I have a couple of photos of my milled PC boards at my robot clubs web
site. I should post more some day. I've been milling PCBs for years and
have gotten good results
http://frontrangerobotics.org/UltraSonic/ - Edward Rupp
Brian Chapman wrote:
>>Can you give me a rough idea of what sort of considerations are
>
> involved in the machine to work at that kind of scale? I don't think
> I've ever seen a mill that small and my drill bits only go to #80.
> :-) I guess spindle runout is a major factor there? <
>
> Roy, sure, trying to stump me right off the bat, eh? <g
>
> I purchased a Sherline tabletop mill and lathe and later converted
> them to CNC using a "turnkey" system from FlashCut. (www.sherline.com)
>
> The Sherline machines, roughly, each are the size of a sewing machine
> and are driven with an IBM 600e laptop I purchased used.
>
> I bought Sherline because, when shopping, all the various reviews I
> read were glowing about the quality of the machines. Perhaps as
> importantly, I bought Sherline's "ultimate" package that included,
> among other things, quality accessories such as Jacobs chucks and also
> quality collets. Quality accessories, as I understand it, have much to
> do with a machine's cutting accuracy.
>
> I use collets only with miniature cutting tools; I've read that
> collets provide greater accuracy than chucks.
>
> I'm a member of the yahoo SherlineCNC list
> (http://groups.yahoo.com/group/SherlineCNC/?yguid=225428826), and
> spindle runout is seldom mentioned there as a problem. More likely,
> threads will deal with problems such as Z axis backlash compensation
> and the limitations of leadscrews vs. ballscrews. A number of smart
> and talented Sherline owners have documented, and posted at the site,
> machine upgrades that they've developed.
>
> But, I don't think spindle runout is a problem. Let me give you an
> example. I have milled a negative mold of the side of a 40-foot long
> highway trailer in 1:87 scale (about 5-3/8" x 1-3/16"). Within this
> space are about 40 horizontal corrugations (grooves) that I cut, iirc,
> with a .012" ball mill.
>
> In between each corrugation (a space also .012" wide), in vertical
> strips, are rivets drilled with a .005" end mill (about 36 vertical
> rows, or more than 1400 rivets). Each rivet is precisely placed; none
> "slide" into the corrugations. To me, this is the kind of accuracy I
> require -- and get -- from this tabeltop unit.
>
> BTW, I've drilled hundreds of holes on this or that workpiece with #97
> (.0059") drill bits and have yet to bust. Any sort of runout problem
> would probably snap these, but I'm guessing only.
>
> Let me ask you a couple of questions, Roy. What are the narrowest
> traces that you would need to mill on a PCB surface (am I thinking of
> a copper-clad PCB ready for etching)? In between traces, what are the
> narrowest clear areas required; that is, what is the minimum
> separation required between traces?
>
> Did I answer your questions?
>
> -Brian
>
> Brian Chapman
> Evansdale, Iowa
>
> PS - I'm hoping, once Curt comes back from the holiday, he can advise
> me whether or not I can easily adapt the CNC Sherline mill for use as
> part of the EDM system I'm intending to assemble.
>
> The EDM plans I have include a logic board for driving the EDM head,
> but I wonder if I can't build the power side of the EDM system only
> and use the mill and CNC software for the rest. . . . I'm way over my
> head at the moment, but I hope to break the surface and tread water
> while I look around and figure out what to do next. <g
>
>
> ---
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