Engine Room Tools Part 3

8/11/2019 Engine Room Tools Part 3

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FIG. 134. MEASURING WITH STEEL RULE.

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It should also be noted that measurement from inside to inside of the

graduations of a rule will give a "scant" measurement, while measurements

from outside to outside of graduations will give a "full" measurement. Neither

one of these measurements is exact. To secure an exact measurement it is

necessary to measure precisely from center to center of the graduation marks.

A steel rule must always be handled carefully. Guard against rough usage that

may cause nicks or scratches, as these reduce accuracy. The rule should be

stored in a leather sheath when not in use and the leather oiled slightly to

prevent rusting and discoloration which would make the graduations difficult to

read.

FIG. 135. OTHER STEEL RULES.

154. Some other rules that may be found aboard ship are shown in Fig. 135.

These are used for making measurements beyond the capacity of the

machinist's rule, or for measuring curved objects, as can be done conveniently

with the steel tapeor theflexible steel rule.

A depth rule, Fig. 136, has a narrow blade which slides through a slotted locking

arrangement. It is used to measure the depth of holes, slots, keyways, and other

recesses. Some of these rules can

FIG. 136. DEPTH RULE.

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FIG. 137. HOOK RULE AND SHORT STEEL RULES.

be used for measuring angles as well as the depth of holes drilled at an angle to

the surface.

The hook rule, Fig. 137, is convenient to use when measuring from an edge,

especially an edge that is out of sight. Short steel rules, sometimes called"tempered steel rules," are used where other rules cannot reach. A number of

small rule sections are provided as a set, with a long-handled holder.

Adjustment is made by a knurled nut at the end of the holder so that the rule

can be held at different angles to suit the work.

Outside caliper rulesare used to measure the outside diameters of rods, shafts,

bolts, etc., in sizes that are within the capacity of their jaws. Inside caliper rules

are used to take measurements of slots, grooves and openings.

FIG. 138. COMBINATION CALIPER RULE.

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The combination caliper rule, shown in Fig. 138, has jaws designed to make either

inside or outside measurements. If the diameter of a hole is being measured,

the graduation that lines up with the mark labeled INis read. When measuring

the diameter of a shaft, the graduation that lines up with the OUTmark is read.

A special type of rule used by some mechanics is known as the circumferencerule. The purpose of the rule is to enable the circumference of a piece of work to

be obtained without calculation, when the diameter is known. The rule has two

sets of graduations on the same face, as shown in Fig. 139. One set is graduated

in

FIG. 139. CIRCUMFERENCE RULE.

inches with subdivisions of 1/16 inch, in the standard method, and is used inmeasuring the diameter. The other is graduated in smaller divisions, the

numbers representing inches and the subdivisions representing 1/8 inch, but

the spaces are not true length.

To use the circumference rule, read straight across from the diameter

measurement to the number on the opposite edge. For example, if it is

necessary to cut a piece of sheet metal so that a cylindrical tube 3 1/2 inches in

diameter can be made, read directly opposite from 3 1/2 inches and obtain 11.

This is the circumference of the tube, in inches, and is very close to the result

that would be obtained by calculation, as 3.5 X 3.1416 = 10.9956. It the tube is to

be constructed with a lap joint, the material will naturally have to be cut wide

enough to allow for the lap.

155. It is important to remember that graduated measuring instruments mustbe handled carefully so that they will retain their accuracy. In addition they must

be kept clean and dry, as dirt and moisture tend to wear and rust away the

graduations. Even the touch of the fingers will tend to corrode steel rules. It is

therefore essential that they be wiped off with a clean cloth and machine oil


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after each use, and then stored carefully so as to be protected against damage

and deterioration.

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FIG. 140. SCALES.

156. Scales.-The scalesshown in Fig. 140 are graduated to indicate proportional

rather than actual measurements, permitting them to be used, for example, in

laying out work to a scale of 1/4 inch to the foot.

157. Straightedge.-A straightedgeis a long, flat, square-edged strip of steel,

ground to close tolerances, but not graduated. It is used to enable a perfectly

straight line of considerable length to be marked across a flat surface. Where

comparatively short distances are involved, a steel scale in good condition can

be used as a straightedge. When using a scriber and straightedge, care must be

taken to make sure that the point of the scriber is drawn along the guiding edge

of the face in contact with the work, as otherwise inaccuracies will result. A

straightedge must be handled and stored very carefully. If dents, bends, or rusty

spots are permitted to occur, the value of the tool will be seriously affected.

158. Scriber.-A well-sharpened scriberis used to make clean and narrow lines

on metal. It is usually a slender piece of tool steel, tapered to a point at each

end, with one end being bent to a 90 angle, as shown in Fig. 141. The

instrument is long enough so that

FIG. 141. SCRIBER.

it can be gripped in the middle, where it is knurled for that purpose.

Before using a scriber it is advisable to examine the point, as it must be sharp

and evenly ground. An oilstone is used to keep the point in good condition.

When using the scriber, hold it firmly,

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and in much the same manner as a pencil. In Fig. 142 a pocket-type scriber, with

a detachable point that may be removed and stored in the head, is shown beingdrawn along a straightedge. Note that it is tilted slightly in the direction of the

line being drawn. Also note how the scriber touches the guiding edge of the

lower face of the straightedge.

FIG. 142. USE OF SCRIBER.

It is often advisable to coat the surface of a piece of metal with chalk before

drawing lines on it, as this causes the lines to stand out more clearly. The use of

chalk is also helpful when using dividers.

159. Dividers.-In order to transfer distances from a rule to the material, dividers

are often used. They can also be used to check and compare dimensions, or to

scribe arcs and circles.

The correct way to set dividers to the desired dimensions is shown in view (a) of

Fig. 143. Note that one leg is on the 1-inch


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FIG. 143. USE OF DIVIDERS.

