Homebrew PCBs

Steve, or anyone,  I suspect that the distance between the print head 
and the PCB is critical.  I suspect most folks are like me, you use 
the PCB material you can get and lately I have been buying off E-Bay 
at really good prices.  However, the thickness varies. 

So, I am planning my mechanical conversion to be adjustable to 
accomodate the various thickness PCB materials.  I suspect this could 
add a lot of complexity in the conversion process, but if I have time 
I want to do it.  I just don't have any idea what would be the 
acceptable range between that print head and the PCB material being 
printed - anyone?

CHris