A screw micrometer is one of the types of measuring instrument consisting of a calibrated screw which has a very high level of accuracy.
The precision even reaches 0.01 mm or 0.1 cm. Therefore, this tool is generally used to measure an object that is usually in the form of a plate and has a very thin length and thickness.
When compared to other measuring tools such as rulers and calipers, this tool has a higher level of difficulty, but this is directly proportional to the level of precision or accuracy as well.
This is because the screw micrometer has two scales, namely the main scale and the rotary scale or the nonius scale.
Parts of the Screw Micrometer
A screw micrometer itself consists of several components, each of which has its own function and is certainly interrelated in the process of its use.
Therefore, the first step before you can understand how to use and read a screw micrometer any further is to know exactly what the parts are:
1. Anvil Face
This anvil part can also be referred to as a fixed axis, which means that its position will not be able to move or be dynamic (still in the same or fixed position). Used to clamp the object to be measured so that it does not move to and fro.
2. Spindle
Another name for the spindle can also be called a shear shaft which is cylindrical and driven by a thimble.
3. Lock Nut
Also known as a lock. As the name implies, this part is used to lock the sliding shaft or spindle.
4. Sleeve
This section is a circle where the measurement scale is written, both the main scale and the rotary scale or the nonius scale which will later be seen to calculate the final result of measuring the thickness of an object.
5. Thimble
This part is movable and must be moved manually by the user’s hand.
6. Ratchet
The shape of the ratchet is actually the same as the spindle or sliding shaft, only smaller. As for the function of this part is actually the same as the thimble, which is to move the sliding shaft or spindle. Only in a more subtle and slow way.
7. Frame
The frame or frame has a shape resembling the letter C which functions as a union between the fixed axle (anvil) with other components. The shape is relatively sturdy and thick to be strong enough to accommodate the parts of the micrometer screw.
How to use the Screw Micrometer
After understanding with certainty the parts of a screw micrometer, the next thing to do is to know how to use it, namely:
- Place the object to be measured on the part between the anvil or fixed shaft and the spindle or sliding shaft
- Rotate the thimble and ratchet until the object is clamped perfectly by the anvil and spindle
- Turn the lock nut to the maximum position or until it can no longer be turned
- Read the results of the main and nonius scales listed
How to Read the Screw Micrometer
The last step that is no less important to understand is how to read a screw micrometer, namely:
- Make sure the thimble position on the main scale has passed the number 5 at the top
- Notice the horizontal line at the bottom has passed 1 strip
- On a screw micrometer, for 0.5 mm it equals 5 + 0.5 = 5.5 mm. Where 1 strip represents 0.5 mm. But this only applies after passing 5 strips or lines above
- When you have crossed the 5 line limit and start to enter the 6th strip, the reading method is different again. The total distance can be read as (5 + 6) x 0.5 mm = 5.5 mm
- Unlike the case with the nonius scale, the way to read it is if the main horizontal line has touched or coincided with the number 28, then 0.28 mm is added to read it.
- The final step to reading the micrometer screw is to add up the two numbers from the above process. In this case the example is the number 5.5 + 0.28 = 5.78 mm for the results and the level of accuracy is 0.01 mm
Screw micrometers are often used to measure plates that are very thin or micro (small) because they have a high level of accuracy, up to 0.01 mm (about 10x more precise than a caliper).
If the object being measured has a thickness of more than 1 mm, the micrometer is rarely used because it will be easier and more precise if you use other measuring tools such as a ruler or caliper.
This length measuring equipment is generally often used in physics learning materials in schools. Understanding exactly how to read a screw micrometer before using it can certainly simplify the process of using it.