Hi Chris ( & the rest of us on this issues )

On one of my previous projects I've got just that requirement = almost
flush base cut .
Tried all sorts of tungsten blades , super thin grinding disks on hyper
speeds with vacuum take off ;
costly unsafe unrepeatable , you know it all .
What we finished up with was in-house build rig consisting of a high
speed diamond blade with >polished< top (Teflon coat if you feel
extreme) gliding on geared time feed ( or lever if you have a girl with
feel, don't give it to guy) below few chrome steel separating wires
(.020 gauge in your case) on which the pcb is resting (in a nest ;
unless you designed tool holes for top clamp fingers) .
Both top touch clamp and bottom blade mounted with silicon foam
suspension to ensure positive but gentle action
If you design the top clamp on grid > you can change the fingers
position according to your top geography ; say if you have 8 slits
running from a center to glide & lock clamping fingers easy to a free
spot on board .
The wires we >tensioned< with cam lock lever ( piano wires & mechanics
may do you )
Again, keep the cams sliding > so you can adjust wires in between the
bottom topography on different boards .
Check the status of separating wires periodically , the constant
polishing kills them eventually
If you have them on reels > just unlock the cams , pull fresh length in
, lock again .

Let me know if get stuck .

See you
Paul Klasek
http://www.resmed.com

> ----------
> From:         Chris_Smith[SMTP:[log in to unmask]]
> Sent:         Friday, 17 July 1998 4:39
> To:   [log in to unmask]
> Subject:      [TN] Lead Trimming Question ?
>
>      All,
>         I have a lead trim operation that uses a Q-corporation LOM II
>      trimming system with a vacuum fixture.  We are using the standard
>      cutting rings with a 30 degree angle.  The Vacuum fixture being
> used
>      is quite snug and there is very little vacuum loss in the
> process.
>         The issue I have is the height requirement we're trying to
> meet is
>      .020" max length.  This strict requirement is resulting in pcbs
> being
>      cut into and damaged, some flagging, and some solder fractures.
> This
>      seems to be a very operator dependent operation and costly if not
> done
>      correctly.  I have tried varying the speed the cutter is moved
> across
>      the board, having Q-corp sharpen the blades instead of us doing
> it and
>      using a QB-1 PCB brusher which was purchased for this product.
>         Is there anyone out there with a similar trim height
> requirement
>      and what types of things do you perform to insure a repeatable
>      process?  Also anyone with suggestions please let me, I need to
> get
>      this resolved if at all possible.
>
>      Thanks
>      Chris Smith
>      Manufacturing Engineer
>
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