ISO 1101 amendment 1

ISO 1101 is the principle ISO standard for geometrical tolerancing. It was last revised in 2004, just five years ago, but there are already a number of amendments queuing up to be incorporated into it.

The first of these, Amendment 1, is concerned with 3D annotation, and is going through the final stages of approval prior to publication. It is likely to come into effect some time in the next 12 months.

What is '3D annotation'?

It is established practice in most industries to use a 3D CAD model as an essential part of a component specification. The 3D model represents the 'nominal' geometry of the part, and as many manufacturing operations, and some inspection operations, can be driven directly from this 3D model, there is no longer a necessity to duplicate this data with dimensions on a 2D engineering drawing.

This has paved the way for the 'minimum content drawing' approach that is now widespread. The 2D drawing is used to convey information about datums, tolerances, surface finish and sometimes inspection requirements, but no longer needs to define the fundamental geometry of the part.

The next stage in the evolution of this process will be to apply the information about datums, tolerances etc directly to the 3D model, eliminating the requirement for a 2D drawing at all. This is what is meant by '3D annotation'.

Eliminating 2D drawings does not really become a practical proposition until everyone involved in the specification, manufacture and inspection of the component can work fully in 3D. For most of industry, that prospect is a distant one, so 2D drawings are going to be around for many year yet.

However, CAD software is increasingly providing the facilities to apply all specification requirements directly to the 3D model, and some manufacturing organisations are starting to work in this way.

The CAD software is currently a little ahead of the standards in this respect. While most 3D annotation requirements can be met quite happily by applying the 2D annotation elements in a 3D environment, there are some situations where this is not sufficient. Some specification elements depend on the positioning of a geometrical tolerance within a drawing view to convey part of the requirement. Working in 3D, we no longer have drawing views to position or orientate the geometrical tolerance, so other means have to be found to convey that information.

Amendment 1 provides some illustrations to indicate how a geomtrical tolerance requirement can be indicated in a 3D specification as well as in a 2D specification. More importantly, the amendment introduces some new annotation elements to enable all geometrical tolerance requirements to be fully specified in 3D. Symbols have been introduces to define 'intersection planes' and 'orientation planes', which can be used to define the location or orientation of a tolerance requirement relative to the 3D model.

The amendment also ties up one or two other loose ends. It will indicate how the 'all around' symbol can be used in 3D (although in my view there is no need to use it in 3D at all). There is also a new symbol to help make it clear when a derived feature, rather than a surface, is being used as a datum feature.

Finally, there will now be the facility to define offset tolerance zones. This last was something of a disappointment for those of us who argued in favour of adopting the American (Y14.5) symbology in the interests of simplicity, clarity and universal harmony. The ISO approach will be different from the Y14.5 approach, but at least we managed to avoid using the same symbol as the Americans', but with a different meaning (a very real possibility at one stage). Sometimes, these tiny, common-sense achievements rank as great victories when developing international standards.

BS 8888:2010

We are now starting to plan the next revision of BS 8888, which is due out in October 2010.

BS 8888 is currently up-dated every two years. I think this is far too frequent, and in principle, I would like the standard to be much more stable, and only up-dated every four or five years. This has been one of my objectives since I took over the chair of TDW/4/8, which is responsible for BS 8888.

However, BS 8888 acts as an interface to the ISO system of standards, and has to be kept up-to-date with changes in the ISO system, and this is what fundamentally drives the revision cycle.

In recent years, there have been a lot of developments within the ISO standards, and BS 8888 has had to change frequently to keep abreast of these changes. Right now, there are some more major changes in the pipeline, and a further revision of BS 8888 for 2010 is unavoidable.

So what changes are on the way? Four major ones at least:-

1. Amendment 1 to ISO 1101 (the main ISO standard for geometrical tolerancing).

This mainly deals with 3D annotation.

2. Amendment 2 to ISO 1101.

This introduces some new symbols, and also extends the system in several ways. For instance, some of the filtration options which can be used with surface texture specifications will be available for form tolerances.

3. ISO 5459

This is a major up-date of the datum standard, which is long over-due.

4. ISO 14405.

This is a new standard for linear sizes. It will replace ISO 8015, and provide a more comprehensive range of options for how we define sizes of features.


I'll give further details about some of these developments in future posts.

Geometrical Tolerancing, standards and related stuff

Does the world really need another blog?

I'm about to find out. This is my first experiment with blogging, and it really is an experiment. If it generates some interest and dialogue, then I will keep it going. If it doesn't, then I'll quietly close it down at some point.

I run my own business. I provide training and consultancy in geometrical tolerancing, engineering drawing, and related issues. I am also involved in the development of the standards which govern this field, through technical committees at BSI and ISO.

The people I work for are mainly in the aerospace and defence sectors, companies like Airbus, BAE Systems, and MBDA.

I also work for organisation like Toyota, Siemens, Thales, several in the Oil and Gas sector, and numerous SMEs across a wide range of industries. My clients include some of the Formula 1 teams, and scientific establishments like the Rutherford Appleton Laboratory - all of them fascinating in different ways.

I will be recording here, on an occasional basis, my thoughts and experiences on running a business, on working with tolerances and specifications, and on developing the British and ISO standards.

This is not going to be a free help-line on tolerancing issues, although there may well be discussion about the standards like BS 8888, ISO 1101, ISO 5459, etc. In part, I hope that this blog will throw some light on how these standards are developed.