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IndustryArena Forum > Other Machines > PCB milling > Advice wanted (mil for PCB)
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  1. #1
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    Advice wanted (mil for PCB)

    I'm a total newbie to cnc milling.

    People I heard weren't to enthusiastic about these machines for PCB prototyping.
    There are many problems with the machines for this purpose according to them.

    I'm an electronics hobbyist that hasn't much time for him hobby but when I start I want to have something at the end of the day :-)
    My guess was that an milling machine would do a much better job than the chemical way of making PCB's.

    I found out that zero backlash is very important, the power of the spindle and so on.
    In my simple brains it's very simple: buy a machine, unbox it and start making the perfect PCB's from PCB design software.
    But things are different in the real world.

    What do I need to know to get as close as possible to my ideal way of making a PCB from scratch.
    It seems that a PCB design can be exported from Eagle PCB software to (Mach3?) software to be milled in the machine.

    What could be my expectations after buying a machine and start cutting?
    What width of PCB traces I can expect from a cheap machine?
    Is the price of the machine an indication for what quality of PCB I can expect?

    Where can I read more about this?
    Is there an Ebay seller that has a descent machine for a reasonable price?
    All info is welcome!

  2. #2
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    Re: Advice wanted (mil for PCB)

    I want to renew this question:

    are there in the meanwhile (cheap) machines that can mill PCB's in a decent way without days and days of setup?

    I found this one: Mini CNC Router Engraver 3020 800W Milling Machine 3 axis 4 axis USB port card | A type CNC milling machine

    Any good?

  3. #3
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    Re: Advice wanted (mil for PCB)

    First off, I'm not knocking you, I am just curious.

    I often wonder what the motivation is behind building a PCB router when, in my opinion, it is almost certainly easier and cheaper to use a service to fabricate PCB's. Unless you put a whole lot of money into your machine you will never be able to achieve the quality and feature sizes that a service like Express PCB or others can produce.

    Reasons to use a service:
    When you design a circuit, often there is no through hole component for one to use.
    With the features of a surface mount device being so small you couldn't possibly be able to mill the traces with a home built router.
    A complex PCB almost always requires a burried power and ground plane.
    Surface mount boards are easy. You can use a toaster oven to reflow the solder better than you could ever solder even a through hole board.
    How do you make a plated through hole in a home shop?
    Silk screens and solder masks?

    Oh, I see, you are in Belgium. There has to be a PCB service there also.

    I would recommend that you get someone else to produce your PC board and you can spend your time on writing the software for it. Your satisfaction level will be so much better when you hook up your ICE and program a board that you assembled that has a CPU, and lots of I/O, all SMD parts and is super small.

  4. #4

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    Re: Advice wanted (mil for PCB)

    Hi, if you would like to start using a CNC Router for prototype PCBs, I have found a cheap, but good machine, the "CNC 1610" here is the link to the machine: https://amzn.to/2TjDNOL as I have made very clean and as small as 0.6mm traces. I have made a two part video on YouTube, on the "process of making a PCB from scratch" using this machine as well as applying UV solder mask on it. Check out my video and my channel for part two for the UV solder mask.

    Here is the link to my the video: https://bit.ly/2G9fo9l
    In the video's description I put the parts and programs I used as well.
    Give it a like and subscribe to see more and tutorials later!

    Also, check out some pictures of the custom PCB with and without UV solder mask using this machine. It's in the video as well.
    In the picture, the traces are 0.6mm.

  5. #5
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    Re: Advice wanted (mil for PCB)

    Hi,

    I often wonder what the motivation is behind building a PCB router when, in my opinion, it is almost certainly easier and cheaper to use a service to fabricate PCB's
    I disagree. When you design a circuit board and have a service make it for you pay for all the photomasks and so on. That's not cheap. If you have 50 boards made it
    certainly is cheaper in the long run.

