Homebrew PCBs

Stefan,
        Drill Rod is cheap and very accurate. You will then need a 
bushing to ride on it. The bushing can be a block of nylon with a 
hole in it. The problem is you might not be able to find a drill bit 
that will produce the correct hole. But that would be a first test. 
You could also hack old printers. You have to test the waters.
        The biggest hurdle is software. Are you going to work in 
Metric or Inches? Then on to the threaded rod. It needs to be fine 
not coarse. I use 20 tpi rod. With a 200 step motor that devides and 
inch by 4000 steps. 20 tpi with a 200 step motor gives a nice .00025 
inches per step. This makes all IC pin centers and connectors dead 
on. A Metric rod with a 200 step motor will produce wacky fractions.

                                        John  




--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan 
<stefan_trethan@g...> wrote:
> well, john, you said you are willing to discuss pcb mill here.
> so what i ask you to discuss maybe it the quality of rail surface.
> 
> i saw some of your designs (and the designs of others) use some sort
> of common pipes or steel profiles.
> 
> especially i saw gass pipes at your page... i wonder which surface 
quality 
> they have.
> I have lots of pipes and sqare stock here, but i have no idea how 
smooth 
> and plain the surface needs to be.
> 
> obviously professional machines only use precision ground surfaces. 
but how 
> much is needed for accurate milling?
> 
> it is hard to describe a surface quality, maybe you can find a way.
> how looks it when you put a straight edge against these pipes? is 
there 
> light shining through?
> are these welded pipes?
> 
> the european pipes may differ from your pipes, and there are lots 
of 
> different surfaces available.
> 
> 
> have you ever had problems with these rails? i mean precision 
problems.
> 
> thanks
> 
> st
> 
> (by the way - don't you use a car for some reason? i mean you write 
a lot 
> about walking here and there and so on..?)