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ASME B1.25-2019 pdf free

ASME B1.25-2019 pdf free.Measurement Uncertainty Factors in the Calibration of Screw Thread Gages.
linearity: a measuring instrument characteristic comparable to accuracy. An instrument is said to be linear” when, for every unit of input, it displays an equal unit of measured value. A simple example of this is a dial or digital indicator. For every 0.0001 in. (0.001 mm) the contact point is moved, the display reading will show a change of the same amount.
National Institute of Standards and Technology (NIST): the national legal authority for measurements in the United States through which measurements may be linked to international standards for length, such as SI, etc. Formerly called the National Bureau of Standards (NBS).
pitch, linear: the distance between corresponding points on adjacent thread forms in the same axial plane on the same side of the thread axis. It is often incorrectly referred to as lead.”
reading: a measuring device’s display of a measured value or its variation from a master.
repeatability: the range within which a device will repeat a given measured value overa short period of time. While an important characteristic of the measurement process, repeatability on its own should not be confused with accuracy or uncertainty.
resolution: the smallest measured value an instrument can display. While a critical feature of any instrument, it is not necessarily an indication of that Instrument’s performance.
ASME B1.25 simple pitch diameter: on a parallel thread, the imaginary cylinder or diameter that passes through the thread form in such a way that the widths of the thread ridge and groove are equal. This diameter is equidistant from the top and bottom of a perfect unrelieved thread form. Also known as thread groove diameter.
threadform: a thread’s profile in an axial plane fora length of one pitch of the thread.
thread form, half angle: the angle of one flank of a thread form. A 60-deg symmetric thread form is defined by two 30-deg half angles.true value: the precise value of a measured feature that is, in practice. unknowable. The difference between this value and that obtained through calibration is the measurement uncertainty for the process.
While handheld portable instruments and thread- measuring wires may be used for measuring product pitch diameter and other dimensions, the level of precision of these methods is inadequate for the calibration of gages. This would be shown by an uncertainty budget for such a process compared to one using suitable equipment.
In this section. the minimum requirements for equipment are shown to assist users In evaluating the suitability of their equipment for calibration work. In all cases, it is assumed that the instruments, thread-measuring wires, and masters being used are in a known state of calibration.
4.1. Bench Micrometers and SimiLar Devices
Bench micrometers and similar precision-measuring devices function much in the same way as outside micrometers; the axis of the gage may be vertically oriented, or the gage may be horizontally mounted on the centers for measurement of pitch diameter, etc. Devices similar to bench micrometers include micrometer-like devices with adjustable tailstocks, floating carriage-measuring machines designed specifically for calibration work, and universal length-measuring machines (ULMs). Of these devices, IJLMs offer the highest order of precision.
The basic requirements for bench micrometers and similar devices are as follows:
(a) changeable measuring forces that comply with the requirements of the thread standard
(b) 0.00001-in. (0.0002-mm) resolution or finer
(c) measuring faces that are flat and parallel within 20 iin. (0.5 tm)
(d) retractable, adjustable measuring face(s) to facilitate insertion of thread wires.ASME B1.25 pdf download.

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