Customer Print Spec. 5

[metaldork]

I have a callout for a .250 dia. hole with the letters w.h. next to it can anyone please tell me what it means. The hole appears to have no functional purpose.

 

[CheckerHater]

“Wall Hydrant” according to the standard.

Seriously, if hole serves no purpose, it can be used to hang the part for painting; then it means something like “wire hanger”.

Still you are better off asking person/organization that produced the drawing.

 

[btrueblood]

Might be "weep hole" if the part has a cavity, and this hole could drain said cavity.

 

[MintJulep]

Why Hole?

 

[CheckerHater]

Where Wolf?

 

[metalonis]

We'd really have to look at the drawing, but weep hole appears to be a good bet, especially if the hole seems to have no other purpose.

 

[Jboggs]

metaldork - Please understand me on this! I have seen similar questions on this and other forums many times. There is only one right answer - the notation means what the customer intended it to mean. No matter how many good and valid opinions you get, they are still that - opinions. Their only real value is that they confirm that the notation can be easily misinterpreted.

After you make the part and the customer complains because you got it wrong, do you really want to tell him you made it that way because some guys on a forum said to? Not good.

Ask the customer. He is the one that decides if the part is right or not. He will appreciate your asking rather than assuming something.

 

[looslib]

Just because a hole seems to have no purpose in that part, it may serve a function when used in a higher assembly.

As Jboggs said, only the customer can give you the correct definition.

Fundamentally, if you are a contract house making parts to your customer's prints, why are you questioning what the customer has ordered? Make it to the print, ship it and get paid.


"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

 

[KENAT]

No, it needs to be verified in case it's meant to call up some special treatment or something.

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[CheckerHater]

OK, I am trying to learn something.
Now, when all the experts are here, will somebody educate me: what kind of “special treatment” the weep hole is getting that justifies using its own unique call-out?

 

[tz101]

I don't know if you would classify it as a special treatment, but a weep hole, not being as critical in function as, say, a shaft bore or pin location, might have looser location tolerances specified. Perhaps even a looser tolerance on hole Ø (after all, fit would not be a concern with any mating component). I have seen drawings where we would specify all holes within ±.002 for location, but weep holes could fall within ±.010 for all intents and purposes. The only other reason we might specifically designate "W.H." on the hole callout would be for reference for the machine shop, so that they know that this hole is not as critical as others on the same print. Allows them some freedom in machining that feature.

 

[CheckerHater]

Thank you tz101,
This is about what I expected, and here are my next questions:
As a fan of ISO 2768 (and for some other reasons) I am interested in topics like “industry standards”, “customary accuracy”, “critical- and non-critical dimensions”, etc., and how they connect to the world of strict written standards.
Did you try to actually specify loose tolerances, or specify no tolerance at all and rely on “title block” or “general tolerances” instead of using non-standard designations?
What in yours (and anyone else’s) opinion is the best way to tell the shop to just keep “effortless” level of quality?
Are the benefits really that great, for example, in specifying loose tolerances for ‘some’ holes, if ‘all’ the holes will be produced on the same CNC?

 

[tz101]

If all holes are machined on the same CNC setup, then in actuality all those features will be precisely located and within feature size tolerances. By "precisely" I am saying that most CNC machining centers hold feature tolerances within ±.0005 easily unless it is somehow out of calibration.

Where I have used differing tolerance ranges and weep hole designators is in instances where the part will have multiple machining operations done to it using multiple setups. The advantage of specifying looser tolerances where multiple setups and machining operations are involved is that it allows the manufacturer (not always the same as where it was designed) some leniency in using whatever manufacturing process they deem capable of holding those tolerances.

The biggest advantage to accurately tolerancing each component feature based on its intended function and importance, is that you do not always know where a particular part will be manufactured, or exactly what processes will be used. Specifying CNC-capable tolerances on non-critical features may well drive part cost up substantially at a machine shop where they do not have the same CNC capabilities and have to rely on manually operated milling, drilling or turning centers.

Having said all that, it is my belief that is always best practice to individually tolerance critical features and let non-critical features fall back to default title block tolerance ranges. This is a happy balance that allows for least cost in most situations.

I hope this was helpful.

 

[CheckerHater]

Thanks a lot tz,
I wish more people could see it your way.

 

[KENAT]

TZ101, nice summary. The other related aspect is you may design & tolerance for a certain machine/process capability but say for some reason that tool is unavailable and to meet schedule they want to use some other tools/process that aren't as accurate/preccise. I've had real life examples of this.

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