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.
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.

Posted by at

16 comments:

  1. Mas'ood24 March 2011 at 00:33

    Dear Iain,
    Thank you for putting my question up. We have to wait for feedback.
    By the way, you mentioned that the SZ, UF and CF symbols are developed by ISO. Would you do me a favour and tell me the relevant document numbers (WD/draft/standard...?)
    Thanks again.

    ReplyDelete
  2. Mas'ood7 August 2011 at 12:07

    Hi Iain,

    The new Standard ISO 14405-1 introduces 'CT' modifier for such cases.

    "If the specification applies to a collection of more than one feature of size and this collection is considered to be a feature of size, the specification modifier “number ×” shall be placed as the first element in the specification to indicate the number of features to which the specification applies, and the specification modifier “CT” shall be placed in its position in the specification."

    May be it is to be replaced with the 'UF', which I don't know where it is from.

    ReplyDelete
  3. Anonymous2 January 2013 at 06:02

    Hi, is it possible to use CZ with a datum? Such as parallelism/0.1 CZ/A

    ReplyDelete
    Replies
    1. Iain Macleod3 January 2013 at 08:43

      Yes it is, if the datum is based on, say, two coplanar surfaces rather than a single surface.

      Delete
  4. manish5 March 2013 at 23:51

    hi,is it "cz" similar to "typ" .

    ReplyDelete
    Replies
    1. Iain Macleod6 March 2013 at 14:17

      No, CZ is different. 'TYP' is not formally defined in a standard, but it is normally used to indicate that a requirement applies to more than one feature; the tolerance requirements for each feature would usually be independent of each other. 'CZ' either creates a single tolerance zone for two or more features, or locks the tolerance zones for multiple features together; the tolerance requirements are NOT independent of each other. Hope that helps.

      Delete
    2. Unknown16 May 2021 at 01:49

      Thank you

      Delete
  5. manish9 April 2014 at 23:09

    will you please please tell me about closed loop (CL) in tolerances.
    thanks

    ReplyDelete
  6. Anonymous27 May 2016 at 11:18

    hi, CZ can be use in a feature control frame that is attached with 2 leading arrows with 2 different features, for instance inner and outer profile of a square feature?
    Thanks.

    ReplyDelete
  7. zchurchz10 October 2016 at 09:44

    Hi Iain, How would this differ from establishing a datum with a Profile of a Surface callout and a note "three surfaces". For example, three bosses on a casting.

    Thanks-Rob

    ReplyDelete
  8. Unknown27 February 2017 at 07:22

    Well, that sound lots of terms in GD&T; CZ indicates the common zone where will be used with some matchable parts. Right?

    ReplyDelete
  9. BR22 February 2018 at 06:25

    Hi Iain. Can you use the cz modifier with a parallelism tolerance? The (broken) surface in question needs to be parallel to the primary datum surface which also has a cz modifier.

    Thanks

    ReplyDelete
  10. Roland18 September 2019 at 03:43

    Hi Iain, is CZ modify the tolerance zone meaning? 0,2 CZ equal to +/-0,2 (said my Customer) or +/-0,1.

    Thanks,

    ReplyDelete
  11. Anonymous18 September 2019 at 06:09

    On three nominally planar surfaces (ex. fig 19 ISO 1101:2017) can CZ and UF be used interchangeably and have the same mathematical definition? (CZ inside the FCF and UF above the FCF)
    Thanks
    Andras

    ReplyDelete
  12. RIAZ30 July 2020 at 04:30

    hi, is there a ASME equivalent to CZ (iso)

    ReplyDelete
  13. Unknown16 May 2021 at 01:46

    Hello
    Im hesam, it helped to me too much
    What is the ISO number for ''common zone'' or Coplanarity?
    Thank you

    ReplyDelete

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