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mark instead of at the end of the rule. Since a 3-inch measurement is desired in

this instance, the best method is to compress the legs of the dividers slightly

with the hand, and then loosen the adjusting screw until the legs will open

slightly wider than 3 inches. Then compress the legs nearly to the correct

measurement and tighten up on the adjusting screw, checking and adjusting

until one leg stands exactly in the center of the 1-inch graduation and the other

leg in the exact center of the 4-inch graduation. If the spring tension is not

relieved by compressing the legs as just described, the adjusting screw does all

of the work and the threads are subjected to unnecessary wear.

Handle the dividers carefully while in use, as otherwise they may work loose and

creep open, thus altering the measurement. Points should be kept sharp by

means of an oilstone.

One way to check the setting of dividers is to draw a circle on a piece of scrap

paper or metal. Then measure the diameter of the circle with a rule. If the

diameter measures exactly twice the desired setting, the dividers are set

properly.

When using dividers to scribe a circle or an arc, be sure to tilt the dividers in the

direction of the arc, as shown in view (b) of Fig. 143. Keep the dividers at the

same inclination throughout the complete circle or arc.

FIG. 144. USE OF TRAMMEL.

160. Trammel.-When it is necessary to mark off an arc or circle too large for

dividers, a trammelcan be used, as shown in Fig. 144. In this instance the

trammel points are attached to an extension bar by means of lock screws. When

using the trammel, make sure that there is no sag or bend in the extension bar

and that the

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screws are tight. Incline the trammel in the direction of the arc, and keep the

same angle of inclination constant through the entire length of the curve.

A non-adjustable trammel may be used aboard ship when placing the crank of

an engine on dead center, as explained in another lesson.

161. Surface Plate.-A surface plateis a flat-topped steel or cast iron plate that is

heavily ribbed and reinforced on the under side, as shown in Fig. 145. Its top

surface is precision ground to form a true fiat surface, and this surface is used

as a base for making layouts with precision tools, such as the surface gage.

FIG. 145. SURFACE PLATE.


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FIG. 147. STEEL SQUARE AND COMBINATION SET.

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FIG.148. USES OF COMBINATION SET.

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A combination setis also shown in Fig. 147. This set can be used for various purposes,

some of which are shown in Fig. 148. Note that a scriber, a spirit level and a protractor

are included.

164. Calipers.-Calipersare used for measuring diameters and distances or for

comparing distances and sizes. Several types of calipers are shown in Fig. 149.


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FIG. 149. CALIPERS.

Outside calipersare used for measuring outside dimensions, for example, the diameter

of a piece of round stock. The calipers should first be set approximately to the diameter

of the material to be measured. Then, while held at right angles to the center line of the

stock, as shown in Fig. 150, the calipers are adjusted until their points bear lightlyon the

surface of the work. The points

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FIG. 150. MEASURING WITH OUTSIDE CALIPERS.

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should be moved back and forth slowly while adjusting them, in order to get the "feel."

When the adjustment has been made, the diameter can be read from a rule as shown

in the upper part of Fig. 150.

Inside calipershave curved legs for measuring inside diameters, such as the diameters

of holes, the distance between two surfaces, the width of slots, etc. To measure the

diameter of a hole with inside calipers, first set them approximately to the size of the

hole; then, holding one leg against the wall of the hole, adjust the other leg until it just

touches the point exactly opposite, as shown in Fig. 151. The dimension can then be

determined with a rule, or

FIG. 151. MEASURING A DIAMETER WITH INSIDE CALIPERS.

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FIG. 152. HERMAPHRODITE CALIPERS.

micrometer, as illustrated in the figure. With practice, such a measurement can be

taken with a high degree of accuracy.

Hermaphrodite calipersare generally used to scribe arcs, or as a marking gage in layout

work, as shown in Fig. 152. To adjust them to a rule, set the scriber leg slightly shorter

than the curved leg; then, with the curved leg against the end of the rule, adjust the

scriber leg to the desired graduation on the rule. Hermaphrodite calipers should not be

used for precision measurements.

165. Fixed Gages.-Gages are tools for measuring or transferring distances ordimensions, usually within 0.001 inch or less. They are made both adjustable and

nonadjustable, or fixed.

A fixed gage is made with extreme accuracy to some fixed standard of measurement or


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A feeler gage should next be used to measure the clearance between the faces of the

coupling halves, the clearance also being measured at 90-degree intervals around the

circumference. All four measurements should be equal.

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When the straightedge rests evenly on both coupling halves in all four tests and the

clearance between the coupling halves is equal in all measurements, the coupling isproperly aligned. However, if there is any discrepancy in either test, the coupling is

misaligned.

When a coupling is out of line, noisy operation is likely to occur, bearings will run hot,

packing glands will wear and leak, etc. One or both of the connected units therefore

must be moved until the coupling halves are aligned. In the case of motor-driven

pumps, for example, it is usually more convenient to move the motor.

The alignment of a coupling may also be determined by the use of a machinists', or dial,

indicator. This instrument is described later.

FIG. 155. ANGLE GAGE.

168. Angle and Radius Gages.-The blades of angleand radius gagesare all of the same

thickness, hut with them it is the blade outline that is important. Each blade of an angle

gage, for example, has a different end angle, as shown in Fig. 155, and these gages are

used when it is necessary to measure the same angles frequently.

The rounded corner of each blade of a radius gage is the arc of a circle, and the radius

of the arc is stamped on the blade, as shown in Fig. 156. The gage can be used to check

outside radii as well as inside radii.

169. Wire and Sheet Gage.-The gage shown in Fig. 157 is a U. S. Standard wire and

sheet gage. It can be used to measure

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FIG. 156. RADIUS GAGE.

FIG. 157. WIRE AND SHEET GAGE.

cross sections of wire and to determine the gage (thickness) of metal sheets. Before


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using one of these gages be sure that all burrs are removed from the material being

measured.

