Re: PCB routing with CNC milling machine....

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:

> On Mon, 2003-10-27 at 10:46, Jon Elson wrote:
>
> > The Gerber file IS "gcode", alias RS-274D. It is in a very

specialized

> > style,
> > with suppressed leading zeros and no decimal point.
>
> OK, good to know that.
>
> > The original Gerber
> > photoplotters used off the shelf CNC controls to move thew XY

stage,

> > and therefore were programmed in Gcode.
>
> That makes sense.

Jon keeps posting this nonsense and misleading people into thinking
it is just a snap of the fingers to be able to write your own CNC
machine programs from Gerber files. Note: Extended Gerber is not G-
code as used for CNC machining. It is not documented in the RS-274D
standard, but rather RS-274X, which is a whole different bird. The
flavor used by most modern creators of Gerber files does not even
match the RS-274X standard, and most differ considerable between ecad
design programs. ( ecad- electronic cad design program, ie Eagle, etc)

RS-274X is available for download from the web.

There are several issues that the free and most of the expensive e-
cad programs do not address:

1) drilling and spot drilling for hole location
2) mirror image for the bottom sides of the boards
3) offset for tool size and detection of overlapping toolpaths if
somebody mistakenly uses a 1/8 end mill instead of a 60 degree
engraving point.

Both DeskPCB $95 and DeskCNC $300 have these capabilities, and both
can also save the trace outlines as DXF files, if you want to do
additional routing or processing of the data.

http://www.imsrv.com

Some issues for consideration in making a machine to mill PCB's are:

Spindle speed. The cutter action area is a very small diameter and
even though the board material is very abrasive and has a low
machinability rating, the tiny cutter diameter dictates a very high
spindle speed to enable cutting, rather than dragging, through the
material. Very few have reported any success at speeds below 10,000
rpm, and 20,000 - 30000 rpm is usually much better. Higher speeds
require expensive spindles that are not really within the budget of
most hobbyist/home shop users.

Material flatness is also an issue. The boards should be clamped to
a stiff, flat surface. They will flex a lot, and edge toe-clamping
will suffice for small boards. For larger boards 12 x 12 and up, you
should plan on a good vacuum hold down system. Surface contact height
adjustment (like a sewing machine foot) is not as useful as with
engraving, due to the fragile nature of the thin traces left behind.

Machined boards are usually easy to spot because of the wide expanses
of unconnected copper that are left behind. It is really only
necessary to isolate the traces and not to fully remove the copper
cladding in between, as is usually done with chemical etching
processes. Sometimes this material is removed. For most of us in
the CNC metal machining world, this is done with pocketing. Some may
be familiar with the term "erasing", which is essentially the same
process.


Fred Smith - IMService
We are THE source for lowcost Cad-Cam
http://www.imsrv.com/hobby for group discounts and specials.