Are these Runout and Parallelism callouts legal?

[Vishal2015]

Hello Everyone,

While referring to some old camshaft drawings, I come across Runout and Parallelism Gtol. (on Cam Lobe Surface)

Please help me to understand this.

Vishal.

 

[SeasonLee]

It’s okay for me except the missing of the diameter symbol Ø on the parallel callout, since the tolerance zone is a cylinder on the datum axis while the circular runout tolerance zone is the radial distance between two coaxial circles.

Circular runout is a surface to axis control but the parallel is an axis to axis control.

Season

 

[desertfox]

I would ditch the parallel tolerance and change the runout to total runout.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[3DDave]

Interesting that the cam is not entirely cylindrical, but the circular runout tolerance isn't limited to reflect it.

I would have expected the parallelism to be applied to each element to refine the circular runout tolerance in a way that using total runout does not. This especially as the axis of the feature is not in contact with any mating part; controlling the axis is a waste of effort.

 

[Vishal2015]

1. Can we use runout on non circular profile like cam lobe?
2. Can we use parallelism on curve surface?

Instead Profile Of A Line would serve the purpose.
Please provide your suggestions.

 

[mkcski]

Vishal2015:

Runout can only be applied to surfaces-of-revolution (circle, cylinder, cone) and a cam lobe is not one of the shapes. I would recommend profile of a surface relative to datum axis A-B for location. I would then assign a profile of a surface with no datums and a smaller tolerance to refine the shape within the "location". You can also have the width of the profile tolerance change as you go along (around) the cam - the retract zone could have a greater tolerance than where the cam is actuating (under load). The entire shape of the cam must be defined by BASIC dimensions or an electronic part (3D) model

Certified Sr. GD&T Professional

 

[Belanger]

I once saw circular runout used on a gear. The intent was to only check the outer tip (the crest) of each tooth, which would form a circle. A little dubious, if you ask me; maybe if they had a note on there I would have been more accepting of it.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

John-Paul:

In my way of thinking, inspecting the OD of a gear is a waste of time - only the teeth do anything (functional). If you apply runout to cam the FIM tolerance would have to be equal to the difference in the axis-to-surface radii at the low and at the high points of the lobe - a big value. And it would not provide meaningful control of any of the functional characteristics of a cam

Certified Sr. GD&T Professional

 

[Vishal2015]

mkcski:
1. Can we use runout on non circular profile like cam lobe?
Can not apply on curve surface...

Please provide your view on below point
2. Can we use parallelism on curve surface?

Thank You.

 

[mkcski]

Vishal2105

Yes you can, ....but..... assuming the cam has width (thickness), parallelism can only be applied to LINE elements on the "face" that are parallel to the axis of rotation (the center of the cam). It cannot be used to control the "contour" of the cam. Assuming there is a roller following the cam, I would avoid using parallel and would highly recommend applying profile of a surface with datums as the primary control and if necessary composite profile to add refinements to the cam contour. I need to see drawings before I can recommend anything more specific.

Certified Sr. GD&T Professional

 

[3DDave]

Parallel applied to "each linear element" is a good use on this cam considering that most cams have line contact with their mating part.

Composite surface profile is a more costly to check to make a similar gain in limiting the gap the line of contact has with the mating part.

 

[mkcski]

3DDave;

I don't disagree but.... there is no defined relationship between each line, i.e. the tolerance on the entire shape. So although each line is parallel, the offset between each of the lines is not and consequently the roller could "jump" from one line to another.

Certified Sr. GD&T Professional

 

[3DDave]

There is always the chance of 'jump' no matter what the callout is. Different callouts and values affect how much that jump is. Parallelism is to refine a profile that has limited 'jump' in order to limit edge loading due to line contact without having to make the entire surface similarly perfect when it doesn't matter. It is easy to make that refinement 10X smaller than the profile if required, but difficult to verify an entire cam surface with a composite improvement of the same amount.