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Countersink dim

Countersink dim

Countersink dim

(OP)

 
The question is Countersink dim. for a 4-40, 100 deg. c'sink
 
Helical sharp dim. for this screw is .225
 
print size callout is .231 + - .005  =  .226 to .236
 
is this a aerospace standed
 
the low end seams to close to helical Max dim. of .225
 
or a case of lazy engineering, just use =   + - .005
 
 

 

RE: Countersink dim

(OP)
What's the position tolerance or equivalent on the hole?


+ - .005

What's the assembly condition, fixed or floating?

Fixed

What's the primary design consideration, flush head?

Flush


 

RE: Countersink dim

So, as it's fixed, what is the position tol on the mating part hole, .005?

If .005 this corresponds to pos tol dia .014 (give or take a tenth of a thou)

So, to guarantee flush you need the minimum counter sink size to be the 'max sharp diameter' of the screw head, + pos tol of csk hole + post tol of threaded hole.

So if your numbers and my assumptions are correct that'd be:

.225+.014+.014 = .253 minimum.

My guess, it's a case of lazy/uneducated engineer.

Note - that while this guarantees flush, it does not optimize stress under the head or anything else, just guarantees the head should always be flush or below flush.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Countersink dim

(OP)
Thanks Kenat

You put in black and white the hole picture as I also see it

Dockken

RE: Countersink dim

Sharp as ever there, KENAT.

"Good to know you got shoes to wear when you find the floor." - Robert Hunter
 

RE: Countersink dim

(OP)
They have been making it for year that way
If I get an opportunity will try, but they are reluctant to change
 

RE: Countersink dim

Well there's the rub, because of how good a lot of C&C processes are these days etc they're probably hitting near the middle of the tol ranger fairly repeatedly.  The above is for worst case.

Plus the head of the screw and/or the material it's going into probably deform a bit.

Plus, unless they're really looking for it they may not notice heads just a few thousandths above flush.

However, there are situations where not being truly flush, or generating more stress under the screw heads can be a real problem.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Countersink dim

(OP)
The part is machined to size and thinkness and drilled, 6 to 12 holes per part, may be 20 to 50 parts, but the C'sink is done manualy

dockken

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