Jun 17

Standards Tuesday – Fundamental Rules of Dimensioning

Tag: Drawing Standards — Alex R. Ruiz @ 5:00 am

Over the past few weeks I have written about the different ASME standards that impact areas of your drawing including the Drawing Title, General Notes & BOMs.  All of these pale in comparison to ASME Y14.5M-1994, Dimensioning and Tolerancing. I live by this standard; it has been both good to me and the bane of my existence. For the rest of you who actually have lives and don’t like to spend their free time reading standards, I am here to help. Over the coming weeks I will be covering various aspects of everyone’s favorite standard.

Fundamental Rules for Dimensioning and Tolerancing

  1. All dimensions in a drawing must have a tolerance applied except when designated as MAX, MIN, REF or STOCK. Calling out tolerances globally in a title block or the general notes satisfies this requirement. Most companies use a combination of global tolerances and local tolerances applied to specific dimensions.
  2. Dimensions created on a drawing must be clear and understandable without the need to scale the drawing. Scaling a drawing refers to using a scale, such as an engineering scale, to determine the size of a feature.
  3. Each drawing must be fully defined, without overdefining the part, with using reference dimensions sparingly.
  4. Drawings should not dictate the manufacturing process unless it it absolutely required to achieve the design intent.  No offense but despite how you feel about your machining skills most of the time the machinist would know more.
  5. You can specify a dimension as NON-MANDATORY when they may be affected by finish, shrink, etc…
  6. Arrange dimensions to be read easily and should only reference visible lines. Do not dimension to hidden lines, no matter how tempted you are by peer pressure, there is always a better way.
  7. When items such as wires, sheet metal and rods use a gage or other code to to describe it size; use the linear dimension as the primary dimension and you may include the code in parenthesis as reference.
  8. An angle of 90° is implied when two lines are perpendicular making a right angle that is not dimensioned. I have had many fun times trying to convince people of this. Take my advice, if you get disputed… bring out the book.
  9. Unless otherwise noted on the drawing all dimensions apply at 20°C or 68°F. I hope your QC department brought their sweaters.
  10. All dimension apply to free state condition.
  11. Unless you specifiy otherwise on the dimension, it should apply to full depth, length or width of the feature.
  12. Dimensions on a part apply only at the part level, it does not apply to the next assembly. If you want a dimension to also be applied at the assembly level you must include it in the assembly drawing.

This has probably been my shortest post since I started Standards Tuesday, don’t get used to it :) Next week We jump into the fun stuff…so get some rest and I will see you next week.

  • Josh

    man, i really like this post. good quick points. easy to print out and pass out. very nice man.

  • Alex Ruiz

    Josh,

    ASME standards are tolerable if taken in small doses. Much like my sense of humor.

  • Gary Skinner

    Mr. Ruiz, Thank you for sharing your knowledge, I don't understand number 9 or 10; please explain. Thank you. Sincerely, Gary Skinner

  • Alex Ruiz

    Hi Gary, Wow, Mr. Ruiz sounds so formal. Alex is fine, we are pretty informal here. :) Let me see if I can answer your questions: First, Rule #9: As I am sure you know ,different temperatures effect each material differently. In some extreme cases, only a few degrees can effect the measured dimension of a part. This can be disastrous in extremely precise components and assemblies. To maintain dimensional consistency of parts the ambient temperature should be controlled when performing inspections. If the dimensions on the drawing are to be applied at any temperature other then 68° it should be noted on the drawing. Next, Rule #10: "Free state condition" basically refers to the state of the part being inspected when at rest minus any outside forces applied to the part during the manufacturing process. One possible example of this is a spring. Depending on how it is manufactured, when you take the spring from the machine and set it on a table it may be of a different shape then when it was being manufactured. Well Gary, I hope that answered your question and keep them coming!

  • Gary Skinner

    Hi Alex, Thank you. You've answered my questions very well. Sincerely, Gary Skinner

  • chris

    “An angle of 90° is implied when two lines are perpendicular making a right angle that is not dimensioned.”

    Since many people may not be familiar with this rule, it would be better to play it safe and include the dim.

  • chris

    “An angle of 90° is implied when two lines are perpendicular making a right angle that is not dimensioned.”

    Since many people may not be familiar with this rule, it would be better to play it safe and include the dim.

  • http://www.theswgeek.com TheSWGeek

    <html><body><div><FONT face=verdana,geneva color=#000000>Hi Chris,</FONT></div>
    <div> </div>
    <div>Of course, it all depends on your internal drawing standards. However, if you tried to dimension all the right angles in your drawing, it could get pretty cluttered. If you feel like it needs better clarification, you can always add a general note or something in the title block that states the implied 90° rule. But if your title block refers to ANSI Y14.5 or ASME Y14.5, it is a bit redundant.
    </div>
    <div><FONT face=verdana,geneva color=#000000></FONT>
     </div>

    ——– Original Message ——–
    Subject: [theswgeek] Re: Standards Tuesday – Fundamental Rules of
    Dimensioning
    From: “Disqus” <>
    Date: Wed, August 27, 2008 3:57 pm
    To: blog@theswgeek.com

    chris <cbalduc@hotmail.com> (unregistered) wrote:

    “An angle of 90° is implied when two lines are perpendicular making a right angle that is not dimensioned.”

    Since many people may not be familiar with this rule, it would be better to play it safe and include the dim.

