How do you correctly call out coaxial holes that need to be inline so that a bolt could go through 2

[eeyew]

I'm attaching a sketch of a situation that I'm encountering where I need to make sure that the co-axial holes on a clevis remain inline after the stamping is complete. The holes are done at the last stations and I need to be able to locate both holes correctly so that I will be able to get a correct length on the assembly equipment. I don't believe the datum scheme lends itself well to control and gage R&R but this is all I have to work with.

Please let me know if I'm calling out the datums correctly and the datums are set to what I'm trying to achieve and to let me know if the composite position tolerance I have there is called out correctly and will locate this hole at a distance away from the cylinder and inline with each other.

Thanks for everyone's help.

 

[drawoh]

eeyew,

How close do the fits in the holes have to be? Bending and welding are not accurate processes. Your specification looks reasonable to me, although the position tolerances should have diameter symbols.

You need either to open up your holes and tolerance so that bending and welding will create conforming parts. If you need the thing to be accurate, you will have to apply the tolerances, and accept that the fabricator will machine after welding.

--
JHG

 

[pmarc]

The composite position tolerance as it is now is incorrect, because of two reasons:
1. Like drawoh said, the diameter symbols should precede tolerance values in both segments.
2. Datum feature referenced in the lower segment is not a subset of datum features referenced in the upper segment.

Additionally nothing controls location of these hole in x direction. Basic 230.7 dimension suggests that the end face is intended to serve as datum feature for locating the pattern in x direction, but at the moment the print does not say that.

As for datum feature C, perhaps it would be reasonable to consider entire width 74.3 between clevises as datum feature instead of picking one of the faces. Is there any particular reason for that?

Is this part rigid or subject to free state variation?

 

[eeyew]

drawoh and pmarc, thanks for your responses. Thanks for the correction on the true position feature control frame To answer some of your questions.

The hole location only needs to be accurate to position tolerance of 1.5mm but from hole to hole they must be lie within 0.5mm to each other so that the customer can fit the bolt through both holes without any additional force.

The part will be subject to free state variation I believe. It is assembled into a strut assembly. There will be assembly variation as well as variations on all edges of the clevis as it isn't controlled other then general notes.

The cylindrical part of this part is formed and is subject to variation due to the process. The end face is toleranced as a profile of 1.5mm but was not included in the drawing by my error. It is not a datum.

To correctly call out the location of the holes, what would need to be done? If the face of that cylinder is datum A and then surface of the leg is datum C, would that allow the callout that I had to be valid?
If I wanted to call-out positions from the centerline of the cylinder to locate the holes, would I need to add an extra D datum to the face of the cylindrical portion and called out the top part of the composite feature frame to A and D and the bottom feature control frame to C, would that allow for the control I'm looking for?

Thanks.

 

[randy64]

"Datum feature referenced in the lower segment is not a subset of datum features referenced in the upper segment."

pmarc, can you give more detail to this statement? Are you saying that C is not a subset of A & C? Or are you saying that the datum in the lower segment must be held to a feature that IS the upper segment (meaning that the bottom segment is to be a datum feature [hole] that is held to the upper segment {hole])?

 

[pmarc]

randy64,
By subset I meant that lower segment of the composite callout can specify A or in some cases A|C or in some cases no datum feature references. Anything else is illegal.

 

[randy64]

Why would putting C in the lower segment be illegal?

 

[pmarc]

Saying shortly, it is because these are the rules of composite tolerancing. If a datum feature is referenced secondary or tertiary in the upper segment, it can't be referenced primary in the lower segment. For slightly more detailed explanation see para. 7.5.5 in Y14.5-2009.

 

[eeyew]

pmarc,

Thanks for the information. So that means none of the call-outs I mentioned would work as well. So would this be acceptable and allow me to have control over the location of the hole to the datum scheme and secondarily with the hole to hole dimension. The new call out I would use is

TP D 1.5 to A C D and the secondary feature frame of D 0.5 A C

Second question is if I just went with

TP D 1.5 to A D and the secondary feature frame of D 0.5 A would that give me the position of the circles to be parallel but off in the x direction?

