It is our practice to test designs for strain. This includes screws in 
mounting holes of boards to enclosures. This sounds like a reasonable 
clearance for applying a screw. If you are pressing in Pem's I would 
suggest you test the strain, as this clearance is likely too little for 
that application.

Your DFM rules should maintain keepouts from mounting screws, Pem's, panel 
tabs, v-scores, etc.  Test any situation that violates your keepouts to 
ensure the strain limits are not exceeded.



Roger Mack  P.Eng. 
Manufacturing Specialist
Parker Hannifin Electronic Controls
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB  R3T 1T4 Canada 
direct 204 453 3339 x373
[log in to unmask]
www.parker.com/ecd







From:
Ian Hanna <[log in to unmask]>
To:
[log in to unmask]
Date:
11-16-2010 11:11
Subject:
Re: [TN] Military PWB drawing note "CRUSH ZN"
Sent by:
TechNet <[log in to unmask]>



more likely refers to the condition -after- assembly -- is there a PEM Nut 

or other type of compressed fitting installed?





Steven Creswick <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
11/16/2010 12:00 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steven Creswick <[log in to unmask]>


To
[log in to unmask]
cc

Subject
Re: [TN] Military PWB drawing note "CRUSH ZN"






David,

My suggestion is that they are allowing for laminate damage [crush zone]
within a 0.250" diameter around the hole. 

As you make a countersink or counterbore a hole you will end up tearing up
the laminate.

Sharp tools - change often


Steve Creswick
http://www.linkedin.com/in/stevencreswick




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Paluck
Sent: Tuesday, November 16, 2010 11:34 AM
To: [log in to unmask]
Subject: [TN] Military PWB drawing note "CRUSH ZN"

I'm working with an military PWB fab drawing from 1994. It contains a note
saying "CRUSH ZN .250 DIAMETER" with an arrow pointing to a countersunk or
counterbored hole. Can anyone tell me exactly what this means?
Thanks




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