Limit Tolerance Text Placement 2

[Tobin1]

Howdy All,

I have a question about how Limit Tolerance type dimensions should be written. I have some old drawings with diameter dimensions to the Inside of a machined surface and diameter dimensions to the Outside of machined surfaces.

-When displaying a dimension for the inside diameter of a surface the smaller number is on top. Example 9.995/10.005
-When displaying a dimension for the outside diameter of a surface the larger number is on top. Example 10.005/9.995

The purpose seems to be:
1) When a machinist is machining an inside surface the first number he will machine too is the smaller number – so the smaller number is on top or first.
2) When a machinist is machining an outside surface the first number he will machine too is the larger number – so the larger is on top or first.

I’ve always put the larger number on top regardless of Inside or Outside machining, but can’t explain way .

My question is – Is this practice part of any current (or past) written “standard” that can be quoted from? ANSI, ASME, ISO, Global anything?

If not - Is there something in any of the Drafting Standards that defines the placement of the smaller and larger numbers when using Limit Tolerance type dimensioning?

Thanks


Tobin Sparks

http://www.nov.com

 

[KENAT]

ASME Y14.5M-1994 section 2.2 (& figure 2-1)addresses this. High limit is placed above the low limit.

Not sure about historical use though.

KENAT,

Have you reminded yourself of faq731-376 recently?

 

[dgallup]

Back in the day of hand drawings & each company having it's own drawing standards, I worked for a British company that followed that practice. I don't think it is part of any current (inter)national standard.

ISO 406:1987 section 5 says:
The upper deviation or the upper limit of size shall be written in the upper position and the lower deviation or the lower limit of size in the lower position, irrespective of whether a hole or a shaft is toleranced.

 

[Tobin1]

KENAT and dgallup

Thank you for your responses. Both ASME and ISO agree and now I know why I have been putting the larger number on top all along .

Thanks Again

Tobin Sparks

http://www.nov.com