Wednesday, April 10, 2013

Sheet metal Tolerance Standard, Welding Tolerance Standards and General Tolerance Standards.

The following procedure will tell, 

How to select general tolerance for machined components.

1. For discussion a bearing housing is considered with inner diameter turned to ø60mm.

  • To provide a tolerance to the diameter we have to select what kind of fit to be used.
  • Let us considered the load acting on the bearing inner ring is varying as shown below.

Table 1.1
For our case considered the shaft is transmitting Power therefore inner ring is rotating.
  • From Table 1.1, third operating condition the fit is selected as interference fir for Housing
  • Now from Table 1.2, for normal & heavy Duty the tolerance Class is selected as N7
Table 2
  • From Table 1.3, the Tolerance is selected as -0.039/-0.009
Table 3 
Sample dimensioning and Tolerances for a housing

How to select the general machining tolerance as per IS 2102 is discussed below.

2. For discussion a stepped shaft is taken as shown below.

Un Tolerenced Shaft

  • From Table 2.1, given below Tolerances for linear dimensions can be arrived
Table 2.1 General Tolerance for Linear Dimensions
  • From Table 2.2-3, given below Tolerances for Fillets, Chamfers & Angles dimensions can be arrived
Table 2.2-3 General Tolerance for Fillet, Chamfer and Angular Dimensions
  • From the Given Table the tolerance for shaft for general Machining is selected and shown below (Note: this for a general machined shaft, cases where the shaft is going to be seat in bearing, a similar procedure as of housing has to be followed.) 
Shaft with Dimensions & Tolerances 

Sheet Metal Tolerance Standards 

How to select Sheet metal tolerance is discussed below

  • The main thing to be considered for selection of sheet metal tolerance is not just the Linear dimension as like IS 2102, the Reference from where to where the dimension take plays a vital role. Table 3.1 shown the unspecified Sheet metal Tolerance.
  • For edge to edge, hole to hole & edge to hole, tolerances shall be taken from column A
  • For edge to bend and hole to bend, tolerances shall be taken from column B
  • For bend to bend, tolerance shall be taken from column C
  • For Angular Tolerances ± 2 Degree shall be taken

Table 3.1 Sheet Metal  Tolerance for unspecified tolerances

How to select general tolerance for Welding.

Welding Tolerance shall be taken as per ISO 13920 

  • Welding Tolerance for Linear dimensions shall be taken from Table 4.1 
Table 4.1 Welding Tolerance for Linear Dimensions
  • Welding Tolerance for Angular dimensions shall be taken from Table 4.2, in a similar way as discussed in general Tolerance for machined component Discussion (2)
Table 4.2 Welding Tolerance for Angular Dimension


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    Metal welding

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