Using Profile to position a feature?

[randy64]

Very simple part. A rectangular hole in a rectangular block. Rectangular hole size is dimensioned with basic dim's and has a profile callout pointing to it. Three datums called out - bottom (A) of block and two edges (B & C). Profile is called out to all three datums. There are also basic dim's locating the rectangular hole from the edges (datums B & C).

Local "expert" says this is okay, that we can use profile to locate the rectangular hole. I disagree, argueing that profile is a tolerance of a feature size, not a tolerance of location. Therefore, dim's that locate rectangular hole should become unbasic, or just toleranced dim's - OR - add positional tolerance callout to rectangular hole and keep dim's basic.

Who's right?

Thanks

 

[axym]

randy64,

It sounds like you've got the right idea with profile tolerances now. It's the best tool for controlling the location of surfaces.

drawoh,

I'm not sure that I follow your comments on Figure 6-19. The profile tolerance references only Datum A, so it doesn't "position" the cutout at all. It only controls the "size" and form of the cutout. If the position tolerance was not there, then nothing would locate the cutout relative to the rest of the part.

Personally, I'm not a fan of the "boundary position" method, in which position is used to control the MMC boundary of something that is not a feature of size. Especially in conjunction with profile. The situations in which the benefits outweigh the confusion created are (IMHO few and far between.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca