Cylindricity GT usage 2

[eli28]

Hello,
I would like to be given some practical engineering examples in which cylindricity is useful.
I am sure there are some useful cases, but I am not sure the examples I encountered use this tolerance efficiently.

In my opinion, in my workplace people tend to use this tolerance for holes and shafts that mate each other where there is no need for this.
When I asked them to explain this use, they said they want a "good" and "smooth" contact between the mating parts.

Here is a simplified illustration of 2 mated parts (section view):

Here you can see the nominal (in the CAD) clearance between the parts:

Here is a drawing view in which we can see the tolerance of each part:

In the last picture I marked the given cylindricity tolerance I am not quite sure is needed.
An entire contact isn't the design intent, but a minimum clearance between them.
So in my opinion, as long as there is a clearance the shape limit isn't critical.

I am looking forward to your advice.

Thanks!

 

[greenimi]

My quick observation: regardless if ASME or ISO GPS (which looks like being the governing standard) you cannot check cylindricity with a gage (pin).

 

[eli28]

Hey greenimi, thanks for replying...
but I am not sure you replied my question :-/

 

[Tarator]

eli28,

You do not need the Cylindricity callout, or any form callout if you only care about the assembly of both parts. I would change the POSITION callout to PERPENDICULARITY though. The message would be clearer.

 

[greenimi]

This drawing is ISO isn't it?
If yes, what ISO standards this drawing invoke?

What I do know is that in ISO some form errors (straightness) is controlled by the position. I am not sure cylindricity is redundant in this case or not. I am inclined to say that is not (redundant) therefore cylindricity has its added value (specially because the sleeve / ring drawing) does not have envelope requirement enforced)

 

[eli28]

Thanks, so let's try to sum up - for assembly purpose only there is no need in cylindricity.
Do you have practical examples in which it's useful?

 

[Tarator]

eli28,

Cylindricuty can be used for sealing, bearing applications.

 

[greenimi]

Cylindricity: piston in a bore or where you do need a uniform (within some tolerance) space between components.

 

[eli28]

Thank you for replying

 

[mfgenggear]

shafts with bearing journals and yes sealing surfaces.

 

[drawoh]

eli28,

I have been applying GD&T for around thirty years, and I was formally trained twenty years ago. I have never specified cylindricity, or even considered it.

In your drawing, your positional tolerance controls only perpendicularity. If this were my drawing, I would explicitly call up perpendicularity. The shop may be wondering if you know what you are doing. Check out thread1103-322065.

Your diametral tolerance is [±]0.01mm. With rule[ ]#1, this controls cylindricity more tightly than your tolerance. Form tolerances like cylindricity are used to refine other tolerances. If you had called up an ID of 15.5/15.1, cylindricity would impose an additional control. I have never felt a need to do this. Maybe someone else has!

--
JHG

 

[greenimi]

With rule #1, this controls cylindricity more tightly than your tolerance.

Well, rule#1 is not enforced! At least not in the sleeve drawing.
So, why cylindricity is not needed?

Again, in my opinion, cylindricity is NOT REDUNDANT in this case.

 

[mfgenggear]

It really depends which industry one is in.
Design and manufacture of bearings and gear shafts and I have been doing gears over 30 years too. Is very common. It is a very tight requirements.
But often necessary. Tipical requirements is .ooo2-.0003 inch cylindricity.
On other requirements is can be specific
The fit, form, function.

 

[mfgenggear]

In the OP example if a shaft requires a slip fit precise Assembly, it is and can be very applicable. To prevent seizure of the two components.
Any out roundness, straightness, to taper
Will cause interference. And is not acceptable.

 

[drawoh]

greenimi,

What do you mean by rule[ ]#1 not being enforced? It is part of the standard. In the OP's drawing, the MMC/B condition is a perfect circle 15.09mm[ ]diameter. The imperfect circle at 15.07mm cannot exceed this outline, thus cylindricity is controlled.

--
JHG

 

[mfgenggear]

Here is a good example
Take a bore gage inspect the op part.
It will verify size up and down the bore.
Or even a CMM. If the correct program is not used, it will pass.
Now take shaft that has been precisely
Machined can and will seize because the bore is out of straightness.

 

[Belanger]

drawoh -- I think the lack of Rule #1 comes from the fact that there is a circled E on the shaft's drawing. That implies the ISO standard, which does not observe Rule #1 (well, at least without the circled E).

 

[greenimi]

I think the lack of Rule #1 comes from the fact that there is a circled E on the shaft's drawing. That implies the ISO standard, which does not observe Rule #1 (well, at least without the circled E).

That's one reason.

The second reason is: MMVC is a term specific to ISO set of standards.
In ASME the term is "simply" VC not MMVC.

 

[eli28]

Now I am quite confused
I tend to agree that 15.08 +/- 0.01 mm indeed controls the form as well, and a form tolerance can contribute if it's tighter, e.g concentricity of 0.005 mm.
As for the usage of cylindricity for preventing seizure - tha's the first time I encounter this explanation, but I am not saying it's not true!
Has anyone else heard of it?
Is it relevant only in cases of certain touch of 2 surfaces? because if we look at the example I attached here - in the worst case we may have a 0.03 mm clearance...

Thaks everyone for participating and replying.

 

[eli28]

In addition - what does rule #1 mean?
And why using the Envelop symbol (E) means it does not observe Rule #1 ?