"TRUE" Meaning

[ewh]

I've just had a customer ask about the use of "TRUE" with a hole callout. Per ASME Y14.5-1994, it is used when dimensioning a radius in a view which does not show the radius' true shape (para 1.8.2.3). For years, I've also used it for hole callouts, because holes are so closely related to radii. Am I wrong to use it in this way?

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[dingy2]

You are correct about the "TRUE" radius as per Y14.5M-94 on 1.8.2.2. It reflects a theoretical radius when it can not be shown that well in the view.

Generally, "true" means theoretical such as true position is the theoretical centres while true profile is the theoretical profile. In both cases, they are usually shown with basic dimensions.

A lot of people use true position when they should be talking about the positional tolerances of holes or pins.

Dave D.

http://www.qmsi.ca

 

[ewh]

But can it also be used for holes as well as radii?

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[ctopher]

I quit using it a long time ago because a lot of machinists that don't understand GD&T or other terminology on dwgs, think that "True" means that the cut bit needs to cut straight...or true. I explain to them the radius part, it doesn't make sense to them.
I see no issues with using it on a hole.

Chris
SolidWorks/PDMWorks 08 2.0
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[MadMango]

I'm not sure of an "official" ruling, but I have always used it for holes as well, in addition to radii. It saves having to create an alternate view in some cases.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[ewh]

Thanks guys!
I feel pretty comfortable about leaving things as they are with regards to "true" holes. It is not a great leap of logic to see how it can apply. What does bother me though, is that the customer actually had engineers asking the meaning. But, then again, seeing how they use GD&T, it isn't all that suprising after all ;-)

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]

 

[KENAT]

Bit late but...

Isn't a hole just a continuous rad anyway so I don't see why you couldn't use it.

KENAT, probably the least qualified checker you'll ever meet...

 

[ewh]

That is pretty much my reasoning...

Believe it if you need it or leave it if you dare. - [small]Robert Hunter[/small]