3D Math Data, GD&T and FAI - My issue lies more with Profiles

[Micronus]

How I can best handle this issue:
We have an part approval process (FAI) that is dimension driven. What I want to do is have the majority of the drawing controlled with GD&T (Mostly Position & Profiles) referencing the 3D math model as master. This will greatly simplify our drawings while keeping the design intent. Positions should not be a major problem because each feature has an independent ID and adjusting our FAI report should be possible.

My issue lies more with profiles. For a complicated gasket a couple all-around profiles would define the part. As there will be no linear dimensions on the drawing how can I make our FAI report meaningful for engineers & and our suppliers. At times we use more than one supplier for a specific part.

I have seen a table of points used but I feel this is just a move one step back. Perhaps we could include specific points in the math model that define where we would like profile points taken? This still seems to be an extra step. I would assume there must be some process that can allow for GD&T, 3D math as master and meaningful FAI reporting. Any ideas?

Peter
-OO-

 

[Stijloor]

How I can best handle this issue:
We have an part approval process (FAI) that is dimension driven. What I want to do is have the majority of the drawing controlled with GD&T (Mostly Position & Profiles) referencing the 3D math model as master. This will greatly simplify our drawings while keeping the design intent. Positions should not be a major problem because each feature has an independent ID and adjusting our FAI report should be possible.

My issue lies more with profiles. For a complicated gasket a couple all-around profiles would define the part. As there will be no linear dimensions on the drawing how can I make our FAI report meaningful for engineers & and our suppliers. At times we use more than one supplier for a specific part.

I have seen a table of points used but I feel this is just a move one step back. Perhaps we could include specific points in the math model that define where we would like profile points taken? This still seems to be an extra step. I would assume there must be some process that can allow for GD&T, 3D math as master and meaningful FAI reporting. Any ideas?

Peter
-OO-

Hello Peter,

Welcome to The Cove Forums!

If you use your 3D model as a "master" that means that you would consider all the dimensions defining this model as "basic" which is defined by ASME Y14.5M-1994 as "True Profile." Is my assumption correct?

Let's focus on the GD&T control: "Profile."
Considering your 3D model, that would be considered "Profile of a Surface."
Now, how much variation would you allow from True Profile? That must be specified. If you take the "one-size-fits-all" approach, it could make the part unnecessarily expensive.

I have more concerns.

I wonder if you can share some more specifics. Is it possible to scan and post some sketches? That would help my Fellow GD&T Covers.

Stijloor.

 

[David DeLong]

I agree with Stijloor that math data is considered basic.

Please do not apply GD&T on features that have no function or relationship to either other features on the part or the mating part. It doesn't help anyone and it takes away from features that a really important..

I agree that holes that have fixed located fasteners going into them should have positional tolerances in the feature control frames and also profile of a surface (or line) is applicable in certain areas on the surface where there is a function or relationship. Others holes or surfaces, just use coordinate tolerancing with a standard tolerance of some sort.

You will have to generate a drawing of some sort with the applicable feature control frames using the math data as basic.

If you have a profile tolerance isolated in an area rather than the complete surface, you will need the co-ordinate locations of the area as you suggested. This drawing should also have points at the ends of the isolated surface shown with letters (F or G as an example) reflected with basic dimensions. Below the profile feature control frame, place something like "F <----> G" to reflect that the profile tolerance only applies in this designated area.

Hope this helps.

 

[Micronus]

Your comments are appreciated and correct. However, my concern is with how to document the results of a profile in a meaningful way. With linear dimensions I just record the results on a first off report. How can I record the results of a profile callout.

For example, I have attached a sketch of a simple part with linear dimensions and one with a profile. The linear dimensions can be easily documented in a standard form. The profile callout can be measured, but how would I document the results in a report?

We plan to use GD&T more often in the future, but we will need to formulate methods for dimensional documentation.

Peter
-OO-
(I hope the attachments showed up)

 

[David DeLong]

Let's say the profile of a surface is 0.4 mm about the basic dimension (dimension inside a rectangular box) of 45 mm. It really means that the surface cannot be more than +/- 0.2 about the theoretical dimension or nothing above 45.2 nor below 44.8. These are called upper and lower boundaries.

Profiles can also be reflected with co-ordinate points on some sort of curve but the intersecting points must be basic dimensions.

Now back to the example.

One could have an actual range of less than the 0.4 profile but also could be outside the upper boundary. Here is how I would report an out of specification situation on this profile.

Profile of a surface 0.4 - Actual is 0.35 but is 0.05 above the outer boundary

Hope this helps.

 

[Micronus]

I have attempted to upload the sketches again.

