Form Tolerance & Profile Tolerance in GD&T 5

[sasi2707]

Hi members,

Is it possible provide parallelism control & Profile of a surface control on a flat plane from a datum plane(say lane A)???????????. please help me...

Thank You,

sasi

 

[powerhound]

Yes, it is possible as long as the parallelism control is a refinement of the profile control. Just make sure that the parallelism tolerance value is smaller than the profile tolerance value.

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

How do you dimension your surface?
If you have basic dimension between datum A and surface in question, then you can use parallelism to refine the profile requirement.
If you have regular toleranced dimension between A and surface, then profile itself is a refinement of direct tolerance and is acting as parallelism, so adding another parallelism will only add confusion.

 

[CheckerHater]

Found some more time to elaborate on my statement.

Profile is a powerful and versatile control and it can take place of other controls for better or for worse.

When profile is used to control surface that is flat and parallel to something it can take place of flatness and parallelism. Profile without datum acts as flatness, another “datumless” control, and acts as a refinement of toleranced dimension. The tolerance zone in this case is unrestricted.

When you add datum your tolerance zone becomes restricted in its movement and profile control becomes similar to parallelism control.

When you add basic dimension, profile tolerance zone becomes bound to its theoretically perfect location. In this case parallelism or flatness can be added as a refinement.

As powerhound mentioned, the value of refinement should be smaller than value of profile. The parallelism and/or flatness tolerance zones will be “floating” within profile tolerance zone.

 

[sasi2707]

hai,

Interesting, Thank you powerhound and checkerhater, but still I have one more clarification for both of you..

@powerhound :

you said parallelism and profile can be given on a surface, why this kind of a control is needed? how can we differentiate both during measurement?

@checkercater :

in your attachment the second method you mentioned profile acting as parallelism :

the tolerance zone given for profile should be less than the tolerance given for shaft diameter right?

 

[powerhound]

Take the two bottom figures in CH's example. Let's say that the tolerance for the profile is 1mm and the basic dimension from datum A is 10mm. This means that the toleranced surface must fall inside a tolerance zone that is 1mm wide and centered exactly 10mm from A. Simplistically, you can say all points on the surface must be 10 +/-0.5 from datum A. This also allows your parallelism error to be up to 1mm. Now if we add a parallelism refinement of 0.5mm we are saying that the surface must still be located within that 1mm wide tolerance zone but wherever it lands, it cannot be out of parallel to datum A more than 0.5mm.

When measuring the surface, all the points must be somewhere inside that 1mm tolerance zone but the distance from the highest point to the lowest point cannot be more than 0.5mm.

Did I explain that well enough?

John Acosta, GDTP S-0731
Engineering Technician
Inventor 2013
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[CheckerHater]

Sasi,

Powerhound pretty much explained it in his post, but just in case I provide link to some old picture. I’ve already used this picture couple of times before in other discussions:

http://files.engineering.com/getfil...bf33-484c-ac71-fd99ff92ad94&file=FLATNESS.bmp

There is no profile in it but it shows how one control can be used as refinement for the other one.
And yes, you are correct; the geometrical tolerance zone is smaller than size tolerance

 

[sasi2707]

hi,

power hound and checker hater both of you explained my well I thank you for your valuable inputs...

 

[PaulJackson]

One more option.
Paul