Basic dimension without position tolerance 1

[tost]

Hi,
Is it correct to have only basic dimension without a position tolerance for a part ?

 

[weavedreamer]

Are you using another type of geometric tolerance? If not, then the Basic Dimension only, is incomplete definition.

 

[tost]

Weavedreamer,

Please see the attached example, that would explain more precisely. Dimension which is questionable is 54.52

 

[weavedreamer]

It looks like a Tolerance of Position to me.

 

[tost]

Yes it is but given on Surface which means simulated plane will be parallel to surface at a distance of ± 0.05, but this toleranc is applicable on angular basic dimension and not on 54.52.

 

[weavedreamer]

The 54.52 half locates the basic angle vector. Consider Fig. 5-28 on pg. 129, Fig. 6-22 on pg. 174

 

[tost]

There is a similar example in ISO 1101 p37, only difference being datums precedence is otherway but tolerance zone remains same.
What I do not understand is, if basic dimension 35 is not basic would it make any difference. The tolerance zone would still be same ?

 

[weavedreamer]

Which standard are you referencing on your document to have it defined by?
The basic angle does not appear to be able to stand by itself per ASME according to the single view shared. Another three dimensions appear to be required along with the 54.52 to complete the location of the axis of the Positioned Feature of Size.
ISO is a bit outside of my forte.

 

[TheTick]

The way I read it...

The position callout controls the "vertical" position of the circular end face from datum "A".

 

[drawoh]

tyagimayank,

The standard for GD&T is that each feature has a dimensional requirement it must meet. If you change your positional tolerance to a profile tolerance and add two more datums, your drawing will meet this standard. The lack of datums[ ]B and[ ]C make your drawing ambiguous.

It has been pointed out in one of the other threads that positional tolerances are for features of size.

JHG

 

[weavedreamer]

Looking at that example again, ISO appears to treat that position callout similar to ASME using a Profile of Surface callout.

 

[tost]

Weavedreamer,
I have attched an example from the standard.
Do you feel it is incomplete ?


Drawoh,
I have my doubts if position tolerance is for FOS. Please refer the attached example

 

[vc66]

ISO and ASME standards are different. Drawoh is very correct, that in ASME, position can only be used for a feature of size. If I remember correctly ISO uses "position" for a lot of different things.

V

 

[michal77]

Hello tyagimayank,

In my understanding drawing and the way of tolerancing is clear (acc. to ISO). Of course I can be wrong.
Please take a look on attached drawing.

Position tolerance means in this case that true profile should be between 2 opposite lines which are tangent to circles attached to theoretical profile. So you can also attache theoretical circle to you center point of the shaft. Then you know your positional tolerance for this point. But as I said before, it's only my way and I can be wrong

 

[drawoh]

tyagimayank,

I have applied tolerances to a fair number of angled mirror mounts, so I am familiar with something similar to your problem. I am not sure how I would inspect your feature, given your tolerances.

In your latest figure, your dimensions and datums are adequate to specify geometry. Your original figure was not.

On my angled mirror mounts, the angle is very critical, and the location of the surface is much less so. I apply a composite tolerance showing a profile of[ ]0.4mm, and and angular tolerance of[ ]0.02. This means that the entire face must be located entirely within an envelope 0.4mm thick with respect to the datums. When I fixture the face at 105[°] using datums[ ]A and[ ]B, I should see a variation in the surface of no more than[ ]0.02mm. Note that flatness is tightly controlled, even though I did not call it up.

I would interpret your positional tolerance as something similar to the profile tolerance, but you have not imposed controls on the shape of the feature. The mean, central position of the feature could be within your[ ]0.05mm, and the feature could be out of flat by way more than[ ]0.05mm. I do not think your positional tolerance controls the angle. Your figure would make more sense to me if you specified flatness, and applied a tolerance to your angle.

JHG

 

[axym]

As far as I know, the ISO standard uses Position to locate planar surfaces but allows the use of Surface Profile. In Y14.5, Surface Profile would be used as Position is limited to features of size.

I would see the requirement as the entire surface being within the 0.1 wide zone (not just the center point). The zone is oriented and located to datums A and B. Pretty much what Michal77's diagram shows.

This would indirectly control the angularity and flatness of the surface to be within 0.1 as well.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[tost]

Drawoh,
Idea was to control the angularity and the height of centre point which should be within plusminus .05sin(theta). In case axym and michal77 is also thinking in similar fashion than it is achieved.

Keeping my requirement in mind could you please let me know the way you would have approached it, ASME way. Please consider my second JPEG if you are more comfortable reading that.

 

[drawoh]

tyagimayank,

For starters, your centre point is a figment of your imagination. If it were my drawing, I would dimension either to the nominal maximum height, or to the intersection point of the angled surface and datum[ ]A, both of which are figments of my imagination.

You are trying to control a surface. Profile tolerances are totally appropriate.

You can control the height, the angle, and the flatness, all using one composite Feature Control Frame if you want. On my mirror mount drawings, the angle matters, so I set up my tolerances to show the fabricator what my priorites are. I do not know what matters to you.

Note that the profile tolerance controls flatness and angle, so there is no point specifying flatness or angle unless the profile is not accurate enough. The angle tolerance controls flatness too, etc.

JHG