170. Snap Gage.-A snap gageis used to check the outside diameters of shafts on which

it is impossible (because of construction) to use a ring gage. The gage shown in Fig. 158

(A) is a combination snap and ring gage.

Adjustable snap gages have anvils that can be set to the desired dimensions by means

of a micrometer or gage blocks. The gage

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FIG. 158. SNAP GAGES.

shown in Fig. 158 (B) has two adjustable anvils; one can be set for the allowableminimum diameter and the other for the allowable maximum diameter.

171. Center Gage.-The gage shown in Fig. 159 is a 60 center gage. The notches in the

edge of this gage also have an angle of 60 and are used to check the grinding of

thread-cutting tools, as American National thread has a thread angle of 60. The center

gage can also be used for setting thread-cutting tools square with the work.

FIG. 159. CENTER GAGE.

Center gages are usually marked on both faces and along both edges with scales that

are convenient for measuring the number of threads per inch of bolts, studs, etc. One

face has 20 divisions to the inch on one edge and 14 divisions to the inch on the other

edge. On the opposite face of the center gage there are 24 divisions per inch on one

edge and 32 divisions per inch on the other edge. The different sized divisions are used

to check the pitch, or number of threads per inch, of screw threads. The different

numbers of threads per inch for which each scale is suitable are those which divide into

the scale number without a remainder. For example, the edge with 20 divisions is

suitable for measuring 1, 2, 4, 5, 10 and 20 threads per inch, and also for any multiple

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of 20, such as 40, 60, 80, etc. The edge with 14 divisions may be used for measuring 1,

2, 7, or 14 threads per inch and for any multiple of 14. The scales with 24 divisions and

32 divisions are used similarly.

172. Thread Tool Gage.-A thread tool gage is useful in checking the size and shape to

which a lathe tool is ground when preparing it to cut a thread. A thread tool gage for

American National Coarse (NC) thread is shown in Fig. 160. Each notch of the gage

FIG. 160. THREAD TOOL GAGE.

is shaped for a particular thread, the figure opposite each notch denoting the number

of threads per inch. The threading tool is ground to fit the notch corresponding to the

thread that is to be cut.

A worm-thread tool gage is shown in Fig. 161. This type of gage is used to check the

shape and size of a tool used to cut worm


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FIG. 161. WORM-THREAD TOOL GAGE.

threads, the numbers indicating the number of threads per inch.

173. Surface Gage.-A surface gageis used to measure height and for scribing layout

lines on vertical surfaces. The commonly used universal type, Fig. 162, has a base plate,

an adjustable extension

FIG. 162. SETTING A SURFACE GAGE.

arm, and an adjustable scriber. When a surface gage is set to a combination-square

rule, as shown in the illustration, both the square and the gage base must rest on a flat

smooth surface, preferably a surface plate.

174. Machinists' Indicator.-A machinists' indicator is a measuring instrument used to

test or measure variations in dimensions, the changes in measurements being

indicated visually by means of a pointer and a scale or dial. When arranged with a dial,

this type of instrument is known as a dial indicator. The indicator shown in Fig. 163 gives

readings in thousandths of an inch. It is often helpful to mount a dial indicator on the

extension arm of a surface gage, or make some other suitable arrangement, and use

the set-up to check the trueness of work in a lathe, the deflection of a shaft, the

alignment of couplings, etc. By setting the indicator in position with its contact stem

bearing against a shaft, for example, the shaft can be turned slowly, and if it does not

run true, the dial hand will indicate the deviation. In operation, the instrument can be

adjusted so that it reads zero at the beginning of the

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FIG. 163. DIAL INDICATOR.

reading. When the shaft or other piece of work is rotated, if the total of the maximum

plus and minus readings should be 0.004 inch, for example, the actual deflection would

be 0.004 / 2 = 0.002 inch.

175. Small-Hole Gages.-One common method of finding the diameter of a small hole is

to try various twist drills in it until one is found that just fits in the hole. This method is

satisfactory if the right drill is available and absolute accuracy is not all-important.


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The split-ball type of small-hole gage, Fig. 164, is designed,

FIG. 164. SMALL-HOLE GAGE.

however, for accurate determination of the diameters of small holes. There are usually

four of these gages in a set, designed to measure any hole diameter up to 1/2 inch. To

use the gage, the ball end is placed in the hole and the two halves expanded by turning

the handle. When the "setting" is just right, the gage is locked by means of the knob at

the end of the handle. The gage is

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then withdrawn from the hole and the diameter of the ball end measured with a

micrometer.

176. Micrometers.-The micrometer, or micrometer calipers, is the most commonly used

adjustable gage and it is important that its mechanical principles, construction, use and

care, be thoroughly understood. A 1-inch outside micrometer, with its various parts

indicated, is shown in Fig. 165.

FIG. 165. SECTIONAL VIEW OF 1-INCH OUTSIDE MICROMETER.

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Micrometers are commonly used to measure distances to 1/10,000 inch (0.0001 inch)

and the measurements are usually expressed or written as a decimal. Any person using

a micrometer, therefore, should be entirely familiar with the method of writing and

reading decimals. As a brief review, remember that all figures to the leftof the decimalpoint are whole numbers; all figures to the rightof the decimal point indicate parts of

whole numbers. Starting from the decimal point and moving to the right, the first digit

indicates tenths; the second, hundreths; the third, thousandths; the fourth,

ten-thousandths; and so on. Thus 2.000 inches indicates exactly 2 inches; 2.3 is read

two and three-tenths; 1.85 is read one and eighty-five hundredths; 4.071 is read four

and seventy-one thousandths; and 0.2318 is read two thousand three hundred

eighteen ten-thousandths. When there is no number to the left of the decimal point,

the quantity indicated is less than 1.

