quick question

[PRuggiero]

Here is a question that I am having trouble finding an answer to...

Say I had a rectangular block with a hole in it. If the block was laying face down I have the bottom as datum A, one of the four sides would be datum B and the hole datum C. Datum A has a flatness tolerance but my question is can I specify a profile tolerance to take care of the four surfaces that make up my block including the surface that is datum B and in that profile tolerance reference only datum A? Or do I need to have a orthogonal tolerance for B and take care of the other 3 surfaces with a profile tolerance? I believe a profile tolerance relative to datum A for all four surfaces takes care of my needs but I'm not sure if it is "legal". I see it as performing the same function as the orthongonal tolerance on datum B....

Any help is appreciated.

Thanks,
Pete

 

[PRuggiero]

Picture attached....

 

[CheckerRon]

You could make the narrow width datum B and the wide width datum C and profile each to datum A respectively. Then locate the hole to A, B, and C. What is functionally most important? Consider that in deciding the datums.

 

[PRuggiero]

Ron,

I appreciate the response; it is a fake part to get a question answered.

Basically I wanted to know if I could have a profile tolerance along a datum (like B in my picture).

It seems the answer is yes and it is pretty much like having an orthogonal tolerance (profile controls orthogonal too).

If I were to do the part as you say, then how would you set up the profile tolerances? Can I just have a profile tolerance that goes all the way around and is with respect to datum A? How tight I make the profile would determine how perpendicular the sides are to each other right?

 

[PeterStock]

Put a profile all around the outside and a true postion to the hole, both referencing A. You do not need B and C. All dims except the hole size and the thickness should be basic.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[PRuggiero]

Peter,

I understand that this part is simple and may not require so many datums, but it was only setup to help visualize my question. The question being, can a profile tolerance be applied to secondary and tertiary datums..

 

[PeterStock]

Yes it can, but in your example the secondary and tertiary datums are not required.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[PRuggiero]

Peter,

I appreciate your help, I was wondering if you could answer one more question. When can you get away with not referencing any datums while using a profile tolerance. My handbook says that there are special situations but doesn't show any of these situations...

Thanks,
Pete

 

[SeasonLee]

Profile tolerance can be specified with a datum reference or without a datum, when a profile control is specified with datum references, it is a related feature control, when a profile control is specified without datum references, it is a form control.

For your case, |Profile|.010|A| plus an all around symbol, datum B and C are not required.


Please be noted the Profile Datum Rule : A profile control should not be applied to the surfaces it references as datum features.

SeasonLee

 

[PRuggiero]

Season,

Thanks for the reply, just trying to make sure I really understand this stuff.

What do you mean by a "related feature control", I understand how the profile tolerance controls the form.

Also is that "profile datum rule" in the standard?

Thanks again,
Pete

 

[PaulJackson]

A sphere with a profile control pointing to its surface… without a datum reference… would control both its size and form.
A cube with an identical control… without a datum reference… would require an "all-over" designation to control both its size and form
Any form other than a single flat surface with a surface profile designated "all-over"… without a datum reference… would be controlled for both its size and form.
For the profile tolerace to control orientation and or location of the surfaces datum references would be required.

Paul

 

[SeasonLee]

Pete

“Related feature control” means that indicated feature’s profile tolerance zone in relation to the datums specified.

“Profile datum rule” is not a part of the standard, but it is a common sense rule. For your rectangular block, you can’t specify the profile tolerance with datum A and B |Profile|.010|A|B|, since the bilateral tolerance zone will not clear and makes confusion on the interpretation :
The width of the whole tolerance value is above the datum plane B or half of tolerance value above the datum B and half of the tolerance value below the datum B?

A clearer way to specify this type of profile tolerance zone is not to use a profile control to tolerance the surfaces it references as datums.

SeasonLee

 

[axym]

PRuggerio,

There are not really any rules governing when you can "get away" with not referencing any datums in a profile tolerance. When applying tolerances to a part, keep in mind the following basic premise: All geometric properties (form, size, orientation, location) of each feature, as applicable, must be controlled in some way. This premise is hinted at in the Fundamental Rules in Section 1.4 of ASME Y14.5M-1994 but not stated explicitly.

All this is saying is that no property of a feature (form, size) or relationship between features (orientation, location) can be completely uncontrolled. This is not to say that every property and relationship needs to be toleranced directly - many geometric tolerances indirectly control other properties and relationships. Controls can also come from plus/minus tolerances, block tolerances, or general notes.

It's true that profile tolerances can control almost any combination of form, size, orientation and location. Exactly what properties and relationships get controlled depends on the specifics of the considered feature/pattern and the datum features. I have a hard time applying any sort of rule of thumb. I have to just analyze things on a case-by-case basis.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[drawoh]

Put a profile all around the outside and a true postion to the hole, both referencing A. You do not need B and C. All dims except the hole size and the thickness should be basic.

The profile tolerance all around would require the datum[ ]B? The profile tolerance is just a flatness specification on datum side, but it works on the other three, would it not?

I would be tempted to apply datum[ ]C as well, depending on how the hole was dimensioned.

JHG

 

[axym]

drawoh,

PeterStock's suggestion is workable exactly as described. Neither datum B nor datum C would be required.

By the way, how would the way the hole is dimensioned affect the need to apply datum C?

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[drawoh]

axym,

The hole is datum[ ]C, and it controls position along datum[ ]B. If you don't care how your block is positioned...

The datum configuration sounds weird to me. If this were my drawing, datums[ ]B and[ ]C would be two orthogonal sides, or the width and the length, or the hole and one side, respectively.

Note how with the hole as the tertiary datum, part of the outline is positioned to the hole, not vice versa.

JHG

 

[MartinSr00]

If the outer profile is dimensioned basic, then use a profile tolerance having only a datum A, using a leader with an all around symbol pointing at the outside of the block (and hole if you wish)-- as long as they all have the same datum sequence (including modifiers)

For a given datum sequence, you constrain the part to your datum reference frame once. Not differently for each feature (unless you want to do otherwise with the "separate requirement" note).

 

[fcsuper]

I don't know if this is exactly what you are looking for, but you may wish to look at ASME Y14.5-2009 and the ALL OVER symbol.

Matt Lorono
CAD Engineer/ECN Analyst
Silicon Valley, CA
Lorono's SolidWorks Resources
Co-moderator of Solidworks Yahoo! Group
and Mechnical.Engineering Yahoo! Group