Drawing standard question

[Tofflemire]

Hi All,

We have our standard drawing formats that have state in the feature control frame that x.xx +-.02 and x.xxx +-.010. Below this we state "Interpret drawing per ASME Y14.5M", then below this we state "Dimensions are in inches". Here is my question, the drawing(s) are dimensioned following the above +- statement and do not show any GD&T symbols next to any dimensions, is this drawing wrong? We do not state the year of the Y14.5M standard we refer to, and we are not using GD&T symbols anywhere on the drawings? What if we used both GD&T symbols and +- dimensions on the drawing?

Thank in advance for any help?

Tofflemire

 

[ewh]

Tofflemire,

ASME Y14.5 does not require that you use geometric tolerancing, as long as the applicable tolerances are stated somewhere on the drawing. The standard specifies how drawings are dimensioned, and, IF GD&T is used, how to apply and interpret any GD&T tolerancing.

Eric

 

[ewh]

I reread your question, and saw that my answer wasn't complete.

The year of issue of Y14.5 should be specified, although since there has been only one release since it changed from ANSI to ASME, this probable won't pose a problem until further releases are available.

It's OK to mix +/- tolerancing and GD&T tolerancing on the same drawing, as long as the part is fully defined.

I hope that helps!

Eric

 

[drawoh]

Tofflemire,

I think the GD&T symbols are overrated in importance. The important thing ASME Y14.5M does is define just what all your dimensions and tolerances mean. I recommend getting a copy of the standard. You are probably going to get some surprises.

Also, I strongly agree with ewh. You need to specify the year of the standard. For example, take the case of a rectangular plate with the length and width specified. ASME Y14.5M-1994 states that the sides of the plate are perpendicular to the base to within the standard angle tolerance on your title block. The length/width measurements are made perpendicular to the two edges.

An alernate interpretation of this dimension would be to use the maximum and minimum dimensions to define a tolerance zone, and require the edges of the plane to be contained within this zone. I was told by my GD&T instructor that this is how the ISO standard works. ASME Y14.5M may adopt this at its next update.

These two interpretations are different from each other. To switch a drawing from one standard to the other requires a careful review of all your tolerances.

JHG

 

[swertel]

To be another one to agree, you MUST put the year of the standard in your title block. I believe it even states that you must do that somewhere in the standard. As a matter of fact, that is the ONLY standard where you put the revision information with it. All others are assumed to follow the most current.

Secondly, I'm suprised everyone else missed this. ASME Y14.5 is "geometric DIMENSIONING and tolerancing." The GD&T symbols you are refering to are the feature control frames for a specific method of tolerancing that complements the [±] sign. That is why you have a MMC, LMC, or RFS modifier. Those modifiers come from the fact that there is always on inherent tolerance on a dimension, unless you BASIC dimension everything, and then you have to put in a feature control frame to add tolerance.

Finally, I have to disagree with drawoh about the importance of GD&T symbols and that they are NOT overrated. They are however, over abused and the most misused symbols on a drawing.

--Scott

For some pleasure reading, try FAQ731-376

 

[Tofflemire]

Hi All,

Keep the replies coming; I really need multiple points of views.
To add something else to my argument, Y14.5 states that all dimensions must have a tolerance, unless it's a reference dimension. I do have tolerances on all dimensions based on the note stating X.XX±.02 and X.XXX±.010. The only difference is that I am using block (square dimensioning scheme) vs. Bonus (circle dimensioning scheme).

Thanks again to all

Tofflemire

 

[ewh]

Tofflemire,

As you may already be aware (since you know about "bonus' tolerancing) your +/-.010 translates to a positional tolerance of .028 dia, which is where the advantage lies.

Swertel,

I strongly agree with you about the importance of symbology and the widespread misuse thereof.
Someone has to inspect those parts, and the symbols you choose to use should reflect how that part will be inspected, i.e. don't use a concentricity symbol if runout will suffice, as that is much easier to verify on the finished part.
It is common to see tight controls on features relative to the major datums, but no controls on those datums. How can you hold a tight perpendicularity relative to a datum which has no flatness control, only the title block +/- tolerance?
It is also common to see datums specified on "imaginary" planes through a centerline. How can these be inspected?

Sorry to rant about this, but just this week we received a complex tooling design from one of our vendors. The design was well thought out, and I am impressed with the designer's creativity. It's a shame that the GD&T was totally off the wall.

Oh, yeah. RFS has been eliminated from ASME Y14.5M-1994. It is now assumed RFS if no other modifier is present.

Eric W Hayden

 

[swertel]

"Oh, yeah. RFS has been eliminated from ASME Y14.5M-1994. It is now assumed RFS if no other modifier is present."

Thus the reason you have to specify the year after "ASME Y14.5". In 1982 version, lack of modifier meant MMC; in 1994 version, RMS. Big difference in meaning and cost.



--Scott

For some pleasure reading, try FAQ731-376

 

[Tofflemire]

Hi Everyone,

My real questions to this topic is Do I have to dimension everything using GD&T feature control frames and referencing ASME Y14.5. Can I not use only ± tolerances or limit dimensions on each dimension without any GD&T feature control frames shown on the drawing? If I do use only ± tolerances, is this Breaking any rules?

Tofflemire

 

[swertel]

No. Most drawings do not require the control of a feature control frame tolerance. Plus-minus tolerancing is usually sufficient. You just have to watch for tolerance stack-ups and make sure your parts fit together.

GD&T was designed for mass producing replaceable parts. If you don't fit within that GENERAL definition, then don't spend a lot of unnecessary time with GD&T.

For example, on my machine designs, I typically only GD&T parts that I determine to be wear items and may need to be replaced. If everything else is meant to stay together, then I can machine it that way (dimension my drawing that way).

--Scott

For some pleasure reading, try FAQ731-376

 

[ewh]

Tofflemire,

As Scot said above and as I stated in my first response, NO, you do not have to use feature control frames. +/- dimensioning is a valid method under this standard. The standard defines how they are used and also defines how drawings are to be dimensioned in general. Following the standard ensures that the drawing will be interpreted the same way, regardless of who is reading the drawing (as long as they are familiar with the standard).

Scot,

The reason I replied above that the year of the standard "probably won't pose a problem until further releases are available" in this case is that it is the very first issue of ASME Y14.5, previously it was ANSI Y14.5. I agree that it will however pose a problem as soon as the standard is revised.

 

[looslib]

Actually on the first page of ASME Y14.5M-1994, it states in section 1.1.3 that the standard shall be referenced as "ASME Y14.5M-194".

This is also stated in ASME Y14.100-2000 in section 4.12.1 that references to ASME Y14.5M on drawings "shall always include the year of issue".


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[SuperXR7]

Yes you can have both