177. Types of Micrometers.-Micrometers are made in several different types, as

shown in Figs. 166, 167, and 168.


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FIG. 166. SPECIAL OUTSIDE MICROMETERS.

The outside micrometer is used for measuring outside dimensions, such as the

diameter of a piece of round stock. The inside micrometer is used for measuring inside

dimensions, such as the bore of a cylinder. The screw-thread micrometer shown at the

upper right in Fig. 166, can be used to measure the minor diameter (diameter at root of

thread) of a screw thread. The screw-thread micrometer shown at the lower right is

used to determine the pitch diameter of a screw thread. The depth micrometer is used

to

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a. micrometer head d. lockscrew

b. extension rods d. lock screw

c. standard ring e. collar

FIG. 167. INSIDE MICROMETER.

measure the depth of holes or recesses. The ball-anvil micrometer can be used to

measure the thickness of tubing or bearing inserts, the ball shape fitting the contour of

a cylindrical shape and reducing the possibility of damage to soft bearing metal. The

tube-wall micrometer is also suitable for measuring the thickness of tubing.

178. Range of Micrometer.-Micrometers are usually made so

FIG. 168. 1-INCH INSIDE MICROMETER AND DEPTH MICROMETER.

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that 1 inch is the longest movement possible between spindle and anvil. The frames of

micrometers, however, are available in a wide variety of sizes, from 1 inch up to as large

as 24 inches for special work. The rangeof a 1-inch micrometer is from 0 to 1 inch; in

other words, it can be used on work where the dimension of the part to be measured is

1 inch or less. A 2-inch micrometer has a range from 1 inch to 2 inches, and will

measure only work that is between 1 and 2 inches thick. A 6-inch micrometer has a

range from 5 to 6 inches, and will measure only work that is between 5 and 6 inches

thick. It is necessary, therefore, in selecting a micrometer, to find the approximate size

of the work to the nearest inch and then use a micrometer that will fit it.

When it is necessary to use an inside micrometer of the type shown in Fig. 167, an


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extension rod of the correct size must first be inserted in the micrometer head. The

extension rod used must be the one that will enable the micrometer to measure the

desired dimension. As the micrometer shown in the illustration has a movement of

only 1/2 inch, a standard ring, which can be slipped over the extension rod, thus

moving the collar 1/2 inch from the micrometer head, is provided. This permits an

additional adjustment of 1/2 inch to be obtained. The combination of various parts

therefore enables various measurements to be taken, within the range of the

instrument.

To measure a cylinder with a diameter of approximately 6% inches, for example, the

extension rod labeled "6 - 7" would be used, and the range of the instrument would be

from 6 to 6 1/2 inches. If the diameter of the cylinder were approximately 6 3/4 inches,

however, the standard ring would be slipped on the rod before insertion in the

micrometer head. This would permit measurements from 6 1/2 to 7 inches to be taken.

179. Mechanics of Micrometer.-A micrometer actually records the endwise travel of a

screw during a whole turn or any part of a turn. The micrometer screw has 40 threads

to the inch, that is, when the screw is turned 40 times, it moves the spindle exactly 1

inch either toward or away from the anvil. A clockwise turn moves the spindle of an

outside micrometer toward its anvil; a counterclockwise turn moves the spindle away

from the anvil. It is clear, therefore, that a single turn of the micrometer screw moves

the spindle 1/40, or 25/1,000 (0.025) inch. (1.000 inch / 40 = 0.025 inch.)

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180. Reading the Micrometer.-As just explained, if the thimble of a micrometer is

turned through one complete revolution, the micrometer opens or closes 0.025 inch.

Hence, to change the opening distance of 0.001 inch, the thimble should be turned

through only 1/25 of a revolution. To measure in thousandths of an inch by using the

micrometer, therefore, the problem involved is to count the number of complete

revolutions, plus any part of a revolution, in twenty-fifths, that the thimble makes to set

the spindle and anvil exactly against the work being measured. For this purpose, the

barrel and thimble of micrometers are marked as shown in Fig. 169.

FIG. 169. READING THE MICROMETER.

The revolution line on the barrel should be understood first. It is graduated in 40

divisions, each 0.025 inch in width, and a complete revolution of the thimble moves the

thimble exactly 0.025 inch along the barrel, or from one graduation to the next. The

spindle moves the same distance and in the same direction. Two complete revolutions

move the thimble 0.050 inch, 3 revolutions 0.075 inch, and 4 revolutions 0.100 inch(1/10 inch). The numbers

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at every fourth graduation on the revolution line therefore indicate tenths of an inch,

and there are 10 such numbers.

Assume, for example, that the micrometer is in the closed position, and the thimble is

then turned counterclockwise through 4 whole revolutions. When this has been done,

the edge of the thimble would exactly coincide with the fourth graduation (marked 1)

on the revolution line, and the opening between the spindle and the anvil would be

1/10 inch. If the thimble were turned further until the edge coincided with the next

(fifth) graduation on the barrel, 5 revolutions would have been made and themicrometer would be opened 0.125 inch.

As the graduations on the barrel divide the inch into parts of 25/1,000 (0.025) inch, as

just explained, and since there are 25 graduations on the circumference of the thimble,


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each graduation on the thimble represents 1/25 of 0.025 inch, or 0.001 inch. With the

zero line of the thimble on the revolution line, for example, and then turning the

thimble just enough to move the next thimble graduation to the revolution line, the

spindle is moved exactly 0.001 inch. As the thimble is turned, each time a graduation on

the thimble passes the revolution line on the barrel, the micrometer opens or closes

0.001 inch.

181. For the purpose of this explanation, assume that the micrometers of Fig. 169 are

being used to measure the thickness of three different pieces of metal, and that the

thimble has been turned in each case until the spindle and anvil are bearing (but not

forced) against the material being measured.