Thanks for any help.

 

[randy64]

pmarc, thanks for the info. Makes sense.

eeyew, there is an example in Y14.5-2009 that is nearly identical to your situation. See figure 7-45. In it, they use a three segment composite tolerance. Not sure if this does what you're looking for, but it's so similar, I thought I'd bring it to your attention.

 

[eeyew]

randy64

Thanks for the response. I do not have a copy of the latest Y14.5 spec so can you please explain to me what it says in that figure? Thanks a lot for your help.

 

[randy64]

Go here:

http://mach.jlu.edu.cn/jxcx/standars/AGMA-ANSI/ASME Y14.5M-2009.pdf

Page 140 for the figure.

 

[drawoh]

randy64,

Should they be posting that? I am pretty sure it is copyrighted.

--
JHG

 

[randy64]

drawoh, not sure. I just googled it and it came up.

If I have somehow broken some Eng-Tips posting rules, I apologize and will understand if an admin edits or deletes my post above.

 

[3DDave]

It's from Jilin University. I wonder if ASME is willing to go after China with a take-down notice. Probably make Google send it to page 40,000 of the search results if they can get Google to call JLU a pirate organization. Should be fun.

http://en.jlu.edu.cn/University/Sub...ubPageName=About Us&spmBlockNamw=JLU Overview

Jilin University

Jilin University, founded in 1946, located in Changchun, the capital city of Jilin Province, is a key national comprehensive university, under the direct jurisdiction of the Chinese Ministry of Education, supported by Project 211 and Project 985. In 2000, the former Jilin University merged with four other universities, namely former Jilin University of Technology, former Norman Bethune Medical University, former Changchun University of Science and Technology, and former Changchun College of Posts and Communications. In 2004, the former University of Military Logistics also became part of Jilin University.

 

[eeyew]

randy64 and community,

Thanks for the help. It helped me out a lot. I've attached another sketch and am hoping that this makes sense. It seems like there's a circular reference in there that may make it invalid so I want to make sure that if that's not possible, I'll have to find an independent way of doing so.

The cylinder will be a wrapped cylinder and therefore the surface that I'm trying to make a datum will vary and I'm trying to limit that variation. I care about that surface so I can't just label it a datum with general notes. Please review the sketch and let me know what you think.

 

[Tunalover]

You can apply a single positional tolerance to control both holes if you declare the two holes to be one continuous hole using the CF (Continuous Feature) symbol.

Tunalover

 

[3DDave]

When the two in-line holes are placed, what orients them and locates them and in what order? It looks like the cylinder surface does the primary location and orientation and the flat on the left does a secondary location; it still leaves one degree of freedom - rotation about the cylinder that needs to be fixed.

Unless it's a sloppy fit into the next assembly, it should not use MMC for the cylinder.

The in-line hole callout is a width dimension, so there's no location tolerance closer or farther from the flat on the left. Use a radial leader to indicate the diameter of the in-line holes.

 

[eeyew]

3DDave, Pmarc, randy64 and all

Thanks for your comments. It makes sense to me that there's still a single degree of freedom available. So I've attached a new markup adding another datum to the surface profile that should set that last degree of freedom. I changed the call-outs to reflect this. Can you please let me know if my call-outs are legal and it's doing what I think it's doing.

In the die, the legs are bent into it's final location via a few stations, the holes are then pierced at the same time after the legs are in their final location.

Thanks for your help.

 

[randy64]

tunalover, if you use CF, is the QTY of the hole(s) callout 2X, or just 1?

I would assume also, that each hole is held to the tolerance in the FCF independently, correct?

What I'm getting at is that CF doesn't offer any refinement or special inline alignment between the two holes, right? It would be the same as calling out each hole separately.

Not trying to be argumentative, just trying to make sure I understand how CF would work on holes like this.