BS 8888: 2011

We (that is committee TDW/4/8 at BSI) have recently finished putting the final touches to the next revision of BS 8888. With the new revision, why have tried to do something significantly different with the standard, which we hope will make it much more useful for industry.

BS 8888 first appeared in the year 2000, when BSI withdrew BS 308 and adopted the ISO system of standards for technical specification.

The ISO system for technical specification is documented in a large number of ISO standards (probably around 250 in total).  At present this is like a large, disorganised technical library, consisting of numerous documents from different authors with very different styles of writing.  Some documents provide a broad overview of a large area of technical specification, while others go into minute detail in a very specialised topic.  Some documents deal with specific manufacturing processes, such as casting and forging, while others deal with general topics such as dimensioning or drawing views.  Some documents have overlapping content, and in many cases, you would have to use two or three documents together to properly understand a particular topic.

ISO are making some efforts to bring structure and organisation to this collection of standards, but this is a slow process, and will take many years.

BS 8888 was introduced to help engineers work with the ISO system, and initially did so by providing an index, along with some additional commentary to help explain some topics.

With the new revision of BS 8888 we are taking this a step further.  There were two fundamental reasons behind our approach to the new revision:

• Industry has in many cases found BS 8888 unsatisfactory to work with, because they expected BS 8888 to be a replacement for BS 308, and to contain the same level of information.  Some poor marketing from BSI early on encouraged this misperception, and the subsequent disappointment felt by many who purchased the standard.
• The ISO system is difficult to work with because of the way in which it is spread over a wide range of different standards, which are interrelated, but often in a fairly haphazard manner.

Our aim within the technical committee has been to use BS 8888 as a vehicle to address both of these problems.

In order to make the ISO system more accessible, we have taken the core content of a number of key ISO standards, such as ISO 1101 and ISO 5459, and incorporated it directly into BS 8888.  In this way, we intend to make the essential elements of the ISO system available together within a single document.

In order to make the ISO system more useable, we plan to use BS 8888 as a filter.  We will include the main elements of the ISO system, which are relevant to most users, but screen out some of the more specialised aspects of the ISO system, which would have very little relevance to most engineers (and would only tend to confuse matters).  BS 8888 will continue to index and reference all these ISO standards, but the aim is to maintain a central body of content which provides access to the fundamental elements of the system.

The 2011 revision of BS 8888 is currently scheduled for publication in December.  It is not perfect, but we hope that does mark a significant step forward in terms of the usability of both BS 8888 itself and the ISO system.

I will lay out some of our plans for the further development of this standard in a future post.

ISO 8015 & ISO 14405

First the bad news.  With a couple of minor tweaks, none of which addressed the fundamental objections put forward by the UK and USA, ISO 8015 has now been approved.  The UK, USA and Canada all opposed this, but it was passed with a comfortable majority of other nations voting in favour.  The invocation principle, which requires all mechanical engineering specifications to be interpreted according to ISO GPS rules unless an alternative standard is specified, is now enforced.  The voluntary nature of standardisation, which has always applied in the past, has in this case been removed.  You no longer have to opt in to the use of this standard, you now have to opt out, which places a responsibility on anyone involved with mechanical engineering specifications to be aware of the standard and its rules.

With the new version of ISO 8015 now published, much of the content of the previous ISO 8015, dealing with size and the envelope requirement, has been moved to another standard, ISO 14405-1.

ISO 14405-1 is the first standard to really address the whole issue of size properly, and gives a thorough, and long overdue, breakdown of the different ways in which size can be defined.  It also provides tools which enable size to be defined in different ways on a specification when necessary.  In the absence of any other indication, the previous definitions of size still apply by default.

This is a good standard, which brings clarity to an area of specification which is often poorly understood.

There is also in the pipe-line an ISO 14405-2 standard.  This is really concerned with explaining how a specification will inevitably be ambiguous if datums and geometrical tolerances are not used.  The UK felt that this content should be produced as a technical report rather than a standard, as it is really just an informative document, but again were over-ruled.  However, the content is perfectly valid, and may be of interest to anyone who is not convinced of the necessity of using geometrical tolerancing to specify products.

Multitasking

An interesting article here, suggesting that while we are all under constant pressure to multitask more and more, it may not be a good idea.

http://www.pbs.org/wgbh/pages/frontline/digitalnation/interviews/nass.html

see what you think ...

Symbols

Mas'ood asked about some of the symbols I mentioned in the last post.  I'm working on a document to publish here which will show where all the different symbols are to be found in the ISO GPS system.  Real soon now!

Paris and Helsinki in February

February was a busy month for travel.  The ISO TC 213 conference was held in Paris, so I was there for five days.  At one meeting, with a fairly tight schedule, it was tentatively suggested that lunch could be restricted to 50 minutes, but the French delegation vetoed this idea immediately.  They take their lunchtimes seriously over there.

I also had to deliver a geometrical tolerancing course in Espoo, just outside Hesinki in Finland.  Helsinki in February rarely gets warmer than -20C, so that was an interested experience.  Many of the cars have cracked windscreens over there, which I assumed was due to the extreme temperatures.  However, locals told me that it is nothing to do with the temperature, but due to spikes from snow tyres being flung up from the road.  They went on to point out that you never see motorcyclists in Finland in the winter!

The picture on the left shows the view from the back of the training venue.  This is on the coast, and between the camera and the trees in the distance is an inlet from the sea, but completely frozen at this time of year.  Just behind the 'stop' sign on the left of the picture, you may just be able to see a boat frozen in.

On one evening we went to the Zetor restaurant in Helsinki, which has an unusual kind of farming theme.  Some of the tables are built onto old tractors.  Farming implements cover the walls.  Old buckets are used for lampshades.  The food was very good.

Common Zone modifier

First post since November! It has been a busy few months, but I must try to do better than that.  I'll put up some more posts about what has been going on shortly.

Mas'ood occasionally sends me interesting (or awkward, depending on your point of view) questions about geometrical tolerancing.

I am going to put some of his questions here - feel free to comment if you have a view.

First question is about the use of the 'common zone' modifier, CZ.

This is placed in a geometrical tolerance frame to indicate that two or more features have to satisfy the requirements of a single tolerance zone.

CZ used with a flatness tolerance

Mas'ood's question was whether the CZ modifier can be used with the envelope requirement.

Personally, I don't see why not.

ISO devised the CZ modifier with a view to it being used in the tolerance frame only, but as long as the meaning is clear, I see no problem with applying it to the envelope requirement as well.  It would be a way of indicating that two features-of-size, of the same size and in alignment with each other, should be treated as a single feature.

CZ applied with the Envelope Requirement to two features

I would feel less comfortable with this approach if it was being applied to two features which were produced with separate machining or manufacturing operations, but we are well into the realm of 'designer's descretion', as the standards provide no guidance in this area.



CZ applied with Envelope Requirement to two features produced with separate operations



ISO have developed several different symbols in recent years, such as Common Zone (CZ), Separate Zone (SZ), United Feature (UF), Contacting Feature (CF), etc, and are currently reviewing these to see if they can minimise this 'symbol inflation'.  The 'UF' symbol was to be used to indicate that several features were to be treated as if they were a single feature, but ISO TC213 will be reviewing whether the CZ symbol could be used as an alternative, or even remove the requirement for the UF symbol altogether.