    Link: http://www.theswgeek.com/2008/06/17/standards-tuesday-fundamental-rules-of-dimensioning/#comment-1879603

    –
    You may reply to this email to post your response. To turn off notifications, go to your Disqus settings at: http://disqus.com/settings/notifications/

    </body></html>

  • http://www.theswgeek.com TheSWGeek

    <html><body><div><FONT face=verdana,geneva color=#000000>Hi Chris,</FONT></div>
    <div> </div>
    <div>Of course, it all depends on your internal drawing standards. However, if you tried to dimension all the right angles in your drawing, it could get pretty cluttered. If you feel like it needs better clarification, you can always add a general note or something in the title block that states the implied 90° rule. But if your title block refers to ANSI Y14.5 or ASME Y14.5, it is a bit redundant.
    </div>
    <div><FONT face=verdana,geneva color=#000000></FONT>
     </div>

    ——– Original Message ——–
    Subject: [theswgeek] Re: Standards Tuesday – Fundamental Rules of
    Dimensioning
    From: “Disqus” <>
    Date: Wed, August 27, 2008 3:57 pm
    To: blog@theswgeek.com

    chris <cbalduc@hotmail.com> (unregistered) wrote:

    “An angle of 90° is implied when two lines are perpendicular making a right angle that is not dimensioned.”

    Since many people may not be familiar with this rule, it would be better to play it safe and include the dim.

    Link: http://www.theswgeek.com/2008/06/17/standards-tuesday-fundamental-rules-of-dimensioning/#comment-1879603

    –
    You may reply to this email to post your response. To turn off notifications, go to your Disqus settings at: http://disqus.com/settings/notifications/

    </body></html>

  • Randy Paap

    I have used GD&T, based on the ANSI Y14.5M-1982 and 1994, from a Quality stand point previously as a CMM programmer. It always seemed simple to understand without any grey area. I wish I could convince more engineers to apply it. I have a question in regards to 'reference dimension'. It has always been my understanding that when an engineer puts parentheses around a dimension, that dimension was considered a reference and not subject to tolerance. Is this a correct interpretation? I seem to have this argument a lot with fellow workers and engineers the like.
    Thanks
    Randy

  • Randy Paap

    I have used GD&T, based on the ANSI Y14.5M-1982 and 1994, from a Quality stand point previously as a CMM programmer. It always seemed simple to understand without any grey area. I wish I could convince more engineers to apply it. I have a question in regards to 'reference dimension'. It has always been my understanding that when an engineer puts parentheses around a dimension, that dimension was considered a reference and not subject to tolerance. Is this a correct interpretation? I seem to have this argument a lot with fellow workers and engineers the like.
    Thanks
    Randy

  • http://www.theswgeek.com TheSWGeek

    Good morning Randy,
    Yes you are correct. When you specify a dimension as reference with parenthesis (or any other method) it means that the value shown is toleranced somewhere else on the print with an overall dimension or direct tolerance. Reference dimensions are just that; reference. Tolerances are never applied to a reference dimension.

    If you or your fellow engineers have a question, feel free to ask :)

  • http://www.theswgeek.com TheSWGeek

    Good morning Randy,
    Yes you are correct. When you specify a dimension as reference with parenthesis (or any other method) it means that the value shown is toleranced somewhere else on the print with an overall dimension or direct tolerance. Reference dimensions are just that; reference. Tolerances are never applied to a reference dimension.

    If you or your fellow engineers have a question, feel free to ask :)

  • dadstillsurfs

    Marvelous beginning on Dimensioning practices. I thought I was the only Designer that applied these standards and principles on a regular basis.
    I do think you've overlooked one very important concept; features must be dimensioned in the view that they are in true shape, eg. profile of a tab vs the end view which does not describe the feature's shape. Don't know how many times I've called a supplier to ask a question like “Does XXX dimension refer to the valve or to the housing?”

  • dadstillsurfs

    Marvelous beginning on Dimensioning practices. I thought I was the only Designer that applied these standards and principles on a regular basis.
    I do think you've overlooked one very important concept; features must be dimensioned in the view that they are in true shape, eg. profile of a tab vs the end view which does not describe the feature's shape. Don't know how many times I've called a supplier to ask a question like “Does XXX dimension refer to the valve or to the housing?”

  • abdulsamad vc

    please sent me a pdf formate of this rules. i will wait for you in every seconds

  • john191

    I would just say one thing to you and that is, “FANTASTIC”!! Keep it up and wish to get more details from your blog.
    regards
    sears parts

  • odelle

    Tolerancing specifications define the allowable variation for the form and possibly the size of individual features, and the allowable variation in orientation and location between features.
    masini de inchiriat

  • nikuniku

    Menopause or menopauza symptoms can be a real problem for middle aged women. The body suffers a lot of modifications and because of other problems like urinarry stress incontinence this can prove to be a very hard period for any kind of woman. Luckily there are products like the Zoft gum or similar which help reduce these simptoms but overall it's a tough stage in any woman's life.

  • http://www.lemoncayennepepperdiet.com lemonade diet

    please sent me a pdf formate of this rules. i will wait for you in every seconds

  • http://www.pk24.com/ pk24

    wow. I have been looking for this for a long long time! You make it look so simple!

  • http://www.pillzmart.com Vigrx plus

    good post, like it…thanks