Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Hi all,

I'm about 80% of the way towards getting my CNC mill up and running,
will eventually be able to feed it a JPEG/GIF/PNG file of the PCB
artwork, and it will cut the tracks, auto-detect the holes from the
artwork and drill those too, using a narrow-tapered conical diamond bit.

The completed unit will have a total desktop footprint barely larger
than a sheet of A3 paper.

All reasonable IMHO for a final parts cost circa US$150 all up.

The X-Y tracks have been a pain though. As someone who's very skilled
with software, reasonable with hardware but largely clueless with the
mechanical engineering, this has been a pain.

What I've got for each X and Y direction is an aluminium platform, with
lengths of aluminium angle bracket along the short edges, riding on top
of aluminium angle bracket, shown below as cross-sectional view, excuse
the rough ASCII graphics:

∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗∗ PCB
///////////////////////////// chipboard to absorb drill
================================ upper platform
+---- ----+
| _ |
| | / \ | | upper rail
| | \_/ | |
| |
----+ +----- lower rail
===================================== lower platform

(circle in middle is threaded rod, driven by unipolar stepper motor).

With liberal spraying of CRC lubricant (will grease it later), the top X
and bottom Y platforms are moving freely enough for the stepper motors
to be able to turn the threaded rods (@ 1:1 gearing) through the full
movement range in both X and Y directions. Getting reasonable movement
speed, rotational/translational stability, plus precision of around 0.04mm.

But at some time, I would like to replace this crude abomination with
something similarly simple but better.

Can someone recommend better ways to do the tracks, using inexpensive
and easily available materials that don't need specialised tools to
deploy? Preferably materials which can be easily sourced in a small city
without 8 hours searching the Yellow Pages?

(The other extreme is ready-made precision linear bearing parts, but
these are hideously expensive within NZ).

All ideas appreciated.

--
Cheers
David