problem making pcb with mk II

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    Default problem making pcb with mk II

    Hi,
    I've a problem with making a pcb, the edges around the tracks are blunt and not cut well. I've tried with different speeds of the tool but the result never changed (the spindle max speed is 12000 rpm). How I can get a better pcb?


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    Default Re: problem making pcb with mk II

    What tools are you using and at which speed? I use 30 degrees V-bits and get excellent results. My guess is that you are going too fast for the slow spindle speed. I think you should keep around 300mm/min to get better results.

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    Default Re: problem making pcb with mk II

    I also had some "burring" recently when I used v-bits (multiple flutes) and when I switched to an engraving tool (0.3mm flat edge) the surface looked fine. It is as if certain tools push the material out of its way, rather than cutting it off cleanly. I would try a different tool first, 1 or two flute max.

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    Default Re: problem making pcb with mk II

    I'm using a 30 degree v-bit at 12000 rpm and 250 mm/min. I've tried also with a feed rate of 50 mm/min, but the result never change. I'm milling at 0.08 mm



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    Default Re: problem making pcb with mk II

    Another though tipt @AndreaRoss- what is the width of your cut? If your cut is too shallow (several overstepped routes needed to clear one trace) the worksurface (copper) is being cut by a very small part of the tool, but at the tip of the tool the speed at which the tool rotates, approaches zero. Maybe try adjusting cut depth a bit deeper and set your tool width slightly wider in the import parameters?

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    Default Re: problem making pcb with mk II

    The spindle speed should be high 12K or more. The cutter should be a sharp vcarve bit as others indicated, preferably carbide. What software are you using to create the gcode? PCB2GCODE? If you are using Eagle to design the PCB and then using PCBGCODE to get the gcode there are many setting in PCBGCODE that can help clean up your outputs.

    Russ



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    Default Re: problem making pcb with mk II

    To convert from pcb to gcode I use FlatCam. I've also adjusted the depth (from 0.07mm to 0.1mm) and I've obtained a better result, how can I do for smd pads that are torn off during milling? (depth of milling: 0.1mm, spindle speed: 12K and 200mm/min)

    Andrea



    Attached Thumbnails Attached Thumbnails problem making pcb with mk II-20170803_184650-jpg  
    Last edited by AndreaRoss; 08-03-2017 at 01:48 PM.


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    Default Re: problem making pcb with mk II

    Hard to see you picture big enough, but here is a board I did with SMT parts and connectors and you can do SMT pads for sure.
    Russ
    problem making pcb with mk II-img_1196-jpg



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    Default Re: problem making pcb with mk II

    Does look a lot better. Great stuff! You could try adjusting the feed speed down a bit for the force on the smd pads. I am guessing the smd pads get dislodged due to the small area of copper and the temperature not being able to dissipate quickly enough. I use a soldering iron when I need to remove unwanted islands of copper after routing, it's much more effective than prying it off when it is cold. You could try cooling the area to test the theory? A fan on the pcb during routing?

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    Default Re: problem making pcb with mk II

    Most smt are ok, the problem is the smallest smt (TSSOP-14) where the pads are ripped off.

    Andrea



    Attached Thumbnails Attached Thumbnails problem making pcb with mk II-20170803_195537-jpg  


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    Default Re: problem making pcb with mk II

    There are also quite a number of very thin traces of the copper pour that is distorted and causing shorts to adjacent tracks in your photo. I am myself still trying to find a nice balance with track width and copper pour clearance...

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    Default Re: problem making pcb with mk II

    Yeah, when you do very tiny SMT parts like TSSOP-14 you must use very sharp engravers with very small diameters at the tip. The other trick I normally do is to make all the traces bigger than normal as the milling process sometimes removes too much copper unless you have the configuration of PCBGODE set perfect and you machine has very tight tolerances. Check the parameters like step over and make them smaller.

    Russ


    problem making pcb with mk II-dsc_0745-jpg



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    Default Re: problem making pcb with mk II

    Or if you want to punish yourself, edit the G-Code to lift the bit slightly when you get to the tiny smt pads

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    Default Re: problem making pcb with mk II

    Nice resolution on that board Russ! You even have the diagonal line in the "zero" of the text. My own capabilities are not nearly the yet.

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    Default Re: problem making pcb with mk II

    There are several tricks you can use to help address issues. For one you can lie to the software and tell it you cutter is wider than it actually is, so when the software builds the gcode it does fewer step overs to get the right amount of separation between traces, etc. I sometimes make sure my z axis is set .003 about the surface and call that zero. These are the ways you can address the short comings when building your own pcbs. I ruined several test pieces of copper working on these kind of adjustments and you will find the right mix that seems to generate a PCB that is usable. I have seen some people on the zone get even better resolution than I got, most had very tiny dedicated machines for making PCBs, they used tiny spindles that were powered by dc motors which has next to no run out so their lines were very consistent. I have a 3KW water cooled spindle and it has about .001" run out maybe a little less but that makes the vee shaped cutter cut a wider path than you want, so all of these things contribute to our challenges.

    Russ



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