    What happens if you are still experimenting with your circuit design? The circuit is too complicated to breadboard and not really finalized and tested......that's where isolation
    routing comes into it own. You can design a circuit and have it milled and ready within hours....if it proves that one of more components need changing say you can do
    so and make another board....all without a trip to your PCB service provider and associated bill.

    I regularly make surface mount boards, my machine (home made) can handle 0.2mm trace widths, 0603 resistors/caps and 0.5mm lead pitch ICs. As I hand solder
    I find that the machine exceeds my ability to place and solder parts.

    One area where etched circuit boards hold a distinct advantage is through holes. I use PCB rvivets (small diameter copper rivets with a hole bored through it)
    and they are not bad.....but still not as good as plated though holes.

    At one time I was using REALLY THICK COPPER board, 12oz or 0.42mm!! Very few services can handle copper that thick, most can etch upto 4oz max and have to plate
    up to get thicker conductors. I use 0.5mm diameter endmills and can isolation route boards very nicely. The only commercial services that can handle copper boards like
    that wanted $1000 USD/sq foot.

    While I agree there are advantages to etching boards including things like multilayer boards with ground planes, solder resists, silk screens and so on......so also does
    PCB routing.

    Craig

  6. #6
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    Re: Advice wanted (mil for PCB)

    Though this is a month old, I'll add my thoughts. I have a decent CNC mill that I use for a lot of things (and the list seems to always grow). I've routed several PCBs but, honestly, you get a vastly better product using a service. And the services are fairly cheap. I'm in the US and can get 5-10 boards up to 4"x4" made in china for less than $50 and less than 2 weeks time. I will sometimes route a simple board to try out a new SMT part but would never make a final product with my mill. Even a one-off board.

    I guess it depends on what quality level you are willing to accept. But I want my boards to look professional and routed boards (or home etched, for that matter) never do.

  7. #7
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    Re: Advice wanted (mil for PCB)

    I've been down both paths.

    A bit of a story: A long time ago, in a galaxy... actually, this galaxy... on this very planet, too... And a long time ago was the early 2000s... 2002? 2003? Anyway... there were no good PCB layout programs for the newly released Mac OS X. So, I (naively) figured, well... it's just circles and straight lines... how hard could it be? So, I set out to write my own; learning the then-new Cocoa programming framework along the way.

    Well, back then, PCB prototyping was really expensive... like, hundreds of dollars for a few small boards, expensive. And I had a MaxNC 10 benchtop mill, with ballscrews and upgraded steppers, so I figured I'd build isolation routing into the program that I was writing. A bit of path trimming logic and geometry monkey-business later (OK - a fair amount of monkey-business); and it was successfully generating g-code for the NC 10 to mill around the traces, and drill holes for the thru-hole parts.

    It worked... eh... OK, I guess. It would probably work better now; the blank PCB material that I had available to me then was surplus and varied in thickness across it's surface, so using a V bit generated varying isolation widths. Tiny carbide end-mills (which would have been immune to the issue) were prone to breaking, so I just mostly stayed with larger parts (i.e, DIP). Were I to take up PCB milling again; I would have the machine scan the surface of the PCB with a probing cycle, and adjust the Z depth accordingly. However, at the time, the control software for the MaxNC didn't have a way to export that data; and it had no documentation on the drive that it used (I later did open it up, and, well, wasn't very impressed by what I found inside... but I digress).

    Routing thru the PCB material did generate some nasty dust; fortunately at the time HEPA vacuum cleaner bags were "a thing", so to speak, and not too expensive.

