[An...] Posted June 15, 2020 Share Posted June 15, 2020 See attached.Pic_4-17.pdf Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/ Share on other sites More sharing options...
[Me...] Posted June 15, 2020 Share Posted June 15, 2020 That's the virtual condition of the feature at least material. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83490 Share on other sites More sharing options...
[Aa...] Posted June 15, 2020 Share Posted June 15, 2020 Indeed. The 24.4 diameter is the diameter that the entirety of the surface of datum feature B must be outside. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83492 Share on other sites More sharing options...
[An...] Posted June 15, 2020 Author Share Posted June 15, 2020 Please sign in to view this quote. If we talk about a datum B simulator of an outer geometry: the entirety of the surface must be inside. That means: the diameter must be 25.1000 not 24.4000Pic_4-17_b.pdf Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83494 Share on other sites More sharing options...
[Aa...] Posted June 15, 2020 Share Posted June 15, 2020 Please sign in to view this quote. What you've just described would be accurate if this were an MMB reference. MMB simulators for external features must enclose their features, but LMB simultaors for external features must be enclosed by their features. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83496 Share on other sites More sharing options...
[An...] Posted June 16, 2020 Author Share Posted June 16, 2020 Please sign in to view this quote. BUMP! Impossible in the real physical world. See attached.Pic_4-17_d.pdf Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83498 Share on other sites More sharing options...
[Ri...] Posted June 16, 2020 Share Posted June 16, 2020 The least material requirement defines a true geometrical ideal feature that have to full inside of workpiece material. The extracted feature of size shall not exceed this true geometrical ideal feature. I haven't seen any examples from the standard that show having a Datum with LMB. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83500 Share on other sites More sharing options...
[Aa...] Posted June 16, 2020 Share Posted June 16, 2020 Fig 4-17 (Andreas' initial attachment) is an example. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83502 Share on other sites More sharing options...
[Aa...] Posted June 16, 2020 Share Posted June 16, 2020 Please sign in to view this quote. I don't disagree. LMC and LMB cannot be simulated using fixed-limit hard gauging. That's no secret. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83504 Share on other sites More sharing options...
[Ri...] Posted June 16, 2020 Share Posted June 16, 2020 Please sign in to view this quote. What standard is this from? Is there an explanation that they give on it then? To me LMC/LMB only makes sense for pre-machining inspection (essentially making sure that there is enough material to properly clean-up when machining). In that case, functional testing doesn't make a lot of sense. In my previous life, I had a customer apply LMC on an OD that mated into a housing (for position). I still couldn't wrap my head on why they would allow more positional deviation as the OD grew. On later designs, they swapped it to MMC. I think they messed up, and were too stubborn to change it. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83506 Share on other sites More sharing options...
[Aa...] Posted June 16, 2020 Share Posted June 16, 2020 It's from Y14.5-2009. I've attached the unredacted figure. I didn't realize Andreas had removed the explanations from the figure.4-17.JPG Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83508 Share on other sites More sharing options...
[Aa...] Posted June 16, 2020 Share Posted June 16, 2020 Please sign in to view this quote. MMC/MMB is for ensuring clearance. LMB/LMC is appropriate for features used to position/guide the mating component. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83510 Share on other sites More sharing options...
[Ri...] Posted June 16, 2020 Share Posted June 16, 2020 OK. I think that I had my wires crossed there for a moment. Thanks for the clarification. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83512 Share on other sites More sharing options...
[An...] Posted June 17, 2020 Author Share Posted June 17, 2020 An error has occured. See attached.Pic_4-17_f.pdf Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83514 Share on other sites More sharing options...
[Aa...] Posted June 17, 2020 Share Posted June 17, 2020 Please sign in to view this quote. True, but a thousand pictures with no words is not always helpful. Please offer some explanation of what you are illustrating. I'm not sure what's going on for those first two pages, but the third page looks like you still insist that LMB simulators must enclose their corresponding simulators. That is not according to the standard. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83516 Share on other sites More sharing options...
