Simple dimensions 1

[bw009]

We don't use much GD&T. A question came up recently about squareness related to our drawings. We are considering subbing out some work that we have always done in house before. Don't linear dimensions and linear tolerances alone imply the allowed deviation from square under ASME Y14.5-1994? Also, would a general angular tolerance also apply to assumed 90 degree bends? I don't have a copy of the ASME standard. Any help on this would be greatly appreciated! --Barry

 

[Belanger]

Don't linear dimensions and linear tolerances alone imply the allowed deviation from square under ASME Y14.5-1994?

They do not. Length, width, and height are all to be met on their own terms -- not necessarily square to one another. So a part drawn as a perfect square could tilt into a parallelogram and still meet the dimensions displayed on the print. So...

Would a general angular tolerance also apply to assumed 90 degree bends?

Yes. This is the only thing that would save the square mentioned above from becoming too much of a parallelogram.
(In case you need legal ammo to back this up to your colleagues, this is all taken from paragraph 1.4 of the Y14.5 standard.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

http://www.gdtseminars.com

 

[bw009]

Thanks for the reply!

 

[Gilmiril]

For additional 'legal ammo' refer also to section 2.7 of ASME Y14.5-2009.

Para 2.7.1 states that limits of size also limit the allowable variations of form (straightness, flatness, etc); this is called the 'envelope principle' or 'rule 1' or sometimes 'perfect form at MMC'. Para 2.7.4 explicitly states that limits of size do NOT control the relationship between individual features, so no limits to perpendicularity (squareness) are implied by just the size tolerances.

Without any geometric controls, you're left with only the general angular tolerance on the assumed 90-degree angles.

 

[pmarc]

J-P is right on this.
I would just like to add that relying on title block angular tolerances for 90 degrees angles in ASME is the last thing I would do if I wanted to define clear and unambiguous geometrical requirements.

 

[Gilmiril]

Absolutely agree.

 

[drawoh]

bw009,

This question has been asked in the past...

thread1103-261904

thread1103-337980

--
JHG