precision shaft tolerances 1

[cervantes]

Hi

i am a little bit confused about tolerances given for induction hardened and hard chrome plated linear shaft
(see attachment)

let's analyze diameter 4: for ISO h7 tolerance, default circularity at level 0.005 - ok for me
cylindricity (parallelism) at level 0.01 - ok for me
but straightness - 0.3/1000 = 0,0003 ????

straightness must be usually lower than circularity - but is it ever possible to machine such a good way?....
or maybe I miscalculated something here?

I reviewed also Bosch Rexroth specifications, they are using similar descriptions and values

but why not to use runout as it is a mix of circularity of straightness?

M

 

[pmarc]

I am not sure if anyone, apart from the ISO organization and people working in the GPS technical committees/groups, have complete set of the standards

 

[pmarc]

Well, there is a book by Henrik Nielsen, chairman of the ISO TC 213 committee, "The ISO Geometrical Product Specifications – Find your way in GPS", but as far as I see it has no comparison between both systems.

There is also quite extensive publication by Georg Henzold, "Geometrical Dimensioning and Tolerancing for Design, Manufacturing and Inspection" that has a chapter on comparison, but in my personal opinion it (the book) needs to be treated carefully as it contains many figures with dimensioning and tolerancing schemes that are not shown in any ISO standard and simply reflect author's personal approach to some concepts. But it is a good reference anyway.

 

[mkcski]

Pmarc: Your first is laughable. I really appreciate your letting me know what to search for. In reality it appears comparisons between the two are not for the "faint-of-heart". Given your depth of knowledge, might I ask if you are on the Y14.5 Committee or attend meetings regularity?

 

[greenimi]

mkcski,
I will just jump a bit into this discussion and I will say that pmarc is better than some folks on the Y14.5 committee on ASME stuff and far better / way better than the majority of them on ISO GPS stuff.

I know, I might not be able to support my point of view (expressed above), but just reading what he is posting here and on linkedin I already make up my mind and is hard to convince me otherwise.

 

[mkcski]

greenimi: What a super complement! And from my short time on the Forum, I totally agree.

 

[pmarc]

 

[cervantes]

Thanks everyone for this prolific discussion. As usual innocent question brought interesting results.

 

[pmarc]

mkcski,
My apologies, but somehow I did not notice your question.

No, I am not on the Y14.5 committee and have never attended any committee meeting.

 

[mkcski]

pmarc: Geeez. Your position must provide you a lot of exposure to GDT to have this level of understanding on all of the topics related to the numerous controls AND the ability to communicate it to others so clearly.

 

[pmarc]

That is true. I am exposed to a lot of different GD&T stuff at my workplace. But I also spend a lot of time reading standards, books, articles, visiting different GD&T forums. That definitely requires much more than just 8 hrs a day from Monday to Friday. I would not like to go to "if you have a passion for something, you will be good at it" kind of things, but I can tell for sure that without a passion for GD&T I would not know a half of what I know, regardless if it is a lot or not.

As for "the ability to communicate it to others so clearly", I am flattered to see/hear that, especially that English is not my native language.

 

[mkcski]

pmarc: Thanks for the window into your back round. My background: I have been "around" GDT for over 35 years. I am a machinist by trade (my first exposure to GDT) and a mfg engr by profession. I have never been in a design position. I have a Senior level certification since 1999 and I am the GDT "guru" at my place of work. I have been teaching introductory GDT to companies and colleges in my region for over 30 years. Recently I was asked by our design dept to lead some GDT Case Study sessions to improve the understanding and application of GDT. This has been a challenge and is how I discovered this Forum - looking for some other opinions/approaches to product definition. I too read everything I can get my hands on, but my budget for materials is close to zero. Another reason to tap the knowledge available through this Forum.

 

[pmarc]

mkcski,
The more knowledgeable people with different backgrounds on the forum the better. This is what makes it great place to be.