Is the Actual Mating Envelope and Datum mean the same thing for this Feature of Size (10 mm Pin) ?
No. they are different concepts.
The datum is a theoretical surface (perfect points, lines, and planes). Measurements cannot be made from theoretical surfaces. It is the perfect cylinder of the pin, theoretical.
The purpose of datumes is for the location and orientation of features, it is the origin from which the location or geometric characteristics of features of a part are established
The mating envelope of the 10 mm pin, that happened to be also a datum, is not a theoretical surface. The diameter of this perfect cylinder can get bigger or smaller as required, and more ever is not the size of the pin but the size of the smallest hole in which the actual pin size goes in. So, it is an actual size, not a theoretical one. The actual mating envelope of a pin is the smallest similar hole counterpart that fits over the pin and contacts the pin at the highest points.
There are two types of envelopes:
1. Unrelated actual mating envelope: It is closest fit counterpart perfect feature without considering any datum feature or constraint.
2. Related actual mating envelopes, It is also the closest fit counterpart perfect feature while constrained either orientation or location, or both by applicable datum(s).
1. Unrelated actual mating envelope: It is closest fit counterpart perfect feature without considering any datum feature or constraint.
2. Related actual mating envelopes, It is also the closest fit counterpart perfect feature while constrained either orientation or location, or both by applicable datum(s).
What is the connection between a datum and the actual mating envelope?
If we want to simulate the datum -A-, from the measurement point of view, when you want to measure the location or orientation of other features to the datum -A- we need to be clear first which pin 10 mm you should simulate as a datum -A- for the measurements?
The datum -A- is simulated by the Unrelated Actual Mating Envelope because is closest fit counterpart perfect feature. The size of the Unrelated Actual Mating Envelope is considered to be the size of the hole and it is the axis of the Unrelated Actual Mating Envelope is considered to be the axis of the hole.
Its is not the Related matting envelope because the Related Actual Mating Envelope is always perpendicular to a datum.
To which datum in our case?
In this case the pin 10 mm it is the datum -A- itself, primary datum.So its axis should be related to itself. The other surfaces are not datumes. The 90° angle of the axis of the Related Actual mating Envelope constrain the orientation or location of the 10 mm to the datumes, but not to itself. To itself it is only the axis of Unrelated Actual mating Envelope simulates the location and orientation of the primary datum -A- with 3 points of contact with mating part.The Unrelated Actual mating Envelope is the perfect the theoretical feature and the origin from which the location or geometric characteristics of features of a part should be measured and evaluated if they are within their print specifications.
Its is not the Related matting envelope because the Related Actual Mating Envelope is always perpendicular to a datum.
To which datum in our case?
In this case the pin 10 mm it is the datum -A- itself, primary datum.So its axis should be related to itself. The other surfaces are not datumes. The 90° angle of the axis of the Related Actual mating Envelope constrain the orientation or location of the 10 mm to the datumes, but not to itself. To itself it is only the axis of Unrelated Actual mating Envelope simulates the location and orientation of the primary datum -A- with 3 points of contact with mating part.The Unrelated Actual mating Envelope is the perfect the theoretical feature and the origin from which the location or geometric characteristics of features of a part should be measured and evaluated if they are within their print specifications.
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