Yes, Ray, as a matter of fact, I do recall that design. Very neat.  PEMs sure,
they can be pressed in no problem and will grab the FRP fine but call it
"personal preference" [and a lot of time spent with machinists who cuss about
their use] as they don't like countersinks so I havce learned not to either!

Counterbores, WELL, that's a different animal entirely.  CB's are great because
you can use a counterbore tool that self-centers itself and you can then bore
exactly the depth you want.  Piece of cake.  Ideal, of course, for my favorite
fasteners, socket head or Torx head cap screws.  I do have to ocassionally use
flatheads but I try to avoid them in favor of counterbored sockets.

Bob

----- Original Message -----
From: Ray Humphrey <[log in to unmask]>
To: Bob Landman <[log in to unmask]>; <[log in to unmask]>
Sent: September 27, 1999 3:15 PM
Subject: Re: Re: [DC] PCB countersunk holes


> 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)
> > > >
> > > >
> > >
> >
>