Question, What is the difference between A & B? 1

[ryandias]

I am a bit stumped. Can someone please explain the difference between callout A and callout B?

 

[fcsuper]

looslib, I'm not buying. As long as the company states the rules, there's no issues with this.

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

 

[MechNorth]

There are (or at least have been) problems with a number of CAD packages in that you were not able to set the trailing zeros option. In other cases, once the company standard was defined, you couldn't override it on an individual drawing, so if you set for inches, your metric drawing would still have trailing zeros. Then there's my favorite; typically if you use dual dimensions, then both the metric and inch dimensions both either have, or have not trailing zeros. The net effect is that regardless of whether or not there are trailing zeros (or preceding zeros incorrectly applied to metric decimal fractions), it is still critical that the user of the drawing check the units specified on the drawing, otherwise you could be off by a factor of 25.4.

Now, as Matt says, as long as a company states the exceptions to the ASME Y1.5 rules (i.e. documents it and circulates that document), then it is accepted.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[looslib]

Matt,

If you state on your drawing that it complies with a standard, then only apply parts of that standard where you see fit, how does someone else know your changes. My point is that standards are developed for ease in communicating things without having to send out a book of design rules with evey print you send out.

If you say your drawing complies, then make them comply.

If your CAD system doesn't have built-in rules for compliance with Y14.5, then lobby them to do so. The 2 systems that I have most experience with both claim to fully support Y14.5 and priduce drawing to that standard. Yes, you can override the settings in both packages.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[MartinSr00]

Interesting Posts PaulJackson and Jim Sykes

I see your point about the basic 4 hole pattern having perfect form. I would be in 100% agreement if the drawing showed a pattern that was 32.00mm square (41.00-9.00).

But in example (A), if the pattern can float, how would you tell how much it could float, and from where? Without referencing B and C in the feature control frame, and without specifying their order, how could you constrain any more than two rotational and one locational degree of freedom on the DRF that are locked in by Datum A?

I'm not saying you are incorrect. I'm just asking how do you measure off the datum reference frame for the two 9.00mm dimensions, when you don't have sufficient information to constrain the part on such a DRF in the first place? I guess what I'm saying is, I'm not sure with example (A) that I could correctly orient the pattern to the rest of the part in accordance with the basic dimensions shown.

That's why I came to my conclusion in the earlier post. But when once you mention it, I'm not so sure.

As an aside, a better way would be to box the 50.00 dimensions, assign an all around surface profile tolerance relative to datum A, then all the features of the part could be constrained to a DRF once for all features, for best effect.

I'd be interested in hearing your input.

Martin Smith
GDTP-S

 

[PaulJackson]

I see your point about the basic 4 hole pattern having perfect form. I would be in 100% agreement if the drawing showed a pattern that was 32.00mm square (41.00-9.00).

It does! Everything is there… “4X” declares the pattern, the FCF declares the type of control, and the datum feature(s) specified reveal which degrees-of-freedom are constrained (translation in Z, and rotation about the X and Y axes). It is not necessary for the designer to show the 32 X 32 basics as long as they can be equivalently derived from those given to relate the features according to the FCF (although I recommend that they do because inspection has to construct basics oriented to the features they are measuring to do the inspection even if the lazy designer snapped an XYZ endpoint on the axis of an angled hole).

But in example (A), if the pattern can float, how would you tell how much it could float, and from where?

Is the pattern floating relative to the edges of the part or are the edges of the part floating relative to the pattern? Certainly if the part edges breech the patterned hole edges then they have gone too far! Maybe one could declare the pattern and control the profile of the part edges to fix that. I think that I would figure out what functionally locates and orients what and consider controlling features likewise because that is what the assembly has to bare.

Without referencing B and C in the feature control frame, and without specifying their order, how could you constrain any more than two rotational and one locational degree of freedom on the DRF that are locked in by Datum A?

You can’t!

I'm not saying you are incorrect. I'm just asking how do you measure off the datum reference frame for the two 9.00mm dimensions, when you don't have sufficient information to constrain the part on such a DRF in the first place? I guess what I'm saying is, I'm not sure with example (A) that I could correctly orient the pattern to the rest of the part in accordance with the basic dimensions shown.

MechNorth said,

the two callouts (A) and (B) are in conflict, as (A) is not a refinement of (B); they both have the same tolerance of 0.2 on position (ignoring the preceding point about absence of diameter symbol), and both refer to the same four features. Thus, they are in conflict.

True! If they were to coexist… scenario A should be a functionally required refinement of the pattern… if not eliminate it. If the holes functionally locate the edges eliminate scenario B’s control… declare the pattern , as I said above, and tolerance the edges to the pattern.

You know we could be making a mountain out of a mole hill… ryandias just asked

Can someone please explain the difference between callout A and callout B?

As an aside, a better way would be to box the 50.00 dimensions, assign an all around surface profile tolerance relative to datum A, then all the features of the part could be constrained to a DRF once for all features, for best effect.

Sorry if I had remembered that you wrote this while I was typing my responses above I could have saved some keystrokes.

Paul