Complex Surface Profile as a datum

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Coleman Donnelly

#1
I have a part that has a complex surface (free form surface/sculpted surface) which produces vectors in all 3 axis.

This surface acts as the primary datum in terms of how the part will seat/mate functionally in the assembly.

My intent is to identify this surface as Datum A with a profile tolerance which is essentially creating a virtual condition boundary for the form of the feature.

My question is - this is rather unorthodox and I am not sure how to identify the basic dimensions as they relate to datum A. I have not been able to find an example of this having been done before either.

Typically a datum control frame establishes a coordinate reference frame. If you consider the concept of a classical 3-2-1 control frame you have a plane, a line and a point constraining all 6 degrees of freedom. The plane and the line create the orientation of your coordinate frame and the convergence of the 3 features represents your origin point.

In my example all 6 degrees of freedom are constrained by Datum A. However, there is no flat plane that defines the orientation of my coordinate frame or location that represents my origin that is specific to the feature.

Any help?
 
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Paul F. Jackson

Quite Involved in Discussions
#2
The basic profile must be defined 3D from a coordinate system reference so that reference location will be your X0,Y0,Z0 for translation and the fit of the "imperfect form" relative to the "perfectly defined form" will establish the 3 rotations.

It doesn't matter where the coordinate translation reference X0,Y0,Z0 is relative to the form as long as the definition remains basic.

Paul
 
C

Coleman Donnelly

#3
Exactly what I expected.

Is it fair to utilize the model to identify the correct relationship to 0,0,0?

Also - Can you provide me with an example of this for reference?
 

Paul F. Jackson

Quite Involved in Discussions
#4
Yes it is good to share the parametric model as it can often be utilized to tool, manufacture, as well as inspect the resultant part.

No I have no examples to share. Post your form up that we can mark-up and discuss.
 

Michael_M

Trusted Information Resource
#6
I don't know if this will help:

Can you set "tooling" points that give the "measure from" points. I did a quick mark up of your drawing (very quick). You define the 6 points (I only show 5 as my example) based on distances from 'edge'.

All defined dimensions, profiles, and objects are called from these tooling points. This might make it easier to measure as they have something tangible to measure too.
 

Attachments

C

Coleman Donnelly

#7
Thanks for the response :)

Thats part of the problem - the geometry is not based on discreet points. The mating geometry is a mirror of the surface in the print, and the "best fit" could be represented by any points in the surface - and the points will vary from sample to sample.
 

Paul F. Jackson

Quite Involved in Discussions
#8
• Is the mating geometry the basic profile of the contoured primary?
• Is the part rigid?
• When a part is fitted on the mating geometry is there any definition of a true or conforming profile of the remaining surfaces?

• If possible use the mating profile as the datum simulator for your inspections.
• For comparison digitize a grid of conforming points from the conforming surface and create an array of the translation displacements making sure to increase saturation of points in any areas that have abrupt contour changes like edges etc.
• Fit the copies on the datum simulator and gather the mapped grid points for comparison to the conformance array.

• If it is not possible to use the mating profile as the datum simulator then you are going to have to digitize the true or conforming profile and store it in an array and scan/digitize the same grid on datum feature surface of the replica then run a best-fit pattern routine on the two arrays (you may have to iterate the process by shifting and rotating the grid on the replica until you are unable to significantly reduce the error between the true profile and the candidate profile). Once you have established the coordinate system on the replica then you can gather grid point data for all the remaining geometry and compare it to the true profile.

Paul
 
C

Coleman Donnelly

#9
The mating geometry is a mirror image of the contoured geometry. The part is rigid. When the primary mating part is attached there is only contact between 2 surfaces. However, clerance and wall thickness are an issue, and other surfaces will assemble with other parts. There are some holes that will eventually be added, but it is still early in this design. Holes will mate with other parts in the assembly.

The concern here is not so much how to inspect, but how to document the correct information on the drawing...
 
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