Homebrew PCBs

Stefan Trethan wrote:

> 
> 
>>I think the best approach is like the commercial units. Have the drill
>>under the table. Mine is above the table, but will convert it sometime
>>down the track. The advantage of having the drill come up from the
>>bottom is you have a flat table top to work on, with no drill motor in
>>the way. Of course this means you now must have a means to view the hole
>>location from above.
> 
> 
> I think that has the big disadvantage of the drill lifting the PCB,  
> requiring a hold down foot or firm pressure by hand. I do not see big  
> disadvantages of the upside-down version.
> 

You could be right, I haven't tried it so I don't know. Also the 
comments about the commercial units having a clamp above thats operated 
by the foot pedal also complicates construction for us hobbyists.
Ok, So lets stick to conventional top side drilling. The problem I see 
now is the lens system cannot be perpendicular to the plane of the PCB. 
Did your lens experiment work ok when viewing the PCB at a angle ?
What diameter was your lens ?
How about just a large diameter lens without worrying about a screen ?

I think its important to be able to look at large areas of the PCB for 
course placement and seeing areas that remain undrilled. So this means 
the projection assembly cannot get in too much in view of the whole PCB.