Separate block tolerances for "holes"? 2

[GarnierGary]

In David Madsen's GD&T book, several example drawings have a separate set of tolerances for "holes" in the title block. By inference from his examples, Madsen seems to interpret any turned or drilled female cylindrical feature as a "hole", including counterbores.

Does anyone out there follow this practice (separate block tolerances for holes)? If so, how do you define a hole - is a 2.000 dia, .10 deep counterbore a "hole"? How about a 4" diameter blind feature, likely produced with a boring bar?

Have you ever had interpretation disputes with machine shops over this question? I think I'd be hard-pressed to reject a part with a large, shallow counterbore that met general block tolerances but exceeded the tighter tolerance for a "hole".

It would seem far better to have a note (referenced from the title block): [1] All untoleranced internal diameters +.003/-.001.

(Standard block tolerances would apply to external diameters not directly toleranced.)

Can anyone point to a paragraph in Y14 that would address this?

Thanks.

 

[GarnierGary]

pierdesign, I'd love it if you could cite chapter and verse from a standard saying anything with an internal diameter dimension is a hole. Better yet that TB hole tolerancing is suggested/required. I was of ctopher's frame of mind on this when I posed the question (that is, NOT every female round feature is a "hole"), but I am ready to be converted.

Can you steer us to a standard that supports what seems to be the majority opinion among respondents here, that "any feature with an ID is to be read as a hole"? This sounds like a sarcastic challenge - it's not. I honestly hope there is such a definition out there. (A hundred people saying "everybody knows that" doesn't cut it for me, though - I'm worried about the one machinist who doesn't.)

BTW, I'm still hoping for more responses on how common the practice of title block "hole" tolerancing is. All of pierdesigns employers have; none of mine have. More data, please.

This started out just a nit-picking jab at a textbook that I don't like, but there is a real concern here: if I dimension a large dia shallow spotface intending it to take the (non-hole) TB tolerance, and the shop takes extra time ($) to meet the "hole" tolerance, I've cost myself money.

 

[KENAT]

Gary,

As far as I can tell "hole" isn't explicitly defined in ASME Y14.5M-1994 though used frequently. Section 1.8 seems to go to pains to state 'round holes" but that's about it.

It's not defined in 14.100-2004 either that I could see.

Given this, I'd be very surprised if it's defined anywhere in the way you seem to be looking for.


KENAT,

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What is Engineering anyway: faq1088-1484

 

[EdMcCabe]

By that logic a tapped hole is a hole, and those tolerances (i.e.: .XX = +/-.005) seem a little loose. In other words if a drawing calls out Ø.25-20UNC-2B, doesn't the title block allow too much tolerance for minor, major and pitch diameters?

 

[cadman1964]

I know someone will correct me if I'm wrong. But, i wouldn't apply those tolerance to tap sizes. They are determined through your machinery handbook.

Solid Edge V20

 

[PeterStock]

My copy of Machinery's Handbook 25th edition gets its data for UN threads from ANSI/ASME B1.1-1989, other thread standards exist. It is a good idea to call out the standard that should be used for threads used on a drawing.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[KENAT]

In fact ASME Y14.6-2001 Actually recommends to reference the thread spec on the drawing. Which would then overcome the tolerance on threads issue.

KENAT,

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What is Engineering anyway: faq1088-1484

 

[fsincox]

KENAT, this is another example of what we are talking about in the ISO forum. It seems lots of people’s companies here, too, make the similar title block compromises to save time. What does your title block say?
This is also another example of how I feel the ISO system is elegant. I believe they would do something like: 20 H13. (I think it is large “H” for hole, sorry if I have that wrong).
I was once told that a German machinist carried a card in his pocket with the ISO/DIN hole size tolerances and was expected to know it himself, therefore the drawings didn’t need any more than that. He is expected to know his job. I feel that may be part of the problem, our “machinists” can’t be expected to read.
I would like to know if I am wrong about that.

 

[fsincox]

Speaking of the hole tolerances I notice the ISO, by applying the “H” tolerance for drilled holes, apparently drops the undersize side of the tolerance band completely. The metal cutting tool institute data does indicate drills statistically tend to cut oversize.

 

[KENAT]

fsincox, this is maybe a bit of a thread hi-jack, might be better to keep it over in thread182-247563. I'll reply there if I think of anything intelligent to add;-).

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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What is Engineering anyway: faq1088-1484