My issue is that on testpart1 I can easily record the actuals for the 28, 2, 13, 4X R2, etc. in a dimensiona report and have a record of the results. For example, ignoring tolerance, I can document the dimensions like this:

Nominal, Actual-1, Actual-2, Actual-3
28, 28.101, 27.999, 28.099
2, 2.010, 2.033, 2.012
etc...

Using this dimensioning method, I can check any dimension in the future and determine if it has changed from the original documented results.

Does anyone have a good way to record similar variable information for the same part with the profile dimensioned in testpart2? It assumes math data is master.

I would like to use GD&T to make our designs easier to maintain and reduce the amount of time dimensioning drawings with improved design intent. My stumbling block at the moment is finding a viable method to record the profiles in a meaningful way where we can determine changes in the part over time.

See my original post for additional info.

-OO-
Peter

 

[Paul F. Jackson]

AxisTool,

To report the profile tolerance deviations to a specification that declares the "solid model" as basic... I would:

Describe, define, illustrate, yada-yada "Inspection Points" on the DCP (dimensional control plan)... by doing so the location of each target point will detail a basic X,Y,& Z location for the profile touch.

If the contour surface is nominally "at right angles" to the coordinate system X0, Y0, Z0 established by datum features |A|B|C| then one of the coordinates when subtracted from the basics will reveal the displacement from true profile the other two should be approximately equivalent to the basic. SHOW THE ACTUAL PROFILE TOLERANCE DEVIATION AS + (MORE MATERIAL) OR - (LESS MATERIAL) FROM THE TRUE PROFILE in comparison to the specified TOTAL PROFILE TOLERANCE "as specified" by default equal bilateral 1/2 total +/- or unequal bilateral or unilateral as detailed (+ value / - value).

If the contour's surface has only one right angle to the coordinate system then two of its coordinates will exhibit deviations from true profile (square them, add them together, find the square root, and report the deviation as detailed above in comparison to the "FIGURED BASIC DISPLACEMENT" from X0,Y0,Z0 coincident with the surface normal vector that is basic to that surface.

If If the contour's surface has no right angles to the coordinate system then all three of its coordinates will exhibit deviations from true profile (square them all, add them together, find the square root, and report the deviation as detailed above.

Paul

 

[Dave Dunn]

Being on the receiving end of drawings with comments like "all other features - refer to math model" I would recommend caution in minimalizing a drawing. While the designers and engineers at your suppliers will have CAD workstations to be able to interrogate the part design, the people doing the inspection of the resulting parts for qualification and ongoing production will almost certainly not.

My request for any customer on their drawing would be this: tell me on your drawing what is important, do it clearly, and accurately. If you have a position or profile specified on the drawing, I want to see a datum structure that restrains degrees of freedom correctly, is meaningful, and accurate to the design intent, and I want to see all required basics to be able to measure them.

By leaving required information off the drawing, you open it up to interpretation. If you have simply a profile callout, I will interpret it as requirement of flatness, straightness, form, etc., and not necessarily measurement about a true profile contstrained by a basic. If you have a position callout with no basics, I will come back to you and request that the drawing be corrected.

Just from one on the receiving end.

 

[Paul F. Jackson]

Dave,

My comments in red respectfully, I know the struggle!

Being on the receiving end of drawings with comments like "all other features - refer to math model" I would recommend caution in minimalizing a drawing. While the designers and engineers at your suppliers will have CAD workstations to be able to interrogate the part design, the people doing the inspection of the resulting parts for qualification and ongoing production will almost certainly not.

Agreed Dave but the world of interrogation is changing! "Y14.41-2003 Digital Product Definition data practices" is ushering in a new era of "expected capabilities" for manufacturers to interrogate product specifications.

My request for any customer on their drawing would be this: tell me on your drawing what is important, do it clearly, and accurately. If you have a position or profile specified on the drawing, I want to see a datum structure that restrains degrees of freedom correctly, is meaningful, and accurate to the design intent, Agreed as well and I want to see all required basics to be able to measure them. Unfortunately... unless you have a compatible CAD reader you may not!

By leaving required information off the drawing, you open it up to interpretation. THAT IS TRUE! but if the product if correctly detailed in the "contract" electronic model then it is not true!!! If you have simply a profile callout, I will interpret it as requirement of flatness, straightness, form, etc., and not necessarily measurement about a true profile contstrained by a basic. "That is unfortunate", I would stress that this is where open communication with the customer will resolve questions!!! If you have a position callout with no basics, I will come back to you and request that the drawing be corrected. "Agreed!!!"
Just from one on the receiving end.

Just my thoughts, Paul

 

[Micronus]

Looks like there may be no easy answer.

I appreciate everyones input.

-OO-