Floating Carriage Micrometer
Floating Carriage Micrometer
A floating carriage micrometer is an instrument for measuring the sizes of threaded specimens such as plug gauges and screws. It's used to figure out what the major, minor, and effective diameters.
It includes a centre, a fiducial indication, a micrometer drum, and a clamping screw, among other features.
The basic setup consists of two pillars with a task or master setting cylinder placed in the middle.
The micrometer drum is mounted on one end, while the fiducial indication is fixed on the other.
To hold the task or master setting cylinder, a clamping screw and anvil are connected.
The main diameter is measured using a bench micrometer to provide higher precision. Variations in measuring pressure and pitch error are ignored in this approach.
The fiducial indicator ensures that all measurements are performed at the same pressure. The instrument contains a micrometer head with a vernier scale that allows it to read with 0.002 mm precision.
Setting standard is a calibrated setting cylinder with the same diameter as the primary diameter of the thread to be measured.
The reading is obtained after the standard has been established by holding the setting cylinder between the anvils.
The cylinder is then replaced with a threaded work piece, and new measurements are taken for major and minor diameters, with the wire fastened at the pitch gap to determine the effective diameter.
The below image (Figure 1) shows the thread parameters using two wire method.
2. Thread Parameters
Major diameter (External):
A thread formed on the outside of the work specimen is called Major diameter.
Minor diameter (Internal):
A thread formed on the inside of the work specimen is called Minor diameter.
Effective diameter (Pitch dia):
It is an imaginary line which is co-axial with the axis of the thread and cuts the flank of the thread so that the thread width and space width are equal. The below image (Figure 2) shows the calculation of major diameter, minor diameter and effective diameter.
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