A Single Set-up For Manufacturing
The designer tends to see the product from a functional standpoint without regard to Manufacturing. The Manufacturing Engineer sees the product from a processing standpoint.
Consider the part below. For reasons required by the product, the designer has specified various surfaces to be held within Profile Of A Surface values to three separate datums. This implies three separate manufacturing set-ups.
The Manufacturing Engineer would much prefer to hold the part in one set-up and make all three of the specified cuts while remaining in that one set-up. The question then becomes how tightly must the three surfaces specified be held relative to datum [A] in order to meet all of the requirements on the print.
First consider what the requirement is for each of the profile tolerances. Start at the surface that is the farthest away from datum A. The top surface has a profile callout of 0.1 relative to datum [C]. Therefore the max distance allowed between datum [C] and the end surface is 5.05. The minimum distance allowed between datum [C] and the end surface is 4.95.
The max distance allowed between datum [B] and datum [C] is 5.1. The minimum distance allowed between datum [B] and datum [C] is 4.9.
The max distance allowed between datum [A] and datum [B] is 16.15, and the minimum distance allowed between datum [A] and datum [B] is 15.85.
The designer tends to see the product from a functional standpoint without regard to Manufacturing. The Manufacturing Engineer sees the product from a processing standpoint.
Consider the part below. For reasons required by the product, the designer has specified various surfaces to be held within Profile Of A Surface values to three separate datums. This implies three separate manufacturing set-ups.
The Manufacturing Engineer would much prefer to hold the part in one set-up and make all three of the specified cuts while remaining in that one set-up. The question then becomes how tightly must the three surfaces specified be held relative to datum [A] in order to meet all of the requirements on the print.
First consider what the requirement is for each of the profile tolerances. Start at the surface that is the farthest away from datum A. The top surface has a profile callout of 0.1 relative to datum [C]. Therefore the max distance allowed between datum [C] and the end surface is 5.05. The minimum distance allowed between datum [C] and the end surface is 4.95.
The max distance allowed between datum [B] and datum [C] is 5.1. The minimum distance allowed between datum [B] and datum [C] is 4.9.
The max distance allowed between datum [A] and datum [B] is 16.15, and the minimum distance allowed between datum [A] and datum [B] is 15.85.
See the figure below for the solution.
Remember to start at the surface farthest away from the primary datum. In order to keep the end surface and datum [C] within 0.1 of each other, divide the 0.1 between the two surfaces. This still allows some tolerance for surface [C] relative to datum [A] while keeping the distance between [C] and the end within max 5.05 and min 4.95.
Now having established the tolerance on datum [C] as being a profile of 0.05 relative to [A], look at datum [B]. Remember that the distance between [B] and [C] must always between 4.9 and 5.1. If datum [B] has a profile tolerance of 0.15, then there will be a total of 0.2 allowed between [B] and [C]. Thus the distance between [B] and [C] will always be held between 4.9 and 5.1.
With a profile tolerance on [B] of 0.15, the original profile tolerance of 0.3 on [B] is more than met.
Remember to start at the surface farthest away from the primary datum. In order to keep the end surface and datum [C] within 0.1 of each other, divide the 0.1 between the two surfaces. This still allows some tolerance for surface [C] relative to datum [A] while keeping the distance between [C] and the end within max 5.05 and min 4.95.
Now having established the tolerance on datum [C] as being a profile of 0.05 relative to [A], look at datum [B]. Remember that the distance between [B] and [C] must always between 4.9 and 5.1. If datum [B] has a profile tolerance of 0.15, then there will be a total of 0.2 allowed between [B] and [C]. Thus the distance between [B] and [C] will always be held between 4.9 and 5.1.
With a profile tolerance on [B] of 0.15, the original profile tolerance of 0.3 on [B] is more than met.
Note that the single set-up has driven some tighter tolerances than would be required with multiple set-ups. That's a trade off that is made when choosing the single set-up. The positive to doing this is that those tighter tolerances are likely to be easier to achieve with a single set-up than they would have been with multiple set-ups.