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  1. #1
    Forum Newbie simes's Avatar
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    Default General Newbie CAD Question - UNDER RAD / OVER RAD !?!?

    Hello,

    New boy here! I am currently carrying out a role where some of the work involves some CAD work (using BOBCAD) - I am taking engineering drawings of engine parts and drawing a cross-section.

    Now, the bad news, I have almost no CAD experience and the last time I did any engineering drawing was my O level about 35 years ago!

    The good news, I am managing OK getting to grips with the software.

    The question. Some of the drawings I am working from have things on the labelled as being "UNDER RAD" or "OVER RAD" and I have almost Googled myself senseless trying to find out what this means and how to do the necessary calculations to get the drawing right?

    Can anyone explain these terms to me please? Or point me at a website that will explain them?

    Thanks in advance,

    Simon

  2. #2
    Quantum Mechanic ReMark's Avatar
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    Could RAD be short for RADIUS? Could it be a "tolerance"?
    "I have only come here seeking knowledge. Things they wouldn't teach me of in college." The Police

    Eat brains...gain more knowledge! I've gone over to the dark side.

  3. #3
    Super Moderator SLW210's Avatar
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    Could you post some images? Did you try the BobCAD forum?

    This is CNC software. What are you trying to do with these drawings?
    “A narrow mind and a fat head invariably come on the same person” Zig Zigler



  4. #4
    Forum Newbie simes's Avatar
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    ReMark - yes, the RAD is an abbreviation for radius. I don't think that it is a tolerance as such, but hey that is part of the reason I am asking the question.

    SLW210 - I am using BOBCAD for drawing 2D cross-sections. I had no choice in the software, it is what they use here. I don't have access to the BOBCAD forums (yet) ... but then my question is of a generic drawing nature. It is not software specific.

    I had hoped that the terms would be commonly understood amongst much more experienced CAD people than myself.

    underrad.jpg

    The blueprint I was drawing from had a label pointing at the end of the angled line indicating that I had to draw a R4 curve between the angled line and the horizontal line "UNDER RAD at Diameter 600". I did it in the end by trial and error - what I am looking for is the mathematical / non-trial and error of doing what I had to do.

    I hope that this makes some kind of sense. :-)

    Thanks,

    Simon
    Last edited by simes; 26th Jul 2011 at 03:53 pm.

  5. #5
    Full Member QualityEngineer's Avatar
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    UNDER and OVER RAD are old terms of convex and concave RADIUS tolerance features and really are no longer really used in modern geometric dimensioning and tolerancing. (When I say modern, the last 10 years..) The modern or standard BSEN or ISO standard is a simple R with a numerical indicator of the size and tolerance, or a min max dimension. It difficult to explain when youre using terminology that is deprecated that long ago in the drawing world, and google will only recognise the modern terminology. if you do have any such problem understanding old or foreign GD&T referencing in CAD when learning, please do PM me and ill take you through any Geometric Dimensioning and Tolerancing Questions you may have....

    Hope this helps

    QE
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    What do they have in common? They see the same Therapist...."

  6. #6
    Forum Newbie simes's Avatar
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    Thank you QE for that explanation. I found out this morning from another helpful source that I am only likely to encounter this terminology on drawings from one particular OK company. As for old, well yes, the drawing I was working from was hand-draughted in 1999! Thanks for the offer to PM you with other questions that might pop up. I'll take you up on that offer at some point I am sure.

  7. #7
    Full Member QualityEngineer's Avatar
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    One other thing that will come to be helpful simes is that since 1988, there have been 4 significant reviusions of BSEN and ISO regulations however, where the regulations have been updated, the previous references are NOT disallowed or not to be used at all, they are only deprecated by the standards committee, so you will always come accross stuff that you may or may not have seen. On the otehr side of this, drawings ahve been amended to reflect new guidelines for GD&T, but the CAD themselves ahve not been graphically updated to reflect the change. To make a bit more sense, I had a drawing that under the previous 1994 guidelines for CAD and drafting the drawing feature "T" for Tangent has been deprecated in favour of a non graphical feature and a metion in the tolerance block notes.. HOWEVER....The drawing itself used hatch lines to correctly show the section, but sine the Tangent feature had been taken off, the HAtch lines detracted your eye from the feature. Only by looking at the CAD, did you realise that it was a Tangent and not a secondary radius as indications pointed out, and what 3 of the CNC setters assumed it was and made the Master samples to this tolerance feature. What im saying is that when you are working on existing drawings that are not on CAD or not current and, taking in your experience with CAD and tolerancing (trying not to be insulting here at all so pleae dont take it wrong) that any slight significant unsureness or assumption based upon what you feel to be correct and not fact, could indeed throw the tolerance out and others therfore producing a part that will be out of tolerance, or completely incorrect.... And trust me, this happens on a regular basis... Ive seen it happen loads of times and in some occasions ive had to mop up the mess.... Just be very wary and careful. What I can do, if itll help is send you over a full complete exaustive list ofa ll geometric dimensioning and tolerancing to ISO BSEN and ANSI guidelines with examples. I wrote a manual a few years ago and have kept it updated ever since. If it would be of any help to anybody else here, let me know....
    "The Difference between Relative and Absolute is this.... One is in denial seeking therapy and would like to be somewhere else, the other is depressed, somber and jealous of the other as he'd like to be somewhere else.... and seeking therapy...

    What do they have in common? They see the same Therapist...."

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    Forum Deity Organic's Avatar
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    I didn't know the tangent one there was depreciated.
    Last edited by Organic; 29th Apr 2013 at 01:45 pm.

  9. #9
    Full Member QualityEngineer's Avatar
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    Registered forum members do not see this ad.

    yeah, in BSEN, the tangent tolerance feature under maximum machine and virtual tolerance is no listed as a valid tolerance indicator, but alot of designer still use it.. BUT in order to design to BSEN, ISO and ANSI Y regulations, youre not supposed to use it. It really just proves that legislators do operate in a complete different universe....

    Ill send you the manual later on today...
    "The Difference between Relative and Absolute is this.... One is in denial seeking therapy and would like to be somewhere else, the other is depressed, somber and jealous of the other as he'd like to be somewhere else.... and seeking therapy...

    What do they have in common? They see the same Therapist...."

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