Chapter 12 Tolerancing
Tolerancing: Basic Hole System
The basic hole system of calculating tolerances is based on using standard reamers, broaches, and other standard tools to produce holes. Shafting is machined to any size desired. The minimum hole size is taken as the basic size and tolerances are applied to both the shaft and hole.
Given the following specifications find the limit dimension for both the shaft and the hole using the Basic Hole System”
Nominal size |
2.0000 |
|
Fit |
|
RC8 |
Using the American National Standard Running and Sliding Fits table cross reference the nominal hole size (2.00) with the Standard Limits values
Hole |
Shaft |
+4.5 |
-6.0 |
-0 |
-9.0 |
Convert the numbers to thousands by moving the decimal point 3 places to the left or dividing the numbers 1000.
Hole |
Shaft |
+0.0045 |
-0.0060 |
-0.0000 |
-0.0090 |
Add or subtract the values to the nominal size to find the upper and lower limits dimensions of the hole and shaft
Hole |
|
|
Shaft |
|
2.0000 |
2.0000 |
|
2.0000 |
2.0000 |
+0.0045 |
-0.0000 |
|
-0.0060 |
-0.0090 |
2.0045 |
2.0000 |
|
1.9940 |
1.9910 |
The limits dimension for the hole diameter is (2.0000-2.0045) and the limits dimension for the shaft is (1.9910-1.9940).
The minimum allowance is the difference between the smallest hole and the largest shaft.
Minimum Allowance |
|
|
2.0000 |
Smallest Hole |
|
-1.9940 |
Largest Shaft |
|
0.0060 |
Minimum Allowance |
|
The maximum allowance is the difference between the largest hole and the smallest shaft.
Maximum Allowance |
|
|
2.0045 |
Largest Hole |
|
-1.9910 |
Smallest Shaft |
|
0.0135 |
Maximum Allowance |
|
Source: http://web.acd.ccac.edu/~dference/edd240/edd24020.doc
Web site to visit: http://web.acd.ccac.edu
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