ANSI STANDARD LIMITS AND FITS CALCULATOR

ANSI standard limits and fits calculator is developed to work in line with ANSI B4.1-1967 (R2004) standard which is based on inch units. According to input parameters of nominal size and fit type selection from running and sliding [RC], locational clearance [LC], locational transition [LT], locational interference [LN], force and shrink [FN] fits, size limits for hole/shaft are calculated. The schematic representation of the fit is also drawn. This calculator is applicable to non-threaded cylindrical parts.

Author's Note: The main reference that used during the development of this calculator is ASME B4.1-1967 (R2009). Please refer to latest version of the reference from ANSI webstore if further information or cross-check of results are needed.

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Limits and tolerances for shaft & hole fit

Calculator:

INPUT PARAMETERS
Parameter Value Unit
Nominal Size Inch
Fit Type Fit Detail

Note : Use dot "." as decimal separator.

 


RESULTS
HOLE
Parameter Value Unit
Hole Tolerance --- ---
Hole Upper Deviation --- thou(0.001 inch)
Hole Lower Deviation --- thou(0.001 inch)
Maximum Hole Size --- inch
Minimum Hole Size --- inch
SHAFT
Parameter Value Unit
Shaft Tolerance --- ---
Shaft Upper Deviation --- thou(0.001 inch)
Shaft Lower Deviation --- thou(0.001 inch)
Maximum Shaft Size --- inch
Minimum Shaft Size --- inch
FIT
Parameter Value Unit
Fit Type --- ---
Maximum Clearance --- thou(0.001 inch)
Minimum Clearance --- thou(0.001 inch)



Definitions:

Nominal size: Size of a feature of perfect form as defined by the technical drawing.

Deviation: The difference between a size and the corresponding nominal size.

Upper deviation: The difference between the maximum limiting size and the corresponding nominal size of a feature.

Lower deviation: The difference between the minimum limiting size and the corresponding nominal size of a feature.

Tolerance: The difference between the maximum and minimum size limits of a part.

Clearance Fit: A fit type where clearance exists between assembled parts under all tolerance conditions.

Interference Fit: A fit type where interference exists between assembled parts under all tolerance conditions.

Transition Fit: A fit type where clearance or interference can exist between assembled parts depending on tolerance conditions.

Hole Basis Fit System: A fit system in which hole lower deviation is zero. In other words the lower limit of size of hole is equal to nominal size. The required fit (clearance, interference etc.) is obtained by keeping hole as defined and applying various tolerance classes to shaft.

Allowance:  The difference between the maximum material limits of mating parts. Minimum clearance (+ allowance) or maximum interference (- allowance) between parts depending on the fit type.

Running and Sliding Fits [RC]: Intended to provide a similar running performance, with suitable lubrication allowance, through out the range of sizes. The clearances for the first two classes, used chiefly as slide fits, increase more slowly with diameter than the other classes, so that accurate location is maintained even at the expense of free relative motion.

Close sliding fits [RC1]: Intended for the accurate location of parts which must assemble without perceptible play.

Sliding fits [RC2]: Intended for accurate location of parts but with greater maximum clearance than class RC 1. Parts made to this fit move and turn easily but are not intended to run freely, and in the larger sizes may seize with small temperature changes.

Precision running fits [RC3]: The closest fits which can be expected to run freely, and are intended for precision work at slow speeds and light journal pressures, but are not suitable where appreciable temperature differences are likely to be encountered

Close running fits [RC4]: Intended mainly for running fits on accurate machinery with moderate surface speeds and journal pressures, where accurate location and minimum play is desired.

Medium running fits [RC5]-[RC6] : Intended for higher running speeds, or heavy journal pressures.

Free running fits [RC7] : Intended for use where accuracy is not essential, or where large temperature variations are likely to be encountered, or under both of these conditions.

Loose running fits [RC8]-[RC9]: Intended for use where wide commercial tolerances may be necessary, together with an allowance, on the external member.

Locational clearance fits [LC]: Intended for parts which are normally stationary, but which can be freely assembled or disassembled. They run from snug fits for parts requiring accuracy of location, through the medium clearance fits for parts such as ball, race and housing, to the looser fastener fits where freedom

Locational transition fits [LT] : A compromise between clearance and interference fits, for application where accuracy of location is important, but either a small amount of clearance or interference is permissible.

Locational interference fits [LN] : are used where accuracy of location is of prime importance and for parts requiring rigidity and alignment with no special requirements for bore pressure. Such fits are not intended for parts designed to transmit frictional loads from one part to another by virtue of the tightness of fit, as these conditions are covered by force fits.

Force Fits [FN] : Force or shrink fits constitute a special type of interference fit, normally characterized by maintenance of constant bore pressures throughout the range of sizes . The interference therefore varies almost directly with diameter, and the difference between its minimum and maximum value is small to maintain the resulting pressures within reasonable limits.

Light drive fits [FN1]: Fits requiring light assembly pressures and produce more or less permanent assemblies. They are suitable for thin sections or long fits, or in cast-iron external members.

Medium drive fits [FN2]: Suitable for ordinary steel parts or for shrink fits on light sections. They are about the tightest fits that can be used with high-grade cast-iron external members.

Heavy drive fits [FN3]: Suitable for heavier steel parts or for shrink fits in medium sections.

Force fits [FN4]-[FN5]: Suitable for parts which can be highly stressed or for shrink fits where the heavy pressing forces required are impractical.

Supplements:

Link Usage
Interference (press & shrink) fit calculator The calculator which calculates press fit force, required temperatures for shrink fit, fit stresses and other parameters necessary for interference fit design

Reference:
  • ANSI/ASME B4.1 - 1967 (R2004) Preferred Limits and Fits for Cylindrical Parts