Re: [CAD_CAM_EDM_DRO] Re: PCB routing with CNC milling machine....

----- Original Message -----
From: "Fred Smith" <imserv@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, October 28, 2003 8:27 AM
Subject: [CAD_CAM_EDM_DRO] 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.
>
>
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