Milling super-fine PCB traces by hand

Discussion in 'The Projects Forum' started by ezhang, Jan 7, 2014.

  1. ezhang

    Thread Starter New Member

    Jan 2, 2014
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    Hi all,

    I am trying to mill a PCB board using the Zen Toolworks CNC machine that I have bought and assembled. One glitch: I cannot find end mills that are fine enough (8 mil) to etch critical traces.

    The bottleneck right now is the MCP73838 chip, whose pads are ~8 mil (0.2 mm) apart. I have a 20 mil (0.5 mm) end mill that will work well for the rest of the board, where size is less strict, but it will not work for the chip. I cannot find 8 mil end mills which are quick shipping/locally (I'm in Brooklyn), and I do not want to bring the board to a fab house because 1) we are in the prototyping phase and 2) I just bought a mill for this exact purpose. Also, it is relatively time sensitive :/

    So, is there any way/tools that will allow me to do the 8 mil isolation traces by hand? For example, some X-acto blades are thin enough to do the 8 mil job.

    Thanks!
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    What I was recommended were engraving mills, I think it was a single flute with 60° angle tip that was supposed to work well with PCBs. I never actually got to running mill.
     
  3. Metalmann

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    Dec 8, 2012
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    If working/milling by hand, you won't beat a Foredom Flex Shaft tool.:

    http://www.foredom.net/seriessrmotorkits.aspx
     
  4. strantor

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    Oct 3, 2010
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  5. ezhang

    Thread Starter New Member

    Jan 2, 2014
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    Hmm, okay, thanks for the responses.

    @Metalmann, looks like a great solution, but I do not want to spend too much extra money on another tool

    @Strantor and everyone else:
    I noticed on the precisebits website that the engraving microbits have the correct dimensions that I am looking for but they are MUCH cheaper than the end mills.
    What is the reason for this? Are there any tradeoffs between using end mills and engraver's v-bits?
     
  6. atferrari

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  7. strantor

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    I use precisebits.com for PCB drills. I've never milled PCBs. I can say that the quality of their drill bits is very good. I would not hesitate to buy their endmills. Wherever you are getting your endmills currently, is probably overcharging. Places like MSC, grainger, McMaster, et. al. are retailers and you pay considerable markup when you buy from them. precisebits sells the mills/drills that they make (I believe), so there is no markup.
     
  8. Metalmann

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    Dec 8, 2012
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    "Wherever you are getting your endmills currently, is probably overcharging. Places like MSC, grainger, McMaster, et. al. are retailers and you pay considerable markup when you buy from them."



    Very true.
     
  9. Metalmann

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    Dec 8, 2012
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    Hehe, in the old days maybe.;)

    .00787" is a pretty tight fit for hand milling, but it has been done.
     
  10. mcgyvr

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    Oct 15, 2009
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    please don't lump grainer into mcs/mcmaster.. :(
    Grainger "should" have been out of business years ago because they have such a high markup.. The other 2 do not.. I typically find mcmaster to "usually" have slightly better pricing but in this case msc wins hands down..

    Lets see..
    lets assume .010" end mill 2 flute uncoated solid carbide .150 doc..
    precisebits.com price = $34.95/ea
    msc price = $19.48/ea <--- winner
    mcmaster $36.93

    and finally
    grainger $60+ :mad:

    Grainger is typically higher though because they have brick and mortar stores with high overheads.. well and because people are too stupid/lazy to check around.
     
  11. mcgyvr

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    Oct 15, 2009
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    and ezhang.. In the future I might suggest these guys for prototypes..
    http://imall.iteadstudio.com/open-pcb/pcb-prototyping.html
    amazing pricing and great quality.. typically takes a few weeks though for shipping unless expedited.
    But you will be hard pressed to beat that pricing..
    example 10 boards 5cm x 5cm = $9.90 + shipping (and thats $9.90 for all 10 boards.. not each so $0.99/each)

    They also do ENIG finish which is a must for fine pitch..as HASL will not do it reliably.
     
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  12. strantor

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    Your example with the endmills supports your argument, but in my past experience pricing similar products between the three, the difference between them is not as drastic as this endmill example. I find often MSC is more expensive than the other two. Grainger and MSC seem to be hit-or-miss, and McMaster seems pretty consistent down the middle.