    I have since removed the isolation milling code from my PCB layout program; and although I still have it, sitting in a pile of other obsolete code, I doubt that I'd ever re-install it in the program. There are several reasons for this:

    • Isolation milling is a pain to do. It makes nasty fiberglass-containing conductive dust; and if you are using V bits, you have to get the depth - relative to the local top of the material - exactly right or you'll blow out the trace you're trying to create (typical machining practice is to find a reference point and work off that - this requires warping the cutting path to match a non-planar reference surface).
    • You don't get soldermask from the machine.
    • You don't get vias without hand work.
    • You can only do surface mount parts that have accessible pins on them - BGAs, QFNs, etc more-or-less need soldermask.
    • Drag soldering doesn't work as well without soldermask. It's do-able, but likes to make solder-bridges.
    • Multi-layer PCBs, although possible, are tricky to get to work right.
    • You don't get a silkscreen.
    • Compared to a professionally made board, it just looks bad.
    • The price on PCB prototypes from a service has fallen thru the floor. Before ordering PCBs, I always check on pcbshopper.com to see who has the best deal at the moment. Right now, for 5 each 100mm square boards, green solder-mask (other colors are available at the same price, but adds 4 days to the build time), delivered via DHL to California in 7 days, JLC will do the job for $18.81. If I want 10 of them instead; it's $21.81. The majority of the cost is the DHL shipping... base price is $2 for 5 each, and $5 for 10 each.


    So... um... yeah. I don't mill PCBs anymore; I just send them out. I've usually got other stuff to do in the meanwhile; so the waiting isn't that bad... and as often as not; the PCBs will get here before all the parts that go on them do.

    P.s.... if you are ever writing a Gerber "photo-plot" file generator; ignore the fact that g-code for a mill is called RS-274; and Gerber files are called RS-274x. Ignore the fact that it looks like it's a dialect of the same g-code standard that milling machines use. It's really not. You must follow the block order given in the examples listed in the specification; even though the specification doesn't say you have to. Otherwise, the PCB house's CAM software won't read it correctly... in spite of the Gerber viewer software on your PC (that you downloaded from three independent companies) not having any problem with it! <sigh>


  8. #8
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    Re: Advice wanted (mil for PCB)

    Quote Originally Posted by philba View Post
    And the services are fairly cheap. I'm in the US and can get 5-10 boards up to 4"x4" made in china for less than $50 and less than 2 weeks time.
    "Cheap" is relative concept - where I live $50 is a serious amount of money, especially for a single small PCB (and the nine other ones I have absolutely zero use for: I never needed more than one of anything), especially considering my small desktop CNC can crank the (functionally) same thing out for basically free, as FR4 costs almost nothing. You could of course point out that the price of said CNC is supposed to be much further out of my league than the $50 I seem to be so worked up about, and you would not be wrong at all - but as things happen I came to own that CNC for unrelated reasons and means; and once I have it, it makes PCB fabrication accessible to me in a way that a "cheap" $50 service absolutely never possibly could. And that's without even considering that by the time a Chinese-fabbed PCB would arrive to me I would not even remember what I wanted it for, and its purpose would long be either patched up with something else or moot by then.

  9. #9
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    Re: Advice wanted (mil for PCB)

    Just to put things in perspective... at the local diner; a decent lunch costs me about as much as a batch of PCBs does. Unfortunately, due to varying currency values, my PCB to sandwich-cost ratio is going to be rather different than yours...


  10. #10
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    Re: Advice wanted (mil for PCB)

    Quote Originally Posted by blinkenlight View Post
    "Cheap" is relative concept - where I live $50 is a serious amount of money, especially for a single small PCB (and the nine other ones I have absolutely zero use for: I never needed more than one of anything), especially considering my small desktop CNC can crank the (functionally) same thing out for basically free, as FR4 costs almost nothing. You could of course point out that the price of said CNC is supposed to be much further out of my league than the $50 I seem to be so worked up about, and you would not be wrong at all - but as things happen I came to own that CNC for unrelated reasons and means; and once I have it, it makes PCB fabrication accessible to me in a way that a "cheap" $50 service absolutely never possibly could. And that's without even considering that by the time a Chinese-fabbed PCB would arrive to me I would not even remember what I wanted it for, and its purpose would long be either patched up with something else or moot by then.
    Well, if you've got a PCB mill, you probably spent a fair amount more than that on it. But you should definitely do it however you want. I won't dwell on all the negatives as I'm sure you already know them but a milled PCB really is inferior to one from a production house.

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