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what is best way to control location of coaxial hole

what is best way to control location of coaxial hole

what is best way to control location of coaxial hole

(OP)
On drawing I need to drill a multi-stepped hole on a thick wall. There are say 6 coaxial diameters on the hole. What is the best callout to control the location of the diameters with positional tolerance control?

1. Use positional tolerance control for each diameter with same datum features reference. I think this would make the drawing kind of verbose. Is there a better way?

2. I see drawings drafted by my colleague show a single positional tolerance control applied to the axis of the hole. I guess the control of this callout is equal to the first one. But I'm not sure if it is an appropriate way because it just reminds me of the datum symbol placed on an axis.

3. Use a composite position tolerance control with a notation like 6 COAXIAL DIMATERS. This is a nice one but there are fewer people understand exactly what it means. Besides, the design intent, I guess, is not to control the coaxiality of the diameters. It just wants to control the location of each diameter individually.

Thank you for inputs.

RE: what is best way to control location of coaxial hole

bxbzq,
If the intent is to control location of each bore individually relative to external datum features, I see the approach from your option #1 as the best one, with a modification though - if the position error allowable is the same for each bore, you can use method shown in fig. 7.24 of Y14.5-2009. However if those values are different, 7-25 is a way to go, so something similar to your proposal.

RE: what is best way to control location of coaxial hole

bxbzq,
If the intent is to control location of each bore individually relative to external datum features, I see the approach from your option #1 as the best one, with a modification though - if the position error allowable is the same for each bore, you can use method shown in fig. 7-24 of Y14.5-2009. However if those values are different, 7-25 is a way to go, so something similar to your proposal.  
 

RE: what is best way to control location of coaxial hole

bxbzq
Stay away from "option 2". You are absolutely right, it IS similar to applying datum to axis. Just take a look at the drawing and ask yourself: is the axis derived from DIA2? DIA2? DIA3? Combination of DIA1 and DIA6?
One should always control feature.  It could be surface of the feature or axis/center plane derived in unambiguous way.
 

RE: what is best way to control location of coaxial hole

Is this ISO? Are you using ISO general tolerances?
Frank

RE: what is best way to control location of coaxial hole

(OP)
pmarc,
In my case the hole is not exactly a counterbored hole. See attached. I think the approach you recommend still applies, right?

CheckerHater,
I guess the argument from my colleague would be: I understand the problem of applying datum to common axis because datum has to be established from a feature unambiguously. But in this case, since I want all the diameters to be located in a common tolerance zone centered around the common axis. Why bother to specify them individually? A single positional callout serves the purpose fairly well.
I'm not comfortable with the single positional callout, I just don't have a strong logic to argue back.

Frank,
Yes, the print invokes ISO. But the department who drafted the drawing is in process switching from asme to iso. I assume the drafter is very asme guy. Any difference between asme and iso here?

RE: what is best way to control location of coaxial hole

You really set this up when you say "the best way", the best way is to specify all the tolerances (your choice 1) per each functional requirement ISO or ASME.
Does everyone do it? No! Just like the other people you see!

Yes, not only are there are differences but ISO standard tolerancing, in particular, gives you another option of using as system of general tolerances to cover coaxiality on the less critical features and state only the ones that are not acceptable under the general tolerance values. (ISO 2768-1 & -2)
You can use a general note to do it under ASME but the ISO system is much more sophisticated.
Frank
 

RE: what is best way to control location of coaxial hole

It still makes a difference which bore(s) you use to establish the datum.  It is entirely possible for the same part to pass based on one datum definition and fail based on another.  You as the designer know the function of the part and need to communicate that to the people making and inspecting the part.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 

RE: what is best way to control location of coaxial hole

bxbzq,
You are not showing which features are datum features. Like I said, if the intent is to control location of all the holes independently relative to some "external" datum features (and not relative to one of the holes in the group), I sustain my initial recommendation - use Position callout for each of the holes. The only thing which I would think about a little bit is the longest, interrupted hole that could be somehow treated as a continuous feature (even in ISO GD&T).

