What is the internal radius of a counterbore?

[v6samurai86]

I've recently been asked to justify why we do not call out the internal radius at the bottom of a counterbore. Generally, we call out the thru hole diameter, the diameter of the counterbore and the depth of the counterbore with no mention of the radius allowed. Is there a standard for this? I've searched and can not find one. I have never seen a radius callout with a counterbore, but I think it is a fair question.

Thanks for any help!

 

[ctopher]

I normally call out R .02 MAX to allow for machining ease.

Chris
SolidWorks/PDMWorks 08 2.0
AutoCAD 06
ctopher's home (updated 10-07-07)
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[KENAT]

We have a note to remove all burrs & sharp edges and give a value (normally a max).

As the corner on the c'bore would otherwise be a sharp edge I'd say this applies. However, I doubt most tolerance analysis we do take this into account.

I thought I'd seen a suggested or typical value somewhere, may have been in Machineries.

KENAT, probably the least qualified checker you'll ever meet...

 

[ringman]

I think this was discussed previously. I believe the consensus was that you should call out the diameters as required and the depth as required and specify the radius. the term (countebore) is not required. Oh yes, control the runout of the larger dia.

 

[MintJulep]

I suspect that the true answer to your question is "historical precedent".

 

[powerhound]

In the 25th edition machinist handbook on page 1466 is a figure that shows the specification of the counterdrill in the bottom of a counterbored hole. I don't know if this is where you were talking about or if you meant the corners where the wall intersects the floor of the counterbore.

Why do you have to justify not doing it? Shouldn't they justify why it should be done if they are the ones that want it implemented?

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[v6samurai86]

OK, thanks for the replies. It sounds like there isn't a "standard" for this.

Yes, I am referring to where the wall of the CB diameter meets the floor of the CB. I've never seen a radius specified for this, but it sounds like it is needed. I need to justify it because someone noticed it isn't dimensioned and therefore the drawing is incomplete unless I can argue otherwise.

 

[ctopher]

If not dimensioned, it can vary based on the cuting tool. I call out a max dim that is bigger than the tool radius.

Chris
SolidWorks/PDMWorks 08 2.0
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[v6samurai86]

So do you also show a section view to show the radius? Or is it added to the CB call out?

 

[ctopher]

There is no need to show the radius unless you have to. If so, show a section view and add a note with leader (separate from the CB callout).

Chris
SolidWorks/PDMWorks 08 2.0
AutoCAD 06
ctopher's home (updated 10-07-07)
ctopher's blog

 

[WHITMIREGT]

Usually, I make the diameter of the CB extra large to permit a tool radius and eccentricity to the through hole, but they are not specified. If a radius is specified, it will require time consuming inspection. If the design is critical where I cannot rely on good workmanship or if the parts are going to be made in another country, I add the information.

 

[ringman]

The radius should be sufficient to clear the side of the head of the screw used in the hole.

 

[Xplicator]

For guidance here, see para. 1.8.11 and Fig 1-36 in the Y14.5M standard , the radius is specified in a section view.

However, I do not find this necessary and I have always included a note like the one KENAT gave or perhaps use this "Unless otherwise specified, all tooling radii to be MAX R___."

One way or another however, I do specify or cover it.