Countersink positional tolerance interpretation

[Burunduk]

Considering the tolerance of position for a countersink as shown in this video

Would you interpret the position requirement (when considered for the countersink feature), as applying to the cone axis, or to the center point of the circular element which is controlled for size ø.675-.685?

 

[greenimi]

I think the intent is to control the cone axis (whatever that means and with whatever method you will determine that cone axis)
Same idea copied from the c'bore and extended to the cone (with only one positional callout FCF)

 

[CheckerHater]

Unfortunately discussion about position of a cone goes back some 10 - 15 years on this forum.
Unwillingness of the committee to deal with it goes even further.
To begin with, what exactly is cone at MMC?
So, good luck.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[greenimi]

I agree with CH.
I just would like to add "Unwillingness of the Y14.5 committee to deal with it goes even further."
I think Y14.8 guys clarified a little (getting warm) by introduction of the full feature FF note. Therefore, by default the position is applied to the circular element unless FF is added and then the meaning to the full feature is meant.
(but again that is the casting, forging and moulded standard and NOT dimensioning and tolerancing Y14.5)

 

[greenimi]

See this discussion ---- Dean Watts about FULL FEATURE FF (applied on the RFS basis only).

https://www.eng-tips.com/viewthread.cfm?qid=474434

 

[3DDave]

What's your interpretation?

 

[jassco]

Hi, Burunduk:

Position tolerance only applies to feature of sizes. A cone is not a feature of size. So, it does not apply to the cone.
This is because tolerance of position is a cylinder. I see reasons why Y14.5 committee does not want to deal it from a math perspective.

Best regards,

Alex

 

[greenimi]

Position tolerance only applies to feature of sizes. A cone is not a feature of size.

Here we go again.
Yes, it is. A cone is an irregular FOS.

People's opinions are devided on this issue. If YOU chose one side I can surely go the other side (and use appropriate arguments)

iFOS/2009 b.) a directly toleranced feature or collection of features that may contain or be contained by an actual mating envelope other than a sphere, cylinder, or pair of parallel planes

 

[drawoh]

CheckerHater,

I am fine applying positional tolerances to countersunk holes. To me, specifying this at MMC is wrong. The countersink centres with zero play. MMC affects where the top of the screw winds up. The MMC should not be part of that specification.

--
JHG

 

[Burunduk]

What's your interpretation?

No easy answer, but I tend toward the circular element. My considerations are:
1. There is no solid definition in the Y14.5 standard.
2. Both interpretations answer the functional requirement adequately.
3. The MMC modifier implies a correlation between the size and required location (location requirement depends on size). Since size is only directly controlled at that one circular element, the circular element is a better candidate than the full cone to be location-controlled.

 

[3DDave]

Ok - this topic has previously been beaten to death, so is this synoptic?

 

[jassco]

Hi, greenimi:

According to definition on ASME Y14.5, a cone is NOT an irregular FOS. Rather, a cone is a complex surface. That is why we profile to control it instead of position. It is an open surface.

Late Prof. Don Day from Tec-Ease demonstrated this on one of his presentations.

Best regards,

Alex

 

[jassco]

Hi, greenimi:

If you think cones as contour surfaces, you will agree with Y14.5 committee's decision on this "issue". Contour surfaces have no sizes, neither do cones.

Best regards,

Alex

 

[greenimi]

jassco,

I told you :Here we go again" and I told you the opinions are split.
Read this thread.

https://www.eng-tips.com/viewthread.cfm?qid=460720

I don't want to copy and paste

Mark Foster (credential in the above discussion) has a different opinion than late prof Don Day.
Who is right and who is wrong. No one. Just different opinions.

And by the way,

I am NOT disputing your statement "That is why we profile to control it instead of position."

I am disputing THIS statement " A cone is not a feature of size"

Why? Because TODAY I want to be on Mark's Foster side.
Tomorrow I might be on different side. All depends.

 

[3DDave]

What is fun is the video displays the screw as stopping the instant it makes contact with the countersink. This will leave the fastener loose in the typical installation or subject to the creation of a gap with thermal transients and differential coefficients of thermal expansion. It will also be subject to wear, increasing the gap and allowing the interposing part to come loose.

It's an analysis that is done absent ever looking at how a countersunk/flat head fastener works.

This is a cause I think of the schism. Arguing about MMC, when there is no extra clearance in typical cases and then thinking that the axis of the countersink actually aligns to the axis of the conical feature of the screw under conditions like a fixed-fastener case ignores that the fastener has to deform to accommodate the slightest difference, even due to the runout of its own head with respect to its own threads.

 

[jassco]

Hi, greenimi:

Did you change your position on FOS of cones since Dec. 19, 2019? I saw this discussion below.

**************************************************************************
greenimi (Mechanical)2 Dec 19 19:37
Quote (dtmbiz)
Conical features, Linear Extruded features, and Complex features are clearly irregular Features of Size as defined with examples shown in 2009 ASME Y14.5.

Could you, please, provide evidence of your statement?
- examples, figures from 14.5-2009, 2018?
- examples (from other training companies) training materials?

In my understanding a FOS can be: regular or irregular. On both you can apply position.
IMHO, a cone is neither.
My supporting evidence: never seen an ASME example where position could be applied to a cone.
Did you?
If yes, please provide some good examples.

Great post!

Report
greenimi (Mechanical)2 Dec 19 19:46

https://www.eng-tips.com/viewthread.cfm?qid=439737

Above is another discussion on why a cone could not be IFOS (irregular feature of size):
Reasoning is the same: CANNOT contain or be contained by an AME

 

[Burunduk]

I am fine applying positional tolerances to countersunk holes. To me, specifying this at MMC is wrong.

So, what the tolerance zone controls - the cone axis, or the center point of the outer circle? And, what would be a simple method to inspect it at RFS?

 

[greenimi]

Did you change your position on FOS of cones since Dec. 19, 2019?

Just temporary for the sake of this discussion.

Same idea different subject: Straight threads should be modified at MMC or RFS?
If you say, MMC, I will go to RFS and vice versa.

 

[jassco]

Hi, Greenimi:

There is nothing in ASME Y14.5 that indicates cones are features of size. Have a nice weekend!

Below is what ASME Y14.5 says on IFOS in section 3.35.1

3.35.1 Irregular Feature of Size
irregular feature of size: there are two types of irregular
features of size, as follows:
(a) a directly toleranced feature or collection of
features that may contain or be contained by an unrelated
AME that is a sphere, cylinder, or pair of parallel planes.
See Figure 7-41.
(b) a directly toleranced feature or collection of
features that may contain or be contained by an unrelated
AME other than a sphere, cylinder, or pair of parallel
planes. See Figures 7-40 and 11-29.

 

[Burunduk]

jassco,
If the conical surface is not a FOS,
Could the positional tolerance in the example apply to the ø.675-.685 circle? Or do you think it can't apply to any element of the countersink altogether?