ME: 121 Engineering Practices. Precision Measuring Instruments Inside, Depth, Height and Angular Measuring Instruments. Precision Measuring Instruments. VERNIER CALIPER OUTSIDE MICRO METER INSIDE MICROMETER CALIPER INSIDE MICROMETER DEPTH MICROMETER VERNIER HEIGHT GAUGE
Precision Measuring Instruments
Inside, Depth, Height and Angular Measuring Instruments
2”-3”...... up to 12”.
0 – 25 mm,
25 – 50 mm,
50 – 75 mm,
75 – 100 mm
1. Frame :- The frame is made of Cast iron on which the whole assembly is attached.
2. Barrel/Sleeve:- Main scale is graduated on it with 0.5 mm distance.
3. Thimble:- Divisions are marked on this cylindrical portion. Knurling is made on it for better gripping.Construction of Outside Micrometers
7Construction of Outside Micrometers
4. Spindle:- Spindle is one of the contacting surface during measurement. It moves to and fro as thimble rotated.
5. Anvil:- It is the another contacting surface which is fixed in Frame.
6. Lock nut:- This nut is used to lock the movement of the spindle.
7. Ratchet:- Ratchet is used to apply uniform pressure during measurement.
In metric micrometer the pitch of the spindle thread is 0.5 mm. Thereby in one rotation of the thimble, the spindle advances by 0.5 mm
Barrel graduationGraduation of Outside Micrometers
The circumference of the bevel edge of the thimble is graduated into 50 divisions
The distance moved by the spindle during one rotation of the thimble is 0.5 mm.
Least Count of Outside Micrometer
The least count of a Metric Micrometer is 0.01 mm. It is the ratio of value of 1 main scale division and total graduations on thimble. i.e. 0.5/50
Zero Error of Outside Micrometer
When the anvil and spindle of the micrometer touch each other, the scales should read zero.
If not, there is a zero error in the micrometer.
If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative.
} 3 divisions
supposing observed reading is 2.87 mm, then
corrected reading = observed reading – zero error
= 2.87 – (-0.03)
= 2.90 mm
Thus 13.00 mm + 00.50 mm
Next read the thimble graduation, which is 13. Multiply it by L.C. which is 0.01mm. = 13 x 0.01 mm = 0.13mm.
reading on sleeve = 4.5 mm
reading on thimble = 0.12 mm
actual reading of object = 4.5 + 0.12
= 4.62 mm
How to Read 0 -1” Micrometer
All inside measuring instruments fall into TWO categories
Direct Reading Instruments: The size of the hole can be read on the instrument being used to measure the hole, e.g. Inside Micrometers, the Intrimik, and the Vernier Caliper.
Transfer Type Instruments: Set to the diameter of the hole and then this size is transferred to an outside micrometer to determine the actual size, e.g. Inside Calipers, Small Hole Gages and Telescope Gages
To Use an Inside Micrometer Caliper
Adjust the Jaws to slightly less than the diameter to be measured
Hold the fixed jaw against one side of the hole and adjust the moveable jaw until the proper “Feel” is obtained
Move the moveable jaw back and forth to ensure that the measurement taken is across the true diameter
Set the lock nut, remove the instrument, and check the reading.
To Measure with an Inside Micrometers
Measure the size of the hole with a rule.
Insert the correct micrometer extension rod.
Align the zero marks on the rod and micrometer head.
Hold the rod firmly against the micrometer head and tighten the knurled set screw.
Adjust the micrometer to slightly less than the diameter to be measured.
Hold the head in a fixed position and adjust the micrometer to the hole size while moving the rod end in the direction of the arrows.
Carefully remove the micrometer and note the reading.
To this reading, add the length of the extension rod and collar.
Using an inside micrometer to measure the size of a hole
Reading Inside Micrometers
The inside micrometer reads in the same manner as the standard micrometer. Since there is no locking nut on the inside micrometer, the thimble nut is adjusted to a tighter fit on the spindle thread to prevent a change in the setting while it is being removed from the hole.
