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I am trying to reply to the essence of your question, which is WHY people model their parts at MMC. I can't say I completely agree with it, but here are the arguments. The reason I got from designers that use that approach is simple: to be able to locate interferences. When drawing at nominal...

Suds, What I teach my student is You can't do real GD&T on a part without it's assembly, because it depends on the situation. in your case you show the mating part in red I beleive so good. Ideally, when practical, your datum should be in contact with another part. A surface that touches...

Cup909 Technically speaking, you should inspect the part per drawing. What I worder is if engineering selected either the datum correctly of the tolerances correctly. I came across long shaft (aerospace engine shaft) that needed precise runout. usually, the Datum should, when ever possible...

Thank you all for your replies. Honestly, they're all quality answers. 3DDave, as usual, you demonstrate excellent comprehension of the standard. mfgenggear, jassco, and, well, everyone else, I don't remember reading replies from you before, but you make very valid points, and I thank you...

Thanks for your input, mfgenggear. As a teacher, my job is to take existing experiences and summarize them so that students don't start from scratch. My predecessors used to teach GD&T symbols and their meanings. I try to teach them the effect of GD&T on practical cases: I don't want them to...

I agree with Burunduk. Don't forget that Datum are mathematical models. The way I can explain it is with cad. imagine scaning a very crooket part and importing it in your favorite cad. lets assume that the order of precedence is A then B and then C. For datum A You would create a plane (P1)...

Hello all, As some of you might know, I am teaching GD&T at the college level. I was wondering if there was a rule of thumb about the value to give for datum tolerances. I got a tip about that a few years ago from someone in the aerospace industry. The rule of thumb was to make the datum 10...

Burunduk, 3DDave, Thank you for your answers! It confirms my original theory. I am trying to mix GD&T Design theory and Metrology in the same course in order for future designers to understand how the GD&T work and will be inspected and make the subject more "real". As I said, I understand...

Hi tw, Here is what the result might look like. I've inserted two example from ASME Gee

Blue33, I would add the following information. In ASME Y14.5 2018 the profile tolerance explainations are better and there are new ways to control the location. The way profile controls the location vary depending on your datum selection and if you use all around or all over. It made me better...

Hello All, Following thread1103-507627 that has been closed since, I had additional questions on the evaluation of the run out when two datum with two diameters are called in the drawing. I understand the limitation of using V-blocks to setup the inspection. This being said, when calculating...

This being said... why do you use concentricity and not runout or location on the other cylinder?

I teach my metrology students that cylindicity is a runout of a cylindrical surface rotating on itself, while flatness is the parallelism of a part with regards to itself. It's counter intuitive but make sense as the datum of the cylindrical feature is not the surface itself but the axix of the...

Thank you all for your responses, they will weight in my reflexion (Ok ... I don't know if this is proper English... makes sense in French) Maybe the stackup analysis is too far fetch. I will try to convey what I want more explicitly and use some of this semesters drawing as what NOT to do. Gee

Usually, tolerancing is supposed to reproduce the use of the part. how to reproduce the conical effect of the thread without tightening the nut? how to check the face once tighten? I feel like it's a case of theorically correct drawing that is near impossible to check. Maybe by screwing this...

I am a still new college teacher. Last semester, I tried to convey what is a proper assembly drawing to my GD&T class student, effectively trying to make them forget the nice looking yet not always practical exploded view they saw in the much more interesting previous CAD classes. yet, I...

I saw many drawing with non referenced Datum this week! They were from my own student...[banghead] I removed 10% on all those drawing... What am I doing wrong???

Hello, Pardon my English... not my native language. While I would personnaly always add the all around symbol, per Y14.5 2009 it is not mandatory when the extent of the surface is clear. As for the way to interpret it, this is what I tell my students. for the upper part : the pointed...

I really feel stupid asking this question... I'm going to put it on the account of me teaching 7 hours of lecture in one day.

Thanks for taking the time to answer. When you say "slightly" do you mean the difference is slight yet significant or is it negligeable?