Measuring and Layingout
Reference Lines and Marks:
Arguably the most accurate and reliable reference line available is the plumb line, since it operates by gravity. Like God’s grace, gravity is constant, reliable, true, omnipresent and everywhere available. By definition, a level line is perpendicular to the plumb line and is usually gauged by a spirit level, which also operates by gravity. String and chalk lines, if carefully done and not deflected, tend to be reliable. Surveyors’ optical and laser tools provide excellent precision.
Establishing Vertical:
A plumb bob is better than a spirit level for critical verticals, i.e. wall corners and columns. Remember that gravity operates 24-7. Out of plumb is a bad thing that lasts for the life of the structure. When plumbing down from a high known point, allow the bob to oscillate freely and by eye note the center of the swing arc. When plumbing up from a known low point, establish a temporary reference point on the high piece, plumb down, determine the off-set of the down-plumbed point from the true spot and lay off this amount from the temporary reference. Modern laser equipment properly used will make this job easier.
Establishing Horizontal:
Messing up on the foundation and floor level will cause nothing but trouble for the rest of the job, and the whole building will be in danger of being out of whack.
The best tool for leveling, other than a surveyor’s instrument, is a long spirit level (at least 6-ft.). Check the bubble centering by rotating the level. Check the level’s quality by seeing how much the thickness of one penny (or dime) placed under one end will move the bubble. Your level should detect this error. The more the bubble moves with this test, the more sensitive the level. Sequential leveling, like sequential taping, is undesirable. Use a surveyor’s or builder’s optical or laser level to establish elevation over a long distance.
Establishing Right Angles:
A surveyor’s transit or theodolite is the most precise angle-measuring tool, but is impractical to use for short distances, where a tape is more convenient. Most every carpenter is familiar with the 3,4,5 sides of the right triangle. However, a much stronger and better combination is 20, 21, and 29 and its multiples, such as 100, 105, 145. This combination creates a nearly 45 degree angle at the acute corners thus providing a more accurate right angle.
Chalk and String Lines:
When chalking, make sure the line is taut and when snapping, be sure it’s pulled exactly perpendicular to the surface to be marked (especially important when marking across a sloped surface such as a roof). Do not use lengthy chalk lines since they often become misaligned when snapped; instead use a string or laser.
String or chalk all critical edges such as plates, wall sills, wall top plate, etc. Strings for alignment must be taken from accurate reference points; e.g. when stringing to straighten a wall, make sure the end-points of the string are anchored to accurately plumbed, secure corners. And do not lean ladders on the wall as you are trying to align it! Off set the reference line a small amount so as to keep it from being moved (string) or obscured (chalk). Use a gauge block to test conformance with the reference line.
Measurement and Marking Practice:
Linear measurements are made by reference to an “artificial” standard. Not all measurements are perfect to a zillionth of an inch, nor always mistake free. Since they are always susceptible to mistake and error, they are of less reliability. Right angles, when established by linear measures, also are of lesser reliability.
Your project may have been staked out by Surveyors, who usually measure in feet and decimals of a foot. Carpenters measure in feet, inches, and eighths (or sixteenths). It’s useful to remember that 1/100 a foot is nearly equal to 1/8 an inch.
Precision: Try to achieve +/- 1/8 inch in 100 ft. = 1:10,000 relative precision. Check diagonals of perimeter to 1/8 inch or 1/100 foot.
Length of studs, plates, rafters, joists, etc. should be accurate to better than +/- 1/8 inch, down to +/- 1/16 inch.
Smaller details require comparatively more precise measures. 1/32 inch is probably the smallest practical limit (we’re not making furniture).
Check all the tapes. Make sure everyone on the crew has a tape that accurately conforms to a standard tape. For measuring long distances, steel tapes are preferred over woven or fiberglass types, which will stretch unacceptably. Replace damaged or kinked tapes.
When measuring, keep the tape straight. Make sure the tape has no twists, kinks, or “esses”. Watch the sag in the tape when measuring long dimensions. Put tension on un-supported tapes, at least 10 lbs.
When laying out stud intervals, etc. use the entire tape length instead of sequentially adding smaller segments.
If plan dimensions are horizontal, so should the layout measure be! Be careful not to incline the tape when measuring a horizontal dimension. Also, keep the tape plumb for vertical measurements.
When careful measures are needed, do not use the hook at the end of the tape, instead “bury” ten inches or a foot and read the gauge lines.
When measuring inside a closed space where the full tape cannot be stretched, measure in two directions to an intermediate temporary reference line, and add the two values.
Trim the ends off lumber to obtain a clean, sharp end from which to measure.
Mark carefully for cuts. The lead in a carpenter’s dull pencil is usually too fat to make narrow lines needed for precision cuts. The thinner the mark, the more precise the cut. For extra precision, mark the cut line with a sharp pencil or even with a knife. Place the marker at the dimension mark then slide the straight edge to it for striking the line, rather than vice-versa.
Cut to the line, (unless it marks the center of the saw kerf, in which case cut it out) and make sure the saw kerf is on the correct (waste) side! Radial arm, table, and chop saws are capable of more accurate cuts than hand-held “skill” saws.
