Re: Are there any standards for general tolerances. Molded parts depend on the size, but often mimic machined parts. On larger parts with less criticality, tolerances can be per inch, such as +/.005 per inch. There is no absolute standard for the title block. However, there are an ASME and ISO standards that can be employed. TOLERANCE:Tolerance is the allowable variation for any given size in order to achieve a proper function. Tolerance equals the difference between lower and upper limit dimensions. Example; for 0.500-0.506 inch the tolerance would be 0.006 inch.
Mechanical Tolerance Standards Charts
Geometric Boundaries II GD&T Reference Book
The following links are to General Tolerance Table Charts for Standard Shaft Hole Fits per McDonald Douglas Design Guide 'Machining Tolerances'. The size ranges given are for typical size ranges utilized within industry.
For more industry standard tolerance data see: Mechanical Tolerance Standards Charts
Select 'Class XX' based on required functional fit to access page.
Class I - Loose fit - Use for all possible hole - shaft applications where function will permit.
Class II - Free Fit - Running fits with speeds of 600 R.P.M. or over and journal pressures of 500 lbs/sqin or over. Wobble or shake between mating parts very slight. Part will turn and slide freely.
Class III - Medium Fit - Running fits under 600 R.P.M and journal pressures under 600 lbs/sqin and for sliding fits. Wobble or shake between mating parts noticed only on parts with short bearing length.
Class IV - Transitional Fit (Snug) - Closest fit which can be assembled by hand and necessitates work of considerable precision. Should be used where no perceptible shake is permissible and, where moving parts are not intended to move freely under a load.
Class V - Interference Fit - Considerable pressure is required to assemble these fits and the parts are considered more or less permanently assembled. Bushings and similar uses.
Note:
Material basis is steel. The coefficient of expansion of material considered should be checked against the basis temperature of 70 deg F .
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TOLERANCE BLOCK
TOLERANCE BLOCK
UNLESS OTHERWISE SPECIFIED:
DIMENSIONS ARE IN INCHES.
TOLERANCES:
.X±.1
.XX±.01 (could be .XX±.015 too!)
.XXX±.005
.XXXX±.0005
ANGLES±1º
My question is 'could be .XX±.015 too!'. Is it permissible to use a 3 place decimal tolerance on a 2 place dimension?
The other question I had was if one can use ordinate dimensions with 2 and 3 place dimensions from the same 0 reference to control the tolerance.