In the upper illustration it is clear that the thimble is slightly outside the 3 mark on the

revolution line. The material is therefore larger than 0.300 inch. No other graduations

are visible to the right of the 3 mark, hut is noted that the 4th graduation (the one just

before 5) of the thimble is on the revolution line. The measurement is therefore 0.304

inch, as demonstrated in the following:

0.300 (largest number on revolution line between zero and edge of thimble)

0.000 (no graduations between 3 and edge of thimble) 0.004 (number of

graduations on thimble between zero and revolution line)

-----

0.304 inch

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In the middle illustration of Fig. 169, the largest number on the revolution line between

zero and the edge of the thimble is 2, which represents 0.200 inch. Then it is necessary

to add the distance represented by the number of unmarked graduations between the

2 and the edge of the thimble. Although not clearly shown in the illustration, the

thimble has just uncovered a graduation line, which represents an additional 0.025

inch. The zero on the thimble has also passed the revolution line in the opening

direction, and the first graduation on the thimble is on the revolution line. The total

opening of the micrometer, and therefore the thickness of the material being

-measured, is shown in the following:

0.200

0.025

0.001

----

0.226 inch

In the lower illustration of Fig. 169, the largest number on the revolution line between

zero and the edge of the thimble is 2; there are no unmarked graduations visible

between the 2 and the edge of the thimble; and the 24th graduation of the thimble is

on the revolution line. The measurement represented by the reading is therefore

shown in the following:

0.200

0.0000.024

----

0.224 inch

It should be noted, in this last example, that the edge of the thimble appears to

coincide with the 0.025 graduation on the barrel; but if this were true, the zero line on

the thimble would coincide with the revolution line, which it does not do. The fact that

the 24th graduation of the thimble is on the zero line shows that the 0.025-inch

graduation on the barrel has not been reached. In the middle illustration of Fig. 169,

however, the fact that the 1st graduation of the thimble is on the zero line presents

evidence that the 0.025-inch graduation on the barrel has been reached.

182. In each of the illustrations of Fig. 169, one of the thimble graduations is exactly

aligned with the revolution line. This

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alignment will not always occur in actual practice; in many cases when the

measurement is taken the thimble graduation will be at one side of the revolution line.

An example of this type of reading is shown in Fig. 170, where the revolution line is

between the 14th and 15th graduations of the thimble.

FIG. 170. READING BETWEEN LINES.


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For reasonable accuracy the reading of Fig. 170 can be taken to the nearest graduation,

the 15th. The reading in this case would be:

0.300

0.025

0.015

----

0.340 inch

For closer work, however, the position of the revolution line relative to the thimble

graduations can be estimated. In this case it is about 7/10 of one graduation past the

14th graduation, and the reading can be taken as:

0.300

0.025

0.014

0.0007

----

0.3397 inch

183. Vernier.-In the illustrations of Figs. 169 and 170, the micrometers are constructed

to take measurements to 1/1000 inch, measurements less than 1/1,000 inch being

estimated, as explained in the preceding article. Many micrometers, however, have avernier scale on the barrel, enabling measurements to be taken to 1/10,000 inch.

The fundamental idea of a vernier scale is to divide a line of known length into equal

parts, and to compare the size of the divisions with those on a line the same length as

the first one, but

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FIG. 171. VERNIER SCALE MICROMETER.

divided into one less part. This is illustrated in Fig. 171, the left-hand view representing

the barrel and thimble of a micrometer, but flattened out for the purpose of this

explanation. The graduations, marked 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, on the barrel, comprisethe vernier scale.

Observe that 10 divisions of the vernier are exactly equal to 9 divisions on the thimble.

Since each division on the thimble represents 0.001 inch, each division on the vernier

represents 0.0009 inch. This is shown as follows:

9 X 0.001 / 10 = 0.0009

It is apparent, therefore, that each division on the vernier represents a distance 0.0001

inch smaller than is represented by each division on the thimble. It can also be seen in

Fig. 171, that when zero on the vernier coincides with zero on the thimble, the next

graduation on both vernier and thimble will be 0.0001 inch apart, the second pair will

be 0.0002 inch apart, and so on, until the graduations coincide again at zero on the

vernier.

When the zeros of the vernier exactly coincide with lines on the thimble, a line on the

thimble also exactly coincides with the revolution line on the barrel, and the reading is

in thousandths. This is the condition shown in the left-hand view of Fig. 171, where the

reading is 0.2470 inch.

In the right-hand illustration of Fig. 171, however, the zero lines of the vernier do not

exactly coincide, and the graduation

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on the thimble does not coincide with the revolution line. To take this reading, the

procedure is the same as before: 0.200 inch for the 2 on the barrel; 0.075 inch for thethree divisions visible to the right of the number 2; and 0.011 inch because the 11th

graduation on the thimble has passed the revolution line on the barrel. In addition,

however, observation of the vernier scale shows that the vernier line marked 2 is the

one that exactly coincides with a graduation on the thimble. Since each graduation of


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the vernier scale represents a difference of 1/10,000 (0.00001) inch, 2/10,000 (0.0002)

are added, and the reading is 0.2862 inch.

184. Using Micrometer.-The use of an outside micrometer in measuring the

dimensions of a piece of metal is shown in Fig. 172.

FIG. 172. USE OF MICROMETER.

As explained previously, a micrometer of the correct size for the work must be selected.

In view (a) of Fig. 172 a 1-inch micrometer is used because the material is less than 1

inch in thickness. In view (b) a 2-inch micrometer is used because the dimension is

between 1 and 2 inches.

