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.
Saturday, 2 July 2011
Monday, 2 May 2011
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 ...
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!
Wednesday, 23 March 2011
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.
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!
Monday, 21 March 2011
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.
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.
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 |
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.
Saturday, 6 November 2010
FDIS 8015 gets negative vote
The Invocation Principle - see previous post - was part of the latest revision of ISO 8015. The FDIS (Final Draft International Standard) of 8015 has just recently been out for vote, and the results are back.
In order to be approved, two thirds of member organisations must vote in favour of the FDIS (66.66%), and no more than 25% of members must vote against. The actual results were 65% in favour, and 32% opposed. The FDIS has thus received a negative vote, and has been 'disapproved'.
Phew! But far too close for comfort!
In order to be approved, two thirds of member organisations must vote in favour of the FDIS (66.66%), and no more than 25% of members must vote against. The actual results were 65% in favour, and 32% opposed. The FDIS has thus received a negative vote, and has been 'disapproved'.
Phew! But far too close for comfort!
Monday, 1 November 2010
The Invocation Principle
How do you know which standards govern the interpretation of a specification, such as an engineering drawing? That is the problem that this principle is intended to address.
When we had our old British BS308 standard, it was easy. You were asked to put a note on the drawing along the lines of ‘DRAWN TO BS 308’. With the new British Standard, BS 8888, we suggest a similar note, such as ‘CONFORMS TO BS 8888’, and the Americans require that drawings produced to the American standard show a reference to that standard, ‘ASME Y14.5-2009’.
ISO have never had a formal method of indicating that drawings or specifications conform to ISO standards. One of the key ISO standards is ISO 8015, which defines the Envelope Requirement and how size tolerances are interpreted. ISO 8015 itself contains the requirement to mark specifications ‘TOLERANCING ISO 8015’ if they are to be interpreted according to its rules. As a result, this marking has become the way in which many organisations indicate that they are working to the ISO system, and is even now a requirement of BS 8888.
Arguably, specifications which are to be interpreted according to the ISO system should list all the other applicable ISO standards on the specification as well, or at least list them in a document referenced by the specification. For most organisations, this would be a lengthy list, including references to standards such as ISO 1101, ISO 2768, ISO 5458, and many others. Unsurprisingly, many organisations don’t bother.
The invocation principle was intended to avoid this difficulty, by introducing a rule which stated that if you are using one part of the ISO system, you are using all of it. This seems sensible to me. This approach does not require you use bits of the ISO system that you were not using previously, it just means that if you make use of any particular part of it, such as surface texture specifications, then all the relevant ISO standards apply. You don’t have to list them all, you just have to have some means of showing that one part of the ISO system applies, such as the ‘TOLERANCING ISO 8015’ indication.
The contentious stuff starts with a second part to this rule, which states that use of any ISO GPS symbol is sufficient to indicate that you are working to the whole ISO GPS system. In other words, you don't need to state ‘TOLERANCING ISO 8015’ or anything like that, you only need to use a geometrical tolerance, or a boxed dimension, or some other GPS symbol, and that makes it an ISO GPS document unless otherwise stated.
This is a REALLY BAD IDEA.
Reasons why:
1. In the UK, standards have a voluntary status. Their use cannot be imposed, and they work on an 'opt in' basis. This requirement would mean that many ISO standards would be imposed, quite possibly without the document owner being aware of this, unless they specifically 'opted out'. A requirement which is enforced by the absence of any alternative marking is liable to lead to confusion, misunderstanding, and resentment (and bring the system into disrepute).
2. ISO do not have ownership of all the symbols which are used in ISO GPS standards. Many symbols are shared with ASME, and many national standards organisations have used them in national standards which are still current. Some symbols are even used differently in other ISO standards
This requirement would mean that if someone forgot to put ‘ASME Y14.5’ on a drawing, it would then be regarded as an ISO GPS drawing, irrespective of the intention. It means that a sketch on the back of an envelope, which happened to include a dimension with a box around it, would suddenly be subject to the rules and requirements of an ISO GPS standard. It means that civil engineering or architectural drawings with tolerances might become subject to ISO GPS rules and requirements, without the relevant professions even being consulted.
3. As many of the symbols which ISO regards as ‘GPS symbols’ are either in the public domain, or widely used in different ways, in different contexts, an attempt to impose a requirement like this without consulting as widely as possible (other ISO technical committees, professional bodies, industry organisations, etc, etc,) is simply irresponsible.
4. A further consequence is that we would then need to introduce an exemption symbol or marking, such as ‘NOT AN ISO GPS SPECIFICATION’ for cases where it didn’t apply, at which point it is starting to get a bit silly.
5. What happens in the case of a nation which is not a member of ISO? What happens if ASME introduce a rule saying 'in the absence of any other marking, a technical specification is to be regarded as an ASME Y14.5 specification'?
