perpendicularity AC, perpendicularity CA

[[Lu...]]

Hello,
I would like to ask you for a little help. I´m solving an issue about perpendicularity.
There is a perpendicularity on the drawing:
|⊥|0.05|C| - Plane A to reference Datum C (cylinder). Cylinder C is short cylinder, D=100mm, Length=4mm. I understand when you have a short cylinder, it can be an issue to evaluate the perpendicularity correctly. I understand there is a difference between evaluations when you change the order of references.

1. |⊥|0.05|C| - Plane A to reference Datum C (cylinder)
2. |⊥|0.05|C| - Cylinder C to reference Datum A (plane)

Our supplier changed the evaluation from Plane A to reference Datum C (cylinder) → Cylinder C to reference Datum A (plane) and obtained better results. But I think their results are not following the drawing.

My question is:
When I have on the drawing perpendicularity |⊥|0.05|C| I cannot change the order of references, have I right? If I understand correctly the drawing says that only one evaluation is possible. (I have attached a picture).


Thank you for any help.

Regards,
Lukas

Perpendicularity 1.JPG

[[An...]]

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[[Da...]]

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No, you cannot change the features without written permission.
That's why the best you can do, go talk to the designer and convince her/him to put the second option on the drawing:
- 2. |⊥|dia 0.05|A| - Cylinder C to reference Datum A (plane) <- with diameter symbol before tolerance value

In some cases the designer would also see, that this would not help to control much of anything and even throw that perpendicularity away- because of the lenght/diameter ratio.

[[An...]]

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[[Mi...]]

Without worrying about feature sizes because you don't have an ideal situation...

When you have a Plane as the toleranced feature and the Cylinder as the datum the result will almost always be worse than the opposite due to the fact that the Flatness of the plane becomes part of your perpendicularity. That will explain the huge difference. So no, flipping them isn't correct.

If you create a flatness characteristics and 2 perpendicularity's, one each way, match Evaluation Modes, you should see the difference be almost the flatness value.

It is likely that the drawing was intentionally done like this by the designer, but it is a confusing callout. Where we have it we ask them to throw Tangential Plane modifier on the callout, and control a tight flatness separately.

Even if they do that and reduce the allowed tolerance, it's easier to maintain as it's clear to everybody what is wrong when the result is high.

[[Ma...]]

Since plane is Ø100mm and cylinder has length 4mm then you could switch features, BUT you have to accordingly adjust tolerance.
Tolerance 0,05mm on 100mm diameter -> 0,002mm tolerance on 4mm cylinder length.

[[Lu...]]

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Thank you for your reply.
But I have doubts about your answer.

When you have a Plane as the toleranced feature and the Cylinder as the datum the result will almost always be worse than the opposite due to the fact that the Flatness of the plane becomes part of your perpendicularity. That will explain the huge difference.

I think this option can also affect the result of the perpendicularity:
When you have a Plane as the toleranced feature and the Cylinder as the datum the result will almost always be worse than the opposite if the Cylinder C has a worse cylindricity. That will explain the huge difference.

So I think both what is mentioned above can affect the results of the perpendicularity (Flatness A is worse or Cylindricity C is worse)

What do you think?

Regards,
Lukas

[[Lu...]]

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Hello Martin,
yeah, that seems logical. It's a good point.

Thank you.

[[Mi...]]

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Well first, are you talking ASME or ISO, because in ASME what I said is correct and directly from the standard. This is something our facility had to learn last year when we started getting parts with this callout. MY answer only applies to ASME.

When a Cylinder is the toleranced feature, in ASME, it's from the axis with no form. When the Plane is the toleranced feature it is WITH form, that is the key difference. Now if this is ISO where it would be Cylinder with form, the game changes and somebody else needs to help as I'm only well versed in ASME.

So the question is, ISO or ASME? That answer changes the answer to your question.

Perpendicularity Plane Vs Cyl.jpg

[[Ma...]]

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There is one thing to point to.
Plane is reffered as rectangle/square - any rotational deviation will increase deviation in perpendicularity.
If plane is perpendicular in ZX but in ZY is not, then referred length will be size of plane. If it's not perpendicular on both axis, then it's like triangle - referred length will increase and so perpendicularity reported value.

Make alignment to keep one axis perpendicular ( check A1 or A2 angle on plane ). Recall points of plane into new one with that alignment - then it will keep true values.

It would be much better to have plane as datum, since such cylinder can not guide anything to be datum.

[[An...]]

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[[An...]]

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[[An...]]

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[[Ma...]]

Here is perpendicularity on one axis
Here is perpendicularity when plane is rotated by 45°deg

[[Mi...]]

Many times you have to think about what that piece is for, most likely it is a bearing seat or flange.
Consequently I think we work to respect the use. At best grinding, otherwise lathe. Therefore the diameter and plane will be made in the same phase and/or with the same tool. This means that they will be perpendicular regardless.
Perpendicularity when there is a cylinder as a datum is influenced by the flatness of the plane and is proportional to the size of the two.

If I ever see such a drawing in our company, I will go to the technical office with a stick.

[[An...]]

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[[An...]]

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[[An...]]

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[[Lu...]]

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Thank you for your response.
I have attached more details about my evaluation. I have followed the cookbook from Zeiss where you can find the ´´recipe´´ how to evaluate perpendicularity.

1.Plane A is a toleranced plane
ASME+ISO have same ´´recipe´´

Plane A is a toleranced plane
Cylinder C is a datum
Perpendicularity to the axis for functional check
Toleranced plane- LSPL least Squares Plane (only probing points are calculated)
Bore as datum – MICY Maximum Inscribed Cylinder

2. Plane A is a datum
ASME+ISO have different ´´recipe´´

Plane A is a datum
Cylinder C is a toleranced element
Perpendicularity to face for functional check- ISO
Toleranced bore- LSCY Least squares Cylinder
Plane as datum – OTPL Outer tangential plane

Perpendicularity to face for functional check -ASME
Toleranced bore - MICY max. inscribed cylinder without form (new feature created in Calypso by ´´recall of one feature)
Plane as datum – OTPL outer tangential plane

What do you think? It´s correct?

Regards.
Lukas

Perpendicularity AC vs CA.jpg

[[Mi...]]

AC, the Plane is the Toleranced Feature and the Cylinder is the Datum is correct by the control frame you have for ASME. Cylinder is C and that's what's listed as the datum in your text.

If you create a Flatness characteristic for A, the Flatness result will very close to the difference between the two options you have there. I don't read german and can't translate Andrea's pictures but I believe he is showing you a "Tangential Plane Modifier" which is a special circumstance of this that releases the Flatness from the result.

[[An...]]

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[[Lu...]]

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Thank you for your answer.
I have attached the picture with the form of the plane A and the form of the cylinder C. It doesn't seem like the difference between these two measurements is only the Flatness of plane A.

Plane A + Cylinder C.png