How to simulate center plane datum from width datum feature on CMM?
How to simulate center plane datum from width datum feature on CMM?
(OP)
I think this is a very simple question but I don't find the answers.
I understand for slots, one may use adjustable parallels to fit into the slot to serve as datum simulator. But for outside width feature, what are the tools?
I understand for slots, one may use adjustable parallels to fit into the slot to serve as datum simulator. But for outside width feature, what are the tools?





RE: How to simulate center plane datum from width datum feature on CMM?
Or, if the CMM is scanning enough points on the outside surfaces, you might not need a physical tool to simulate -- the CMM could calculate the center of the actual mating envelope (see Fig. 4-13 of the Y14.5 standard).
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: How to simulate center plane datum from width datum feature on CMM?
http://www.wiltontools.com/us/en/p/super-precision...
Season
RE: How to simulate center plane datum from width datum feature on CMM?
Belanger,
I'm not from inspection area, but I learned the proper way to establish datums is to hit on the simulator surfaces, not on the part surfaces. Do you agree?
RE: How to simulate center plane datum from width datum feature on CMM?
I just meant that sometimes in a pinch you could derive a datum from the surface itself by doing the mathematical analysis (if enough points are sampled on the surface) to find the tangent plane or envelope.
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: How to simulate center plane datum from width datum feature on CMM?
I do have a question... With a hard gage, let's say, with a self-centering vise, the part would sit on its "high" points inside the vise... but on CMM, how do you guarantee you "scan" the high points? or can the software take care of that?
RE: How to simulate center plane datum from width datum feature on CMM?
In many cases it isn't required to find the exactly perfect high points, only to be certain that the finding is within the bounds of accuracy required to be sure the check is a good one.
For example, on a simple (as anything can be simple) length measurement: If the tolerance is +/-1.00 unit and the accuracy is only .25 units on the measuring equipment, but the measure is .25 from nominal, then it is likely the part is acceptable and lies somewhere between 0.00 and .50 of nominal. If a different copy of the part is at .999 and the measure with the .25 accuracy is .99, then one can't be sure, so a more accurate method is required for that copy.
The theoretical gauge is perfect, but practical applications are always a trade-off between cost, time, and likelihood of accuracy.
RE: How to simulate center plane datum from width datum feature on CMM?
John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
RE: How to simulate center plane datum from width datum feature on CMM?