Micrometer Operating Principles
Micrometer Operating Principles
A micrometer is a device that uses a graduated screw mechanism to produce precise linear displacement of a spindle along its axis. Distance measurement is achieved referencing the linear displacement of the spindle to a fixed measuring face on the axis of the spindle (the anvil). The main components of a micrometer are shown in Figure.
The inner sleeve, which has the guide threads of the feed mechanism, is fixed to one end of the frame. The anvil, which serves as a fixed measuring face, is attached to the opposite end of the frame.
The spindle has a measuring face at one end and an external thread at the other. It is fitted to the inner sleeve, which ensures the linearity of the spindle motion in the axial direction. The spindle’s external thread engages with the internal thread of the inner sleeve.
Micrometer caliper parts
The measuring face of the spindle serves as a contact point for measuring the workpiece. Measurement is performed by feeding the spindle so that both the anvil measuring face and the spindle measuring face touch the workpiece.
The outer sleeve has graduations that correspond to the spindle’s thread pitch and an index line to aid reading of the graduations on the thimble.
The thimble is fixed to the spindle so that both components turn together and is knurled for ease of turning.
starrett outside micrometers series
The ratchet stop applies constant pressure to the workpiece being measured and consists of a leaf spring and a ratchet mechanism.
The clamp, fixed to the spindle guide section of the frame, locks the spindle against the inner sleeve.
A standard micrometer has a screw thread of 0.5 mm pitch with a thimble graduated in fifty equal divisions around its circumference. Micrometers are manufactured in size ranges of 0 to 25 mm, 25 to 50 mm, …, 575 –600 mm etc. As an example a dimension of 19.45 mm would be measured with a 0 to 25 mm micrometer and a dimension of 580.25 mm with a 575-600 mm micrometer.
A micrometer is a mechanical device designed to measure distances as small as 1/10,000 of an inch (0.0001 in).
Micrometers are only one (1) inch long.
The micrometer is used with different types and sizes of frames to provide precise measurements of many different objects.
Small engines uses three (3) types of micrometers:
1. Micrometer caliper
2. Inside micrometer
3. Depth gauge micrometer
Micrometer calipers are available in mechanical and digital models.
Micrometer caliper
A micrometer caliper uses a frame that allows the micrometer to measure the thickness of objects.
For small engine use, different frame sizes are used to provide a wider measurement range.
- One inch
- Two inch
- Etc.
Reading Micrometer Caliper-parts
The first step in being able to read a micrometer is learning the names of the parts.
The face of the anvil and the face of the spindle are the contact surfaces.
The spindle and thimble turn together.
The ratchet/friction stop improves the repeatability of measurements for beginners.
A micrometer caliper is read at the point were the edge of the thimble crosses the barrel scale
Insure the lock is released before trying to turn the thimble.
Reading Micrometer Caliper-barrel
• A micrometer caliper is read just like an ruler.
• Start by determining the smallest whole unit, and then determine the values of each sub division.
• The smallest whole unit is determined by the frame size.
- One (1) inch frame = 0.0 smallest whole unit
- Two (2) inch frame = 1.0 smallest whole unit.
- Etc.
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