On Monday 04 July 2005 12:19 pm, 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
Nah. I'm ∗real∗ new at a lot of this stuff...
> I purchased a Sherline tabletop mill and lathe and later converted
> them to CNC using a "turnkey" system from FlashCut. (www.sherline.com)
Ok. I'm still thinking DIY here, but we'll see where things end up,
eventually. I'm in no hurry, and don't have the money to spend on that
stuff anyhow.
> The Sherline machines, roughly, each are the size of a sewing machine
> and are driven with an IBM 600e laptop I purchased used.
I think I saw one or two at that Cabin Fever Expo a while back.
> 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
I carry it here as well, but don't find much to contribute just yet. :-)
> (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.
That's SMALL!
> 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.
Cool.
> 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.
I would think so, yeah. What kind of z-axis feed rates are you using there
for that stuff?
> 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?
I'm not real sure, to tell you the truth. A lot of hobbyists are going
headlong into teeny little surface mount stuff, and I've decided that
anything I'm going to build isn't going to involve anything like that. My
eyesight just ain't what it used to be, among other things. Sometimes
lately when I'm scavenging parts I think my fingers have gotten bigger, too.
So figure 0.1" pin spacing, and ∗maybe∗ a trace would need to run between
two pads there, but that's not too likely to be common. I'm looking at
fairly simple stuff overall.
> Did I answer your questions?
Sure.
> -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.
There's another area I know next to nothing about. It wasn't until reading
posts in the past few days or so that I was aware of that stuff being done
with the work immersed in some kind of fluid...
> 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
I don't see offhand why that wouldn't work...