Homebrew PCBs

Phil wrote:

> please help me understand why 600 is so good.  I'm not disputing it, 
> mind you but it seems kind of at the edge.  If I am doing the math 
> correctly, a 10 mil trace on a 600 DPI device is 6 dots wide.  8 mil 
> is less than 5 dots.  That seems kind of tight to me but maybe its 
> ok.  With my ink jet (1440 dpi) and copier (not sure what its 
> effective DPI is but its pretty high), I get really clean traces even 
> at 8 mil. I can get them to transfer but am fighting smearing which I 
> believe to be due to poor temperature control.  
> 

   Note that there is more than one resolution at work.  The drum has a very 
fine coating, and can have very accurately placed edges, well beyond the print 
resolution of the toner.  Your lines and text have nice smooth edges, so you 
think you have high resolution.  I bet if you try and copy even just 100 
vertical lines with 100 vertical spaces in an inch, you will get a total mess. 
You're fighting smearing because few copiers have high resolution toner, you are 
simply smashing your large toner particles in the transfer.  600 DPI printers 
have a smaller particle size, I get little if any smearing from my prints even 
though ironing by hand with a wide range of temperature and pressure.  Don't mix 
the copier's high edge resolution (from being analog) with it's poor dot 
resolution from having lower grade toner.  Very few copiers have good fine 
toner, it's not generally required to make an ok copy.  Copy a nice curvy line 
and the edges will look smooth and high res.  Copy two fine matched curve side 
by side lines with fine spacing and you'll likely only get one curved line out 
of this same copier, or two lines with lots of blobbed joins.