A difficulty encountered in measuring hole sizes with instruments employing only two measuring faces is that of properly measuring the diameter and not a chord (a group of notes, usually three or more surrounded together in harmony) of the circle. An instrument that eliminates this problem is the Intrimik.
The Intrimik consists of a head with three contact points spaced 1200 apart; this head is attached to a micrometer-type body. The contact points are forced out to contact the inside of the hole by means of a tapered or conical plug attached to the micrometer spindle.
The construction of a head with three contact point permits the Intrimik to be self-centering and self aligning.
Construction of the Intrimik head
The Intrimik, which has three contact points, measures holes accurately
Intrimik Ranges and Accuracy
The range of these instruments is from .275 to 12.000 in., and the accuracy varies between .0001 and .0005 in., depending on the head used. Metric Intrimik have a range from 6 to 300 mm, with graduations in 0.001 mm. The accuracy of the Intrimik should be checked periodically with a setting ring or master ring gage.
It is more accurate than other methods because it provides a direct reading, eliminating the necessity of transferring measurements to determine hole size as with telescope or small hole gages
Telescope gage are used to obtain the size of holes, slots, and recesses from .3125 to 6.000 in. (8 to 152 mm). They are T-shaped instruments, each consisting of a pair of telescoping tubes or plungers connected to a handle. The plungers are spring-loaded to force them apart. The knurled knob on the end of the handle locks the plungers into position when it is turned in a clockwise direction.
To Measure Using a Telescope Gage
In transfer measurement the size of an object is taken with an instrument which is not capable of giving a direct reading. The size is then determined by measuring the setting of the instrument with a direct-reading instrument or gage of a known size.
Small Hole Gages
Small hole gages are available in sets of four, covering a range from .125 to .500 in (3 to 13 mm). They are manufactured in two types
The small hole gages have a small, round end, or ball, and are used for measuring holes, slots, grooves, and recesses that are too small for inside calipers or telescope gages.
The Small hole gages with a Flat Bottom are used for similar purposes. The flat bottom permits the measurement of shallow slots, recesses, and holes impossible to gage with the rounded type.
Both types are of similar construction and are adjusted to size by turning the knurled knob on the top. This draws up a tapered plunger, causing the two halves of the ball to open up and contact the hole.
Dial Bore Gages
Although rules and various attachments can be used for measuring depth, the depth micrometer and the depth vernier are most commonly used where accuracy is required.
Micrometer Depth Gage
Micrometer depth gages are used for measuring the depth of blind holes, slots, recesses, and projections. Each gage consists of a flat base attached to a micrometer sleeve. An extension rod of the required length fits through the sleeve and protrudes (extended) through the base. This rod is held in position by a threaded cap on the top of the thimble.
Accurate height measurement is very important in layout and inspection work. With the proper attachments, the vernier height gage is a very useful and versatile tool for these purposes. Where extreme accuracy is required, gage blocks or a precision height gage may be used.
Vernier Height Gage
The scriber reaches below the gage base
The digital height gage has an easy to read display that can be very quickly set to any dimension. The readout display is in .0001 in. (0.002 mm), and it has a zero function that allows the zero to be set at any position on the job or workpieces. This type of height gage is becoming very popular because it eliminates or reduces the errors common to height gages having vernier scales.
A depth gage attachment may be fastened to the movable jaw, permitting the measurement of height differences that may be difficult to measure by other methods.
Another important use for the vernier height gage is in inspection work. A dial indicator may be fastened to the movable jaw of the height gage, and distances between holes or surfaces can be checked to within an accuracy of .001 in. (0.02 mm) on the vernier scale.
Universal Bevel Protractor
The universal bevel protractor is a precision instrument capable of measuring angles to within 5\' (5 minutes) or (0.083°).
Universal Bevel Protractor
The reading is
Number of full degrees = 50°
Value of vernier scale (4 X 5\') = 20\'
Reading = 50°20\'
Note: A double-check of the reading would locate the vernier scale line on the other side of zero, which coincides with a protractor scale line. This line should always equal the complement of 60\'. In Fig. the 40\' line to the right of the zero coincides with a line on the protractor scale.
This reading, when added to the 20\' on the left of the scale, is equal to 60\', or 1°.