Framing Square:
Most carpenters have retired the classic framing square and adopted instead the “speed-square.” This 45 degree triangle contains gauge lines for laying out angle cuts for common and jack rafters, and is simple to use and convenient to carry. Unfortunately, this handy gizmo cannot help with face angles, seat cuts, length of jacks, or odd pitches.
The framing square, with its mysterious number tables, is a useful tool that should be available on every project for solving unusual framing problems. Its use is really not that complicated. The key is to understand roof pitch (or slope) which is expressed as rise in inches per foot of horizontal run. On the body (the longer leg) of the square is a table of numbers arranged underneath individual inch marks. The inch value associated with the mark represents the pitch rise per foot of horizontal run and the corresponding table contains settings for marking various cuts of rafters and jack rafters for that pitch, using the tabulated value on one arm of the square, and the appropriate index (12 normal or 17 for 45 degrees) on the other arm.
Story Stick:
For short, frequent and repeated measurements, use a story stick cut to the proper length. For installing out-lookers and other short pieces placed at right angles to another member, use a story stick cut to the size of the diagonal of a right triangle, with the leg lengths marked on it. This is less cumbersome than a framing square and more accurate than a speed square.
Door Frames:
Properly operating doors require accurately installed frames. A frame that is out of square, or with a post out of plumb, or a door with the plane not coincident with the wall, or a frame with the top plate not level, will bind, swing or latch poorly, fit poorly with gaps, besides just looking bad.
To make the plane of the frame flat and in line with the wall, string a line from the frame’s top left corner to the bottom right corner, and another string from the top right corner to the bottom left corner. These two strings should barely touch where they cross. If not, the door frame is out of plane. After making one side post fixed and plumb, adjust the bottom and top corners of the other side until the strings just touch and the top plate is inline with the wall. Check the plumb of this last post and the level of the top plate, and fix in position. (Thanks to Bernie Gueldner for this tip.)
Trimming to Length:
Sometimes it’s difficult to make accurate measurements. Try measuring accurate lengths to fit studs for a new 12 foot wall that frames onto an old existing wavy ceiling! The amount to trim off a piece to be placed in an existing space is given by the formula C = d^2/2h, where C is amount to cut off, d is the distance by which the trial piece off sets or leans, and h is the nominal length.
Example: A 12ft. replacement stud is too long to fit between the top and bottom plates in an existing wall; when put nearly in place it leans over out of plumb by 8”. The trim cut is (8x8)/(2x12x12) = 32/144 = or about 0.2 inch for a snug vertical fit.
Reference Lines and Marks:
Arguably the most accurate and reliable reference line available is the plumb line, since it operates by gravity. Like God’s grace, gravity is constant, reliable, true, omnipresent and everywhere available. By definition, a level line is perpendicular to the plumb line and is usually gauged by a spirit level, which also operates by gravity. String and chalk lines, if carefully done and not deflected, tend to be reliable. Surveyors’ optical and laser tools provide excellent precision.
Establishing Vertical:
A plumb bob is better than a spirit level for critical verticals, i.e. wall corners and columns. Remember that gravity operates 24-7. Out of plumb is a bad thing that lasts for the life of the structure. When plumbing down from a high known point, allow the bob to oscillate freely and by eye note the center of the swing arc. When plumbing up from a known low point, establish a temporary reference point on the high piece, plumb down, determine the off-set of the down-plumbed point from the true spot and lay off this amount from the temporary reference. Modern laser equipment properly used will make this job easier.
Establishing Horizontal:
Messing up on the foundation and floor level will cause nothing but trouble for the rest of the job, and the whole building will be in danger of being out of whack.
The best tool for leveling, other than a surveyor’s instrument, is a long spirit level (at least 6-ft.). Check the bubble centering by rotating the level. Check the level’s quality by seeing how much the thickness of one penny (or dime) placed under one end will move the bubble. Your level should detect this error. The more the bubble moves with this test, the more sensitive the level. Sequential leveling, like sequential taping, is undesirable. Use a surveyor’s or builder’s optical or laser level to establish elevation over a long distance.
Establishing Right Angles:
A surveyor’s transit or theodolite is the most precise angle-measuring tool, but is impractical to use for short distances, where a tape is more convenient. Most every carpenter is familiar with the 3,4,5 sides of the right triangle. However, a much stronger and better combination is 20, 21, and 29 and its multiples, such as 100, 105, 145. This combination creates a nearly 45 degree angle at the acute corners thus providing a more accurate right angle.
Chalk and String Lines:
When chalking, make sure the line is taut and when snapping, be sure it’s pulled exactly perpendicular to the surface to be marked (especially important when marking across a sloped surface such as a roof). Do not use lengthy chalk lines since they often become misaligned when snapped; instead use a string or laser.
String or chalk all critical edges such as plates, wall sills, wall top plate, etc. Strings for alignment must be taken from accurate reference points; e.g. when stringing to straighten a wall, make sure the end-points of the string are anchored to accurately plumbed, secure corners. And do not lean ladders on the wall as you are trying to align it! Off set the reference line a small amount so as to keep it from being moved (string) or obscured (chalk). Use a gauge block to test conformance with the reference line.
