Simple True Position Question based on blueprint 1

[brandnew1]

Hi all,

i have this blue print given by a customer and i wanted to confirm two aspects of the bp related to the true position of Datum B (inside the red box).

A) It calls the true position of diameter .280 to be in a diametrical zone of .010 to Datum A. However Datum A is the plane perpendicular to diameter .280. Is this a valid call out? Or should this be to datum C.
(side note: i don't see any basic dimensions

B) i see also that a chamfer is right under, is this true position in regards to both the diameter and chamfer? (i know it appears to be obvious that the chamfer would be 'centered' to the diameter but i just want confirmation related to the true position call out).

thank you for your help

 

[Belanger]

It essentially means perpendicularlity. This has been discussed much here on the forums, with many insisting that what you have there is wrong and it should specifically use the perpendicular symbol. That is my perspective, too.
Others will say that the only way to interpret it is perpendicular, so it's no big deal to leave the position symbol. Meh.

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

 

[pmarc]

Regarding A:
What J-P said. This has been permanent debate. In my opinion, as long as the standard does not clearly prohibit applying position tolerance to a SINGLE feature of size relative to nominally perpendicular or inclined planar datum, the debate is undecidable.

Regarding B:
This is very interesting question and I would really love to hear opinions of other guys. There are people who claim that the positional callout applies to the hole AND to the countersink, and to support their standpoint they use Fig. 7-24 from Y14.5-2009 (or 5-37 from Y14.5M-1994) very often.

I personally have at least two doubts about this interpretation:
1. Unlike counterbored holes (which by geometrical nature contain two or more independent cylindrical features of size), chamfer portion of countersunk hole is not feature of size, so theoretically position tolerance should not be used to control its location.
2. If the positional tolerance applies to the diameter at the entry of the countersink (2D circle), like it is very often claimed, how to find the circle on actual geometry? In reality due to technological reasons the circular edge will most likely be chamfered or rounded, so finding it in a repeatable way may be quite a challenge.

 

[fsincox]

I agree it is not illegal, Do you suppose they think they are expressing a positional requirement for the whole boreline as you would if you had called it out in a single callout?
Frank

 

[Tarator]

On this print, the Position control applies to the .300 DIA hole right, not .280 DIA, since it's called-out/located under the .300 DIA? Or does it apply to both diameters (PATTERN)?

 

[greenimi]

[Regarding A:
What J-P said. This has been permanent debate. In my opinion, as long as the standard does not clearly prohibit applying position tolerance to a SINGLE feature of size relative to nominally perpendicular or inclined planar datum, the debate is undecidable.]


Pmarc,
I have a question for you: imagine a round plate with 3 press fit pins; the face of the plate is datum feature A, the pins are not equally spaced and have basic angles between them.
How can I say, that I would like to have the pins on the plate positioned in .010 to A (actually controlling only perpendicularity or what), but I want them to be perpendicular to the plate in .005 and also for each other in .005. In other words, I don’t care too much (in .010) where on the plate they are, but should be perpendicular in .005 to datum feature A and also is important the relationship between each other. The part is assembled with similar mating part.
Can I say composite position PLTZF: Ø.010 to A and FRTZF Ø.005 to A? If I say that, it’s position controlling perpendicularity only?
Or should I use perpendicularity because position is not allowed to control only perpendicularity? But I loose then the relationship between the pins and also the simultaneous requirement?
Thank you

 

[pmarc]

Greenimi,
Since the pattern of press fit pins does not have location to A (in other words it can be located anywhere in the space), characteristics of this pattern that can be controlled are:
1. Orientation of pattern to A.
2. Spacing between features in pattern.

Now, since you are saying that both abovementioned characteristics must fall within the same .005, the ony control that is needed is simple |pos.|dia. .005|A|. Nothing more.

If requirement for perpendicularity to A was tighter than requirement for mutual spacing - let's say .002 and .005 correspondingly - two single segment FCFs would be needed:
|pos.|dia. .005|A|
|perp.|dia. .002|A|

 

[greenimi]

Thank you pmarc,
I got stuck in using “composite position” mode, I assume because of the spacing between pins. I knew “something is missing or not quite right”. Can I say using composite position is legal, but not very clear/recommended? (does not show I am GD and T literate)

Thank you again for your help

 

[ctopher]

What's a blueprint?

