Composite Profile Tolerance - 2 surfaces

[jmarkus]

I have 2 situations that I am unsure about the correct application of a composite profile tolerance.

1. I have two tabs which have cylindrical surfaces to mate to a common cylindrical feature. Both of these tabs are datum A. I want to control each of them with a surface profile of 0.25mm and both of them to each other by the same value.

2. Same part description, but now the two tabs are not datum features. I want to control each of them 0.5 to datum A, and 0.25 to each other.

My understanding of application is:
1. Simply show a single surface profile FCF to 0.25 (no datum reference in the FCF) and put "BOTH AREAS" under the FCF.

2. A composite profile FCF of 0.5 to A, B, C and 0.25 to A, B (assuming) B is the datum in the general direction of the surfaces.

Please let me know if this makes sense.

Thanks,
Jeff

 

[KENAT]

In 1 when you say both are datum A do you mean the pattern is datum A?

I think a sketch might help clarify and get you a better answer. I'm trying to work out if your datum order is correct in your option 2, the way you word it sounds like it might be wrong but I'm not sure.

Also, what standard are you working to ASME Y14.5M-94?

KENAT,

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

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What is Engineering anyway: faq1088-1484

 

[jmarkus]

Yes. The pattern of the two surfaces is datum A.

Please see attached image for clarification.

We are working to ASME Y14.5M-94.

Thanks,
Jeff

http://files.engineering.com/getfil...194-66450adc87fe&file=cylindrical-datum-a.png

 

[axym]

Jeff,

A couple of things about the controls on B. The profile tolerance gives you a 0.5 thick tolerance zone that is oriented to A and simultaneously controls areas B1 and B2. This indirectly controls the coplanarity of B1 and B2 to within 0.5, and the flatness of B1 and B2 individually to within 0.5. So the 0.5 flatness control is redundant. Either the flatness value needs to be tightened to something less than 0.5, or the callout can be removed.

Just to poke my nose in even further, I would question the use of A as a datum feature for B. The A surfaces don't have a lot of height, compared to the distances between the B surfaces (particularly B2) and the A surfaces. Small variations in the shape or tilt of the A surfaces will show up as large apparent deviations in the profile of the B surfaces.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[jmarkus]

Evan,

I want to (somehow) ensure that datum B maintains its orientation to datum A, which effectively means I want the datum B plane to be perpendicular to the axis of the datum A cylindrical targets (within 0.5). If I just kept the flatness, there would be no control of where B ended up oriented relative to A - in my understanding.

Jeff

 

[axym]

Jeff,

Everything you said in your last post makes sense. Maybe I wasn't clear in my post - I was recommending that you keep the profile tolerance and get rid of the flatness tolerance.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[ewh]

Evan is right, since you are controlling the profile to within .005, specifying a flatness of .005 is redundant. It should either be tightened or eliminated, depending on function.

"Good to know you got shoes to wear when you find the floor." - [small]Robert Hunter[/small]

 

[jmarkus]

Okay, thanks for the comments on the relationships between B & A. Any further comments on my original post?

Jeff

 

[powerhound]

Yes, in the way that you have your datum areas configured, you have left it very likely that only one of your datum targets will be used. If A is your primary datum then it will be fully constrained to an axis and when you attempt to engage the secondary datum, only one B datum pad will make contact. The idea should be to constrain the part to the DRF, not the other way around.

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

 

[jmarkus]

So how do I ensure the two tabs (A1 & A2) are 0.25mm to each other?

Jeff

 

[dingy2]

Hope you don't mind if I jump in here.

I assume that datum A is 1 plane do both surfaces are on that plane. If one wanted to control the surfaces to each other by, let's say, no more than 0.25mm, then I would show a phantom line (theoretically is an extension line) between both surfaces and then use profile of a surface of 0.25 to become datum A. This is similar to using flatness except flatness is used on one surface only.

Hope this helps.

Dave D.

http://www.qmsi.ca

 

[powerhound]

You need to tie the 2 radii together by 1) specifying the radius using a basic dimension, and 2) visually linking them together using a phantom line like Dave said. This will ensure that those 2 radial surfaces are never more than 0,25mm from each other.

This still does not address the problem of one of datum B's targets potentially being non-functional. If you look at the attached drawing you see that if you push the part against the radius on the primary datum contact surface and slide it down to contact datum areas B, depending on the part, it will probably only touch one of them. If you move the part off of datum A in order to make them both touch, then A is NOT your primary datum, B is.

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

 

[MechNorth]

Agree with the posts above except one point. The datum targets A1 & A2, establishing datum A, do not establish a feature of size (no directly opposing points, nor effectively more than 180 degrees of included angle), so why is it assumed that Datum A establishes an axis? In fact, this is underdefined in the standard. The standard allows you to use any mathematically formulated surface as a datum feature, but doesn't go into detail about where the datum planes/axes/points will be.

If it is the intent to establish an axis from Datum A, then my recommendation would be as follows;
- show a phantom-lined circle, including basic diameter
- indicate on the drawing how you intend to simulate the datum feature(s); e.g. "Engage Datum Targets A1 & A2 against a 50mm cylindrical gage pin" or "Engage Datum Targets A1 & A2 against an expanding mandrel for best fit".
- graphically show the (vertical & horizontal) origins of measurement as being at the center of the phantom circle
- show basic dimensions from the indicated origins of measurement to the datum B targets


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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[jmarkus]

Okay, but how do I show situation 2? What is the proper way to show a composite or dual surface profile FCF for this situation?

Thanks,
Jeff

 

[MechNorth]

That's a problem, and not a problem. Hopefully you're familiar with PLTZF & FRTZF acronyms as applied to composite positional controls in the '94 standard, because that's the starting point for my explanation. In Y14.5M-1994, the standard does not give any indication that a composite profile control can be used to control the relationships of features within a pattern to each other. While it may have been a logical extension to basic principles, it was not generally used in this way. Hence, the problem. I suspect that you could get away with using the profile control to control the shape/form of the irregular features (Section 5.10.1, Fig. 5-47), and used a composite positional control on the BOUNDARY of the features to control the overall locations of each feature wrt the datum reference frame (PLTZF), and then refine it for inter-feature relationships using the FRTZF. That's NOT exactly the same as a profile control, but very similar. While this method is NOT detailed in the standard, it IS a very understandable extension from principles already defined.

Now, for a more direct approach, you need Y14.5-2009. Sections 8.6.1.2 thru 8.6.1.7. provides good text & graphical explanations of the approach. Basically it indicates the same thought process as for a composite positional control or for multiple single-segment posotion controls, so if you understand composite position tolerancing, it's reasy to grasp the extension to profile controls.

Now, making the bold assumption that your company has not adopted Y14.5-2009, you can still use this new method by invoking / referencing it on the drawing (i.e. under the callout, include a note "PER ASME Y14.5-2009").

Hope that helps.
Jim




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

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com