Best Way to Tolerance a Cylindrical Section on a Part (Customer's Design and Drawing)

[achorste]

Hi all,

I'm not sure if I'm in the correct forum section here, butit seemed the best choice I could see, but anyway - I was looking for some advise from the experts:

We have cylindrical section on on of our parts we make for a customer (it's the customer's design and drawing). We have have an issue with the diameter of this cylindrical section at one point (undersize).

The drawing itself defines the diameter at one end of this cylinder, but does not mention any other points.

What would be the best way to identify on a drawing that the diameter (and tolerance) applies to the whole cylinder and not just at one point?

I've considered cylinricity for this purpose, but from what I can remember, this doesn't define the diameter (for example if the diameter was at bottom limit at the top section, applying cylindricity to the whole cylinder would allow for the product to be undersize at other sections).

Any help would be greatly appreciated!

 

[Stijloor]

Re: Best Way to Tolerance a Cylindrical Section on a Part (Customer's Design and Draw

Hi all,

I'm not sure if I'm in the correct forum section here, butit seemed the best choice I could see, but anyway - I was looking for some advise from the experts:

We have cylindrical section on on of our parts we make for a customer (it's the customer's design and drawing). We have have an issue with the diameter of this cylindrical section at one point (undersize).

The drawing itself defines the diameter at one end of this cylinder, but does not mention any other points.

What would be the best way to identify on a drawing that the diameter (and tolerance) applies to the whole cylinder and not just at one point?

I've considered cylinricity for this purpose, but from what I can remember, this doesn't define the diameter (for example if the diameter was at bottom limit at the top section, applying cylindricity to the whole cylinder would allow for the product to be undersize at other sections).

Any help would be greatly appreciated!

I always start with asking what dimensioning standard does apply to your customer's drawing? Do you know?

Stijloor.

 

[Dave Dunn]

Re: Best Way to Tolerance a Cylindrical Section on a Part (Customer's Design and Draw

Hi all,

I'm not sure if I'm in the correct forum section here, butit seemed the best choice I could see, but anyway - I was looking for some advise from the experts:

We have cylindrical section on on of our parts we make for a customer (it's the customer's design and drawing). We have have an issue with the diameter of this cylindrical section at one point (undersize).

The drawing itself defines the diameter at one end of this cylinder, but does not mention any other points.

What would be the best way to identify on a drawing that the diameter (and tolerance) applies to the whole cylinder and not just at one point?

I've considered cylinricity for this purpose, but from what I can remember, this doesn't define the diameter (for example if the diameter was at bottom limit at the top section, applying cylindricity to the whole cylinder would allow for the product to be undersize at other sections).

Any help would be greatly appreciated!

As Stijloor mentioned, it could depend on the standard that the drawing is made to, but per ASME 14.5M if there's not a note on the dimension (such as x plus draft, x minus draft, at theoretic sharp corner, etc.) then the dimension as you described it already applies to the entire length of the feature.

Cylindricity measures the form of your cylinder, but does not control the size. If you picture two theoretically perfect cylinders that run parallel to each other that encompass all the surface points of your part, the distance between the two theoretic cylinders is the cylindricity value. Since the standard plus/minus tolerance already controls form as well as size, adding cylindricity only has an effect if the cylindricity tolerance is smaller than the total dimensional tolerance. This is called refinement of form.

According to ASME14.5M, Rule 1 states:
“Where only a tolerance of size is specified, the limits of size of an individual feature
prescribe the extent to which variations in its form – as well as in its size- are allowed.”

 

[bobdoering]

Re: Best Way to Tolerance a Cylindrical Section on a Part (Customer's Design and Draw

It's also good to know the usage of the part. Sometimes the print is not clearly dimensioned in spite of the dimensioning standard the customer used. Is it a fit or mating part? True position to MMC meaningful? How do they intend to test it? Pins? CMM? Makes a difference....thanks to fit.

How it is used and how the customer intends to qualify the part should be on the top of your list of questions.

 

[dgeesaman]

Re: Best Way to Tolerance a Cylindrical Section on a Part (Customer's Design and Draw

It's also good to know the usage of the part. Sometimes the print is not clearly dimensioned in spite of the dimensioning standard the customer used. Is it a fit or mating part? True position to MMC meaningful? How do they intend to test it? Pins? CMM? Makes a difference....thanks to fit.

How it is used and how the customer intends to qualify the part should be on the top of your list of questions.

Agreed. If it's a post or a through-hole, they may be using only one end of it as a pilot, and the rest of the cylinder is a manufacturing simplification. In these cases it's helpful for the designer to use a tolerance zone.

David