ASME Standards Archives - Page 5 of 8

Engineering related societies

The following is a list of professional societies related to the mechanical engineering field. These groups either have some sort of certification process or are responsible for the control of various commonly used standards. If other societies should be added to this list, please feel free to comment with their information, or email me directly.

American Society of Mechanical Engineers (ASME)
ASTM International (formerly American Society for Testing and Materials)
International Organization for Standardation (ISO)
National Society of Professional Engineers (NSPE)
Society of Plastics Engineers (SPE)
SAE International (formerly Society of Automotive Engineers)
Society of the Plastics Industry (SPI)

Controlled Radius

It’s been many years since ASME Y14.5M-1994 introduced the controlled radius symbol. Yet, we will still frequent find individuals in the industry who have never seen the symbol, nor know what it is. The symbol is CR.

It’s been many years since ASME Y14.5M-1994 introduced the controlled radius symbol. Yet, we will still frequent find individuals in the industry who have never seen the symbol, nor know what it is. The symbol is CR. Really, a controlled radius is actually just a radius that is a fair curve, with no reversals. I’ve not read ASME Y14.5-1982 in a very long time, but I believe this is actually similar to the original definition of a plain ol’ radius from the older standard.

Since ASME Y14.5M-1994, a simple radius has no fair or reversal limitation. As long as the arc of the radius feature’s profile falls within the tolerance zone, it is considered acceptable. These are represented by R.

So much time has gone by since the introduction of CR, I am left wondering why so many people have never seen it. The reason CR was created, as it seems, was to allow engineers to specify a radius without the need for it to be fair or non-reversed. This is good for breaking edges or filling corners. A CR would be more useful when fit and/or function is important, such as guiding features. In this way, the added expense of a creating a fair and non-reversed curve would only be employed when it is necessary for function.

Interpretation of Limits (ASME)

Some might look at the limits of a tolerance zone as non-absolute, but is that correct? ASME standards tell a different story for Interpretation of Limits.

When reading tolerances on engineering drawings, one of the finer points that comes up during Quality inspection is how to interpret tolerance limits. Some might look at the limits of a tolerance zone as non-absolute.

In other words, if a feature measures 14.004, but the upper limit specified on the drawing is 14.00, then one might be inclined to accept the part because 14.004 can be rounded to 14.00. However, according to ASME Y14.5-2009 (and any earlier versions), this is false reasoning.

All limits are absolute. Dimensional limits, regardless of the number of decimal places, are used as if they were continued with zeros.

The example given is similar to this: 12.2 means 12.20…0 (zero to infinity).

So, with that clear statement, interpretation of limits is always absolute. A measurement of 14.004 is a nonconforming part if the upper limit is 14.00. This is important, as it eliminates ambiguity and the opportunity to fudge with the numbers in a way that can affect quality and even product definition over time.

Drawings represent final product

One comment I’ve seen about ASME suggests that it is geared towards fully detailing product definition. One trap that rookie designers and engineers will often fall into is over-specifying their parts by placing manufacturing process information on the drawing.

The new designer may do this because maybe a machine shop made the part wrong and was trying to work the rookie’s inexperience to weasel out of their responsibility. Maybe someone in Quality Control was confused by a drawing because they don’t have adequate blueprint reading skills, so they come to the new designer to ask that more information be spelled out on the drawing (when it is already fully specified). These are just a couple of examples. Often, new designers don’t know why manufacturing processes are not included on drawings, nor even that there exists standards that forbid it.

ASME Y14.5-2009 (and previous versions) states:

1.4(d)The drawing should define a part without specifying manufacturing methods. …However, in those instances where manufacturing, processing, quality assurance, or environmental information is essential to the definition of engineering requirements, it shall be specified on the drawing or in a document referenced on the drawing.

It is usually pretty obvious when manufacturing methods are necessary to the engineering requirements, even to the individuals new to the field. Unless one is in particular industries, manufacturing methods are almost never required. A drawing should fully detail the final product without over specification.

ASME Y14.5-2009 adds as an example:

Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched, or made by any other operation.

The manufacturer is responsible to provide a final product that complies with the drawing regardless to the processes they use. It is still important for designers to know the processes that will most likely be employed, so they know that the product is economically manufacturable. This does not mean that they should unnecessarily limit the manufacturer to particular processes.

Dimensional limits related to an origin

In SolidWorks 2007 drawing mode, the ability to change the size of individual dimension arrows (so that they were different than the drawing) was limited to a tricky use of favorites. Starting with SolidWorks 2008, that situation improved. SolidWorks now allows the user to set the size for individual dimension arrows. For me, using arrows of a different size from the drawing default was only required once in the past. However, I recently had the need to use this function for dimensioning limits from an origin. This is a special kind of dimension where the tolerance of a dimension is set between two features but applied in only one direction.

From paragraph 2.6.1 of the ASME Y14.5M-1994 standard:

In certain cases, it is necessary to indicate that a dimension between two features shall originate from one of these features and not the other. The high points of the surface indicated as the origin define a plane for measurement. The dimensions related to the origin are taken from the plane or axis and define a zone within which other features must lie.

The origin of such a dimension is shown by replacing that arrow with a circle.

Meaning

This is where we get back to talking about SolidWorks. You can change the shape and size of the arrows on one or both sides of a dimension. The problem is that once the dimension arrow is changed to a circle, its size cannot be adjusted. This means that if the circle is too small (as it likely will be) the size must be changed to the arrow before switching it to a circle.

The following are the basic steps to establishing a dimensional limit related to an origin on a drawing in SolidWorks 2008 or higher.

Instructions 1 and 2

This following chart will then pop up at that location on your drawing view.

Pop up chart

3. Select Size, to bring up the next window.

Arrow size changing window

4. Deselect Use document arrow size and edit the arrow width. Accept by choosing the OK button.

Enter width

No, you aren’t done yet. There’s more. Remember, earlier I said the situation was easier. I didn’t say it was easy.

More steps

Again Again

7. Select the fifth item down on the pop up chart, which is the circle at the end of the dimension line.

Final Product

After all of this, you’ll finally have a dimension that establishes its tolerance from an origin per ASME Y14.5-1994 paragraph 2.6.1 and figure 2-5.

UPDATE: Newer releases of SOLIDWORKS will allow you to apply a size directly to the circle arrow. So, although the above instructions still will work, there are some extra steps that are no longer necessary.

It’s All Over!

When “All Over” is applied to a Profile of a Surface, it pretty much defines the entire shape of a part in every direction.

ASME Y14.5M-2009 has been out for a little while now (after almost a year’s delay). There are significant improvements and clarifications. One addition in particular caught my attention, the ALL OVER symbol. When applied to a Profile of a Surface, it pretty much defines the entire shape of a part in every direction (not just ALL AROUND which applies to the profile of a surface along a particular plane).

The symbol is either a double circle at the vertex of the associated bent leader, or the words ALL OVER placed immediately below the feature control frame.

The symbol indicates that a profile tolerance or other specification shall apply all over the three-dimensional profile of a part. It is applied as “unless otherwise specified” to allow for other existing dimensions and tolerances to take precedence.

The advantage of using this symbol is that it provides control of surfaces over an entire part without regard to part orientation, thus allowing us to directly reference the CAD model as basic and fully controlled, while still detailing critical dimensions and tolerances. This may help companies better parts where they rely on the CAD model to provide complete specification. In fact, where a CAD model is declared basic, companies may be able to effectively place the Profile of a Surface FCF with the ALL OVER symbol right into their drawing title blocks along side other tolerancing information.