# Thread: GD&T profile tolerance help

1. ## GD&T profile tolerance help

I am new to the forum and also to profile tolerances and for the most part I understand the concept of a profile tolerance. the attached picture shows my question the holes have 2 profile tolerances attached to them and I am not sure how this works. could someone please explain this to me?

2. Any and all input would be appreciated...

3. First, let's evaluate the upper most Profile of Line .003 no Datum.

There are two tolerance lines, offset perpendicular to the true radius profile bilateral equal between locations "D" and "E". There are three instances of this tolerance specification.

Second highest specifications:

First, Profile of line .0015. Again, we have two tolerance lines offset bilateral equal to the true profile surface between "E" and "D". There are three instances of the tolerance specification.

Next, Profile of line .0035 Unilateral .0010 relative to datum A at MMB. The Delta Note "A" I think probably specifies which direction the profile tolerance is offset.. This means that there are two tolerance lines parallel to the true profile and offset to one side of the true profile relative to datum A when datum A is at MMB size. The tolerance lines are only between locations "E" and "D".

4. Originally Posted by Kelly Bramble
First, let's evaluate the upper most Profile of Line .003 no Datum.

There are two tolerance lines, offset perpendicular to the true radius profile bilateral equal between locations "D" and "E". There are three instances of this tolerance specification.

Second highest specifications:

First, Profile of line .0015. Again, we have two tolerance lines offset bilateral equal to the true profile surface between "E" and "D". There are three instances of the tolerance specification.

Next, Profile of line .0035 Unilateral .0010 relative to datum A at MMB. The Delta Note "A" I think probably specifies which direction the profile tolerance is offset.. This means that there are two tolerance lines parallel to the true profile and offset to one side of the true profile relative to datum A when datum A is at MMB size. The tolerance lines are only between locations "E" and "D".
Thank you Kelly! Now I have to ask how can the same line have both a .0015 bilateral tolerance (.00075 each side) and the same line have a much bigger tolerance of .0035 (.0025 in the slot and .0010 on the material side with a MMC)? how can the same line have 2 tolerances? If parts line profile is running at .0010 it meet the .0035 unilateral profile tolerance but the part fails the .0015 bilateral tolerance. This is where I am confused

5. m
Originally Posted by bigchainey
Thank you Kelly! Now I have to ask how can the same line have both a .0015 bilateral tolerance (.00075 each side) and the same line have a much bigger tolerance of .0035 (.0025 in the slot and .0010 on the material side with a MMC)? how can the same line have 2 tolerances? If parts line profile is running at .0010 it meet the .0035 unilateral profile tolerance but the part fails the .0015 bilateral tolerance. This is where I am confused

The .0015 Profile of line tolerance is a form control. The goal specified is to limit surface variations to a total of .0015. Keep in mind that the tolerance lines can float up-down or rotate to best accommodate the as-built surfaces.

The Profile of .0035 unilateral by .0010 tolerance is oriented and/or located to Datum A at MMB. These tolerance lines are not allowed to float or move around for a best fit. This specification actually controls the orientation or location and perhaps the size of the surface.

Think of the upper feature control frame as form control (like flatness or straightness) and the lower feature control frame is a orientation/location and potentially size control.

6. Originally Posted by bigchainey
The .0015 Profile of line tolerance is a form control. The goal specified is to limit surface variations to a total of .0015. Keep in mind that the tolerance lines can float up-down or rotate to best accommodate the as-built surfaces.

The Profile of .0035 unilateral by .0010 tolerance is oriented and/or located to Datum A at MMB. These tolerance lines are not allowed to float or move around for a best fit. This specification actually controls the orientation or location and perhaps the size of the surface.

Think of the upper feature control frame as form control (like flatness or straightness) and the lower feature control frame is a orientation/location and potentially size control.

I think I FINALLY understand. the .0015 would an edge finish requirement and this tolerance would reject for things like chatter or poor edge quality. while the .0035 unilateral by .0010 is checking for position and fitment to datum A.