Homebrew PCBs

I have an old small miniature precision drill press.  I drilled a 3/8" 
hole on centerline with the drill bit and cut a pocket in the underside 
of the  base plate and put a piece of 1/8" thick plastic in the pocket.  
The plastic also has a 3/8" hole in line with the baseplate.  I lined 
the hole in the plastic with 3 white SMT LEDs cocked to throw their 
light up through the hole.   Next I took a cheap ($10) webcam that has a 
lens that can be hand adjusted to focus at about 1/2"  (Just keep 
screwing it out until it focuses on a board placed on the top side of 
the base.and pressure loaded it into place with a spring loaded clamp 
(made from 1/2 of a small desk fan clip-on clamp.)    There is still a 
problem in that the "boresight" will be likely  be twisted in relation 
to the flat of the lens.  I.e., when you look at the drill come down 
toward the lens, it will look like it is coming from one side or 
another.  The solution I arrived at to circumvent that (as I tried to 
physically adjust it, and it was just too much of a pain) is take a 
vacuum formed transparent carton of about 0.010" thick sheet such as 
sold in the grocery store that contains fruit like tomatoes, cherries, 
strawberries,  etc.  Cut out a clear, un-molded portion (typically in 
the lid) and preferably about  twice as big as the board you want to 
drill.   Tape it on the top side of the baseplate with a clear section 
over the 3/8" hole the camera is looking up through.  Set the drill to 
down stop just after drilling through this plastic (so you don't hit the 
lens below) and drill a hole with your smallest intended drill.  Now, 
although the drill moves through the image, the hole in the  plastic is 
fixed and exactly where the drill will be.  Put your PCB with the traces 
face down on the baseplate and center a spot you want to drill in the 
center of that hole.  Drill.  You' can easily drill within  0.005" or 
even better if you want to take the time, with no problem.  The 3/8" 
view allows you to see traces around the hole and allow you to know 
where you are on the PCB.

The particular web cam I used was a"Gear Head" unit that comes with 
AmCap software.  It is fairly low resolution, and noisy, but it has in 
addition to the screw lens with enough throw to focus close, the 
capability of having the left-right, up-down reversed in the AmCap 
software.  So when I slide the PCB left, the image moves left.  This 
definitely makes like easier.

Regards,
Charles R. Patton

  . On 6/9/2011 1:16 PM, Bruce Parham wrote:
>
>
> > Hello Group
> >
> > I have a quick question about precision drilling of home made PCBs.
> >
> > Because of poor eyesight, I use a CCD microscope next to my Dremel
> > Model 300 drill press stand. Although this set up is a big improvement
> > over doing thing solely 'by eye', there is a parallax error introduced
> > between the location of the retracted drill tip and where it 
> eventually comes in contact with the PCB. Once I saw a milling machine 
> where one
> > was able to sight straight down into a bulls eye. Is there a way to
> > rig mirrors to do this?
> >
> > P.S. Sincle sided boards are no problem, as I can hold them up to
> > strong light and position a hand held rotary tool with good enough
> > accuracy.
> >
> > Any suggestions would be appreciated.
> >
> > Cheers
> >
> > Chris
> >
> Hi Chris,
>
> You might try to find a metallic first surface mirror that you can
> drill a small hole into on a 45 degree angle
> and mount onto your drill stand with the drill bit going through the
> hole. Position the camera so it looks into
> the mirror from the side and down the drill via the mirror.
>
> A less elegant method is to use two point source lights (small halogen
> desk lamps) mounted 90 degrees apart
> and pointed toward the drill tip. As the drill tip approaches the board,
> the shadows will converge on the target.
>
> Bruce
>
> 



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