ASME B46.1:2019 pdf free download

ASME B46.1:2019 pdf free download.Surface Texture(Surface Roughness,Waviness, and Lay).
See also Sections 1 through 3, 9, and 11.
4-3 PURPOSE
The purpose of this Section Is to foster the uniformity of surface roughness evaluation among contact, skidded instruments and to allow the specification of desired surface texture values with assurance of secunng repeatable results. Special configurations of instruments for special purposes such as small radius skids, long styli, fast response, and special cutoff characteristics do not meet the requirements of this Section but are useful for comparative purposes. The instrument manufacturer shall supply information where deviations exist.
4-4 INSTRUMENTATION
4-4.1 Roughness Average VaLue Ra From
Averaging and DigitaL Readout Instruments
(a) The readout device shall display the average deviation from the filtered mean line in micrometers (microinches). This quantity is the roughness average Ra, formerly known as arithmetic average (AA) and centerline average (CLA), and is explained in further detail in Section 1. The filtered mean line is also described in Section 1.
(b) For uniform interpretation of readings from contact-type instruments of the averaging type, it should be understood that the reading that is considered significant is the mean reading around which the value tends to dwell or fluctuate with a small amplitude. Analog meters are damped to minimize acute deflections; nevertheless, extremely high and low momentary read. ings often occur. These anomalous readings are not representative of the average surface condition, and such readings should not be used in determining roughness average. An instrument with a digital readout integrates these high and low momentary readings and displays the surface roughness averaged over a significant length of surface profile.
(c) If it is necessary to use skid radii smaller than stan-dard, the long-wavelength response of the instrumentmay be affected. Skids normally supplied with conven-
radius to provide accurate readings on surfacesrougher than 12.5 um (500 uin.) Ra. For measurements
with cutoff values of 25 mm ( 1 in.) or more, it is generallypreferable to use an external reference surface rather thana skid.
(d) Situations in which the skid leaves a mark on thesurface may adversely affect the measurement results.Therefore, noncontact measurement techniques shouldbe considered.
4-4.6 Fringe-Field Capacitance (FFC)Probe
4-4.6.1 Probe Tip Radius.The FFC probe does notmechanically track the surface like a stylus instrument;
radius of measurement due to the electrhc ient in the Hc3 size. The profile measurement at each point in the trace corresponds to a weighted spatial average ofheight near the sensor. This physical phenomenon actsto filter higher spatial frequencies from the surfaceprofile in the same way that a stylus tip’s dimensionsprevent the tracking of ultrafine texture.The spatial reso-lution of the FFC probe is not a fixed value, but rather afunction of the average height of the surface measured.Asthe average height decreases, the FFC probe provides afiner spatial resolution.