General tolerance for GD & T - geometric dimension and tolerance

How to give General tolerance for (GD & T) Geometric Dimension and Tolerance as per standard 

GD & T General Tolerance Values 

Straightness and flatness

The general tolerances on straightness and flatness are given in below table. When a tolerance is selected from this table, it shall be based, in the case of straightness, on the length of the corresponding line and, in the case of flatness, on the longer lateral length of the surface, or the diameter of the circular surface.

Perpendicularity :

The general tolerances on perpendicularity are given in below Table. The longer of the two sides forming the right angle shall be taken as the datum; if the sides are of equal nominal length, either may be taken as the datum.

Symmetry : 

The general tolerances on symmetry are given in below Table. The longer of the two features shall be taken as the datum; if the features are of equal nominal length, either may be taken as the datum.

Circular Run Out: 

The general tolerances on circular run-out (radial, axial and any surface of revolution) are given in below Table. For general tolerances on circular run-out, the bearing surfaces shall be taken as the datum if they are designated as such. Otherwise, for circular radial run-out, the longer of the two features&all be taken as the datum; if the features are of equal nominal length, either may be taken as the datum.

for further Reference on Geocentric Dimension and Tolerance comment us we will guide you 

V Groove Pulley Material Selection and V groove Pulley Standard Dimensions

V Groove Pulley Material Selection

For generally purpose V groove pulleys are made by Grey Iron Casting IS: 210-1970

Grey Cast iron Material Grade and Properties
Code of Designation	Grades	Tensile strength	Transverse Test			Typical Applications	Note:
			Breaking load Min, Kgf	Corresponding Transverse Rupture Stress Kgf/mm2	Deflection Min, mm
FG 15	15	15	800	34.0	4.0	Parts Requiring no Special Grade for general Structural Purpose	Damping Capacity Decreases with increases in tensile strength
FG 20	20	20	900	38.2	4.5
FG 25	25	25	1000	42.4	5.0	Parts Subjected to severe strain such as cylinder parts, etc.
FG 30	30	30	1100	46.7	5.5
FG 35	35	35	1350	57.3	5.5	for extraordinary use
FG 40	40	40	1500	63.7	5.5

for general purpose pulley we can select FG 20 for which the equivalent grade is 

SAE 111

DIN 1691/GG22

BS 1452/Gr 12

CSN 42 24 21

V Groove Pulley Design

V groove Standard dimensions as per IS 3142 

How to select V groove pulley standard dimension like width, depth, Pitch line, etc is discussed below.

Based upon the belt used for transmission the pulley dimension are selected there are generally different Types of V belt A, B, C, D, E 

the below drawing shows the Dimensions of the Sectioned double groove v Pulley. 

And the values are taken from standard as shown in the table below 

a sample pulley dimensions are given below 

Bearing Standard tolerance for shaft and Housing, Selection of general tolerance for machined components

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.



• 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.) 





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

General tolerance Selection

sheet metal tolerance Standards

Welding Tolerance Standards