Perpendicularity to Two Datums

[random_guy]

Y14.5-1994 shows perpendicularity to two datums, which I've always used (Fig 6-35, p.182).

Y14.5-2009 and 2018 show perpendicularity to two datums but add an angularity constraint to A|B (Fig 6-4, p.101). I believe the intent is the same, but the addition of the angularity FCF is just confusing in my opinion.

Any reason not to only use perpendicularity, and not angularity?

Wise men learn more from fools, than fools do from the wise.

 

[3DDave]

It even says "Alternative Practice" right in the diagram. It's suggesting the use of Angularity as an alternate to Perpendicularity.

In this special case they are interchangeable.

 

[random_guy]

Ah, total brain fart for me. I'll blame it on the Friday afternoon.

Thanks Dave!

Wise men learn more from fools, than fools do from the wise.

 

[pmarc]

Y14.5-2009 and 2018 show perpendicularity to two datums but add an angularity constraint to A|B (Fig 6-4, p.101). I believe the intent is the same, but the addition of the angularity FCF is just confusing in my opinion.

There are also people who say the perpendicularity symbol is confusing because the secondary datum feature B is not nominally perpendicular to the controlled face. I think this might be the reason why the committee introduced the alternative practice.

 

[random_guy]

I assumed that was the case - it's technically not perpendicular to both planes, but the intent is clear. And if I were to pass this drawing along to a machinist, I'd likely get a call asking why I have angularity on perpendicular faces, and where is my basic angle?

Just another example of the committee overthinking things IMO.

Wise men learn more from fools, than fools do from the wise.

 

[3DDave]

The basic angle is covered in the Fundamental Rules section, which links to "Tolerances for Implied 90° or 0° Basic Angles."

If they don't know that, the confidence they know anything else about ASME Y14.5 hovers near zero.

 

[random_guy]

My point was that a machinist or inspector that sees an angularity callout will likely be looking for a basic angle. I'd probably get a call to ensure that the part isn't 87° or something silly.

And when I say, "oh, it just controls perpendicularity to those two faces", they'd more than likely say to just use perpendicularity then.


Wise men learn more from fools, than fools do from the wise.

 

[3DDave]

I know the point - and if they are looking for it it is likely they don't know enough about the fundamental rules to be using the standard.

It's like getting a call that the company truck won't run anymore after it was filled with fuel, only to find out they opened up the airbox and stuck the hose in there. Only took 6 gallons!

The case here is that one surface isn't perpendicular to the controlled surface so they would be calling about why this wrong callout is on the drawing.

 

[random_guy]

Back in my day, the airbox would take at least 10 gallons....

In my experience, most machinists have a general working knowledge of the standard but I never expect them to know the standard cover to cover - and I have yet to meet a machinist that does.

Chances of getting a call using perpendicularity - 0%
Chances of getting a call using angularity - Pretty much guaranteed

Just as a side note, I greatly appreciate your input, and everything you've contributed to this forum. I must have read hundreds of your responses over the years of lurking here. Thanks!

Wise men learn more from fools, than fools do from the wise.

 

[powerhound]

This reminds me of a time when I had done a drawing for a casting and sent it to the foundry. This was around the 2012 timeframe. I used angularity instead or perpendicularity simply because I knew it was an alternative practice and I could. A couple of days later I get an email from the foundry saying how my drawing was wrong and that if I wanted to control perpendicularity that I had to use a perpendicularity symbol. I figured I could either give them a GD&T lesson over email or I could just change to to perpendicularity. I just changed it because it didn't mean anything different and moved on with my life. I haven't done that since, though.

John Acosta, GDTP Senior Level

 

[pmarc]

I guess somewhat similar mechanism has made people use concentricity instead of position.

 

[greenimi]

I guess somewhat similar mechanism has made people use concentricity instead of position.

So look what that "lack of proper education" end up doing? Are those unintended consequences?
Poor concentricity (and his companion symmetry) was thrown to the ash heap of history.