1. OCAU Merchandise now available! Check out our 20th Anniversary Mugs, Classic Logo Shirts and much more! Discussion here.
    Dismiss Notice

DiY PCB Milling bits and beginner tips

Discussion in 'Hobby Engineering' started by Thalyn, May 24, 2020.

  1. Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    I've recently started trying to mill my own PCBs. Basically copper-clad FR4 boards (wish I could find FR1s for cost reasons) with a cheap 3018 Pro CNC router (typically sold under the SainSmart brand). I'm not expecting miracles, since it's not what I would call a high-grade piece of kit (nor am I able to operate the software to a high grade) but it will hopefully beat perf boards out in time - especially if I'm repeating the same board over and over (such as A/V boosters for retro consoles, of which my brother has many).

    I'm having trouble, though, getting what I would consider reliable cuts.

    Mainly it's the traces themselves. I'm currently using a 0.2mm 30° V-bit to cut them. But because the blanks (as is probably expected) aren't perfectly flat, I'm finding I have to make the cuts fairly deep (in the order of 0.3mm-0.4mm, instead of the 0.1mm I want) in order to reliably do the whole board, even with something as small as 2cm x 4cm. This doesn't make a massive increase, but it does mean some cuts are up to 50% wider, which is a problem when I'm still trying to make sure the traces are not completely cut through (cheap bits, so I don't expect them to be exactly 0.2mm, and I doubt the spindle is 100% true either).

    To that end, what kind of bit should I be looking at? 0.2mm bits are going to be extremely fragile (I've already broken three 0.8mm flat bits dialing in feed rates for cutting the board free), and I've heard similar of narrower Vs (like 10°), but I really feel like I need something with a more consistent width so I can simply cut deeper.

    I'm also wondering if anyone has some tips to offer for starting out - particularly in the case of making sure enough copper is left to connect everything but it's not close enough to easily bridge solder. I'm using KiCAD with the traces set to 0.4mm and flood gap set to 0.4mm. FlatCAM creates the GCode with the assumption that the mill is using a 0.3mm bit just to get a bit more material left behind. I'm thinking I need to go up to a higher flood gap, however (0.5mm? 0.6mm?), but that will naturally change if I start using larger bits for cutting.

    Cheers.


    PS This is my latest run. As you can see (particularly at the bottom left) it just isn't leaving some traces behind and a few pads are a little thin, but it's giving some very nice results (IMO) so I feel like a little more persistence and tweaking should be all it takes.
    20200524_173412.jpg
     
  2. aXis

    aXis Member

    Joined:
    Jun 27, 2001
    Messages:
    5,548
    Location:
    Kalgoorlie, WA
    I've been doing PCB milling for a couple of years, I'm no expect but have made some tweaks to get good reliability. BTW I use a Cyclone PCB Factory - mostly 3D printed DIY jobbie.

    1) *Most important improvement* - modify (or replace) your controller so that it can accept an electronic Z-probe input, and get some software that can do mesh levelling. Clean the board first then use an aligator clip on one edge of the board and another on the milling bit. I then probe across the project cutting area using a 10mm grid or thereabouts.

    2) *Second most important improvement* - hold the board in deliberate curve and clamp the edges well. I 3D printed a wasteboard for mine to suit 10cm x 7cm boards, and it has a 1mm difference between the centre and the two long edges. I then have two hold-down clamps that run the entire length of the long edges. This takes out some unknown warp in the board and makes it *much* stiffer against the cutting tip. The mesh levelling will happily take care of the curve.


    Other tips in no particular order:
    3) If you're using FR4, you'll need good dust extraction, the fibreglass dust is harmful. I've found the safer FR1 / FR2 on ebay and aliexpress plenty of times.

    4) 30 degree carbide v-bits are fine for the traces. I think I've got mine set up for 0.2 to 0.25mm depth, but you'll need a stiff & accruate board for it to work (see #4 and #5). Not all the bits are as sharp as each other, in a pack of 10 I usually have to discard a couple that just seem to make poor cuts or have trouble starting.

    5) I think I'm using a 0.8 or 1.0mm endmill for cutting the boards free, usually about 0.4 to 0.5mm per pass. For the through-holes I use 0.8mm drill bit, it's a good balance for most parts and occasionally I have to enlarge them by hand to 1mm for for bigger components.

