Pemnuts should be properly designed so that they are seated in a T-hole
with the base opposite the side that the screw enters, such that they
are pulling the pwb towards the screw, and cannot be pulled out when
screwed in place.
And they can be repaired, as Mr. Gregory has stated, and the two part
epoxy should be a part of the replacement. I have found that the
repaired pemnut is much stronger than the original in terms of
resistance to turning inside the hole.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Scott Decker
Sent: Friday, June 09, 2006 1:34 PM
To: [log in to unmask]
Subject: Re: [TN] Reworking PEM nut on PCBA
Peter,
I'm not sure if you can re-use the hole since the PEM will dig into,
(so to speak) the board. I did want to mention that PEM has 2 different
nuts and that one is specifically made for PCB use. If by chance the
wrong nut was used and it wasn't the one for PCB's, maybe using the
correct nut in both PCB application and length, you might get away with
it? One other thing. Is the nut, when tightened, trying to be pulled
into the board or from the board? If into the board, you may only need
to get the new nut to stay once or twice during assembly since the screw
that goes into it will hold it in the PCB? If it's the other way, I
don't know how well it will work/last/hold. Best of luck...
Later...
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee
Sent: Friday, June 09, 2006 10:57 AM
To: [log in to unmask]
Subject: [TN] Reworking PEM nut on PCBA
Does anyone have recommendation on a process to remove self-clinching
PEM nut from the board? An incorrect 4-40 size and 1/4" long nut was
mistakenly installed and needs to be removed and replaced with a similar
but shorter nut.
Would I lose much of the clinching strength by re-using the hole? Is
there any work-around to reinforce the hole to achieve the similar pull
strength as before?
Any suggestion is appreciated.
Rgds,
Peter
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