CR Usage question 3

[Twullf]

We are designing a part for a client. This is a cylindrical body with a threaded counter bored hole. Originally I had the outside edge of the part designed with a chamfer (the client had this on their preliminary drawings). Now they wish for some freedom to make this corner either a chamfer or a radius. To allow this freedom while still constraining the feature they asked for a CR callout.

I am not familiar with this callout and actually had to look it up on the internet, where I got the following definition:

Controlled Radius - creates a tolerance zone defined by two arcs (the minimum and maximum radii) that are tangent to the adjacent surfaces. Where a controlled radius is specified, the part contour within the crescent-shaped tolerance zone must be a fair curve without flats or reversals. Additionally, radii taken at all points on the part contour shall neither be smaller than the specified minimum limit nor larger than the maximum limit.

This does not sound as if it will work the way the customer thinks, but I have never used it.

Is there an accepted way to define a corner feature as either a chamfer or a radius but limiting it to a specific size?

Thanks,

 

[ewh]

I don't think a CR is what they want. I have seen such requests noted as "R.05 OR .05 x 30°"

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[drawoh]

Twullf,

Your requirement is exotic enough that even if there was something in the standard, no one would understand it.

How about a detail view showing the alternate corner? You can implement this in 3D[ ]CAD by having two configurations of the part.

--
JHG

 

[Twullf]

Thanks for the advice, both ewh and drawoh. I'm glad I was not mis-interpreting the CR callout.

 

[pmarc]

I agree that CR, as defined in para. 2.15.2 of Y14.5M-1994 and Y14.5-2009, is not what the client most likely wants.

As for "chamfer or radius" drawing specification, this is quite common practice used in different specifications throughout industry. A letter is used instead of a numerical value and a leader associated with that letter points to the edge. Then additional chart says that this letter is for chamfer or radius and a certain value is given.

The thing is this approach works for 45[°] chamfers. If chamfer is other than 45[°], other ways must be figured out.

BTW, per Y14.5 standard it is not allowed to specify chamfer by a note, like 0.5 X 30[°], for angles other than 45[°].

 

[Twullf]

How are these chamfers supposed to be specified, if they are not 45* chamfers?

 

[pmarc]

If the main viev does not show chamfer (which seems to be the case here), I would probably follow drawoh's suggestion and make a detail view showing exactly what is allowed, and which edge the 0.5 requirement exactly applies to.

 

[KENAT]

I've often seen note like ".05 RADIUS OR CHAMFER" now whether that is explicitly supported in the standard is another matter.

Also becareful with .05*45° type call outs. Depending on how critical the chamfer size is and what tolerance you have on angles you may not get what you want. These days I more often use .05 *.05 type call-outs or dimensions schemes due to this.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ewh]

pmarc is correct... note callouts for chamfers are allowable only for 45° chamfers, and then only on perpendicular surfaces. Other angles need to be detailed to define which side of the edge the linear dimension pertains to.
I claim a brain fart. ;-)

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

 

[pmarc]

Kenat,
If the chamfer (or radius) is really critical, I do not think any of the methods is good option.

Here is the snapshot from ISO 14405-2:2011:

http://files.engineering.com/getfil...107&file=rounding_and_chamfers_ISO14405-2.png

If we additionally notice that the vertical and horizontal edges on figures b) and d) are perfectly straight and perpendicular to each other, while in reality this is quite unlikely to happen, the situation with "traditional dimensioning of chamfers and radii" becomes even more complicated.

 

[CheckerHater]

If customer doesn't care if the edge is chamfer or radius, then it probably not very critical.

Here is an example of "radius or chamfer" interpretation. It is not explicitly endorsed by any standard, more of a common sense (if such exists)rule.