Frank,
Please do not make this more confusing. There is no option in ISO 2768-2:1989 to assign general geometrical tolerances for Coaxiality or Position. The standard does not include those two characteristics.

However I confirm that there are differences in interpretation of Position between ASME and ISO. If the print ivokes ISO, one can/should even use Concentricity to control axes offset. ISO's Concentricity is a special case of ISO's Position intended to be used for cylindrical features shown nominally coaxial. ASME's Concentricity is something completely different to ASME's Position though.   

RE: what is best way to control location of coaxial hole

Pmarc,
Circular runout controls coaxiality! I am not sure who is confused?
ISO 2768-2 5.2.5 Coaxiality (NOTE.....)
People use runout to control coaxiality under ASME too. I am not a big runout fan myself but..
Frank

RE: what is best way to control location of coaxial hole

bxbzq,

I was under impression you are looking not just for the best callout to control the location of the diameters, but also for standard way to do so.
The standard way to do things is not always the obvious or easy-looking one.
For example, the drawing you supplied shows 7 coaxial features, not 6.
But if "why bother" is valid argument, then... why bother?

Frank,

I am bigger fan of runout than you, but even I would limit it to shafts, not holes.
 

RE: what is best way to control location of coaxial hole

I think we will all agree on the "best way", safe?
Frank
 

RE: what is best way to control location of coaxial hole

So long as it is justified by function I don't see the problem with approach 2 - it is what is done with counterbores & countersinks most of the time.  (Section 5.7 a of ASME Y14.5M-1994 & figure 5-37).

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RE: what is best way to control location of coaxial hole

CH,
How process oriented of you. Do you have any ISO standard based reference for that, or, is it just a personal preference? :)
Frank

RE: what is best way to control location of coaxial hole


Frank,

I stand corrected: not necessarily a shaft, but at least something you can stick into chuck and turn around.
Yes it is personal preference, and yes it is process-oriented. There was a discussion on this forum if runout could be measured on CMM. Everyone decided to stay away from that, so let's just keep it this way for now.
And if you think of it, isn't the entire concept of GD&T process-oriented? Otherwise we wouldn't have Y14.43, would we?
 

RE: what is best way to control location of coaxial hole

Real-world example: circular runout is used all the time to control the wobble effect of the ID in a washing machine tub. Does that count as a "hole"?  :)

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems
http://www.gdtseminars.com

RE: what is best way to control location of coaxial hole

CH,
I would say no. That is one of the battles in the ASME standard it self, its Foreword and introduction try to divorce itself from process however processes like runout seem to invalidate that. I have always felt you just need to believe it would pass if you could rotate it and a particular process was not required. Naturally, I would say that but it is the only way I can make it consistant with its own stated goal.
Frank

RE: what is best way to control location of coaxial hole

I look at this the same way as I look at any suface callout requirement, do you really have to check every point on a surface? I do not feel you must, you just have to check enough points to establish a reasonable belief that if you could check every point it would pass.
Frank

RE: what is best way to control location of coaxial hole

(OP)
Thank you all for the inputs. Sorry the question was not described clearly.
I was lazy and just copied part of the view from the drawing and datums are not shown in that view. The hole is drilled on the wall of a cylinder-like part. Datums are axis of cylinder and surface of flange at one end. CH is right, there are 7 diameters. I missed a very short one.
I like the way shown in fig. 7-24 in 09' and fig. 5-37 in 94' for counterbored hole. But in this case, the 2 bores sitting at both sides of the interrupt have different diameters. So probably I have to specify positioanl tolerance for each bore in this cross section view.

RE: what is best way to control location of coaxial hole

(OP)
I mean, forget the interrupt.

RE: what is best way to control location of coaxial hole

bxbzq,
Your last try is for sure illegal per ISO 1101:2004. ASME Y14.5 does not specifically say it is forbidden, but offers no example of such approach and does not mention it when listing which methods are allowed (para. 3.5 of '94 and '09 editions).  

RE: what is best way to control location of coaxial hole

(OP)
pmarc,
OK. This is not bad news for me. It shows how my colleague does. Thank you for pointing out.