    6) Within reason, no issue making traces wider. On your board above you've got massive amounts of space, they could be 2mm wide without issue. I'm typically doing 1mm for signals and 2.5mm for power unless I need to route something tight.

    7) The gap between traces can be fairly small, typically mine is only the cutter width so maybe 0.3mm. Just cleanup the surface with a brass wire brush or kitchen scourer to knock off any dags that might bridge it.
     
    Last edited: May 25, 2020
    Thalyn likes this.
  3. dirtyd

    dirtyd Member

    Joined:
    Jan 4, 2006
    Messages:
    4,042
    Location:
    Melbs
    Great tips, another thing you could consider for a wasteboard is to mill a flat area on some chipboard or MDF with an endmill. That way it should be flat to the machine axes.
     
    Thalyn likes this.
  4. OP
    OP
    Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    Appreciate the feedback, aXis. Hopefully, seen as this is a fairly common unit, finding out how to add levelling shouldn't be too difficult (though I am using the stand-alone controller, which might have to be retired for that). Traces that wide may also help with the other issue I'm experiencing (the V-bits I've got like breaking off just the very tip, which in turn tears up more copper than it should). The rest of it I should be able to manage, though again I really wish I could find FR1 boards (I searched an awful lot when looking for blanks and just turned up FR4s or proto-boards, thanks to AliExpress' "helpful" search).

    My surface at the moment is just a piece of 6mm MDF, so there could be room for improvement. I'm also using the provided (and pretty woeful) clamps, which I'm hoping to replace shortly with a 3D printed bracket that fits more closely and some more usable clamps. I figure a good hold-down is worth losing ~1mm around the edge.

    I also have a few more bits on the way to experiment with. Some 0.8mm diamond cut bits for the holes and edges (currently using 0.8mm flat ends) and some 0.3mm 60° V bits to try on the traces in the hope they don't break as much. If they ever show up there's also some 0.2mm ball end stub mills on the way from China which I figure might be spot on for cutting traces.
     
  5. aXis

    aXis Member

    Joined:
    Jun 27, 2001
    Messages:
    5,548
    Location:
    Kalgoorlie, WA
    Unfortunately the copper clad PCB is not flat enough - they have (small) warps and bulges in them that really hurt when you're trying to get a cut depth accurate to 0.1mm. You would have to have a vaccum system to get it flat, hold downs around the edge wont help.


    Yeah definitely don't use endmills for holes, they wander too much when they start and might break. Something with a drill point on it is the go.

    I use something like these for my traces, cant remember if I bought 0.2mm or 0.1mm though. Pretty sure it was 0.2mm.
    https://www.ebay.com.au/itm/5pc-3-1...de-Engraving-Bit-CNC-Router-Tool/163670025361

    A set of twist drills for holes ranging 0.3 to 1.2mm, but really I just use the 0.8mm:
    https://www.ebay.com.au/itm/0-1-3-0...Steel-Carbide-Set-Rotary-Milling/312808774833

    And then a stack of 1mm endmills for curtting out the board:
    https://www.ebay.com.au/itm/10pcs-1...-Drill-Bit-Milling-Cutter-Set-AU/174003266531
     
    Last edited: May 27, 2020
    Thalyn likes this.
  6. OP
    OP
    Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    I did see one guy suggesting a screw in the middle of the board to help with that, but it feels like chasing a moving goal. Sure it'd pull the middle in (hopefully flat) but then it can still have slight ripples between that and the edge. Could add more (and more) screws but that feels horribly wasteful if you're not milling the whole board and preparing to have mounting holes in those places.

    A quick look at automatic levelling... there's a program called Autoleveller which can evidently operate on the 3018s, but I would definitely have to remove the offline controller. It re-writes the GCode, which would work with the OC, but without being able to manually re-position (I've got FlatCAM generating off 0,0) it would be meaningless. More investigation is required, me thinks.
     
