tolerance values

[vgkrishna1412]

UNLESS OTHERWISE SPECIFIED:

DIMENSIONS ARE IN INCHES.
TOLERANCES:
.X±.1
.XX±.01 (could be .XX±.015 too!)
.XXX±.005
.XXXX±.0005
ANGLES±1º

which standard we have to find above tolerance values and where its mention. kindly help me..

 

[Duwe6]

The tolerances have to be placed on the drawing. Without tolerances, a drawing is almost useless. Your 'general tolerances' [above] are in accordance with how I was taught to interpret drawings made without tolerances. But they are entirely unenforceable. If the drawing shows a length of 1525mm, and the fab shop delivers 1537, how can you reject the part? It is closer to the specified 1525 than to 1500 or 1550! If you need it to be 1525 'actual' it needs to be written "1525mm +/-0.5". NOW if it comes in at 1537, it is obviously Out-of-Tolerance, and rejectable.

 

[Gilmiril]

This sounds like a drawing issue and not Boiler and Pressure Vessel issue. There is no 'standard' to invoke for such tolerances, and every company has to come up with their own generic tolerances for their own drawings, so you will see many different values throughout various industries.

For example, the company I work for uses (inch units):
.X = ±.06
.XX = ±.015
.XXX = ±.005
ANGLES = ±1/2º

For comparison, API 6A uses (for inch units):
X.XX = ±0.02
X.XXX = ±0.005
(no specification for angles)

Some companies use different tolerances for machining drawings versus fabrication drawings, and some insist on a single set of tolerances regardless of process (to avoid possibility of mistakes due to assumptions). ASME drawing standards do not specify any particular standard generic tolerances. ISO does have a standard on tolerance grades, but that would require specifying the tolerance grade on the drawing in place of generic tolerances.

There is no single system to invoke, so it seems companies do whatever they decide to do.