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Unequal bilateral positioning 1

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JLang17

JLang17

Electrical
Jan 16, 2009
90
I have a hole that is called out with vertical positioning +-.005 and horizontal positioning +.006,-.001. Is there a way to use a positional tolerance (or any GD&T method) to allow more movement in one horizontal direction than the other? Or does the hole need to be centered in the tolerance zone?

Simply put, the hole can move left .001 and right .006. How do I show that with GD&T?
 
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Jim,

Do you advocate the use of positional tolerance or profile
for rivet patterns?
 
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Kenat, yes ... but I really do like surface profile! I find too many designers believe that they need to control the position and size separately, but then use MMC; I can usually achieve the same thing with a good profile control.[2thumbsup]

Ringster, I've done very limited riveting, and when I did it was with pre-drilled holes. The rivet body didn't completely fill the hole as we were using it for axial clamping force rather than shear strength. In that case we used position though I would have preferred profile as we really were only concerned with boundaries.

In the case of riveting sheet metal without predrilling, I have heard from others that the positions are not typically critical. I'd do some studies on how the head deforms and see if I could use a profile control based on the outside of the crown. This, of course, is based on my limited exposure to rivets. What would you suggest?


Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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Ringster, I believe you, or was it Ringman (one and the same?) have brought this up several times before.

You don't have to use the dia symbol in FCF or invoke MMC with position. You could use position without and it would effectively be the same as +- coordinate dims if you felt this was appropriate, and since the standard says to preferably use position...

Well Mech, for features of size position is preferable per the standard;-).

KENAT,

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

What "net gain" are you trying to achieve with that question?
How could profile possibly apply to a hole pattern anyway?



Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
 
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Hmmm, all the links are really basic GD&T 101. Is this in response to my question about how to apply "profile" to a hole pattern?

Powerhound, GDTP T-0419
Production Manager
Inventor 2009
Mastercam X3
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II
 
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Powerhound,

That was a good question that you posed. My response would be that one must be selective when applying GD and T to a drawing. I is my opinion that it should not be applied to rivet patterns for one thing, inasmuch as most if not all rivet patterns are not intended to be interchangeable.


I have heard the statement that GD and T is like a box of tools and that where one individual might use one another might selelct a different.

Back to the basics from years ago, UNIVERSAL INTERPRETATION, INTERCHANGEABILITY AND 'SHORT HAND' FOR NOTATIONS.

It rather seems that we have departed from these basic principles.

 
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I'm still stuck on how "preferably" means "mandatory". I respectfully disagree that GD&T MUST ABSOLUTELY EVERY SINGLE TIME WITH NO EXCEPTIONS be used on a hole location or the drawing is not valid per the standard.
I am not saying that I don't beleive in using GD&T, just that I'm not going to waste the companies time and money sending a drawing back for correction because a rivet hole was located using +/- rather than true position or profile.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]
 
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Ringster, sorry, it looks like I misread your question. I took it to mean individual rivets as opposed to the pattern of rivets.

Again, though, it always comes down to what you are trying to achieve; pre-drilled holes or blind riveting, interchangeability or not. If you have two parts that both have predrilled holes, shouldn't those two sets of holes match somewhat, and how would you verify that? If there is no predrill, but the relationship overall of the pattern and the rivets within the pattern is important, how would you check it? It seems like that's the only guidance I can seek. I think everyone here understands the basics of composite positional control. As for how a profile control can be used to control a pattern of features...if the profile control applies to more than one feature, as indicated by a note such as "16X" or "16 HOLES MARKED 'M'", then those featues are part of a pattern. Similarly, Principle of Simultaneous Requirements could group a number of features together as a pattern. Of course, this doesn't give you the flexibility of separate PLTZF and FRTZF tolerance zones.

EWH, we all pick the battles that we wage within our companies (and here on this forum[peace]). Hopefully we make a stance on those issues that are comparatively more important to our longterm success and value. I've had shops tell me that they weren't concerned over the GD&T and regular tolerances on the drawing because they just did their best and sent the parts on. Most parts were accepted and occasionally they would have to rework something, but overall it worked well enough for them. Not a battle worth pursuing. What I particularly like about this forum is the opportunity it gives us to try to understand each other's perspectives. We don't always agree, but at least we start to see where each other is coming from.

Jim Sykes, P.Eng, GDTP-S
Profile Services TecEase, Inc.
 
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You can create your own custom positional tolerance zone that is not round, BUT you will have to fully define that zone and how it applies on the drawing to your particular feature. In my opinion, it's not worth the trouble; just still to the rectangular tol zone.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group
 
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Does anyone's experience go back to 1973, when the PLTZ was allowed to be rectangular?
 
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ringster,

Why do GD&T positional tolerances not apply to rivets?

When I call up rivets on a fabrication drawing, my assumption is that the fabricator is responsible for and has the resources to make everything line up. When I inspect the part, I expect to see properly installed rivets. My primary requirement is that they should not look sloppy, so I specify my true position accordingly.

My vendor can fabricate rivet holes separately, accurately enough that they line up. They can drill after assembly. I do not care.

Critter.gif
JHG
 
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IT IS MY OPINION, that due to the patterns not requiring interchangeability, there is really no need to positional tolerance them. There are always some exceptions to the rule, or in this case opinion, but in general, NOT REQUIRED.

Typically edge distances will be of more concern than the distance from the actual TP for the hole.
 
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Drawoh,

Positional tolerances & Rivets...

My favorite was when someone handed me an already released drawing of a rivet with a shoulder containing a concentricity callout relating the shoulder diameter to the body of the rivet (the part that deforms).

For those who are not laughing...remember the function of a rivet is to join surfaces...tolerancing should be done to ensure rivets can do that job.

Michael
 
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ringster,

Any positional tolerances on my rivet drawing will be for the rivets, not the holes. Rivet holes and rivet bodies are are uninspectable once the rivets are installed, at least without an x-ray or a hacksaw.

Critter.gif
JHG
 
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Drawoh

This is an interesting concept that you offer. Could you expand on the method you might use and justify the use of positional tolerancing on the rivets?
 
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ringster, position doesn't necessarily mean using dia or MMC, so I still don't see your point?

KENAT,

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