Hole Position to Self?

[ModulusCT]

Hello,

I was looking at this print from a supplier yesterday and after reviewing it for a while I came across something I just don't understand.

There is a hole controlled (compound feature control frame) with true position with respect to datums C and A and perpendicularity control with respect to datum A. So I go off and hunt down the location of these datums and I see that datum C is shown to be the center of the hole that's being controlled.

Does that make sense to anyone? Or is this a mistake?

See attached pdf.

Thanks,

Mod

 

[SDETERS]

Is that Datum C hanging off of the FCS that is in Question. It looks like a "D" instead of "C". If it is not datum c what feature makes Datum "C"?

 

[ModulusCT]

Look at the view just above the view that contains the FCF in question and you'll see Datum C appended to the axis of the feature.

I really don't know... It looks like they're calling out the axis to be both Datum D and Datum C....?

....?

 

[ewh]

The drawing is not per y14.5 in that a centerline alone is not to be used as a datum. This introduces the ambiguity that we see here; which feature is datum C? It looks as if the intention is to define a plane a datum C, then control the hole to that plane and surface A.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[SDETERS]

Well then we do not know what "C" is then. There is at least two possible features that can make "C". The "small Long pin .100" or the bigger diameter that the Small long Pin is attached to .155/.133. So I see a light mark up in top right view where there was Datum "c" was attached once upon a time. Assuming .155/.133 Feature centerline is datum "C" then the call out for the FCF in question is correct. It is making sure the .1 center is controlled back to the .155/.133 center. It is not being called out back to itself. It is being called out back to .133/.155 That Make Datum "C"

 

[ModulusCT]

That small incomplete datum reference frame is my own sketch... I was simply trying to explain to some other people in my department why this print was incorrect and how it could be remedied.

Of course, none of them really know that much about GD&T but think they do, so I've got to do double duty to convince them of anything. That's sort of the reason why I posted here... To gain a little more input about this.

Thanks for the replies.

 

[KENAT]

As above C doesn't appear to be properly defined per 14.5, Also how can the hole be perpendicular to what they seem to imply C is?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[ModulusCT]

I think they're saying that the axis of the hole should be held perpendicular to Datum A.

Also, it's just occured to me that they were probably trying to call out the axis of the pin on the other side as Datum C and then give the hole a position tolerance to the center of that pin (Datum C).

So it could all be fixed up nicely if they would just move that Datum Reference Frame from the axis of the pin to its outside surface.

 

[KENAT]

The FCF for the hole appears to say [pos|dia.007|C|A] in the top line. To me this is wrong, the hole appears to be intended to be coaxial to C, not perpendicular to it.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[ewh]

Position can control coaxiality as well as perpendicularity.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[ModulusCT]

Does including the perpendicularity tolerance in the FCF function as the only orientation tolerance? Or does the first datum callout for true position in FCF always control orientation whether you like it or not?

 

[KENAT]

ewh, my point was that as I think they intend C should be the secondary datum not the primary.

As to your question ModulusCT. Position does control perpendicularity to an extent, in this case a diameter of .007. The perp control is a refinement. Normally the primary datum contacts on 3 points, so for holes is normally the surface that perpendicularity is measured to.

However, at the end of the day it's just plain wrong and should probably be looked at again based on function.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

What is Engineering anyway: faq1088-1484

 

[PaulJackson]

Just guessing but since you mentioned that there is another long pin on the other side with the axis labeled [C] "I'll wager" that both long pins simultaneously are ment to guide (orient and locate) the male connector pins with their female pin sockets on the mating part.

Therefore "if true" I would suggest that the 2X pattern currently labeled [D] be changed to making both 1.005~0.995 dia pins just the way they function.

Again "if true" I would change the [pos|dia 0.007|C|A] to pos|dia 0.007|A] effectively making the spread between them basic +/- 0.007 and see if that works with your fit stack to the mating part. If it is too large reduce it to what fits and if the value approaches the tolerance refinement for each pattern feature's perpendicularity to [A] then eliminate the refinement.

Or if you cannot change it... then quit making a fuss because that is the way all the other connectors are defined and they have all worked fine so far.

Paul

 

[ModulusCT]

Ahh yes... That's true.

Cool thanks... I guess I'll have to give them a call and ask some questions about the part.

 

[fcsuper]

There's a lot of problems with this print, not just D and C. B is questionable as well, as it seems redundant to the better datum of D. Even datum A may have an issue, as it appears to be attached to only one element of a series of elements, but the inference is that it applies to them all. These all need better definitions.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group

 

[ModulusCT]

I agree with all of you... Thanks for your input.

 

[CheckerRon]

I also agree with Paul. The big pin is the locator and should be secondary datum B. I'm assuming there are 2 pins, one at each end, and those two pins together should define datum B (the pin size, not axis being datum B).

Also that note "PIN FLASHING SHALL NOT EXCEED DATUM A" is rather cryptic. I guess they are trying to say, "NO PIN FLASHING ON DATUM "A" SURFACE."