The piece of work to be measured should be wiped clean. The micrometer should be

opened wide enough to slip over the work

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freely, and the spindle and anvil should be wiped off. The thimble should then be

turned clockwise until the spindle and anvil lightly touch the work. A very light pressure

only is required. If the micrometer is tightened with too much force, the frame will

almost surely be sprung out of shape and readings will be inaccurate. Many

micrometers are equipped with a ratchet stop on the end of the thimble, as shown in

Fig. 165, the ratchet preventing the user from closing the tool with too much force. The

ratchet stop is made so that it will slip and click when a certain amount of force is

applied to it, and so prevent the spindle from moving further. If a micrometer has a

ratchet stop, it should always be used.

Finally, take the reading of the micrometer while it is still on the work. The enlarged

view in (a), Fig. 172, shows the reading on the left-hand micrometer, and the other

enlarged view shows the reading on the right-hand micrometer.

185. The methods used in measuring the diameter of round stock are shown in Fig.

173. When the correct size micrometer has been selected, the procedure is the same as

in measuring a piece of material with flat surfaces. Care should be taken, however, to

insure that the material is measured at points exactly opposite each other; this is done

by sliding the micrometer back and forth across the piece until the right "feel" is

obtained. Note that a micrometer which measures dimensions between 16 and 17

inches is used in (b), Fig. 173.

FIG. 173. MEASURING ROUND STOCK.

184


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FIG. 174. MEASURING INSIDE DIAMETER.

186. The correct use and position of an inside micrometer when taking the inside

measurement of a small cylinder are shown in Fig. 174. As explained previously, thefirst step in the measurement is to find the approximate diameter with a rule; then

select the correct extension rod and insert it in the micrometer head. Be sure that both

the rod and micrometer head are thoroughly clean, and that the rod is screwed in the

full distance. Neglect of either of these precautions may result in an inaccurate

measurement.

In order to use this type of inside micrometer it is necessary to know the length of the

micrometer head, which in this case is M inches, when in the closed position. The

instrument is also equipped with a 4-inch head for longer measurements. The

micrometer heads have a range of 1 inch.

The length of each extension rod is stamped on the rod, a common set including rods

from 1 inch to 14 inches in length, thus enabling the instrument to measure distances

from 1 1/2 inches to 19 inches.

To "mike" the cylinder illustrated in Fig. 174, since measurement with a rule has shown

the diameter to be somewhere between 4 and 4 1/4 inches, the 2-inch extension rod is

used, as it will enable the tool to measure distances from 3 1/2 to 4 1/2 inches.

185

When the extension rod has been properly inserted in the micrometer head, place the

end of the rod against one side of the cylinder and turn the thimble of the micrometer

until the head barely touches the other side at a point exactly opposite. Then read the

dimension while the micrometer is still in position. Never let the micrometer bear

heavily enough to hang in the work with the hands removed from it.

187. Another method used for measuring smaller work, where an inside micrometer

will not fit conveniently, is to use a telescoping gage, as shown in Fig. 175. The

telescoping gage should

FIG. 175. TELESCOPING GAGE.

be adjusted in the work until it exactly touches points directly across from each other,

and is then locked by turning the stem. When this has been done, the gage is removed

and the dimension measured with an outside micrometer as shown in the upper view

of Fig. 175.

For very small holes, the small inside micrometer shown in Fig. 168 is convenient. The

use of this tool is demonstrated in Fig. 176, and the two different readings show that it

is read like other micrometers, except that the numbers on the barrel increase toward


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the left instead of toward the right.

186

FIG. 176. MEASURING DIAMETER OF SMALL HOLES.

188. When it is necessary to measure the depth of a hole, a depth micrometer can be

used, as shown in Fig. 177. Before taking this measurement, remove all burrs and make

sure that the surface of the work around the top of the hole is clean and smooth. The

correct size of extension rod is then selected and attached to the micrometer, and with

the base of the micrometer set firmly against the flat surface, turn the thimble

clockwise until the extension rod just touches the bottom of the hole. If the micrometer

is equipped with a ratchet stop, it should be used. The measurement is read in the

usual manner.

189. As the micrometer is a delicate precision tool, every precaution should be taken toprevent damage to it. Handle it with care and do not allow it to become rusty or dirty.

After it has been used, wipe it off with a clean cloth to which a few drops of fine

machine oil have been added. When not actually in use, keep the micrometer in a

wooden or metal box, with a felt lining.

Micrometers are often ruined by being closed too tightly on the material measured.

Remember that only a very light pressure is

187

FIG. 177. USE OF DEPTH MICROMETER AND EXTENSION ROD.

needed to obtain an accurate measurement. Also, always hold the frame stationary and

adjust the tool by turning the thimble. Do not hold the thimble and swing the frame

around in order to open or close a micrometer.

When using large micrometers, care is needed to see that the frames are not handled

roughly or sprung out of shape. When working with the larger micrometers in cold

weather, it is good practice to use a piece of cloth or waste between the hand and the

frame, as the heat of the hand may expand the frame enough to cause a variation in

the reading.

190. Vernier Calipers.-A vernier caliper, Fig. 178 (a) , resembles a caliper rule and is

used for the same purpose. The difference, however, is that the vernier caliper canmake precision measurements because it has its own vernier scale.

The blade of one common type of vernier caliper has a scale that is divided into inch

spaces. These spaces are sub-divided into spaces of 1/10 (0.100) inch and 1/40 (0.025)


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inch. The sliding jaw carries the vernier scale, and this scale has 25 spaces, each of

which is only 0.024 inch, 0.001 inch less than a space on the blade scale. (There are

actually two vernier scales on the sliding jaw, one marked "outside" for outside

measurements, and the other marked "inside" for inside measurements.)