[Ja...] Posted June 17, 2020 Share Posted June 17, 2020 Please sign in to view this quote. Do you think that they were using LMC to protect the wall thickness at the O.D./I.D. interface? I get how it works that way, but not so much by allowing more error in the direction that'll increase wall thickness and possibly interfere with a mating part. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83518 Share on other sites More sharing options...
[An...] Posted June 17, 2020 Author Share Posted June 17, 2020 @Aaron To be honest,I don't understand the meaning of this text. Any chance to find such paragraphs in Y14.5-2009? Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83520 Share on other sites More sharing options...
[Ja...] Posted June 17, 2020 Share Posted June 17, 2020 Andreas, Aaron is quoting Y14.5.1 - 1994, the mathematical definition standard. As far as Y14.5-2009, please see 4.11.8 (a)/(b). For Y14.5-2018, please see 7.11.8 - more information here than in 2009. The following quote is from Y14.5-2009 4.11.8 Please sign in to view this quote. In (b), for example, the appropriate LMB (boundary) for an external feature is a boundary that the feature(s) will contain. Thus, it is internal to the part material. This is more of a theoretical idea that cannot be simulated through gaging, but has a valid purpose when it comes to application in cases such as wall thickness preservation. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83522 Share on other sites More sharing options...
[Ri...] Posted June 17, 2020 Share Posted June 17, 2020 Please sign in to view this quote. I don't believe so. Like I said, they changed it in later designs to MMC, but left the original at LMC. I think they were just being stubborn. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83524 Share on other sites More sharing options...
[Me...] Posted June 17, 2020 Share Posted June 17, 2020 You're using the wrong calculation, Andreas. Virtual condition on an external feature at MMC is largest size + size of the tolerance zone. Virtual condition on an external feature at LMC is smallest size - the tolerance zone. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83526 Share on other sites More sharing options...
[An...] Posted June 17, 2020 Author Share Posted June 17, 2020 Please sign in to view this quote. I strongly contradict. The MM-principle and the LM-principle can always be simulated through gaging. Just calculate the correct boundaries when designing the gage. My experience of over 40 years in the automotive industry: 1.) variable testing possible 2.) attributive testing possible 1.) Using the CMM and producing lots of surface points. 2.) Using a gage and make a "good-bad-decision" MM and LM can always lead to a "gage situation" and therefore can always lead to a "good-bad-decision" Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83528 Share on other sites More sharing options...
[Ja...] Posted June 17, 2020 Share Posted June 17, 2020 Andreas, I agree with point #1. The CMM is great at simulating material boundaries. Concerning point #2, hard gaging, Y14.43 (Dimensioning and Tolerancing Principles for Gages and Fixtures) goes on to say that simulating datum features at LMB has proven to be impractical and the usage of software/CMM's is a much better gaging option. I'm sure there are cases where datum features can be simulated at LMB, though it'll prove difficult. I'd also be willing to bet that there are some cases that cannot be simulated at all. At LMB, the datum feature simulator (or gage element) is inside of the material. Do you see why it may prove difficult to simulate? Imagine the following case: There is a datum hole that is referenced at LMB. To simulate it, you would use an inverse gage element (pin) at LMB size, which would be the case of least material, and hence the largest hole/simulator pin. Now as the hole gets smaller than the pin (which means the pin cannot fit), you are granted datum mobility. How do you utilize slop on a hole with respect to a larger pin? Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83530 Share on other sites More sharing options...
[An...] Posted June 17, 2020 Author Share Posted June 17, 2020 Please sign in to view this quote. Honestly: this is only adding some values - really no higher mathematics I am pretty astonished. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83532 Share on other sites More sharing options...
[Aa...] Posted June 17, 2020 Share Posted June 17, 2020 Please sign in to view this quote. No amount of arithmetic will allow the surface of a pin to surround the surface of its corresponding hole. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83534 Share on other sites More sharing options...
[Ja...] Posted June 17, 2020 Share Posted June 17, 2020 Please sign in to view this quote. Calculating the boundary size is arithmetic. Putting a .500 pin in a .490 hole is impossible. A .490 - .500 datum hole referenced at LMB would be simulated with a .500 pin. Link to comment https://qualityforum.zeiss.com/topic/15448-datum-and-lmb/#findComment-83536 Share on other sites More sharing options...
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