Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

Register Log in
  • Congratulations MintJulep on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Countersunk Holes and Implied 90 3

Status
Not open for further replies.
engAlright

engAlright

Mechanical
Joined
Jun 12, 2003
Messages
240
Location
CA
Section 1.8.12 of Y14.5-2009 indicates that for countersunk holes "...the diameter and included angle of the countersink are specified.".

In the corresponding figure 1-39 the countersink feature is shown dimensioned with a 90° angle.

Why is an angle dimension required when the included angle is 90°? Would an implied 90° angle (section 1.4i) not apply? This is the only instance I can think of where a 90° angle needs to be shown on the drawing.

Thanks!
 
Sort by date Sort by votes
The implied thing about implied 90° angle is that it is only implied when the right angle is formed by a horizontal and a vertical line.
 
Upvote 0 Downvote
Burunduk,

Would you consider a complete definition of the c'sink if only the hole is defined for its location (fig 1-39)?
Example: Ø6.8 ± size tolerance and position|Ø.xxx|A|B|C|


 
Upvote 0 Downvote
Burunduk said:
The implied thing about implied 90° angle is that it is only implied when the right angle is formed by a horizontal and a vertical line.
Click to expand...

The verbiage of Fundamental Rule (j) doesn't say anything about the relationship of the two lines to the horizon. Only to each other.
See Fig. 7-21 of the 2018 standard for an example of implied 90º where the lines are neither vertical nor horizontal. It's rule (k) in that case, but the same as Rule (j).
 
Upvote 0 Downvote
engAlright,

Ask yourself this - whats the chances you think someone will call you up to confirm if two surfaces at 90deg on the drawing (but aren't labeled) are at 90deg? My guess is pretty much nil. Okay, what about if a 90deg countersink is also not labeled? I would say much higher, considering 82deg is a very common countersink angle, and trying to tell which is which by eye would be tough without a side by side comparison or 3D model to measure from. Its best to be as explicit as possible on your drawings, and try to avoid ambiguity wherever possible.
 
Upvote 0 Downvote
It's a novel interpretation to use on a countersink. Normally it's considered for situations where there is an intersection between the related surfaces, not for elements of one to other elements on itself. I suppose it goes that a point on a sphere taken as a pole is at right angles to all the points on the equator relative to that point.

I don't recall often seeing a countersink depicted as having intersecting sides, at least not by direct contact (an inverted cone cut) or via extension lines, so it doesn't exactly fit, but neither would it fit if there was a chamfer shown on the edge of a rectangular part that cause a similar depiction.

More concerning is that there's no control that the axis of the countersink is parallel to that of the hole, a case I have seen in junky parts and which neither the diameter or position tolerances (when applied) do a great job of restricting - fortunately metal and plastic can bend.
 
Upvote 0 Downvote
Belanger said:
The verbiage of Fundamental Rule (j) doesn't say anything about the relationship of the two lines to the horizon
Click to expand...

Yes, it doesn't say... that's why I said "the implied thing about implied 90° is that it is only implied when..." [wink]
But apparently less so according to the 2018 standard. If one line of the countersink section is at 32° to the horizon of the view and the other one is at 122°, can you tell at a glance from looking at it that the included angle is 90°? I would personally not be sure. Anyway, I also agree with chez311.
 
Upvote 0 Downvote
Still disagree with you. I'm not really referring to countersinks; I am taking issue with your general statement: It's not even implied that implied 90º angles requires horizontal or vertical lines. You're introducing something that is not even remotely intended by Y14.5.
 
Upvote 0 Downvote
greenimi said:
Would you consider a complete definition of the c'sink if only the hole is defined for its location (fig 1-39)?
Click to expand...
Only if the dimensions and tolerances are given the way they are in fig. 7-24, only with the counterbore symbol replaced by the countersink symbol. A countersink is a cone, and it may be a gray area whether a countersink location can be controlled by position, but the only other option is profile, and we don't see that often for c'sinks.
 
Upvote 0 Downvote
Belanger,
I would agree that where there is a physical corner between surfaces (not c'sinks) the implied 90° is clearer regardless of whether the lines are horizontal/vertical or not, so maybe I shouldn't have generalized.
 
Upvote 0 Downvote
engAlright,

I walked into a hardware store here in Canada and I asked for a 90[°][ ]countersink. They stared at me like I was a space alien from the planet Zorklon, and they reminded me that countersinks are 82[°]. They can also be 60[°], 100[°], or 120[°].

You need to call up the angle.

--
JHG
 
Upvote 0 Downvote
Do you want to get what you need? Or just what you end up with?
 
Upvote 0 Downvote
drawoh said:
I walked into a hardware store here in Canada and I asked for a 90° countersink. They stared at me like I was a space alien from the planet Zorklon, and they reminded me that countersinks are 82°.
Click to expand...

Yeah, that hardware store needs to get with the program. A 90 degree countersink is as common, if not more common these days, as an 82 degree. 82 degrees is the included angle for imperial unit flathead screws and 90 degrees is the angle on metric flathead screws. Things here in the US are moving more and more towards metric so those things are in every machine shop I've worked in for the past 30 years.

John Acosta, GDTP Senior Level
 
Upvote 0 Downvote
Thanks for the responses everyone. I appreciate the recommendation to add the 90° angle for clarity, but that could be said about any 90° angle on a drawing. There are many instances where geometry lines or centrelines do not intersect but an implied 90 applies: see Fig. 7-21 of the 2018 standard as mentioned by Belanger.

In this instance I think it's fair to assume an implied 90. If the countersink was 82° an angle dimension would be required. Since no angle is shown, we assume an implied 90 applies.
 
Upvote 0 Downvote
How do you guys usually specify the tolerance for a countersink angle?
For me it is one of the exceptions in which I still use direct tolerances on angular dimensions.
 
Upvote 0 Downvote
engAlright,

In Ontario, if you don't specify your countersink angle, it will be assumed to be 82[°]. Another possibility is that a machinist will pick up the phone and call you to ask for the correct countersink angle, wasting both of your times. He has to pull the correct tool off the shelf.

--
JHG
 
Upvote 0 Downvote
I'd want to be very sure to understand what the c'sink is used for. Sometimes the angle is important, and definitely not 90°.
Like powerhound said, the c'sink angle needs to properly match imperial vs metric flat head screws.

A less frequent C'sink use for us is the chamfer on the clearance hole under a SHCS etc to miss the screw underhead fillet.

Machine center c'sink 60°.

Lugnut seats 45° or 60°. Better get that one right.
 
Upvote 0 Downvote
not calling out the angle and symbol is just laziness
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

franhd
  • Locked
  • Question Question
Basic Dim on Series of Holes
Replies
10
Views
4K
3DDave
3DDave
Gaganaut06
  • Locked
  • Question Question
Call out for a pattern of concentric holes
Replies
11
Views
5K
Gaganaut06
Gaganaut06
K
  • Locked
  • Question Question
Stumped on GD&T Position Holes Multiple Bends/Planes
Replies
9
Views
2K
jassco
jassco
C
  • Question Question
Symmetric to Centerline note is given to below drawing attached, need to understand how manufacturer will punch the holes at what tolerance.
Replies
16
Views
26K
Burunduk
Burunduk
YNIEH
  • Question Question
Dimensioning and Tolerancing Block ASME Y14.1
Replies
2
Views
607
3DDave
3DDave

Part and Inventory Search

Sponsor

Back
Top