To take a measurement with the vernier caliper, first set the

188

FIG. 178. VERNIER CALIPER.

caliper to the thickness or diameter of the material being measured, and lock the

sliding jaw to the blade with the knurled-head set screw. Then read the blade scaletoward the right, Fig. 178 (b), and record the reading of the last graduation on the left of

the zero of the vernier scale. In this particular instance the last graduation on the left of

vernier zero represents 1.425 inches. Then carefully examine the vernier scale, Fig. 178

(b), and it will be seen that the 11th graduation on the vernier exactly coincides with a

graduation on the blade. The reading is therefore as follows:

1.425

0.011

----

1.436 inches

Vernier depth gages are set and operated in much the same way as a vernier caliper.

The vernier principle is also applied to a number of other gages, instruments and tools.

189

191. Gage Blocks.-Gage blocks are rectangular pieces of tool steel, having two

measuring surfaces which are flat, parallel with each other, and a predetermined

distance apart, the distance being accurate to within 0.000002 (two millionths) inch.

These blocks are so exactly machined, finished and lapped, that if the measuring

surfaces of any two of them, when thoroughly clean, are slid together with a slight

inward pressure, they will adhere to one another as though magnetized. Gage blocks

(sometimes called jo-blocks, from Johanson, their originator) are available in three

grades of accuracy:

1. Laboratory set, AA quality, accurate to 0.000002 inch.

2. Inspection set, A quality, accurate to 0.000004 inch.

3. Working set, B quality, accurate to 0.000008 inch.

A full working set of gage blocks is made up of 81 blocks. The set consists of four series

of sizes, as follows:

1. First series. 9 blocks, ranging in size from 0.1001 inch to 0.1009 inch, in steps

of 0.0001 inch.

2. Second series. 49 blocks, ranging in size from 0.101 inch to 0.149 inch, in

steps of 0.001 inch.

3. Third series. 19 blocks, ranging in size from 0.050 inch to 0.950 inch, in steps

of 0.050 inch.

4. Fourth series. 4 blocks, 1 inch, 2 inches, 3 inches, and 4 inches.

By sliding different sizes of blocks together, the machinist can obtain any


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measurement, in 1/10,000 of an inch, from 0.1001 inch to 12.00 inches, and in 1/1,000

of an inch, from 0.100 inch to 12.00 inches.

Gage blocks are commonly used for checking the accuracy of other gages, such as snap

gages or micrometers, although it is practical to use them directly on a piece of work to

be measured.

If it is desired to check the accuracy of a micrometer, any block or combination of

blocks within the range of the micrometer can be used. Wipe the measuring surfaces

clean on the hand or a piece of chamois, and slide them together so that they adhere.Then measure the thickness of the gage blocks with the micrometer being tested. If the

micrometer reading agrees with the known thickness of the gage blocks, the

micrometer is accurate.

192. Speed Indicator.-When it is desired to know the number

190

of revolutions per minute made by an electric motor, turbine rotor, or other revolving

part, the information can be secured by the use of a speed indicator, such as shown in

Fig. 179.

FIG. 179. SPEED INDICATOR.

This type of speed indicator has a spindle that is free to turn in the body of the

instrument, the spindle being geared to the graduated ring in such a way that 100 turns

of the spindle cause the ring to make exactly one complete revolution. The ring is

graduated into 100 equal parts, and is numbered both right-handed and left-handed,

so that the indicator may be used on a shaft that is turning in either direction.

The indicator has a set of interchangeable rubber tips that fit on the spindle.

Cone-shaped, flat end and vacuum tips are usually supplied. The cup-like vacuum tip

works best on the flat end of a shaft; the cone tip is best when the shaft has a

countersunk end.

In order to use this type of speed indicator, a stop watch or a watch with a sweep

second hand is needed. Then slip the correct tip over the end of the spindle and apply

the tip to the rotating shaft. When the zero is observed to pass under the starting mark,

an assistant should start the stop watch. The number of times that the zero passes the

starting mark is then counted. When a minute (or any other desired period of time) has

elapsed, the indicator is quickly removed from the shaft and the position of the ring

noted. If, for example, the ring has made 17 revolutions during the minute and the 60

graduation stands under the starting mark, the reading is taken as 1,760 rpm.

Another type of speed indicator has a small pin on its graduated ring, and is equipped

with a notched disk. Every time the graduated ring makes a complete turn, the pin on it

passes under a spring finger, lifting the spring finger and allowing the notched

191

disk to move one notch. At the end of the test the number of notches that the notched

disk has moved is counted. Each notch represents 100 revolutions of the spindle.

Some speed indicators are equipped with a small rubber-faced wheel which can be

slipped on the spindle. The wheel is used when it is desired to find the speed, in feet

per minute, at which the surface of a piece of work is moving. To do this, the wheel is

pressed against the face of the work whose surface speed is to be found, holding the

spindle parallel to the face of the work and noting the elapsed time carefully. The wheel

is generally of such a size that every revolution of it represents a movement of 6 inches

(1/2 foot) of the surface of the work. The total reading of the indicator, for 1 minute, is

therefore divided by 2, and the result is the speed of the surface of the work, in feet per

minute.

193. Tachometer.-A tachometer differs from the speed indicators previously

described, in that it registers directly the revolutions of the rotating shaft, no timing or

computation being necessary. A tachometer designed for use with either high, medium,

or low-speed machinery is shown in Fig. 180. To use this tachometer on


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FIG. 180. TACHOMETER.

192

an alternator operating at 3,600 rpm, for example, the gear shift would be set in the

HIGHposition and the reading taken from the outer graduated circle. For a machine

operating at 800 rpm, the tachometer gear shift would be set in the LOWposition and

the reading taken from the next to the outer graduated circle.

A self-energized electric tachometer, as shown in Fig. 181, is sometimes used aboard

ship.

FIG. 181. ELECTRIC TACHOMETER.

