Homebrew PCBs

I agree with you. But those better machines are a bit
more than $439....;)

But again, I haven't milled any circuit board material...
still yet...because of those very concerns. It's a thing
that'll take a good bit of practice to get good at.

I do think, though, that I've come up with a pretty good
fixture idea that should work very well.

Here's the finest example I've seen at cnc milling on
one of my early machines....

http://www.youtube.com/watch?v=lhdqBrciQZU

Phil CA glues the board to the thick aluminum plate. To
be released later with some acetone.

The fixture I have in mind would be a, say, 1/2" thick
aluminum plate, but it'd have a layer of 1" thick cast
urethane on top of it as the work surface.

The aluminum plate would allow repeated fixturing without
distortion of the urethane.

(Castable urethane...similar to acrylic in hardness, but it
doesn't melt like acrylic plastics can. Machines like a dream.

http://www.alumilite.com/ProdDetail.cfm?Category=Casting%20Resins&Name=Alumilite%20Regular

)


The urethane layer would be planed/leveled relative to the
bridge. The board glued in place with a tiny bit of CA
glue...no more than is needed.

The urethane is very chemical resistant, so the board can
be released like in the video....maybe have some grooves cut
into the surface to allow the acetone to flow underneath
the PCB easily.

Reason for the urethane is that it's Much easier to machine
than if it were aluminum. It can be replaced...or even resurfaced
as urethane sticks extremely well to itself.

It can be drilled into with no wear or damage to the cutter/bit.
And can be re-leveled to be perfectly flat relative to the bridge
repeatedly if need be. Even pockets can be made as registration
places for repeated alignment of successive copies of a milled
board.

When I run across someone who's getting good at milling
PCB's, I'll make them one to test and see where it needs to
go from there. I think that's as near perfect of an as needed
dead flat surface as can be inexpensively produced. Until it
gets refined anyways....;)

I'd expect it to work very well.

:)
John




> My biggest problem with cnc of pcbs, especially with triangular bits 
> is that the pcb material is not even thickness, and more importantly 
> does not lie flat. This causes traces to be uneven, areas to be not 
> cut at all, and some gouges. The better pcb routers "test" the board 
> before cutting and compensate for these things as they cut.
> 
> Mark