Chris
SolidWorks 13
ctopher's home
SolidWorks Legion

 

[axym]

greenimi,

The case you describe is a special case, that brings up several special rules and confusing details from Y14.5.

The PLTZF of .010 to A controls the following:
-relative orientation/location of the holes
-orientation and location of the holes relative to the datums
-in this case, Datum A can only control location in the direction parallel to the holes and this has no effect
-if there are other Position or Profile PLTZF's or single-segment FCF's, that reference only A, then Simultaneous Requirements applies

The FRTZF of .005 to A controls the following:
-relative orientation/location of the holes
-orientation of the holes relative to the datums, but location control is released
-in this case, Datum A can only control location in the direction parallel to the holes so releasing location control has no effect
-if there are other FRTZF's that reference only A, then Simultaneous Requirements does not apply

A Perpendicularity tolerance to A would control the following:
-orientation of each hole individually, relative to the datums
-no control of relative location
-no Simultaneous Requirements

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[pmarc]

Greenimi,
As Evan said, upper segment of the composite positional FCF (.010 wrt A over .005 wrt A) would actually have no effect.
Is it legal? In my opinion it doesn't really matter since it is meaningless.
And that is why I can't imagine a situation where I would recommend this to anyone.

 

[fcsuper]

Regarding Fig. 7-24 of ASME Y14.5-2009, it isn't just the figure itself, but the statement in the associated paragraph 7.4.2 expressly states that such a FCF applies to all features in the callout, and that if one wishes to apply different positional tolerances to each, they have to add a feature control frame to each (meaning that each feature would have to have its own FCF). You would never have a case where a single FCF in a callout applies to just the last c'bore. Granted, this is specifically for c'bores, so if you believe there is a distinction between c'bores and c'sinks in how their callouts are treated, you are still faced with the fundemental rule that the drawing cannot be ambiguious, so you would be required to add a FCF to each element in this case.

Matt Lorono, CSWP
Product Definition Specialist, DS SolidWorks Corp
Personal sites:
Lorono's SolidWorks Resources & SolidWorks Legion

 

[greenimi]

Pmarc and Evan,

I found why the composite position has been used in my case with the round plate and three fix pins: because, not too long ago PLTZF had a secondary datum B (datum feature B being the OD of the round plate, datum feature A still being the face of the round plate) and someone decided that the secondary datum B is non-functional datum. And he is right: B is non-functional. Nothing touches datum feature B (sitting in the air).
Again PLTZF position Ø.010 A primary and B secondary; FRTZF Ø.005 to A primary. I would say, if B is used, as secondary, make sense to use composite position (but again it’s a useless datum from functionality)
After “revision” became the callout discusses (that special case per Evan), but now the composite callout itself it’s, as concluded, meaningless.
Just removing a non-functional datum did not solve the problem and even creates more issues down the road.

 

[CheckerHater]

someone decided that the secondary datum B is non-functional datum. And he is right: B is non-functional

So, if your holes are no longer related to the OD of the plate, can you drill them OUTSIDE of the plate?

 

[greenimi]

CH,

That was the reason B was there in the first place. But, since B does not stop/arrest any degrees of freedom the second thought was to remove it!! And that’s exactly what we have done. We removed it and now the composite callout is no longer valid. Go figure….

What would you do? Which option would you choose?

 

[CheckerHater]

There are many options.
What first comes to mind, to keep B as a technicality.
Your composite showed holes located to B with less precision that to themselves, which actually was the way of saying that B is less important for function. Best is the enemy of good enough they say.
I can imagine your holes are dimensioned to B, and, as position control is used, the dimension(s) are basic (at least implied 0). So something on the either end of basic dimension should be a datum.
Which brings another option – holes are datum, OD is controlled wrt holes (as position or profile).

Am I the only one who thinks the whole functional thing is taken out of proportion and becoming less helpful and more confusing?

 

[CheckerHater]

Another possibility to control both OD and holes wrt A.
This way you can create relationship between OD and holes thru simultaneous requirement (similar to Fig.4-39)