Geometric Tolerances: Standards & Definitions

[Femme_physics]

Geometric Tolerances - Do standards for defining "general geometric tolerances" exist

For example, if I want to define non-geometric tolerances for the whole part, I just write what type of IT it is. For instance, IT8. And then the manufacturer just looks at the chart to know the tolerances he should use.

Now, if I want to define general GEOMETRIC tolerances for the whole part - is there a standard for that? Or do I have to define everything one by one?

 

[xxChrisxx]

GTOL are fairly specific depending on the datum's used. So it's probably best to define each one individually.

 

[Ranger Mike]

for complete discussion on this consult "Dimensioning and Tolerancing" ANSI Y14.5M published by the American Society of Mechanical Engineers.
I am not sure of latest version.
hope it helps..
rm

 

[Q_Goest]

I'm not aware of any such standard. I've always had to call out all tolerances on all dimensions. However, generally the title block of a drawing defines default tolerances so you don't need to call out tolerances on every dimension such as for linear dimensions (example is in inches):
x.x = +/- 0.100
x.xx = +/- 0.030
x.xxx = +/- 0.005

They do the same for angular dimensions.

 

[Ranger Mike]

Q, just google GD&T..many many links to it and helpful courses
ANSI Y14 is pretty much the tolerancing standard in industry. Every Coordinate Measurement Machine (CMM) sold must conform to this standard relative to how measurements are determined. I have been selling CMMs and been in the Metrology business since 1980. If ANSI had not made this standard we would have total chaos and no one would be able to manufacture anything to any type of quality.
ALL CAD programs must adhere to this standard otherwise how would things be referenced properly to the “ part print” or desired engineering specifications. BTW, AP 219 is the ANSI specification for CAD but has not ben approved as a standard tyo date.
Finally , there are numerous courses taught through out the country teaching students what the standard means and how to properly apply them.

 

[Q_Goest]

Hi Ranger. I'm well aware of Y14.5, but I don't think that's what the OP is asking about. The question I believe is whether or not one can call out a single 'standard' for tolerancing a drawing such that all dimensions put on that drawing have a tolerance automatically associated with them. The example given by the OP is a ficticious "IT8". The OP then says, "And then the manufacturer just looks at the chart [presumably in some tolerancing standard] to know the tolerances he should use."

As mentioned, there is no such standard. Y14.5 requires you to put tolerances either on the drawing or in a title block. There are no 'standard tolerances' that a machine shop can go to once given a dimension. They need to be on the face of the drawing in one form or another.

 

[xxChrisxx]

Q I think you've missed the actual question. It was about geometric tolerances and if you can use a standard tolerance box, like you can with standard dimensions.

You can't really create standard geometric tolerances because they are datum dependent.