with the infromation to fill or remove.
The letters ” c ” and  ” f ” stand for cut and fill, are generally used.
When laying out sloping building plots or ” carrying ” a benchmark ( an officially established elevation ) to the building site, it will likely be neccessary to set up the instrument in several locations.

CONTOUR LINES

Contour lines are lines that run through points of equal level. Such lines can be laid out on an area of ground by setting up the instrument at an appropreiate point and directing the rodworker to hold the rod at the beginning point. Sight the rod and set the target on the horizontal cross hair. The rod worker then moves to the next location and moves the rod up or down the slope till the target again aligns with the scope. set a stake an drepeat the procedure as many times as required.

RUNNING STRAIGHT LINES WITH A TRANSIT

Although the builders level can be used to line up stakes, fence posts, poles, and roadways, more accuracy is gained with the level transet, especially when different levels are involved.
Set up the instrument directly over the reference point. Level the instrument and then release the lock that holds the telescope in a level position. Swing the instrument to the required direction or until a stake is alignedwith the vertical cross hair.
Tighten the horizontal circle so only the telescope can only move on the verticle plane. Now by pointing the telescope up od down, any number of points can be located is a perfectly straight line.

VERTICAL PLANES AND LINES

The level transit cab be used to:
1. Measure vertical angles.
2. Layout and check building walls, flagpoles, or TV antenna masts.
To establish or check vertical lines and planes, first level the instrument, then release the lever that holds the telescope in a horizontal position. Swing the instrument vertically and horizontally until a reference point in the required plane or line is sighted and then lock the horizontal clamp screw. As you tilt the scope up or down , all the points will be located in the vertical plane.
Plumb lines can be checked or established by first operating the instrument up or down on the vertical plane. then move the instrument to a second position, usually about 90 degrees either to the right or left and repeat the procedure that was used for the horizontal angles.
A plumb bob and line may often be the most practical way to check vertical planes an dlines.
For layouts inside a structure where a regular buildre’s level or transit is impractical.

This concludes chapter four.

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