Measurement and Marking Practice:
Linear measurements are made by reference to an “artificial” standard. Not all measurements are perfect to a zillionth of an inch, nor always mistake free. Since they are always susceptible to mistake and error, they are of less reliability. Right angles, when established by linear measures, also are of lesser reliability.
Your project may have been staked out by Surveyors, who usually measure in feet and decimals of a foot. Carpenters measure in feet, inches, and eighths (or sixteenths). It’s useful to remember that 1/100 a foot is nearly equal to 1/8 an inch.
Precision: Try to achieve +/- 1/8 inch in 100 ft. = 1:10,000 relative precision. Check diagonals of perimeter to 1/8 inch or 1/100 foot.
Length of studs, plates, rafters, joists, etc. should be accurate to better than +/- 1/8 inch, down to +/- 1/16 inch.
Smaller details require comparatively more precise measures. 1/32 inch is probably the smallest practical limit (we’re not making furniture).
Check all the tapes. Make sure everyone on the crew has a tape that accurately conforms to a standard tape. For measuring long distances, steel tapes are preferred over woven or fiberglass types, which will stretch unacceptably. Replace damaged or kinked tapes.
When measuring, keep the tape straight. Make sure the tape has no twists, kinks, or “esses”. Watch the sag in the tape when measuring long dimensions. Put tension on un-supported tapes, at least 10 lbs.
When laying out stud intervals, etc. use the entire tape length instead of sequentially adding smaller segments.
If plan dimensions are horizontal, so should the layout measure be! Be careful not to incline the tape when measuring a horizontal dimension. Also, keep the tape plumb for vertical measurements.
When careful measures are needed, do not use the hook at the end of the tape, instead “bury” ten inches or a foot and read the gauge lines.
When measuring inside a closed space where the full tape cannot be stretched, measure in two directions to an intermediate temporary reference line, and add the two values.
Trim the ends off lumber to obtain a clean, sharp end from which to measure.
Mark carefully for cuts. The lead in a carpenter’s dull pencil is usually too fat to make narrow lines needed for precision cuts. The thinner the mark, the more precise the cut. For extra precision, mark the cut line with a sharp pencil or even with a knife. Place the marker at the dimension mark then slide the straight edge to it for striking the line, rather than vice-versa.
Cut to the line, (unless it marks the center of the saw kerf, in which case cut it out) and make sure the saw kerf is on the correct (waste) side! Radial arm, table, and chop saws are capable of more accurate cuts than hand-held “skill” saws.
Framing Square:
Most carpenters have retired the classic framing square and adopted instead the “speed-square.” This 45 degree triangle contains gauge lines for laying out angle cuts for common and jack rafters, and is simple to use and convenient to carry. Unfortunately, this handy gizmo cannot help with face angles, seat cuts, length of jacks, or odd pitches.
The framing square, with its mysterious number tables, is a useful tool that should be available on every project for solving unusual framing problems. Its use is really not that complicated. The key is to understand roof pitch (or slope) which is expressed as rise in inches per foot of horizontal run. On the body (the longer leg) of the square is a table of numbers arranged underneath individual inch marks. The inch value associated with the mark represents the pitch rise per foot of horizontal run and the corresponding table contains settings for marking various cuts of rafters and jack rafters for that pitch, using the tabulated value on one arm of the square, and the appropriate index (12 normal or 17 for 45 degrees) on the other arm.
Story Stick:
For short, frequent and repeated measurements, use a story stick cut to the proper length. For installing out-lookers and other short pieces placed at right angles to another member, use a story stick cut to the size of the diagonal of a right triangle, with the leg lengths marked on it. This is less cumbersome than a framing square and more accurate than a speed square.
Door Frames:
Properly operating doors require accurately installed frames. A frame that is out of square, or with a post out of plumb, or a door with the plane not coincident with the wall, or a frame with the top plate not level, will bind, swing or latch poorly, fit poorly with gaps, besides just looking bad.
To make the plane of the frame flat and in line with the wall, string a line from the frame’s top left corner to the bottom right corner, and another string from the top right corner to the bottom left corner. These two strings should barely touch where they cross. If not, the door frame is out of plane. After making one side post fixed and plumb, adjust the bottom and top corners of the other side until the strings just touch and the top plate is inline with the wall. Check the plumb of this last post and the level of the top plate, and fix in position. (Thanks to Bernie Gueldner for this tip.)
Trimming to Length:
Sometimes it’s difficult to make accurate measurements. Try measuring accurate lengths to fit studs for a new 12 foot wall that frames onto an old existing wavy ceiling! The amount to trim off a piece to be placed in an existing space is given by the formula C = d^2/2h, where C is amount to cut off, d is the distance by which the trial piece off sets or leans, and h is the nominal length.
Example: A 12ft. replacement stud is too long to fit between the top and bottom plates in an existing wall; when put nearly in place it leans over out of plumb by 8”. The trim cut is (8x8)/(2x12x12) = 32/144 = or about 0.2 inch for a snug vertical fit.
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