Combining +/- tolerance & basic dimension to locate a hole. 2

[Madhu454]

Hi All,

One more basic question. Please see the attached drawing.

Only one face of the block is mates with its counter part (datum feature B). the other side is open and does not mates with any surafces. The hole needs to be located with closer tolerances with respect to datum faeture B, the location of the hole from the other free face which can have a wider tolerance. In such case can we combine the +/- tolerance and basic dimensions to locate the hole.

Is it a legal specification in ASME? I have seen few drawings of this kind.

 

[CheckerHater]

So the same hole can have position North-South and location East-West?

 

[Belanger]

The hole's location is controlled in all directions. One direction uses "position," which is one of several GD&T symbol for location. The other direction uses +/- which is also a location method.
(Jim, I ain't defending the +/- but merely saying that it's there.)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[pmarc]

Don't you guys think we are splitting hair on this?
Shouldn't the conclusion be short: do not use +/- dimensions just for your safety because it is ambiguous and someone can misinterpret it?

Location vs. position discussion is important but not the clue of op question here.

 

[Belanger]

sounds good to me!

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[CheckerHater]

Exactly what I suggested 4 days and 6 hours ago

 

[pmarc]

If this discussion was finished 4 days and 6 hours ago I would not earn a star

 

[CheckerHater]

I just gave you another one for being cautious

 

[MechNorth]

OK, if we all agree...let's change the standard!!!

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com

 

[DzineXlence]

Madhu454, according to your hand sketch and description in your original post a rectangular tolerance zone is acceptable, no material modifiers are allowed, and datum shift is not applicable.

Using those as design inputs, you can remove the positional tolerance altogether and locate the hole using toleranced dimensions to both the horizontal and vertical surfaces. Then put a Perpendicular control to Datum A.

It will accomplish the same thing with no ambiguity's.

 

[CheckerHater]

 

[ak762]

Do not know why but I like "A" case from CheckerHater
For shim with irregular outline contour do you think geometrical tolerance was applied wrong?

 

[Belanger]

I like yours better that CH's option "A," because at least you have two holes, and that makes the position symbol legal to use. However, there's still the difficulty of which of the two edges to set up on when checking the two ± dimensions. If that upper left corner is not exactly 90º, then we don't know which side to stay flush with.

This is why -- despite my seeming to defend ± location in earlier posts -- I always discourage it.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[ak762]

I take your point.
But when I represent design in drawing I try to proceed from function. In my sample important only relationship between holes and datum surface.
Dimensions from corner just find location one of them. It is why I mentioned what is a piece.
I have been discourage too sometimes with GD&T standards because some info with samples just pure extract to show possible solutions but do not specified for particular cases.
Anyway I always come back to listen expert and learn lessons

 

[Belanger]

True... function should drive it. I would then suggest profile around the perimeter, relating back to the two holes (the holes together would be datum B). That avoids the issue I mentioned, but I do see your main point.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[MechNorth]

DzineXlence ... your way introduces gross ambiguity, rather than eliminating it. Pls see previous posts and similar threads for explanations.

Jim Sykes, P.Eng, GDTP-S
Profile Services

http://www.profileservices.ca

TecEase, Inc.

http://www.tec-ease.com