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.