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Recent content by McLeod

  1. McLeod

    Confidence level in reliability requirements?

    IRstuff, This is not the same as derating. Whenever a parameter of a statistical distribution is calculated from sample data, there is some uncertainty associated with the estimate. A second sample taken from the exact same population will not give the exact same estimate as the first sample...
  2. McLeod

    Confidence level in reliability requirements?

    How does your company use confidence level in setting its reliability design inputs and test acceptance criteria? Given that the confidence level approaches zero as the bounds approach the nominal Weibull curve, what do you consider a minimum confidence level to set as the acceptance...
  3. McLeod

    Drawing notes @ UL files?

    Some engineers here have begun adding notes to certain component drawings to indicate that the UL report file (no number given) must be reviewed if the design is changed. The intent is to prevent mismatches between the product configuration being manufactured, and that registered with UL. From...
  4. McLeod

    What is the Best Stack Up Analysis Book Out There??

    My favorite is the Dimensioning and Tolerancing Handbook (Drake, ed. 1999), which includes the following chapters on stack-up analysis: 9. Traditional approaches to analyzing mechanical tolerance stacks 11. Predicting assembly quality (Six Sigma methodologies to optimize tolerances) 12...
  5. McLeod

    'Certs Required' note on drawings

    John, IMO, ewh and KENAT are right. A cert is not a design specification or a process, it's just one possible method to verify them. If a vendor did not have an established quality system, we might choose instead to sample and test every lot. In my experience, certs end up on drawings when...
  6. McLeod

    'Certs Required' note on drawings

    - Ask Gary Whitmire, DraftingZone, Mar. 21, 2006. http://www.draftingzone.com/askgary/browse.html?searchText=cert
  7. McLeod

    Specifying revision levels of component parts on assembly drawings

    Looking for opinions on a drawing practice related to configuration management: including revision levels of component parts on an assembly drawing. The standards and drafting guidance documents don't seem to directly address it. Advisable or not? How about if the configuration management...
  8. McLeod

    Tolerance Analysis books

    The best book I've encountered for tolerance analysis is the Dimensioning and Tolerancing Handbook (Drake, et al, 1999). http://www.amazon.com/Dimensioning-Tolerancing-Handbook-Paul-Drake/dp/0070181314 There are also a lot of good papers online at BYU's Association for the Development of...
  9. McLeod

    Fault Tree Analysis worthwhile exercise for small systems?

    Allen! I'm so glad to see that fault-tree.net is back up! We've found the references incredibly useful and entertaining. Thanks for the response. Since I posted that message we've completed two analyses, and they did indeed take more than two or three pages before they were done. We've also...
  10. McLeod

    Confusing failure modes with effects and causes in FMEAs

    FMEA resources online indicate that a common mistake is to confuse the failure mode with the effect or the cause. I've seen this happen quite a bit, and it's usually due to the fact that the cause-and-effect chain is longer than three discrete items for the failure mode in question. So what is...
  11. McLeod

    Fault Tree Analysis worthwhile exercise for small systems?

    In the reference listed below, the author makes a statement about Fault Tree Analysis (FTA) while discussing the use of cutsets: I was wondering if other practicing engineers using FTA have found this to be true. We currently only use Failure Mode and Effects Analysis (FMEA) as our risk...
  12. McLeod

    Run-in procedures for small (96-120 DP) planetary gearboxes?

    What are the recommended run-in procedures for small (~ 1.0 inch gearbox diameter, 96-120 DP gears) planetary gearboxes lubricated with thick (channelling) grease? In the bearing industry, at least one manufacturer recommends that bearings be run initially at 20% of full speed until the...
  13. McLeod

    Global-local w/ solid model - coupling boundary nodes to new mesh?

    This is MSC.Nastran for Windows, not NENastran or full Nastran. I've read about Nastran's superelements and Patran's displacement fields, but have access to neither at the moment. Although I understand how to apply MPC equations, I have no idea how to formulate such equations for an arbitrary...
  14. McLeod

    Global-local w/ solid model - coupling boundary nodes to new mesh?

    I'm trying to do a global-local analysis of a solid model in Nastran for Windows 2003. The global model has been solved, and the original nodes on the sub-structure boundary surfaces have 6dof constraints and displacement loads derived from the output vectors. The tricky part is trying to tie...
  15. McLeod

    Standard for dimensioning sheet metal flat patterns

    Section 18 of Genium's Drafting Manual is "Sheet Metal Practice". In sub-section 7.0, they show three examples. None of them include features which cross a bend, but each includes a note: Does that number refer to a standard, or is it intended to indicate a shop procedure? (We don't work...
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