Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Bob_xyz" <bob_barr@h...> wrote:
> How much do the collars vary in thickness? Might it be workable to
> add shims to make all of the collars the same thickness?
Alternately, 
> could the thicker ones be lightly sanded to make them the same
height 
> as the thin ones?
> 
> Regards, Bob
> 
> --- In Homebrew_PCBs@yahoogroups.com, "Andrew Mawson" <andrew@m...> 
> wrote:
> <snip> 
> 
> >I sat down to design a screw device to force the drill through the 
> > collar until it touches a contact and lights an led, but then
> > realised 
> > that the collars vary in thickness and the critical reference is 
> from 
> > the TOP of the collar to drill tip.
> > 
> > AWEM

The top HAS to be the reference as in fact it rests against a
shoulder 
on the collet to set the position in the spindle. Settting the Z
height 
for each tool isn't an option as I'm using a Heidenhain controller on 
a 
Bridgeport Interact 1 CNC mill, and although tool lengths can be set 
individually when called this is not the case in the event of a 
breakage. Variation in collar thickness isn't much - maybe 0.1mm max 
but enough to spoil your day if you are isolation milling pcbs ! If 
it were just drilling holes it could be ignored and allowed for in 
the sacrificial underpad.

AWEM