3D Best-Fit Base Alignment

[[Do...]]

Can someone please provide an explanation of, or reference documentation for, the correct procedure to create a 3D Best‑Fit Base Alignment using XYZ coordinate data collected from tooling balls on a fixture?

Specifically, I am looking to understand the recommended steps, assumptions, and alignment methodology used to establish a stable and repeatable alignment from discrete tooling ball coordinate data, including any best practices related to datum selection, constraint application, and evaluation of alignment quality.

Any guidance, examples, or standard work that outlines this process would be greatly appreciated.

[[Ri...]]

I guess I'd have to see the drawing and the intent. 

I haven't measured too many fixtures with tooling balls, but of all the ones I've seen while there are tooling balls, they are still broken down to a 3-2-1 alignment. 

In all of my years I've only ever used a 3d best fit alignment once, and that was on a part that was just essentially a free-form blob. 

I think the most use cases for it is in the medical world (mainly orthopedic implants). 

Either way - to use it for tooling balls it should just be rather straightforward. Load the cad model - Created a new base Alignment (3d Best Fit Method) - select your tooling balls - ensure that the nominals are correct - turn on a Loop (probably minimum of 5x with a break condition). 

For measurement of tooling balls, unless there is some crazy requirement or concern, I would just measure the spheres with the Sphere Macro (looks like the Geometry Qualification). If you want to scan them, you can, but most of the time it is unnecessary. 

[[Je...]]

Hey

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.

I'm curious... what's the overall aim of this project?  Sounds interesting.  Is there a reason for best-fitting based on the origin of a tooling ball?  I assume there is, but before commenting on the process, it would help to hear the end goal.

 

[[Do...]]

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I am looking at having to have a CMM fixture that locates the part on the physical datums and then has tooling balls that I can pick up on and off-set a best-fit base alignment based off of the XYZ coordinates of the balls back to the datum structure. I am being told that it is done for parts that have to be physically constrained on the datum where probing of the physical features is not possible. Then the tooling balls are picked up and then the Best-Fit Base Alignment is created from the exact XYZ coordinates that come from the fixture manufacturer and then the part can be measured from that point on.

[[Ri...]]

I assume this is an automotive check fixture. 

[[Ze...]]

If you have a fixture that has surfaces that are datum simulators, why would you need a tooling ball reference? Wouldn't you just measure the fixture surfaces that are datum simulators, put your part in the fixture, and use those for your datums in the program?

Sorry if I'm not understanding. I've heard this scenario before and I'm just not getting it. It must be a car coordinate thing or something.