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Using a CNC router for designing PCBs

Discussion in 'Project Construction Technologies' started by Qubix, Feb 7, 2015.

  1. Qubix

    Qubix

    8
    1
    Feb 7, 2015
    First of all, HELLO EVERYONE , this is my first post here. :)

    I was wondering if buying a CNC router would be a good way to make nice and accurate PCBs, since I don't really want to use chemicals.
    I found something like this on amazon:

    http://www.amazon.de/Gravurmaschine...70754&sr=8-1&keywords=cnc+3020#productDetails

    But I really don't know if it's good or not. What should I pay attention to when buying a cnc router?
     
  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    436
    99
    Aug 27, 2013
    Hey Qubix, welcome to EP!

    The answer to your question is absolutely, maybe, kind of, sort of, yes. I have made a lot of PCBs using my CNC routers...there are some things they are great at and some things that they are not so great at....like all things there are trade-offs. What they are really good @ is inexpensive (material point-of-view) rapid prototyping....what they are really bad at is any type of volume production....They are great for traces/spaces down to ~20mil (~0.5mm) they are very slow with PCBs requiring large amounts of copper removal....Obviously board tinning/silk screening is outside their capabilities....double sided boards can be a real challenge....often better to mill two single sided boards and then connect them using vias or through-holes.....Industry Standard PCB software generally lacks good support for generating the requisite g-code files, though there is a plug-in for Eagle that many report good success with....At the end of the day, it is a mixed bag.....For me, it is absolutely worth the a fore mentioned problems to go from schematic to prototype in a matter of hours....but there is a fairly long learning curve to achieve good results, and I wouldn't consider the resulting boards for anything other than personal use....

    Next thing to consider is the actual cost of the CNC router....the US "teaser price" is ~$520....it does not clearly state if this price includes Mach3, or if it is simply designed to work with Mach3....Last I checked Mach3 cost $175 and does not play well with modern operating systems (XP or later).....Next thing to consider is some type of CAM or CAD/CAM program....a program that will allow you to generate Mach3 compatible g-code (as mentioned, there is a plug-in available for Eagle that many have reported good success with....don't know if this plug-in is freeware/shareware/commercial....I have never used it)....in any case, regardless of the cost of the software, there is a lot to learn before you will complete your first PCB. If you decide to get a CNC router make certain to order PLENTY of engraving bits and drill bits....they are very fragile and you will break many during your learning process....I would suggest you start with 60 degree V-Bits with a 0.1mm tip...these are not great for fine traces, but they are a LOT more durable than the 15 degree to 45 degree bits...you should also look for "used" 1.2mm to 2.4mm carbide PCB end mills in assorted lots of ~50.typically available for ~$1 each (from ebay) with plenty of life left in them....again, you will break more than a few learning about feeds and spindle speeds, and these bits "new" run $6 to $20 each....Same with PCB drill bits, don't be afraid of the "used ones" in lots of 50 from ebay....you will break a lot of these....I have broken as many as half a dozen drills on a single board....(I wouldn't say that attrition rate is common, but it can happen....)

    Next thing to consider is the machine itself.....$520 is CHEAP....I know nothing about the particular machine, but in one of my routers my spindle & VFD cost more....(on the same machine my linear rails cost ~3 times that much!)..the primary two things to focus on in the spindle are T.I.R (Total Indicated Run-out) and RPM....if the T.I.R is more than ~0.0005" (0.013mm) then you are going to break a lot of drill bits...if the spindle is limited to less than 20,000rpm then your feeds are going to be very slow.....the primary concerns for the machine are 1) Rigidity 2) Repeatability 3) Accuracy 4) Speed.....A machine in this price range is almost certainly going to use round rails, likely 12mm or smaller with cheap recirculating Ball Bearings housed in a plastic cage with a very sturdy looking metal housing.....these are great for 3D printers...not so much for CNC routers....you should consider replacing these bearings with bronze bushings....if the machine you choose uses them.....Honestly, you should really consider spending a bit more on the machine if you expect to use it much....in order to sell such a machine for $520, too many corners have to be cut, at least IMHO....look at some of the machines that cost roughly twice or three times as much and you will very likely get a lot more for your money....but, again, I have never actually laid eyes on this particular machine, so I can't say for sure, but based on the price of components....and a fair amount of experience building hobby-oriented CNC routers....the MFG must have cut a lot of corners to put a complete machine together for this price....I can tell you from experience that every corner cut in building your machine will cost you ten-fold in broken tools and ruined materials....so go in eyes wide open....and fore warned, lol.....

    Happy to give more opinions on various aspects of both machine selection and general experience with PCB milling.....

    Fish
     
  3. Qubix

    Qubix

    8
    1
    Feb 7, 2015
    Hey Fish, thanks for the quite long and elaborate answer. The price of the router itself kinda set me back though. I mean I will probably just use it for hobby projects, and 1000-1500 EUR or USD is quite a lot ...
     
  4. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    436
    99
    Aug 27, 2013
    Quibix.....

    CNC routers are a hobby unto themselves :) ....but it is not a cheap hobby.....I have seen some build threads where people salvaged most of the parts from old printers and the like and claim to have less than $100 in what appears to me to be a fairly decent machine, but IMHO the time spent sourcing the parts far exceeds the cost of the materials....If I had to spend 20 weekends driving to various yard sales and dickering over $5 printers to save $1k I would certainly feel like I had "lost" money....but to others that may seem like a fabulous use of time...to each their own....

    If you want to DIY a machine just for PCBs you can take advantage of the 3D printer revolution and get most of the parts pretty cheap....if you go with round rails, bushings, MDF frame, NEMA17's, the cute little NEMA17 drivers favored by the RepRap crowd and a linux based machine controller like EMC2 then your biggest cost will be the spindle....there is a fairly decent 400W spindle available with a mount from China for < $100......I would guess you could put a pretty decent PCB machine together for less than the $500.....but be fore-warned of time sucking vortexs at every juncture, lol.....and be aware that "mistakes" add to your junk pile and increase the cost of the project.....(I know this from LOTS of personal experience!)

    Anyway, good luck! If I can help with anything else, let me know.....

    Fish
     
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