The imposition of such a requirement would benefit no one, and simply lead to confusion, and quite possibly to litigation. ANSI have made their objections well known within ISO, but a number of people from other national bodies seem determined to force this through. I'm not clear on their motivation, but at least in part it seems to stem from a fear of 'Americanisation', and a desire to give ISO a higher status as the 'ultimate default'. These motivations may be sincere, but they are misguided. Industry will not benefit from this, and it will actually lead to the diminishment of the reputation of ISO standards if it goes through.
When we had our old British BS308 standard, it was easy. You were asked to put a note on the drawing along the lines of ‘DRAWN TO BS 308’. With the new British Standard, BS 8888, we suggest a similar note, such as ‘CONFORMS TO BS 8888’, and the Americans require that drawings produced to the American standard show a reference to that standard, ‘ASME Y14.5-2009’.
ISO have never had a formal method of indicating that drawings or specifications conform to ISO standards. One of the key ISO standards is ISO 8015, which defines the Envelope Requirement and how size tolerances are interpreted. ISO 8015 itself contains the requirement to mark specifications ‘TOLERANCING ISO 8015’ if they are to be interpreted according to its rules. As a result, this marking has become the way in which many organisations indicate that they are working to the ISO system, and is even now a requirement of BS 8888.
Arguably, specifications which are to be interpreted according to the ISO system should list all the other applicable ISO standards on the specification as well, or at least list them in a document referenced by the specification. For most organisations, this would be a lengthy list, including references to standards such as ISO 1101, ISO 2768, ISO 5458, and many others. Unsurprisingly, many organisations don’t bother.
The invocation principle was intended to avoid this difficulty, by introducing a rule which stated that if you are using one part of the ISO system, you are using all of it. This seems sensible to me. This approach does not require you use bits of the ISO system that you were not using previously, it just means that if you make use of any particular part of it, such as surface texture specifications, then all the relevant ISO standards apply. You don’t have to list them all, you just have to have some means of showing that one part of the ISO system applies, such as the ‘TOLERANCING ISO 8015’ indication.
The contentious stuff starts with a second part to this rule, which states that use of any ISO GPS symbol is sufficient to indicate that you are working to the whole ISO GPS system. In other words, you don't need to state ‘TOLERANCING ISO 8015’ or anything like that, you only need to use a geometrical tolerance, or a boxed dimension, or some other GPS symbol, and that makes it an ISO GPS document unless otherwise stated.
This is a REALLY BAD IDEA.
Reasons why:
1. In the UK, standards have a voluntary status. Their use cannot be imposed, and they work on an 'opt in' basis. This requirement would mean that many ISO standards would be imposed, quite possibly without the document owner being aware of this, unless they specifically 'opted out'. A requirement which is enforced by the absence of any alternative marking is liable to lead to confusion, misunderstanding, and resentment (and bring the system into disrepute).
2. ISO do not have ownership of all the symbols which are used in ISO GPS standards. Many symbols are shared with ASME, and many national standards organisations have used them in national standards which are still current. Some symbols are even used differently in other ISO standards
This requirement would mean that if someone forgot to put ‘ASME Y14.5’ on a drawing, it would then be regarded as an ISO GPS drawing, irrespective of the intention. It means that a sketch on the back of an envelope, which happened to include a dimension with a box around it, would suddenly be subject to the rules and requirements of an ISO GPS standard. It means that civil engineering or architectural drawings with tolerances might become subject to ISO GPS rules and requirements, without the relevant professions even being consulted.
3. As many of the symbols which ISO regards as ‘GPS symbols’ are either in the public domain, or widely used in different ways, in different contexts, an attempt to impose a requirement like this without consulting as widely as possible (other ISO technical committees, professional bodies, industry organisations, etc, etc,) is simply irresponsible.
4. A further consequence is that we would then need to introduce an exemption symbol or marking, such as ‘NOT AN ISO GPS SPECIFICATION’ for cases where it didn’t apply, at which point it is starting to get a bit silly.
5. What happens in the case of a nation which is not a member of ISO? What happens if ASME introduce a rule saying 'in the absence of any other marking, a technical specification is to be regarded as an ASME Y14.5 specification'?
The imposition of such a requirement would benefit no one, and simply lead to confusion, and quite possibly to litigation. ANSI have made their objections well known within ISO, but a number of people from other national bodies seem determined to force this through. I'm not clear on their motivation, but at least in part it seems to stem from a fear of 'Americanisation', and a desire to give ISO a higher status as the 'ultimate default'. These motivations may be sincere, but they are misguided. Industry will not benefit from this, and it will actually lead to the diminishment of the reputation of ISO standards if it goes through.
Subscribe to:
Posts (Atom)
