# Thread: Unequally Disposed Profile

1. ## Unequally Disposed Profile

Good afternoon,

I got a problem with the total tolerances of shape and location, and I wanted to ask for help in mastering one issue:

We had received a drawing for processing the part and it shows the Profile of a Surface with unilateral tolerance to Datum "B" of the end of the detail . How to correctly interpret this meaning? Do I understand correct that a size of 129 mm from the center of the part - due to this “lead chamfer” can have a tolerance of 129 0/+1mm (129-118 = 11 0/+1mm)?
Please find enclosed pictures

2. Datum B is derived from the two vertical surfaces associated with the 204 +/- 0.5 limits of size. From those two surfaces a center plane is establish regardless of feature size. I like to call this my “zero” location.

The profile of a surface specification “circle U” specifies a unilateral tolerance of 1 from the as-shown, as-drawn location surface.

That Circle “U” indicates that amount of unilateral tolerance to the outside of the as-drawn surface.

Therefore, the location and size of the tolerance boundaries are 129 -0, +1 or minus zero plus 1.

Had the specification been Circle U 0.3 the there would be a requirement of 0.3 to the outside of the as-drawn profile and 0.7 to the inside.

3. Originally Posted by Kelly_Bramble
Datum B is derived from the two vertical surfaces associated with the 204 +/- 0.5 limits of size. From those two surfaces a center plane is establish regardless of feature size. I like to call this my “zero” location.

The profile of a surface specification “circle U” specifies a unilateral tolerance of 1 from the as-shown, as-drawn location surface.

That Circle “U” indicates that amount of unilateral tolerance to the outside of the as-drawn surface.

Therefore, the location and size of the tolerance boundaries are 129 -0, +1 or minus zero plus 1.

Had the specification been Circle U 0.3 the there would be a requirement of 0.3 to the outside of the as-drawn profile and 0.7 to the inside.

Big thanks for explanation, I meet this tolerance the first time on drawings and was a little bit confused )

4. Short Answer: The TOL that comes after the "U" is how far the profile is allowed to be above the true prfoile. It is the upper limit of the Tolerance Zone.

For example if you have .010 U .010 the the tolerance zone upper limit is the surface of the part. If you have .010 U .008, then the tolerance zone start .002 above the geometric surface. If you have .010 U 0. the it is the same as saying +/- .010 (.005 each side), just fancier.

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