Simultaneous requirements is applicable here? 1

[greenimi]

I have a drawing with 3 positional callouts and I know since they have the same datum structure the simultaneous requirement condition is in effect.
Now, if you see the features for POS 1 and POS 2 (see attached sketch) are shown perpendicular to each other (and both of them are positioned at .004 relative to A)

The question I have is (since simultaneous requirement is applicable here) do I need the perpendicularity callout?

How do I make sure the .350 feature and .375 feature are perpendicular to each other?
By having implied 90 ° angle shown and the two positional callouts POS1 and POS2 is this enough?
Or do I need to add the perpendicularity callout ?(marked with question mark)

Thank you

 

[pmarc]

The right angle between these two features is implied by simultaneous requirement, so you do not need any additional perpendicularity callout as long as you do not want to tighten the perpendicularity limits defined by positional callouts on both features.

 

[drawoh]

greenimi,

Your features datum[ ]B and the .375[ ]width, are drawn 90[°] apart. If you do nothing else, your tolerance note about angle tolerances will control this angle.

Is this nominal angle good enough for you? The perpendicular tolerance you specified allows an angular error of up to around 0.4[°].

JHG

 

[SeasonLee]

drawoh

Would you mind to let us know how do you get this figure 0.4°
Thanks

SeasonLee

 

[drawoh]

SeasonLee,

asin(.005"/approx 0.7") = 0.4[°] approximately.

Of course, the two faces are not necessarily flat. The measured perpendicular error could be more complex.

JHG

 

[axym]

greenimi,

The two Position tolerance zones will be basically oriented to each other (i.e. at exactly 90 degrees) because of Simultaneous Requirements. This will indirectly control the "relative perpendicularity" of the two features. Everything is referenced at MMC, so you can envision a functional gage. The gage element for the .375 width would be a .379 slot, and the gage element for the .350 width would be a .354 slot at exactly 90 degrees. The two widths could be out of square within the clearance with those gage elements.

This control isn't quite the same as what the separate .005 Perpendicularity callout would provides, however. The gage element for the .375 width would be a .380 slot, and the gage for the .350 width (datum feature B) would be a .350 slot.

I haven't factored in the size tolerances for the two widths - presumably there is some title block tolerance for those. The sizes of the gage element slots would be increased accordingly.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[greenimi]

Thank you guys for your input.
I would have one follow-up question about this perpendicularity requirement: can somebody explain to me, how should I calculate the maximum amount of perpendicularity?

As Pmarc said the perpendicularity is limited and it's limits are defined by positional callouts on both features. What is that maximum amount of perpendicularity I can use to not be overwritten by the simultaneous requirement rule and to make sure will tighten the default one given by this rule.

I know you would say, how much you need for functionality? I want to make sure how much I need for functionality is smaller than the one already given by default, otherwise does not make sense to have one more callout (perpendicularity) and clutter the drawing.

I could not figure out how can I calculate this requirement. Do you have some good rule of thumbs?

Thank you again

 

[drawoh]

greenimi,

I will ask how much you need for functionality.

If you do not need more perpendicularity than is called up on your title block, do not clutter up your drawing and frighten fabricators with tighter tolerances.

At your assembly level, something is being oriented. How critical is this. This is where you do tolerance stacks.

JHG

 

[pmarc]

greenimi,
That is a very good question, unfortunately, as you already noticed, the answer is not that simple.

I did some quick and dirty calculations on a simplified example without use of MMC and MMB modifiers at all, means all geometrical tolerances were assumed to be based on RFS concept and the datum feature B was referenced at RMB. At the moment I am not able to make a digital version of it, but as soon as I get home I'll try to post something. I'd just like to warn you that (atan) function will be involved in this calculations ;-)

 

[axym]

pmarc,

We'll need to know the size tolerances (or arbitrarily assign some) in order to do the calculations.

Are you going to try to calculate the minimum and maximum angle between the features, with the assumption that they're both perfectly flat?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[greenimi]

Pmarc and Evan,
The size tolerance is ±.005 (for 3 decimal places).
No indication how flat should be the features (except rule#1)
Applicable standard Y14.5M-1994.

Pmarc,
If you already assigned some other size tolerance for the feature (different than ±.005) do not redo the calculation as I am more interested in the calculation method/concept and less on the final number you got. I would like to understand what is the proper way to think/evaluate these problems.

