We need a GD & T guru! 8

[Karman303]

Our company is training for GD & T, and I have a couple of questions for all you gurus out there.
1)What is the correct interpretation of an area indicated by section lines inside the phantom line?
2)Which symbol should be used to express coplanarity of two or more features? (There's a cup of coffee riding on this one!)

3) Can anybody refer us to a pocket-sized reference guide for use on the production floor?
Thanks in advance for any guidance offered.

 

[Heckler]

I've expressed multiple surfaces being in relationship to each other by using the note "Nth surfaces". One can also note these surfaces together using a center line. I would just use the ASME spec by itself.....I have a couple of pocket guides I've gotten from training classes but I use the spec.

Best Regards,

Heckler
Sr. Mechanical Engineer
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Do you trust your intuition or go with the flow?

 

[TheTick]

To group coplanar surfaces, you can use a composite surface profile. There is no "coplanar" callout.

 

[ewh]

OK guys, if the surfaces are all co-planar, how about just labeling the plane as a datum and let that datum encompass the surfaces? Or, if that is not acceptable (it is the way I would do it), how about using parallelism?

 

[looslib]

For GD&T pocket guides, check this page:

http://www.geotol.com/details.htm#gtpg

"Wildfires are dangerous, hard to control, and economically catastrophic."
"Fixed in the next release" should replace "Product First" as the PTC slogan.

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[type26owner]

1.datum target
2.profile of a surface (with a note below stating how many surfaces and all are identified clearly)

 

[ringman]

1. I believe the area cross hatched represents the size of the target area, when specifying datum targets.

2. Check figure 6-20 in the Y14.5 text for an example. I believe that will work for your case.

3. Remember the Standard is the LAW. Handbooks are only for reference, regardless of whose handbook!

 

[drawoh]

Karman303,

There is no co-planar symbol in GD&T. You do not need one. Assign a datum to surface A. Draw surface B co-planar to surface A, and use a profile tolerance to control surface B with respect to surface A.

Connecting the surfaces with a phantom line and applying a profile tolerance should do it too.

I had a pocket guide to ASME Y14.5M-1994, but I passed it on to someone. I forget where I got it from. Why not just buy a copy of ASME Y14.5M-1994? It is quite readable. You might as well go to the source.

ewh,

Labeling the multiple surfaces as a datum does not control flatness, co-planarity or anything else. The actual inspection datum is the set of three points that make contact with the reference surface.

The parallel control does not work at all, since it allows gross displacement of the two surfaces. I think I see what you are getting at. Let's use my solution, above. The part is located by datums_A, B and_C. Your reference surface is Datum_D. Your profile tolerance from Datums_A, B and_C is 0.5mm. Your profile tolerance from datum_D is 0.1. The flatness of datum_D must be controlled to 0.1mm. Joining everyhing with a phantom line and applying the flatness specification should work too.

Your surfaces are located within a 0.5mm tolerance zone. They are co-planar to within 0.1mm.

JHG

 

[btrueblood]

I've seen the flatness callout for multiple-point surfaces, whether as a datum plane or not. An explanatory note is never a bad idea. A confusing obfuscatory note, however ...

 

[type26owner]

Flatness is a low level control which can only be applied to a single feature. Parallel is mid level orientation and form control which must be aligned to a datum. Profile is the top of food chain which can control form, orientation and location. For multiple features that are coplanar it's the only control which CAN be applied.

 

[drawoh]

type26owner,

I assumed that the surfaces are parallel to each other. I made no assumptions about the primary datum. Whether two surfaces are connected or not has a lot to do with the format of the drawing. If I draw a rectangular plate and I cut a notch in one side, I would regard the resulting two surfaces as co-planar to within some tolerance. If the shape is more complex and the two surfaces are not so obviously connected, I would look for some way to make the drawing clear.

I _am_ making the assumption that there is a plus/minus tolerance or a profile tolerance available to control the co-planarity, but that this is not accurate enough. In my example in the previous message, the surfaces can be out by 0.25mm, but they must be co-planar to 0.1mm total.

JHG

 

[type26owner]

drawoh,
Coplanar is a more rigid control than parallelism. Not only do all the features must be parallel but they must also lay in the same plane. Think of coplanar is a flatness control of multiple features. Check out pages 171 & 172 of the ASME Y14.5M-1994. Notice the profile is not aligned to any datum in fig 6-20 so it's used just as a form control.

 

[Tunalover]

Karman303-
Your question: "1)What is the correct interpretation of an area indicated by section lines inside the phantom line?" is unclear to me. Can you rephrase the question please?

As for your question "2)Which symbol should be used to express coplanarity of two or more features? (There's a cup of coffee riding on this one!)" we (me and my coworkers) are using the profile tolerance in a very specific way to control the coplanarity of multiple, nominally aligned surfaces. The method we use closely conforms to an example in ASME Y14.5M-1994. Call my work number 410.329.7929 and I can provide you with a detailed example.

As for your last question: "3) Can anybody refer us to a pocket-sized reference guide for use on the production floor?" my answer is YES. I can provide that information if you choose to contact me for an answer to your second question.

Bruce
aka:


Tunalover

 

[Karman303]

Bruce (Tunalover)-

I would certainly appreciate your input! When would be a convenient time to contact you at the number above? Let me know and I will reach out to you tomorrow, April 18.

Thanks in advance for your time.

Regards,
Karman

 

[ringman]

If you want to discuss the phantom lines, call me @256-457-4340. Anytime

 

[Tunalover]

Karman303-
I'm on the east coast and I'm in the office from 9am to 5pm. As for whether I'll be at my desk when you call is hit or miss. If you get my voicemail, leave a message and I'll call you back as soon as I get your voicemail.


Tunalover

 

[ewh]

drawoh,
After pondering the question further, I have to agree with you. I was trying to avoid using profile, as I felt that it was overkill when parallelism, along with a flatness control on the datum and the phantom lines to indicate that the surfaces are in line, would suffice. Looking at the standard (as pointed out by type26owner), profile does seem to be the preferred method.

 

[drawoh]

type26owner,

I am ignoring heirarchies and levels of control. Either the GD&T specification does what I want, or it does not.

I had not noticed the figure on page 172 before. You could have mentioned figure 6.21 on page 173 as well.

Karman303,

The ASME Y14.5M-1994 standard answers your co-planarity question, precisely. Forget the pocket guide.

JHG