Hope Simple Perpendicularity Question

[brandnew1]

Hi all,

i just wanted to get a verification of what is being asked for in terms of the perpendicularity call out of a blue print.

My question is attached in the pdf (blue print images and examples from the Y14.5-1994).

In words though, there is a perpendicularity call out for the .220/.221 thru diameter to Datum A of .002. i want to verify from what 'perspective' is this call out being made.

In the drawing the top left image shows a 90 degree angle from the side view of the part (blue arrow points from actual part). The second (top center) image shows a 90 degree angle as if the part was rotated 90 degrees north (blue arrow point from actual part) - thus looking as if the .220/.221 thru diameter is in front view.

Or is this required for both perspectives? i copied two images from the Y14.5-1994 standard which appears to indicate it will only be from one perspective and not both.

Guidance appreciated and i hope i explained the question thoroughly...

thanks as always

 

[Belanger]

I think the main issue that is causing your concern is an error on the drawing: Both perpendicularity callouts should have a diameter symbol before their respective tolerance numbers. Then it wouldn't matter which perspective you are looking at, because the perpendicularity tolerance would be 360º.


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

http://www.gdtseminars.com

 

[brandnew1]

Thanks Belanger,

given the error on the blueprint...is the callout then only for one perspective on the part in regards to perpendicularity as in the example from Y14.5?

 

[pmarc]

brandnew1,
Since perpendicularity FCF is associated with size of the hole and there is no diameter symbol preceding perpendicularity tolerance value, the tolerance zone, which is two parallel planes, is not tied to any view of your print.

 

[brandnew1]

Hi PMarc,

i apologize but i don't quite understand your response in the sense, was it just my drawings uploaded that caused for the perpendicularity not tied to any parallel planes or was it the blue print?

i'm attaching another pdf which i just drew out what i referred to the part being rotated 90 degree's...

Given that the call out does not have a diameter symbol preceding perpendicularity tolerance value where is the thru hole (which i'm taking to be a line) suppose to form a 90 degree angle in reference to Datum A?

i added green lines to act as the .002 tolerance range for the thru holes...i know there is a lack of a diameter symbol but based on what i see on the Y14.5-1994, i think the callout requires the thru to be perpendicular to datum A in respect to the front view

 

[powerhound]

brandnew1,

The crux of the issue is that there is no diameter symbol preceding the .002 perp callout. In general, the shape of your tolerance zone should match the shape of the feature being controlled. In this case you are trying to control a cylindrical feature so your tolerance zone should be cylindrical. This is achieved by adding a diameter symbol in front of the .002 as was suggested by JP. Now you have a .002 diameter cylinder that is oriented exactly 90 degrees to datum A and the axis of the hole must remain inside this cylinder from top to bottom. Because the tolerance zone is cylindrical in shape, it applies to all views and has one clear meaning. Leaving the diameter symbol off means the tolerance zone is two parallel planes spaced .002 apart. As evidenced by your question, this does not have one clear meaning. Adding the diameter symbol per JP's recommendation will solve your problem and mean that the tolerance zone is the same in both views.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[brandnew1]

Thanks for the response...i'm not sure if it was noted but this is a customers drawing not mine thus the questions appearing and also i can't add the symbol myself.

But as i look into drawing more thoughtfully, i look at where the original engineer placed the symbol and what perspective (in this case the back view). Unlike the example of fig 6-34 in the Y14.5-1994, the engineer did not place the symbol from a side perspective so i can't just go with that view.

However looking at the view datum A is a plane that i imagine goes on beyond what the drawing shows and the diameter thru hole 'pierces' this plane at 1.235 from Datum B. So looking at it this way in of itself seems to give the same effect that i think all have been saying (relating to adding a diameter symbol). This line that 'pierces' should create a 90 degree angle, from either direction within .002.

 

[powerhound]

I'd say you're trying to get blood from a turnip. There's nothing there. Any interpretation you make is pure speculation. You can try to explain it away like that if you want but the fact remains that the callout is no good. This is a common problem though. GD&T does an excellent job of clearly defining requirements when used properly. When it's not used properly it sometimes creates as much ambiguity and confusion as having no GD&T at all. I'm sure every poster to this topic has had to deal with poorly defined customer drawings.

Look at Fig. 6-39 in the 1994 standard. That shows how to properly tolerance a cylindrical feature. I know your drawing shows a hole but the meaning is the same. Notice the diameter symbol in the feature control frame. That is a critical point. I will reiterate that the shape of the tolerance zone is defined in the feature control frame. In your case it's two parallel planes with no indication as to what the planes are oriented to.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

brandnew1,
The tolerance zone planes in both perpendicularity callouts on your print are not oriented rotationally to anything. That means the planes can rotate frrely around corresponding hole axis while still being perpendicular to datum plane A, which in turn gives infinite number of possibilities.