    Grainger gets most of my business, as you said because they have brick and mortar stores; not, as you said, because I am stupid or lazy. In most cases, my time is worth more than whatever widget I'm searching for. If I spend more than ten minutes shopping around, I just blew any savings right out of the water. When I need something, I just go get in my car and start driving to the nearest Grainger; call and check pricing & availability on the way. If they don't have it at the specific location that I'm headed to, they surely have it somewhere in Greater Houston, and I just make a turn and head that way. Pretty common practice, and not waiting for shipping or shopping around saves companies way more in uptime than they would have saved by paying a reasonable price. That's why they're in business, despite all the highway robbery.
     
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  13. mcgyvr

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    I just order from mcmaster or mcs.. I can order at 4:30 pm and its here in the morning (via ground shipping).. Grainger stores aren't all over the place here.. A trip to grainger means a good hour in the car and 3 times the money out of my pocket..

    This was the last thing I ordered
    mcmaster 1/2" carbide end mill at $70 USD... same at grainger was $184 USD..
    seem to remember mcs was about $90 or so..
     
  14. shortbus

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    Sep 30, 2009
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    But the prices at Grainger are much lower in person and if you have a business, or work for one that buys form Grainger. Some times 50 -60% less than catalog price.

    They used to not want walkin/small guy buyers but now they accept that, at least around here. Due to the economy.


    Back to the mill cutters, an engraving bit is the only way to do what the OP is asking. They have a single flute and can be made much smaller(and not break) than a regular end mill. On a PCB your only cutting ~.005 deep. But they must be run at high RPMs to cut correctly.


    Used to do a lot of cutting with them when I was working. In a pantograph, pre-CNC.
     
    Last edited: Jan 8, 2014
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  15. TDA

    New Member

    Jan 9, 2014
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    I would agree that the engraving tools are the way to go. Keep in mind that the tips are 0.005" so that is your starting diameter.

    The reason that they are cheaper is they are easier to make. Making a 2 flute endmill to .010" +/- .0003" is not easy and requires a different setup that costs more.

    The main difference you need to be aware of is that the board needs to be true to the spindle / router. I would recommend milling an area under where you will mount the board to insure that it's true.

    Also keep in mind that with either engraving tools or endmills this size runout is critical. On a endmill you have about 10% of the diameter of a cutter before you will break it. You get more forgiveness on engraving tools as the tapered design can take more stress.

    For obvious reasons I won't comment on the price comparisons other than to say this. Regardless of who you are comparing there is more to it than just the size and depth of cut on an endmill. Tolerance, tool geometry, and carbide type all play a huge role in both production costs and tool performance. I'll give a quick example. Using ISO grade K20 carbide:
    Chinese YG7 - T.R.S= 1.9 GPa HRA=90
    Sandvik DH20 - T.R.S.=2.8GPa HRA=92.3
    Mitsubishi MF20 - T.R.S.=4.4GPa HRA=92.8
    T.R.S. is transverse rupture strength and HRA is a rockwell A test. Clearly all these carbides are different even though they share the same ISO grade. They are also very different in cost.

    Let me know if I can be of help.

    John Torrez
    Think & Tinker / PreciseBits
     
  16. Metalmann

    Active Member

    Dec 8, 2012
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    "The main difference you need to be aware of is that the board needs to be true to the spindle / router."



    I think you mean to say, that the spindle has to be perfectly "perpendicular" to the workpiece, table of the machine...
     
  17. TDA

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    Jan 9, 2014
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    I primarily use the word true as it has served me best. Every time I use another term people start going down the leveling and adjusting route. Basically it doesn't matter how you do it as long as the depth of the cut stays the same. So as long as the board is "true", level, perpendicular, etc you're good.
     
  18. strantor

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    Hey, cool I attracted the attention of think & tinker. Good business practice, following up on the source of your hits and getting involved.
     
  19. TDA

    New Member

    Jan 9, 2014
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    We try if there's something we can help with. Have to be really careful though. It can be pretty easy to break forum rules if you're not careful. But I'm here if anyone needs anything. And thanks for the kind words.
     
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