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Separate block tolerances for "holes"? 2

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GarnierGary

GarnierGary

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May 15, 2009
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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.
 
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GarnierGary,

In general, the standard allows you to use notes to control tolerances.

Note the assymetric tolerances of the holes as specified on the title block. Drilled holes usually are oversized. There should be a table in your Machinery's Handbook giving you the actual as-drilled hole sizes for a given drill. If I specify a hole as Ø.255/.250", I anticipate the fabricator will use a Ø1/4"[ ]drill.

Yet another issue is that holes are generally intended to clear something. Usually, I am most interested in the minimum allowed size of my holes, so I call it up explicitly. Again, this leads to assymetric tolerances.

I don't see a problem.

Critter.gif
JHG
 
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I don't think I was entirely clear about my root question: Is the definition of a "hole" sufficiently clear and known to all, such that it is safe to specify a characteristic of all "holes" in a drawing and be confident that there will be no misinterpretation.

Is a spotface/counterbore a hole? How about the ID of a 6" opening in a sheet metal part intended to lighten it, or allow access?


 
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Your last statement is one of the problems when using a default positional tolerance in notes. It considers all holes the same importance in their function whether they are to lighten the product or are to receive weld studs on fixed centres.

Needless to say, all holes do not need a positional tolerance shown in the default feature control frame but it is pretty quick to produce for the Designer. Some training companies in GD&T also promote this approach.

If the note does not mention "thru" holes, etc., then I would take it to meaning all holes whether blind, thru or tapered such as in a countersunk hole.

If you are from the Quality field and this drawing covers high volume production, please do not start making attribute gauges for all holes. Find out the function and relationship of each hole and hole patterns. If they have a function importance (certainly not clearance holes or to lighten the product), then contimplate making an attribute gauge for shop floor usage.



Dave D.
 
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What the definition of a hole? Blind or through?

We take it as any round hole, taps, c'bores & c'sinks, unless other specified by tolerance applied the dimension. (see attached file for our TB look)

Misinterpretation is the biggest problem because machinist or quoter's don't look at the title box. Even knowing we have this, once in awhile I'll still get "You want to hold the bolt hole to +/-.001" then ill say very nicely "look at the TB tolerance"

I'm not sure how to get the possibility of Misinterpretation out of that situation unless you tolerance or GD&T the crap out of the drawing.


Solid Edge V20
 
 http://files.engineering.com/getfile.aspx?folder=79f9231e-b04b-4258-b603-8b6ad0073732&file=TB_INFO.pdf
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Defining a hole is an interesting thing. A hole dug in the ground is quite a different beast from a hole in a sweater.

I'd be inclined to think "hole" would need a definition referenced on the drawing somewhere. Or at least more specific, ex. drilled thru hole
 
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Partly in response to dingy2, and to further clarify, the separate block tolerances for holes in the drawings in Madsen's book are on the diameter, not for location. I'm not concerned about gaging, rather about airtight communication of design intent.

I'm not from QA - I guess I am fishing for support of my belief that the term "hole" is not sufficiently precise to be used for a global callout. Also, I'm curious about how widespread is the practice of separate block tolerances for "holes". I had never seen it before in 40 years of engineering work.



 
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GarnierGary,

On most title blocks, you have a notation to the effect "UNLESS OTHERWISE SPECIFIED". Go through your drawing and make sure everything on your drawing that might be a hole either is a hole, or has its own tolerance. You need to look at any drawing you prepare and ask yourself if it can be misinterpreted.

I have gotten used to the metric system of deleting training zeros, which trashes most of the title block defaults. I find that the time I take applying tolerances explicitly to everything, is trivial. It results in better drawings, with more approriate tolerances.

Critter.gif
JHG
 
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I often say things like 'holes to be free of <finish>' and don't recall having any issues on the definition of 'hole'.

I have concerns over block tolerances because they are frequently misused, I'm not sure if having different ones for hole size is an improvement or not.

Of your examples, the only once I might expect a little argument on is spotfaces. To me counterbores are just 2 coaxial holes/a hole with different diameters at different points along it's lenth.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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garniergary

To answer your OP, NO. all our non SHCS c'bore, FLHCS c'sink or anything related to a fastener is either tolerances or the tolerance is derived from the UOS on TB.

Solid Edge V20
 
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Sorry, my last post was in error - the complete block tolerance in the drawings I question:

FRACTIONS ± 1/32
DECIMALS .XX ±.015
.XXX ±.005

HOLE ? .XX ±.005
.XXX ±.003/-.001

It's not that I argue about the general idea of tighter block tolerances for holes, or with the particular numbers this company uses. I'm just uncomfortable with the assumption that everyone will accept (as dingy2 does) that any round internal feature is a "hole".

 
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I think that the use of separate tolerances in a title block for holes could be unclear. It would depend on the drawing though.

If I were in your shoes, and wanted different tolerances for holes, I would probably just put the word "hole" in the callout (i.e. "Dia 9/16 thru hole") to indicate what is or is not a hole. Still somewhat of a pain, but maybe easier than specifying the tolerance of each hole individually.

Or, perhaps put the tolerance in a note. Then, by any applicable feature, reference that note. For example, "Dia 9/16 thru, see note (2)" and note (2) might read, Tolerance on noted features 0 - 1" = +/- .005; 1"-6" = +/- .05, etc

-- MechEng2005
 
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ctopher - I'm glad to hear from you, but we are in a minority here.

Do you have any references to back up your/our position on this?

By the way, so far there has not been one response from anyone whose company uses separate TB tolerances specifically for holes. Do you? Anybody?

I know FLIR Systems does, as recently as '08. Anybody from FLIR on this forum?
 
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"Anybody from FLIR on this forum? "

No, but I work just down the road;-).

Global DRM breifly mentions it at table 5-5 but I don't see anything in the text about defining hole or similar.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies: What is Engineering anyway: faq1088-1484
 
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I am the opposite of you.

Every company I've worked at, every companies drawings I've seen, that use ANSI standard, have separate hole Ø tolerance allowance on drawing title blocks.

In the above discussions what's being omitted is Ø. The example you give includes nomenclature HOLE Ø. Anything dimensioned as Ø / DIA, etc., is therefore to be interpreted as a hole regardless of depth or size.
 
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