Thanks for the info Simon. I ordered some bits and will give it a try.
Chris
--- In Homebrew_PCBs@yahoogroups.com, "spacedcowboy@..." <simon.gornall@...> wrote:
>
>
>
>
>
> --- In Homebrew_PCBs@yahoogroups.com, "Chris" <lcdpublishing@> wrote:
>
> > Hi guys,
> >
> > I have a fairly accurate CNC machine I built for drilling
> > PCBs but now want to see what it can do with isolation
> > milling. I am curious as to what I can expect for the
> > minimum trace width/ spacing?
> >
> > The machine itself should be accurate to within .0005"
> > (13 microns) as it uses linear encoders of that resolution.
> > The spindle does have a bit more runout than I would like
> > as it is about .0015" (38 microns)
> >
> > If you have recomendations for an engraving bit supplier I
> > sure would appreciate hearing your suggestions on that too.
> >
> > Chris
>
> I have an EP2002H machine from EverPrecision, and I can happily (and repeatedly) do a 4mil track/gap.
>
> The process my machine goes though is as follows:
>
> Surface scan:
> =============
> The EP2002H can detect the electrical connection of the milling-bit and the copper-plate, so it moves to every point on a grid (I usually use 10mm, I've not seen any advantages in going smaller) over where the milling will take place, and detects the Z position where the tip of the bit meets the copper. It therefore builds a surface-profile which it uses to see how deep the bit should go at every point when milling. This really helps with the finer tracks and spaces. You'd have thought copper-plate was roughly flat. It's not, or at least, it's flat for large values of "roughly"...
>
> Drilling:
> =========
> Not much to say about this. Drill all the holes of one type. Switch bit. Drill again. Repeat until done.
>
> Through-hole plating:
> =====================
> [sigh] one-day. The t-tech system looks to be the cheapest. The LPKF one looks to be the best (at 3x the cost)
>
> Engraving:
> =========
> At least that's what the software calls it. Make sure you mill an isolation path first, then do copper-removal. The EP2002H allows 3 different tools for copper removal to speed things up. The smaller areas are done first (since the tool is already in the machine after the isolation milling) then progressively larger tools are used to remove larger areas of copper. I usually end up doing a GND copper-pour to prevent huge swathes of copper being removed though...
>
> Second side:
> ============
> My machine allows me to drill 2 fixed-positions into the bakelite substrate before I start, and I can then flip the board, locate it using the fixed positions, and the software calculates where the 2nd side ought to be located (presumably just mirroring the part across the Y axis). Then you can do a surface-scan and engrave on the second side and be confident that they'll match up.
>
> Routing:
> ========
> Once both sides are done, I insert an end-mill bit and it (by default) routes out the FR4 around the edges of the board. The machine reads Gerber 274X files, so I just get Eagle to output the milling layer as a gerber file and I can route out complex edges or holes in the PCB.
>
> I really love this machine - to give an idea, one night last week, at 9:30 I decided I needed a breakout board for an SMT part so I could play with it in a breadboard circuit to try and figure out what was going wrong. By 10:00 I had the part designed in Eagle and milled on the machine. By 10:15, I had the SMT part (a constant-current LED driver) soldered onto the breakout board and started to work with it. The whole process is 100% repeatable and reliable, and the machine was worth every penny :)
>
> Having said all that, I wouldn't ever buy another EverPrecision machine. The customer-service is woeful, and the US dealer is particularly terrible. He won't even get me the latest version of the software because I didn't buy the machine directly from him (I bought it from the previous dealer) and EverPrecision themselves just want me to work through their dealer network. It's sufficiently annoying that I have a longer-term plan to write my own software, then I can have it work on a Mac as well :)
>
> One other thing worth noting is the spindle-speed. The EP2002 s/w controls the spindle-speed depending on the drill size and the smaller the contact-area (tiny drills, small track/spaces), the higher the speed. For accuracy, you might want to consider the same. I think the spindle is the major cost of one of these devices though, so maybe it's not a possibility.
>
>
> The place I get my drills from is from Fred Schultheis <fredpcb@...>. His website is http://www.northbaytechnical.com/ and he's a great guy to work with. Tell him I sent you if you go by - he sold me the EP2002H in the first place but a large part of his business are the drills and accessories :)
>
> Simon.
>