RE: what is best way to control location of coaxial hole

bxbzq,

As you mentioned cylinder, you reminded me my dealings with hydraulics long ago; and I can assure you: the drawings for cavities like in your example can be quite "verbose".
The one on the link is not the most complicated.
So use as many direct and geometrical tolerances as you need to fit mating part properly.
 

RE: what is best way to control location of coaxial hole

Quote (fsincox):

"I think we will all agree on the "best way", safe?"
Looks like I was wrong about that too!

Ken,
I agree your way can be done; I was caught up in terminology of "the best".  I think of best as my interpretation of the ASME's intent: "best describes function" he may mean "best" as in easiest. I also agree that if he calculated a c'bore like you showed in the M42 c'bore thread it could be both. ;)
 
bxbzq & CH,
I suspect the more steps in a bore, like is shown here, the less likely a single tolerance will be the "best" from the functional point of view and more of just a compromise. If you just want compromise, this is why I was also heading down the general tolerance path as an option.
Frank

  

RE: what is best way to control location of coaxial hole

(OP)
Frank,
I should not have used "the best" in the title. Probably "appropriate" would be fine.
I agree your point of function. If I were the designer, I would use composite positional callout to tune the control. Then education to supplier and inspector may be needed.

RE: what is best way to control location of coaxial hole

Your words are fine, comunication is an art, that unfortunately, I am short on. I needed time to understand what you are asking for, I start with my own predisposition of the words and then need to try and understand what you are actually trying to say.
Frank

RE: what is best way to control location of coaxial hole

(OP)
Frank, you probably can tell English is not my native language...Even though, it should not be an excuse. I'll try to write my post with precise wording.

RE: what is best way to control location of coaxial hole

Like pmarc says, the way you've tried to do it (point the FCF to the CL) is wrong.  The way 14.5-94 shows it in 5-37 is correct - that is the FCF is attached to the hole dimension call out.

As for multiple (more than 2) coaxial bores, this is covered in 1.8.11, especially figure 1-37.

Like I said from a drawing annotation point of view it's perfectly reasonable.  However, you'll have to determine if functionally it's appropriate.

Please note that I keep referencing the standard I'm referring too - if you're using ISO or something it may be different.  

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What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: what is best way to control location of coaxial hole

bxbzq,
This is just as true of two people who speak "the same language". It is not just you. :)
Frank

RE: what is best way to control location of coaxial hole

I would look at Fig 5-53 in Y14.5M, so option #3.

RE: what is best way to control location of coaxial hole

CH,
I used to work in hydraulics too.
Do you think your linked example really best represents the ASME's or ISO's intent with just those few callouts shown?
I am curious if anyone else wants to chime in, too. I have no doubt it is common, that is not the question, I mean the ideal intent of the committee's stated intent that all features should have definition and specify the functional requirements?

I know I do not, I am certainly an idealist though.
Frank
 

RE: what is best way to control location of coaxial hole

Quote:

Do you think your linked example really best represents the ASME's or ISO's intent...

No, it's just first relevant picture I found "on the Internets".

My point being - you can have dozen features, some embracing the mating part, some just providing clearance; you can have several criteria from "simple" fit to dealing with sharp edges that can damage rubber seals, etc., etc.

You will not get the good part unless you explicitly specify all your requirements. So looking for "call-out" that will save you some space on the drawing is just plain dangerous direction to go.
 

RE: what is best way to control location of coaxial hole

"and the congregation says: AMEN" :)
Frank
 

RE: what is best way to control location of coaxial hole

This example is typical of hydraulic spool bores and injector bore sets. It eliminates having to designate datum features when there are numerous bore cross-sections and it prevents simultaneous requirement linking of the refined bore pattern position requirements.
Paul

RE: what is best way to control location of coaxial hole

Paul,
Cylindrical zones on surfaces?

If you are not going to specifically tolerance all the bores to their functional limits, to me what you did there is not much different than just placing a straightness on the axis like the old ISO practice.
Frank

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