GD&T: Choosing Datums

Drawings available at:
deanodell.com/...
Reference:
ASME Y14.5-2018
See page 70-147 Section 7

[@vishnusekar4839]

Thank you so much Dean, I've learned so much watching your videos that has cleared so many doubts I have had working with GD&T over the past 5 years into my career

[@RDeanOdell]

Great to hear! Thank you for taking the time to leave a comment.

[@kuei1215]

This guy is a great teacher.

[@RDeanOdell]

This guy appreciates the comment! Thankyou.

[@vanzz3863]

He is indeed

[@Dybel200]

Can sb explain, why at 5:05 base dimensions for hole positions are based to rounded profile on left side (which is not a datum), instead of being based to datum C?

[@Ashnek34]

Thank you, really great explanations to fill the theory gaps with practice.

[@pawanraghav5178]

Thank you very much forgiving me a clear idea of choosing a datum!

[@RDeanOdell]

You’re very welcome!

[@XiaoBuding-ol8og]

The 3 datum targets of the first datum, resulting in the 3 points forming a surface at an angle to the coordinate plane. Question: Is there any negative effect of if the first datum plane is not being parallel to the coordinate axis at too large an angle?

[@amzxar5049]

how to tell if the feature control frame's tolerance bilateral or unilateral? how to indicate that?

[@RDeanOdell]

It can be indicated with the “U” symbol in the FCF, or with a phantom line near the part outline on older drawings.

[@쮸니월드-f1g]

Hello i am recently preparing for the ASME Y14.5 certification. Could you recommend practice problem book?

[@RDeanOdell]

I’m not certified, but my understanding is that the test is based very much on the verbatim wording of the Y14.5 standard. I recommend reading the standard cover to cover, and then have someone quiz you on particulars.

[@danlev6927]

​@@RDeanOdell I'm learning ASME Y14.5 2009 from ASE and it's torture. I'm a CNC programmer/manufacturing tech and have a background in CMM programming and I found the tests to be infuriating because they're based on the wording and not the practical applications of the rules.

[@robertagill]

Your videos are clear, concise and make what can feel like a complex subject easy to understand. Thank you!

[@RDeanOdell]

@Rob Gill Thanks so much! I appreciate the positive feedback.

[@jaydippanchal073]

Great explanation. Can you please explain what would be the interpretation of those A, B & C in circle next to feature frame and the numbers 1,3 shown in the triangle..

[@RDeanOdell]

Thanks! The circles are revision symbols, the triangles are flag notes that refer to the general notes on the drawing. The complete drawing is available at the link in the description.

[@solidkreate5007]

Thank you, it's a little clearer now but this is still the hardest part for me. Could you perhaps show us a complex geometry part? Something with organic and horz/vertal geometry?

[@RDeanOdell]

Hi, I’d be glad to. My website is in the description, if you have an example, you can send it by email and I can take a look.

[@jon-williammurphy9780]

For an assembly like this (a machinists tool) I don't think you would want to make the holes a datum for a reason I didn't hear you mention. Chiefly because threads are typically imprecise and hard to inspect.

[@mustafahayriatl2723]

every single one of the examples are very good. it makes you understand better.

[@GasparinPR]

Mr. Dean you are a great teacher!

[@RDeanOdell]

Thanks! 😃

[@Buitao26898]

It would be greatly appreciated if you would attach a pdf file mentioning what you said in the video as not everyone has a good level of English to understand. Thank you for the video.

[@rahulchaudhari3254]

Best and simple explanation Ihad ever seen.

[@RDeanOdell]

Thanks so much!

[@issamtalbi9528]

really, it's a very good explanation, thanks so much Mr Dear

[@TheRedstonedeluxe]

Thank you for the clear physical examples!

[@RDeanOdell]

Do you mean a clear explanation or a clear part? Either way, thanks so much!

[@TheRedstonedeluxe]

@@RDeanOdell I meant clear explanation but I guess both work haha.

[@ddr539]

Thank U great video for design and cmm programmers

[@chrmeiss67]

I never would use the introduced datums B and C for a functional based specification: There are no contacts at B and C! … only air.

[@Pkstoic]

Always simple and clear

[@RDeanOdell]

Thanks so much!

[@factkarwa391]

Hi...plz tell me the difference between orientation and direction

[@RDeanOdell]

Hi, What context do you mean? Is your issue in CAD and drawings preparation or in inspection?

[@factkarwa391]

@@RDeanOdell In GD&T we always talk about orientation and direction...

[@jeffreyrstapler]

You are very good sir !!

[@RDeanOdell]

Thank you!

[@Mr_amazingly_awesome]

Company criteria rules.

[@paulgallagher2937]

And this is why the US can't compete with Asian manufacturing. I've studied GD&T almost since its inception. I know it extremely well. Requirements are placed on components that significantly increase manufacturing cost without providing any benefit to the customer. Now I'll sit back and let the GD&T experts tell me I'm wrong. I'll sit back and watch the western manufacturing market continue to decline while Asian market destroys them.

[@RDeanOdell]

Hi, great feedback! I won’t tell you you are wrong. I believe the problem is that designers and management are overly conservative in design requirements because of a lack emphasis in the design process in general, of which GD&T is just a portion. In most of my explanations I use two decimals places and .04 of tolerance. I think many textbooks influence designers in a negative way by using 3-4 decimal places and restrictive geometric controls in many examples. In my opinion GD&T is a way to get design, manufacturing and inspection on the same page, and is not limited to critical high performance items with tight tolerances. Is there something else I should be teaching my students that would help us compete with Asian manufacturing?

[@jon-williammurphy9780]

Do you think GD&T is one of the top 5 reasons the US lost the manufacturing market?

[@SquishMe]

Great content

[@RDeanOdell]

Thanks so much!