MDes23c GDT virtual condition

[@adityabhargav1830]

Most lucid explanation I have come across. Immensely helpful. May God bless you for providing this lecture at free of cost. Respect and love from India 🙏🙏

[@margaretrobertson8848]

Thank you so much, Aditya! It is my pleasure.

[@冯孝伟]

5:03, based on the rule 1#, the form must perfect at MMC, why we still can make the tolerance of the pin's OD(±.002) tighter than the perpendicularity which is called out by .006. Hoping for your answer,thanks in advance.

[@margaretrobertson8848]

Perfect form at MMC is the size of the envelope, the hole within which the pin must fit. The pin can be smaller, and it can tip. As long as it fits within the hole, that is all that matters.

[@孙小圣-d8u]

你好

[@QwertyCanada]

Hi, question, for the example shown at 3:35, shouldn't it be 0.881 diameter for the hole in the ring gage? Basically MMC of pin (0.878) + tolerance zone at MMC (0.003)?

[@margaretrobertson8848]

Hi, V.M. - Good question. If A were the primary datum, i.e., listed first in the feature control frame, then you would be correct: The VC would be 0.881. But notice that in this particular example, B is the primary datum, i.e., listed first, so the gage size is the MMC size only. Then if the shaft is not perpendicular, surface A will contact the gage at only one point.

[@QwertyCanada]

@@margaretrobertson8848 wow, I was very confident I'm right but now I learned something that I never read anywhere, thanks a lot!

[@margaretrobertson8848]

@@QwertyCanada My pleasure!

[@QwertyCanada]

​@@margaretrobertson8848 Sorry, I have to come back to this, so in this example (at 3:35) you have datum feature B defined based on datum feature A , but later when you are specifying the tolerances for the 4X hole pattern, you are using B as primary and A as secondary in the FCF, is that accepted practice?

[@margaretrobertson8848]

@@QwertyCanada Hi VM - I'm not sure why the author of this example chose to do it this way. (He is a member of the ASME Y14.5 committee, so we have to trust that his thinking is authoritative.) He probably just wanted to illustrate what happens if you do it this way. If datum B is primary--like in this example--and the shaft is not perpendicular, surface A will contact the gage in only one place. If datum A were primary, then the gage diameter would be .881 (instead of .878), and surface A would have to make 3 points of contact first. I agree with you: making surface A primary would be the more common way to tolerance this part.

[@harikumar4757]

Madam, it is very good teaching GD&T. 2:37 How to make gaga pin for whole pattern hole with pin gage dia .237, do have to still keep the centre main gage pin at (vc) .988.Because mentioned B at M in FCF of pattern hole. So at inspection can make both pin on single gage datum A ,at a time. Kindly reply.

[@margaretrobertson8848]

Thank you. Yes--the six holes are specified at MMC and datum B for those holes is also specified at MMC, so you would make the center gage pin at VC of .988, and you would make six gage pins for the holes at their VC (MMC of .245 minus tolerance of .008 = .237).

[@harikumar4757]

@@margaretrobertson8848 thank you for your kind reply

[@devlimbu4762]

Thank you so much Mam. This really helped me

[@margaretrobertson8848]

You are welcome! I am glad it was helpful.

[@nguyentri5467]

Thank you so much

[@margaretrobertson8848]

You are very welcome!

[@冯孝伟]

Hi, why circularity cannot be applied with a MMC modifier ?

[@margaretrobertson8848]

Good question. Because circularity is a surface control, which means it is applied regardless of feature size. It is measured by contacting the surface, which requires specialized equipment. That is why it is not used often.