 

[pmarc]

Evan,
I am going to operate on angles, sizes of positional tolerance zones and their lenghts (which I am going to assume for the purpose of the excercise). And since I mentioned that for simplicity everything will be at RFS/RMB basis, I do not think size tolerances will be needed.

Everything would be much more complicated if MMC/MMB (like in OP's example) was considered, and in that case it is true that size tolerances would be needed. However at the moment I am just too scared to think about scenario with MMC/MMB

 

[pmarc]

greenimi,
Here is the presentation showing how I would try to calculate maximum perpendicularity tolerance value in order not to be in conflict with specified positional tolerance.

http://files.engineering.com/getfil...cee0b675dc&file=Perp_as_refinement_of_pos.pdf

It is worth to notice that calculated maximum allowable perpendicularity tolerance does not have to be smaller than upper positional tolerance - it is all due to different datums being referenced in both FCF's.

Important things:
- This presentation works only if everything is referenced at RFS/RMB basis. If perpendicularity tolerance value was specified at MMC and the datum feature B was referenced at MMB, the maximum perpendicularity value would be sligthly higher due to possible datum shift/tilt effect between datum feature B (if it was at its minimum size .365) and the datum feature simulator B (fixed at .375).
- It is assumed (for clarity) that lengths of toleranced features L1 and L2 are perfectly located (centered) on datum axis A in directions orthogonal to those controlled by FCF's.
- It may be really difficult to perform any calculations if the considered features do not have clearly limited lengths, which are needed to determine the lengths of tolerance zones (L1, L2). In your example lengths of both toleranced features (and in consequence lengths of their tolerance zones) are not clear and depend on other size dimensions, so if you need really precise results, it may be a painful job to do.

I hope the pdf is clear enough. My apologies if it is not. I also apologize that there are so many limitations in order to be able to get to something satisfactory.

 

[TrailMaker004]

pmarc,
I am just reading this post to try to better understand the simultaneous requirement rule.

In your dwg (case 1a)is it automatically implied that the rectangular feature on one end is held at a basic 90 degrees to the rectangular feature on the opposite end even though the first is niether identified as a secondary datum and accordingly not specified in the FCF for the second?

 

[greenimi]

Pmarc,
I would like to thank you very much for the sketch. I will digest it over the weekend (sometimes I have to use the weekend for this kind of stuff
I will give you a star for your post. I am not sure if that will "help" you much, but anyway....
Again, a BIG THANK YOU

Trailmarker04,
The feauturea are shown 90° apart and according to 2.1.1.4 (Y14.5-2009) 90° basic angle is implied.

"""2.1.1.4 Implied 90° or 0° Basic Angle.
Where center lines and surfaces are depicted on 2D orthographic engineering
drawings intersecting at right angles or parallel
to each other and basic dimensions or geometric tolerances
have been specified, implied 90° or 0° basic angles
are understood to apply. The tolerance on the feature
associated with these implied 90° or 0° basic angles is
provided by feature control frames that govern the
location, orientation, profile, or runout of features.""""

The simultaneous condition rule is in effect because the positional callouts have the same DRF (4.19 same standard)

"""A simultaneous requirement is where two or more
geometric tolerances apply as a single pattern or part
requirement. A simultaneous requirement applies to
position and profile tolerances that are located by basic
dimensions, related to common datum features referenced
in the same order of precedence at the same
boundary conditions""""

 

[pmarc]

greenimi,
It is not about stars.
It is all about to know how to start and proceed when a question like yours comes up. And I can tell you, it comes up quite often.

TrailMaker004,
Yes, that is true. One of those features does not have to be assigned as datum feature B in order to have basic 90 degrees implied between the two. Simultaneous Requirements concept does that.

 

[TrailMaker004]

pmarc and greenimi,
Thanks, very clear. Glad I posted my original question (different thread) as I would not have known that.

 

[greenimi]

Pmarc,
I went over your presentation and calculation for max perpendicularity when simultaneous requirements is in effect. I understood it and it's logical.

Again, Thank You very much.

Just for reference, and for somebody to use this site for academic reasons (as me), in my original picture the max perpendicularity is .010 (same calculation as pmarc's with the same limitations and assumptions, same RFS/RMB, etc)