Isolation Bits

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    Default Isolation Bits

    What bits do you all recommend for doing the isolation routing? Drillbitsunlimited has a pretty good selection but I am not sure which bits are the most useful and I really don't have extra cash to order them all. I mostly do through-hole PCBs using standard DIP, T220, and discrete parts. Would the 30 degree bits be the logical choice?

    The same for drill sizes, which are the most used sizes?

    What speeds and feeds are recommended for the isolation routing?

    Thanks,
    Robert

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    Default Re: Isolation Bits

    A 30-degree V-bit would certainly work (assuming the tip width is something reasonable like 0.1-0.2mm; you wouldn't do much with one 1.0mm tipped 30-degree bit I saw on that site) although you might want to eventually move on to a 15-degree V-bit (this one on the same site seems extra tough and explicitly mentioned for PCB-scoring: 15 Degree, 0.10mm Tip Titanium Coated Carbide V Engraver - ONE Piece - Drill Bits Unlimited.com). Whatever you choose, keep in mind that, at the very least initially, bits are very much consumables - you'll be breaking them routinely until you figure stuff out, so buying 2-3 won't do you much good. Obviously, the pointier and thinner at the tip they are, the easier they break. At any rate, you don't want to go deeper than you have to (normal 1oz copper is 0.035mm thick - I tend to use 0.060mm depth but having the PCB absolutely level is crucial; mill a piece of sacrificial HDF board flat beforehand with a larger tool and/or use software that probes your PCB in a grid and corrects height issues in the final .nc file); with V-bits, the deeper you cut the wider the cut becomes, and that can be a problem with thin traces.

    Drill bits are far more durable normally (well unless you start manufacturing perfboard...), as long as you remember to instruct your CAM software to "dot" the center of each drilled pad _with the engraving bit, during the isolation pass_. You won't believe how nicely that starter dot centers and stabilizes drillbits. As for sizes, that pretty much depends on the common sizes of the components you plan to use - I mostly only handle R/C and IC pins, so I get by with a few 0.65mm - 0.8mm - 1mm bits, but you'd surely need something bigger for TO220...

    Speeds/feeds... eugh, I have no idea. All I know is the faster you can spin your bit the better (20000 RPM would be nice, more would be better, and you don't want to go below 10000 RPM - even lower is possible, but the associated feeds will see you die of old age before your PCB completes...). Trawling through my .nc files, apparently I've used 100mm/min the last time (with 10000 RPM) both for scoring and drilling - and it certainly did work, although I'd assume one could definitely go faster than that, it's just a matter of how many bits are you willing to break to find out by how much.

    Finally, two things: you may or may not want to spread a thin layer of oil on your PCB before cutting - it's certainly not necessary, but it may or may not help with the cutting itself and it definitely keeps the resulting copper and fiberglass dust trapped; second, do expect some burrs - too much is obviously a dull bit or cutting speed problem, but don't worry about a modest amount: just hit it with a piece of ordinary kitchen-variety scotch-brite and it will take the burrs clean off.

    Good luck!



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    Default Re: Isolation Bits

    Thank you very much for the information, it was very helpful. I'll try to get my bits ordered in the next few days!

    One additional question: What software do you use for dotting the drill points?

    I have been using KiCAD for the schematic and layout gerbers. Once I have the gerbers they are imported into FlatCAM to produce the isolation g-code. This all appears to work as expected when I run it in a simulation and while cutting air on both cnc machines (Tormach and Camaster). I have not yet tried hole drilling code so that portion is currently untested. In the end I would like to do the cutting on the Tormach, but I would need to add a high speed spindle of some sorts as the RPM is a slooooow 5K max.

    Thanks Again,
    Robert



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    Default Re: Isolation Bits

    PreciseBits makes some nice trace isolation V-cutters:

    V-tip engraving and carving, PCB Trace Isolation

    ...and rubout end mills for clearing large copper areas:

    Carbide 2-flute Stub End-mills for Metal Cutting and PCB Copper Removal



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    Default Re: Isolation Bits

    As far as software for drilling, I just export the drill file (.drl) and open it in my CAM program, which happens to be CamBam. FlatCAM should support .drl files as well.



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    Default Re: Isolation Bits

    Oh, as far as dotting the holes I usually just cheat: I create a duplicate of the normal drill task, except I set the "drilling depth" just as shallow as the rest of the isolation cut, and I simply run it using the engraving tool instead of a drill... Some software like Line Grinder actually had a specific option just for explicitly dotting pads as part of the isolation pass, but it was a bit problematic if you had mixed through-hole and SMD pads on your board because it dotted ALL the pads... ))



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    Default Re: Isolation Bits

    Stupid question - what is the reason for "dotting"? Why not just drill the holes?



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    Default Re: Isolation Bits

    You certainly can simply just directly drill them, but thin drill bits unceremoniously shoved into copper might decide to waver slightly before biting in and that can be very bad if they hit even slightly off-center - it doesn't take much to break a 0.65 drill (especially the ordinary non-stub version with full 10mm length that we amateurs tend to use) and flexing it continuously by drilling an off-center hole is the easiest way to do it. But much worse, if you're doing reasonably fine work where you have not a lot of room for copper around your holes, a non-stabilized drill might get you an off-center hole making an ugly "crescent moon" out of your nice pad/via. Conversely, a pre-dotted PCB will guide your drill bit preventing any wavering and even self-correcting tiny errors in positioning if you didn't quite hit the right spot with your drilling pass. Sure, we know that shouldn't happen on a proper CNC, but... yeah... I'm a hobbyist with a cheap Chinese 3020, okay...?



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    Default Re: Isolation Bits

    I mean, I'm a simple man - I see spot-on centering results like this (over a board of about 10x20cm), I just shut up and keep dotting...
    Isolation Bits-pcb3-jpg



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    Default Re: Isolation Bits

    If it works, don't change anything. Those are definitely good looking boards.



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    Default Re: Isolation Bits

    Thanks guys all of your comments are helpful...... Nice looking PCB's.

    To me the dotting concept is like using a center punch before drilling in the days before CNC. After I posted my question the usual Duh occured on just setting the drill depth....

    Thanks Again,
    Robert



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