194. Sounding Rods and Tapes.--One of the most common measurements taken

aboard ship is that of sounding the tanks, as a check of the available quantity of water,fuel oil, lubricating oil, etc., must be made often. There are various devices, to be

described in another lesson, which permit the amount of liquid in each tank of a ship to

be measured hydraulically and to

193

be read from a gage located in a convenient position. Not all ships are so equipped,

however, and there are many occasions when it is necessary to sounda tank,

measuring the depth of liquid in it by means of a sounding rod or tape.

If the tank is not too deep, a metal rod, graduated in inches, and with a line fastened to

its upper end, may be lowered through the sounding pipe until it reaches the bottom of

the tank. If the liquid is fuel oil, the depth of oil in the tank is shown on the rod when itis withdrawn from the tank. If water is contained in the tank, the rod should be coated

with chalk before being lowered, as this will enable the depth of water to be seen more

readily on the rod. Even though the tank is an oil tank, it is often advisable to chalk the

lower portion of the rod, as this may help to detect any water that is present, the water


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having settled to the bottom of the tank. In such a case, when the sounding rod is

removed from the tank, small bubbles would be observed on the portion of the rod

that extended into the water.

Chalking of the sounding rod is especially important when checking the measurement

of an empty or nearly empty double-bottom tank, or any other fuel tank that could

possibly leak and admit sea water. A most essential time for this to be done is when the

tanks are sounded before taking on fuel supplies. The sounding rod should be

scrutinized carefully for water, and if its presence is detected, it may very well indicate

that a leak has developed in the tank since the last measurement was taken. If the leaky

tank were to be filled with fuel, the fuel would become contaminated and within a short

time would possibly be unusable and a total loss. A congealing condition might also

result that would make the removal of the contaminated oil very difficult and

expensive.

It is recommended that the sounding rod, or other arrangement lowered into a

sounding pipe, be made of brass or bronze rather than of iron or steel. The iron or steel

might cause a dangerous spark when dropped into an empty fuel tank.

In the ullagemethod of measuring the depth of liquid in a tank, a cup-shaped weight is

lowered until the weight comes into contact with the surface of the liquid. A

measurement is then taken which gives the distance from the surface of the liquid to

the upper end of the sounding pipe. The total distance from the bottom of the tank to

the upper end of the sounding pipe being known, it is only necessary to subtract themeasurement from the total distance in order to find the depth of liquid in the tank.

This method

194

has the advantage that the sounding apparatus does not become so smeared with oil

as would be the case when lowered to the bottom of an oil tank.

The measurements taken with the equipment just described are usually in inches. In

order to determine the quantity of liquid in gallons or barrels, it is necessary to consult

a conversion chart for the tank in question.

195. Torsion Meter.-The torsion meter is an instrument used for determining the shafthorsepower being transmitted by a revolving shaft, such as the line shaft of a turbine-

propelled vessel. The torsion meter measures the torsion, or twist, of the shaft under

operating conditions, and this measurement, in conjunction with the known stiffness of

the material of which the shaft is made, and the rpm of the shaft, enables the

horsepower to be computed.

The torsion meter is usually used during the trial trip of a vessel and is then removed. It

is not ordinarily a part of the permanent installation of the ship. The instrument may be

designed to measure the torque by mechanical means, and there are also electric

torsion meters.

195

ENGINE-ROOM TOOLS, PART 3

EXAMINATION QUESTIONS

Instructions : -Study the lesson very carefully before considering the examination

questions. Then read each question slowly and be sure that you understand it. When

answering the questions, always take sufficient time, prepare the answers in your own

words, and do your best work. In arranging your answers, please leave space between

them so that the instructor will be able to write in helpful explanation, should you make

an error or overlook an important point.After the answers are completed, check them

again very carefully; make sure that all questions are taken care of; correct each error that

you find; and mail your work to us.

1. What is the measurement of the rectangular piece of stock, Fig. 134?

2. What type of rule can be used to measure:

(a) the outside diameter of a shaft?

(b) the depth of a piston ring groove?

3. It is desired to cut a piece of sheet metal so that a tube 20 inches long and

approximately 2 7/8 inches in diameter can be constructed. The edges of the metal are

to overlap 1/2 inch. Explain how the necessary width of material can be determined

without calculation or reference to Tables.

4. When preparing to locate the exact point for drilling a hole in a piece of metal, it is

often helpful to coat the area with chalk. Explain why.

5. Explain how to set a pair of dividers to lay out a 4-inch circle.

6. (a) Explain, in detail, how to line up a coupling.

(b) Explain the care to be given a feeler gage when not in use.


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196

7. Explain why a sounding rod is coated with chalk, especially when sounding fuel oil

double-bottom tanks prior to taking on fuel.

8. What danger may arise from the use of an iron or steel sounding rod?

9. What is the range of a 3-inch micrometer?

10. What is the purpose of a ratchet stop on a micrometer? How does it function?

11. What type of micrometer would be used to measure the thickness of a bearing

insert?

12. Explain in detail how a micrometer of the type shown in Fig. 174 would be used to

measure the exact diameter of a cylinder which has a diameter slightly less than 14

inches.

13. A 2-inch outside micrometer has been opened 32 turns when the measurement of

the thickness of a piece of metal is taken. How thick is the metal? Explain.

14. When the thimble of a micrometer has been turned sufficiently to uncover exactly 8

graduations on the revolution line of the barrel, what distance has the spindle moved?

15. What is the measurement indicated by the micrometer reading at the left, Fig. 172?

16. What is the measurement indicated by the micrometer reading at the right, Fig.

172?

17. What is the measurement indicated by the lower micrometer reading, Fig. 176?

18. Give the measurements indicated by each of the 9 examples shown in Fig. 182. A

1-inch micrometer is used in each instance. Number your answers in accordance with

the illustration.

197

FIG. 184.

19. What measurement is indicated by the 1-inch vernier micrometer, Fig. 183?

FIG. 183.

198

20. Give the measurements indicated by views (a) and (b) of Fig. 184. This is a 1-inch

micrometer.


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