Sorry, Bob, but I do not agree with your assessment.  Sometimes, a
counter-sink or counter-bore hole is the only or best option.  Many times, I
have designed DUT boards (usually, 0.125" thick) with counter-sunk holes for
fixture attachment.  Also, counter-bored holes that have PEM nuts installed
by the PCB fabricator are common.  I have had no problems with depth, angle,
fit or function.  (Just make sure your fab drawing is clear and accurate.
Remember the one I sent you?)

Ray

----- Original Message -----
From: Bob Landman <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 27, 1999 10:53 AM
Subject: Re: [DC] PCB countersunk holes


> Jack,
>
> I wouldn't do a countersink hole on a PCB.  What is it for?  The laminate
is
> nicely sealed by the top layer of resin.  If you c'bore, you dig down into
> laminate and end up exposing the glass mat - nasty stuff.  I do a lot of
> mechanical stuff and countersinks are the worst kind of hole - depth is
very
> difficult to control - the bottom of the hole can break out and then the
flat
> head screw bottoms out into whatever you are fastening to.  If the screw
must be
> flush, then I suppose you have to do it and take your chances but in .062
> material - that's not going to be good odds.  A split washer and a
Phillips or
> socket head cap screw is a better choice, esp, if you solderplate one of
the
> holes for a mechanical ground.
>
> Heck, my machinist can't set a C'sink that well with a Bridgeport milling
> machine on aluminum!  Chatter and such make the job really iffy.
>
> Bob Landman
> H&L Instruments
>
> ----- Original Message -----
> From: Gfranck <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: September 27, 1999 10:50 AM
> Subject: Re: [DC] PCB countersunk holes
>
>
> > Jack,
> >
> > One other gotcha... all the other comments have been good, especially
use a
> > unique hole symbol.  You gotta do that.
> >
> > Fab suppliers like to drill the unplated holes on the rout machine.  The
> > counterbore requires some z-axis (depth) control, so they will move the
board
> > to the drill machine to do the c'bores.  Don't let them do this.  They
can
> > introduce all kinds of registration problems between the center of the
c'bore
> > and the center of the hole.  Make sure your suppliers know to drill the
> > unplated hole and c'bore on the same machine with the same set-up.  Been
> > there, done that, not pretty.
> >
> >
> > Jack Olson wrote:
> >
> > > I have never been asked to provide countersink mounting holes on a PCB
> > > before.
> > > Since I have never had a drafting class, can I ask if any of you
typically
> > > do this?
> > > I was just going to add a note to the fabrication dwg saying:
> > >
> > > x.) Countersink mounting holes (8X) 82 degrees x .230 on component
side.
> > >
> > > Is this adequate?
> > > Are there any "gotchas" I need to keep in mind?
> > >
> > > Jack (the new guy)
> > >
> > >
> >
>