  7. ericks

    ericks Member

    Joined:
    Nov 3, 2012
    Messages:
    86
    Location:
    Adelaide
    I used a depth controller on my 6040 to do pcb's and engraving signs...no need to have the board flat with this attachment. The unit is expensive but i am sure you will be able to make one yourself :)
     
    Thalyn likes this.
  8. aXis

    aXis Member

    Joined:
    Jun 27, 2001
    Messages:
    5,548
    Location:
    Kalgoorlie, WA
    I'm using bCNC, which is a basically a GRBL job manager. It takes the input GCode file (generated by my pcb software) and then sends/queues it to my arduino GRBL controller.

    bCNC has a user interface for driving the router around, and also tools for probing and autolevelling. You load a file with the extents of your job, manually drive to where you want X0 & Y0 to be then zero those co-ordinates, probe the surface once and use that as Z0 reference, then autolevel probe the rest of the job area across a grid. When you start the GCode job it will modify the z-axis dimension on the fly to do the levelling. I use the outline cutout as the extents for my job as all of the traces will then fall inside that, it will still remember the autolevel details as you load the traces and/or drill holes files.

    The Sainsmart pro says it uses GRBL so you should be able to drive it with bCNC too.
     
    Last edited: May 28, 2020
    Thalyn likes this.
  9. OP
    OP
    Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    While I perhaps could, without a little more specific information I'd probably wind up making the wrong thing. Still, it could be interesting to find out what I've made and what it actually does....

    Sounds like it could be a much better option. Will have to dig out the laptop (or maybe the RPi2?) to run the mill, but I guess at least that does away with the SD card shenanigans. Just so I'm looking in the right place, though, that would be by "vlachoudis" on GitHub, yeah? If so, that looks like a very interesting piece of software - especially given it claims to do CAM stuff, too (since I currently lack a way to do normal wood operations).

    Once again, I appreciate the feedback and advice. Hopefully I've got the wherewithal about me to put it into action.
     
  10. aXis

    aXis Member

    Joined:
    Jun 27, 2001
    Messages:
    5,548
    Location:
    Kalgoorlie, WA
    Yep that's the one.

    I run it on a windows laptop, just make sure you dial back all the power saving features otherwise the jobs might fail halfway through. I have a mate that runs it successfully on an RPi2.

    The CAM operations do my head in, the learning curve is a bit steep but don't let me stop you from having a go. Loading gcode, probing etc is not too bad though, I found some tutorials I think.
     
    Thalyn likes this.
  11. ericks

    ericks Member

    Joined:
    Nov 3, 2012
    Messages:
    86
    Location:
    Adelaide
    If you look at cncstep....they sell accessories including a depth controller, they even have a video showing how it works. I have one and it's possible to make something similar :)
     
    Thalyn likes this.
  12. OP
    OP
    Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    I was wondering about some kind of spring-loaded mechanism like that. Actually fitting it could be interesting, of course, but seeing that it actually works is giving me ideas that I probably shouldn't be having. I wonder how well a PETG bracket would hold up...?

    Excellent. That it's know to work on an RPi2 is even better, but for sure I'd be starting on a laptop. Good call on the power saving.

    Gonna quickly throw one other question your way, aXis, if you don't mind. You've mentioned you had no trouble finding FR1/FR2 boards - is there any kind of keyword/s I should be using? I've found a handful of what I think are FR1 (they list as SF) but they mostly come in either small boards (5x7, which is likely fine for now) or singles with stupid shipping. FR4s show up a plenty, at roughly $2 per 10x15; though of course it's not for certain that they're actually FR4s and not just using that as a keyword.
     
  13. Mathuisella

    Mathuisella Member

    Joined:
    Dec 3, 2002
    Messages:
    7,540
    Location:
    in your gearbox...grindin
    I don't know if this would help, but why not vacuum/suction from the underside in the middle of the board, that way you don't miss out on real estate or have to modify any designs and it sits flat ? :)
     
  14. OP
    OP
    Thalyn

    Thalyn Member

    Joined:
    Jun 2, 2005
    Messages:
    458
    It's something to consider for sure. But given the limited vertical space (this isn't exactly a huge unit) and the potential cost of implementing it (it wasn't an expensive unit, either), it's probably something better suited to a higher grade of production than what I'm trying to do. After all, I'm hardly producing these things to sell - this is just to whip up boards which might need to be duplicated for little projects, like AV booster modules or cartridges to suit 8-bit computers.
     

Share This Page

Advertisement: