Homebrew PCBs

One possible problem with using a front surface mirror is that due to 
the size of your camera, you may find the the distance from the lens to 
the board surface is longer than if you can mount the camera somewhat 
more in the vein of my previous suggestion of directly underneath.  The 
downside side of mounting with a longer optical path is that the image 
magnification will thereby be lessened and with low resolution webcams, 
this can significantly affect your ability to resolve where your drill 
will hit.  This factor is why I tried to make the lighting very thin and 
get the lens front as close as I reasonable could from the underside.  
As a side note:  By the use of the clear plastic with the drilled hole 
on the top side, even though I'm drilling with the camera underneath, I 
have surprisingly little drill dust coming down on the lens.  Apparently 
the drill acts as a pump and draws the dust up and away.

Another observation: About the technique of putting a marker on the 
screen.  I tried this early on and found that there was significant 
error having to do with the parallax error due to the thickness of the 
glass on an LCD screen.  In my case, I have a thicker than normal glass 
as I have added anti-reflection coated museum quality glass (such as 
used for photo and  painting) mountings. But I also noticed that the 
point seemed to drift -- probably because of camera thermal mechanical 
instabilities.    This thermal mechanism will be worse with the front 
surface mirror due to extra mechanical "stuff"  and that coupled with 
the smaller image of the pads may be something to watch out for.

And a final warning as I mentioned in  a previous post on this subject.  
Watch out when drilling.  As you concentrate on the screen, you can't 
see where your hands are in relation to the drill.  I started drilling 
my thumb -- not a good thing to do.  Now I'm definitely more careful to 
look out and take care that as I move the PCB, that I haven't placed a 
finger in the drill path.

(Also someone requested photos of my setup -- I'll try to get take some 
next week -- I'm tied up with a consulting project right now.)

Regards,
Charles R. Patton



On 6/12/2011 10:08 AM, schenckcharles wrote:
>
>
> Hello Group
>
> I have received many great suggestions. Thanks very much!
>
> It seems like all of them would work. Although bottom drilling seems
> like the most accurate 'manual' method, it would be impractical with 
> my Dremel drill press stand. Likewise, placing a front surface mirror 
> around the drill bit would be mechanically cumberrsome. After thinking 
> about it for a while, I have decided to place an angled FS mirror and 
> CCD camera beneath the drill platform. This setup would have the 
> additional advantage of keeping all elements aligned and would be very 
> easy to calibrate. Although there may be a problem with lighting the 
> underside of the drill platform, my CCD has led illumination. 
> Hopefully, the mirror should serve the dual function of conveying the 
> image and illuminating it.
>
> Yesterday, I mail ordered an FS mirror, got some wood and built the 
> contraption. Hopefully, the contraption should work after the mirror 
> arrives!
>
> Thanks again for all your sage advice!
>
> Cheers
>
> Chris (W1EH)
> --- In Homebrew_PCBs@yahoogroups.com 
> <mailto:Homebrew_PCBs%40yahoogroups.com>, "schenckcharles" 
> <schenckcharles@...> 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
> >
>
> 
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