[Mi...] Posted October 7, 2019 Share Posted October 7, 2019 Ok, I have a couple issues that I'm having a hard time dealing with. What I was doing with a composite position was finding the TP for each hole in a given pattern called out to the top DRF. Then I would create a characteristic position, pick "best fit bore pattern", select elements (select the holes in the pattern) and set to the bottom DRF. I just read in the cookbook that I could use the best fit bore pattern for the top DRF if I click off the rotation and translation boxes. Am I close so far? Well, now I have an advisor that the company hired telling me that the best fit bore pattern is for circular patterns only and that the composite tolerance is for each individual hole not the group since it's not a circular pattern and it's just a perpendicularity call out so I should just use a position with the DRF called out for each individual hole. Now, I have a composite position call out that really has me confused. The top DRF is Ø.014 ABC and the bottom is Ø.009 ABC. Is the bottom DRF allowed to be the same as the top? Is it just the top gets no rotation or translation and the bottom does? Link to comment Share on other sites More sharing options...
[Gr...] Posted October 7, 2019 Share Posted October 7, 2019 As far as I know, you can't have the top and bottom both be ABC. What would be the point? To me, it sounds like a typo. Are you allowed to post a pic? Link to comment Share on other sites More sharing options...
[Me...] Posted October 7, 2019 Share Posted October 7, 2019 You can have ABC on both. The second half of the composite releases the translational but not the rotational DOF. As far as the BF pattern, it depends on what DOF are called out in each half of the composite tolerance. If there are DOF unconstrained then they may be best fit. I think your advisor is mistaken. As long as the holes are noted as a pattern they are treated as a pattern. i.e. if it says 8x then they are a pattern of 8. Link to comment Share on other sites More sharing options...
[Mi...] Posted October 7, 2019 Author Share Posted October 7, 2019 Gregory, no I can't post a picture of it. Our engineers looked at it and say that the top and bottom DRF can't be the same as a composite but as a single segment frame they can but it's shown as a composite. But I can see what you're saying Robert, so basically it's just a matter of turning off the rotation and translation on top and leaving the translations on for the bottom? I think the advisor was mistaken also. I don't think the BF pattern is for specific shaped patterns but for holes in a group that is controlled by a single tolerance and DRF. Link to comment Share on other sites More sharing options...
[Me...] Posted October 7, 2019 Share Posted October 7, 2019 Please sign in to view this quote. I disagree. ASME-Y14.5-2009 Please sign in to view this quote. Yes, based on what you've told me. Link to comment Share on other sites More sharing options...
[Mi...] Posted October 7, 2019 Author Share Posted October 7, 2019 Robert, thank you. that explains it to me and gives enough to go forward. Thanks again. Link to comment Share on other sites More sharing options...
[Br...] Posted October 7, 2019 Share Posted October 7, 2019 Please sign in to view this quote. This is absolutely false. the lower segment of a composite tolerance controls the Feature to feature relationship whereas the upper segment controls the entire pattern in relation to the datum reference frame. The two types of segments are referred to as the Feature-Relating Tolerance Zone Framework or FRTZF, and the Pattern-Locating Tolerance Zone Framework or PLTZF respectively. The PLTZF is treated like any ordinary single segment FCF. The FRTZF on the other hand, is only constrained by the rotational degrees of freedom regarding the Datum Reference Frame. Their location is relative to the other features in the pattern. Hence "Feature-Relating Tolerance Zone Framework" If the composite position was only to control perpendicularity to the DRF, It would be completely redundant and arbitrary because there already is a perfectly good way to do this with a perpendicularity tolerance. Ask this "Advisor" if he has his Senior GDTP Certificate from ASME. I would never hire a GD&T consultant who doesn't have this credential. Almost anyone who does any training or consulting regarding ASME Y14.5 should have this on his/her resume. Please sign in to view this quote. The top is the same as you normally would treat a position tolerance. For the lower one, You can just copy the characteristic, and check the best fit box for "Translation", but not rotation because the rotation is being constrained still by the DRF. Link to comment Share on other sites More sharing options...
[Br...] Posted October 7, 2019 Share Posted October 7, 2019 This video might help to clear it up as well. https://youtu.be/GFgoctqNkRo Link to comment Share on other sites More sharing options...
[Mi...] Posted October 7, 2019 Author Share Posted October 7, 2019 Brett, thanks. I got it now... I think... That is pretty much how I understood. The way I am using the best fit seems to be correct to me as well as a lot easier to manage. When creating the position characteristic for the top line I have the rotation and translations off because it's being constrained completely by the DRF. When creating the position characteristic for the bottom line I have the rotation off and transitions on because the only the rotation is being constrained by the DRF. Is that pretty much it? Link to comment Share on other sites More sharing options...
[Da...] Posted October 7, 2019 Share Posted October 7, 2019 Related thread -> viewtopic.php?f=13&t=669 Link to comment Share on other sites More sharing options...
[Ri...] Posted October 7, 2019 Share Posted October 7, 2019 I don't remember this at all from AUKOM. I think my brain would have malfunctioned. This is a new one for me, and while I don't fully understand it, I'll take it and run with it. Great information. Link to comment Share on other sites More sharing options...
[Mi...] Posted October 8, 2019 Author Share Posted October 8, 2019 Dane, yep... I read a bunch of threads on the subject before posting. This is a great place to get info. Most of what I read I already had a handle on but I still didn't get the 3 datum composite reference frame and I was getting conflicting information on how to report composite positions so I figured I would just air it all out. Maybe help someone that might have similar problems. Richard, yes, my brain shorted out yesterday. Took a couple cold ones to get it started again! Link to comment Share on other sites More sharing options...
[Br...] Posted October 8, 2019 Share Posted October 8, 2019 Having all three Datum features repeated in the lower segment doesn't always make sense. Only when the tertiary datum feature can constrain a rotational degree of freedom does it ever make any sense. Below is the actual drawing that goes with the figure that Robert posted from the standard. You can see Datum Feature C is a slot that constrains the final degree of freedom to keep the part from spinning about the Datum B axis. So the lower segment would unlock the translational degrees of freedom but still control the orientation of the 4 holes in respect to the DRF. Link to comment Share on other sites More sharing options...
[An...] Posted October 8, 2019 Share Posted October 8, 2019 Del. Link to comment Share on other sites More sharing options...
[Mi...] Posted October 8, 2019 Author Share Posted October 8, 2019 Thanks Brett, yes, my Datum -A- is a plane, -B- is a Ø.125 pin on the plane and -C- is a Ø.125 pin to stop the rotation. Link to comment Share on other sites More sharing options...
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