[An...] Posted June 4, 2020 Share Posted June 4, 2020 See attached.Pic_4-21.pdf Link to comment Share on other sites More sharing options...
[SH...] Posted June 4, 2020 Share Posted June 4, 2020 Mobility of the datum reference frame. Link to comment Share on other sites More sharing options...
[Ja...] Posted June 4, 2020 Share Posted June 4, 2020 Datum reference A(M) is a cylinder at MMC 16.0. Datum feature A is free to translate/rotate throughout this boundary. The issue here is that in the real world, and if the part was held as drawn, gravity would interact and force datum feature B to fall flat on the faces of the datum feature simulator (actually, it would fall flat on the faces of the simulator for datum B, which would be normal to the simulator of A). It is probably not the best image to explain a primary datum referenced at MMB, but the theory is understandable. Link to comment Share on other sites More sharing options...
[An...] Posted June 4, 2020 Author Share Posted June 4, 2020 A datum simulator: From a view of technical logic.Pic_4-21a.pdf Link to comment Share on other sites More sharing options...
[Er...] Posted June 4, 2020 Share Posted June 4, 2020 Well, if the designer utillize mmb on A in that case, he, she or it needs a face slap. Link to comment Share on other sites More sharing options...
[Ja...] Posted June 4, 2020 Share Posted June 4, 2020 Andreas, that would work if A were referenced at RMB. Link to comment Share on other sites More sharing options...
[An...] Posted June 4, 2020 Author Share Posted June 4, 2020 Please sign in to view this quote. The moveable segments of the datum simulator A,driven by the spring forces, ensure the mobility of the complete system,if necessary. Target: keep the datum A-cylinder always untilted and simultaneously profit by the difference of maximum-material and actual-material. Link to comment Share on other sites More sharing options...
[ch...] Posted June 4, 2020 Share Posted June 4, 2020 Please sign in to view this quote. This is your invention or any standard?? Link to comment Share on other sites More sharing options...
[Aa...] Posted June 4, 2020 Share Posted June 4, 2020 MMC and MMB modifiers were created to establish fixed-limit boundaries. I find nothing in the ASME standards that says MMB datum features must be kept untilted, and in this case, I would ask: you're keeping it untilted relative to what, exactly?Y14.5.1M-1994, 4.3.4.jpg Link to comment Share on other sites More sharing options...
[An...] Posted June 5, 2020 Author Share Posted June 5, 2020 The cylinder as primary datum A stopps 4 degrees of freedom: 1.) X - coordinate (translation) 2.) Y - coordinate (translation) 3.) a1 - angle (rotation) 4.) a2 - angle (rotation) Stopping the rotation means: Tilting is not allowed. Translation is allowed within in the MM-boundary. (my personal point of view) Evaluation in this case is: MINIMUM CIRCUMSCRIBED CYLINDER See attachedPic_4-21b.pdf Link to comment Share on other sites More sharing options...
[Aa...] Posted June 5, 2020 Share Posted June 5, 2020 Please sign in to view this quote. Where does it say that? Link to comment Share on other sites More sharing options...
[Aa...] Posted June 5, 2020 Share Posted June 5, 2020 Bear in mind, there is no requirement that the axis of the datum be parallel to or concentric with any resolved axis (regardless of technique) of the datum feature. Only that it meet the requirements stated in 4.3.4, quoted above. Link to comment Share on other sites More sharing options...
[Gr...] Posted June 5, 2020 Share Posted June 5, 2020 Aaron How would a primary datum that is a cylinder be placed if not by the central axis of that cylinder? Link to comment Share on other sites More sharing options...
[Aa...] Posted June 8, 2020 Share Posted June 8, 2020 Please sign in to view this quote. The datum is not a cylinder, it's an axis. The datum feature simulator is a cylinder, and the datum feature is an imperfect cylinder. The datum axis for a cylindrical datum feature must be selected from among the "candidate datums", and should be selected to give the optimal results for the impacted feature control frames.Y14.5.1M Candidate DRFs explained.JPG Link to comment Share on other sites More sharing options...
[An...] Posted June 8, 2020 Author Share Posted June 8, 2020 Following the rules of technical logic. See attached.Pic_4-21k.pdf Link to comment Share on other sites More sharing options...
[Aa...] Posted June 8, 2020 Share Posted June 8, 2020 Making a statement that contradicts what's contained in the standards and labeling it "technical logic" doesn't change the fact that it contradicts the standards. The fact that you don't think the standards should be written the way they are doesn't change the fact that they are written that way. "The datum mobility works always translatory !" I don't know where you are getting this. Link to comment Share on other sites More sharing options...
[An...] Posted June 9, 2020 Author Share Posted June 9, 2020 "That's one small step for man,one giant leap for mankind" 51 years ago. See attached.Last_Post.pdf Link to comment Share on other sites More sharing options...
[SH...] Posted June 9, 2020 Share Posted June 9, 2020 Please sign in to view this quote. 🙄 🙄 Link to comment Share on other sites More sharing options...
[Aa...] Posted June 9, 2020 Share Posted June 9, 2020 Please sign in to view this quote. No, that would not be ambiguous. The secondary planar datum would be required to be perpendicular to datum A, just as you have drawn it. But it would not be required to contact a minimum of three points on the surface of the corresponding datum feature. ... Link to comment Share on other sites More sharing options...
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