Drawing conversion from plus minus to comply with GDT Std

[SeasonLee]

I am trying to convert a plus minus drawing to GD&T compliant drawing, first page on the attached file is the original plus minus drawing and the 2nd page is GD&T drawing. Here are the changes:

1. Datum setup
* Top surface is primary datum with a flatness control.
* The lower hole is secondary datum and the tertiary datum is the flat portion.

2. Bi-directional position tolerance
1.548±.010 convert to |position|.020m|A|Bm|C|
.928±.015 convert to |position|.030m|A|Bm|C|

3. Profile tolerance
Dimensions on the upper portion from M to N mostly are 2 place decimals; the general tolerance is ±.015, so I will have a large tolerance
|profile|.020|A|B|C|
Dimensions on the lower portion mostly are 3 place decimals, the general tolerance is ±.005, then a small tolerance selected.
|profile|.010|A|B|C|

Questions

1. Can I add a note “Untoleranced dimensions are basic” to simplify the drawing as shown?
2. How to convert an unequal bilateral tolerance .438+.010-.015 to a basic dimension?

Please let me know all my problems and all I missed, thanks for all of your comments.

SeasonLee

 

[DesignBiz]

1. 5.2.1.1 making all dims basic; “Untoleranced dimensions locating true position are basic.”
Aren't basic dimensions used for profile definition locating features too? I believe so.

2. You actually have Datum B as the pattern now since the datum symbol is attached to the leader that has “2X”. (shouldn't there be a "2X" on the FCF for the holes location?) If in fact just one of the holes is Datum B then a separate leader is shown to one of the holes with the datum symbol. In this case since this is not a cylindrical tolerance zone I believe the “boundary” rule (placed under the positional FCF’s) should be invoked.

3. You noted that some dimensions were omitted for clarity. Just as a thought about the Profile callouts between M and N; at point N there can possibly be a “step” of .025 were the two tolerance zones meet. Additionally consider the potential radius at “M”. Is it acceptable or is further control required? (e.g. MAX R) ( maybe a surface transition note added)

Good comments above contrasting the benefits of GD&T above. I like Axym’s point about just giving a more liberal tolerance for features that functionally allow it. Also the important point about explicitly defined datums to communicate functionality.

In addition benefits for GD&T;

Maximum number of parts “accepted” at inspection which will functionally work. (saved costs in accteping perfectly functional parts that could possibly be rejected without the GDT standard applied. Also the reverse is possible)

Noted "fundamental rules" along with rule #1 and #2 to aid in interpretation of a drawing.

A mental checklist for allowable feature form, orientation, fit, location that are often overlooked without review in light of compliance with a noted GD&T standard.

Cylindrical tolerance zones vs. rectangular tolerance zones for more accurate tolerance stacks.

Additional positional tolerance based on material condition is possible.

Possible "zero position" tolerance at MMC or LMC

Pattern location with refined Feature related location

Projected tolerance zones

And I suspect many more.


DesignBiz

 

[ringster]

DesignBiz

Cylindrical tolerance zones vs. rectangular tolerance zones for more accurate tolerance stacks.

The above statement from your last post caught my attention. Might you expand somewhat on the intent here?

Thanks

 

[DesignBiz]

Ringster,

Tell me what the size of a clearance hole resulting in a minimum of .50 clearance for a 25.0 dia pin should be; based on a rectangular tolerance zone of +/- 2.5 (feel free to choose english or mm units)

Attached sketch

DesignBiz

 

[DesignBiz]

correction for #3 of my previous post: .015 step mismatch for profile tolerances at point N.

DesignBiz

 

[ringster]

DesignBiz,

You have clarified your intent. I understand and agree. I had supposed you just MIGHT be making some reference to the use of rectangular pattern for PLTZ (composite tol)

 

[DesignBiz]

Ringster,
Tricky business to get everything clarified 1st time round

DesignBiz

 

[SeasonLee]

DesignBiz

Thanks for the comments, you are right.
The pattern hole ( 2X ) on datum B had been changed and the point N moved on my latest post.

SeasonLee

 

[DesignBiz]

Sorry about that SeasonLee, I see on a later drawing posted that 2X correction was already made. Didnt see before my post.

I agree with some of the comments above that you are doing a good job with improving this drawing.

DesignBiz