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IndustryArena Forum > Other Machines > PCB milling > First CNC PCB mill build started, advice etc appreciated
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  1. #1
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    First CNC PCB mill build started, advice etc appreciated

    Hi,

    Started collecting parts and looking into building an Arduino based PCB mill.
    I opted to go for a DIY solution as that is what is half the fun imho.

    The parts I've got:
    3x Nema 17 stepper motors 42oz
    1.8°step angle (200 steps/revolution). Each phase draws current 0.4A at 12V, allowing for a holding torque of 26Ncm(36.8oz.in).
    1x Arduino UNO with grbl 0.9
    3x easy driver stepper motor driver boards
    1x 550 18V motor to drive the spindle axle via belt and pulleys.
    The spindle axle is fixed using four ballbearings that will be held in place on the Z-plate by alu-clamps.

    1x 400mm ballscrew with anti-backlash-nut, bearings etc...I got a kit off ebay.
    4x 8mm x 400mm chromed hardened steel rods with mounts.
    A bunch of rail bearings or what they are called, english is not my first language.

    I've gotten as far as getting the Arduino, easy driver boards, and stepper motors working together.
    I'm currently working on the limit switches.
    It's more or less copied from a schematic I found on this forum using google image search.
    I used 430R pullup resistors as that was what was closest at hand, and from my limited understanding, it won't make a huge difference.
    My question about this is that the switches are not isolated from eachother, they have contact, via resistors though, that may not matter?

    I've got a 12V 5A supply for the stepper motors, a 18V 4A supply for the spindle motor, I have supplies to spare, should I power the Arduino board from a supply other than USB?

    I did notice the stepper motors getting warm, not hot, during a brief test of Z-movement without any real weight on the Z-plate. The Easy Driver boards though, they got hot. I use heatsinks on the IC and plan on putting a 120x120mm PC fan blowing over the boards.
    I had not at that point adjusted the current trimpot on the easydriver boards, it was set about midway when I recieved them.

    I've swapped the wiring to thicker since testing the electronic part.

    I know the wood-halfbaked-look isn't going to win any beauty competitions. And it is temporary, unless of course it works great.

    For the X-axis I haven't decided on ballscrew kit or leadscrew as I use on the Z-axis.

    The ballscrew kit is on it's way and intended for the Y-axis, not having a moving gantry but rather a moving Y-plate.

    I hope I make some sense, I'm not familiar with terms etc when it comes to these things.

    My goal for the build is to be able to mill atleast TSSOP28 package components.

    Do I need to do anything to the firmware on the Arduino to use the limit switches?
    I definetly want to probe the PCB's to get a good a result as possible, how would that wiring look? And as above, do I need to do anything with the firmware?

    Any and all hints, tips, advice and help is grately appreciated.

    /Jonas

  2. #2
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    Re: First CNC PCB mill build started, advice etc appreciated

    I'm using grbl to drive my PCB-making CNC too, but that's where the similarities end - I don't use EasyDrivers, limit switches or probing, so there's not much I can help you there with. Two pages related to wiring up and configuring grbl you might be interested in are this one and this one - by the way, you switch wiring looks fine. As noted in the linked page, your probe goes to the A5 pin, just as if it were another switch: it just senses contact between your PCB copper and the tip of your tool. To use the limit switches, you'll have to enable them in the grbl settings - see the linked wiki page for details (setting $21 and thereabouts). To use probing, you should only need some piece of software that knows to send the right probing G-code command to grbl. Again, I don't have first-hand experience with any of that.

    Regarding heat, my drivers are older TB6560 chips which do unsurprisingly heat up, but they have a heatsink to match and a small fan for the whole box. No idea what's normal for Easy Drivers, but at any rate heatsinks are a good idea. You could limit your idle waste heat if you want by connecting your stepper driver's enable pin to the appropriate grbl "enable" outputs, so motors don't eat current when they don't move. However, that would also mean the don't "hold" the relevant axis and there might (or might not) be issues related to how fast the enable signal gets sent and processed before a new move, so you might not want to bother with that. Personally, I used not the enable input of my drivers but their current selection pin (which your drivers don't seem to have) for the same purpose, so my motors still "hold" when stationary just not with full current / torque.

    Personally, I'd go with ball screws all across the board - I'm not saying you won't be doing 0.65mm pitch PCBs, but I am saying you'll need any and all help you can get for that sort of precision - I never went that far. Good luck!

  3. #3
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    Quote Originally Posted by blinkenlight View Post
    I'm using grbl to drive my PCB-making CNC too, but that's where the similarities end - I don't use EasyDrivers, limit switches or probing, so there's not much I can help you there with. Two pages related to wiring up and configuring grbl you might be interested in are this one and this one - by the way, you switch wiring looks fine. As noted in the linked page, your probe goes to the A5 pin, just as if it were another switch: it just senses contact between your PCB copper and the tip of your tool. To use the limit switches, you'll have to enable them in the grbl settings - see the linked wiki page for details (setting $21 and thereabouts). To use probing, you should only need some piece of software that knows to send the right probing G-code command to grbl. Again, I don't have first-hand experience with any of that.

    Regarding heat, my drivers are older TB6560 chips which do unsurprisingly heat up, but they have a heatsink to match and a small fan for the whole box. No idea what's normal for Easy Drivers, but at any rate heatsinks are a good idea. You could limit your idle waste heat if you want by connecting your stepper driver's enable pin to the appropriate grbl "enable" outputs, so motors don't eat current when they don't move. However, that would also mean the don't "hold" the relevant axis and there might (or might not) be issues related to how fast the enable signal gets sent and processed before a new move, so you might not want to bother with that. Personally, I used not the enable input of my drivers but their current selection pin (which your drivers don't seem to have) for the same purpose, so my motors still "hold" when stationary just not with full current / torque.

    Personally, I'd go with ball screws all across the board - I'm not saying you won't be doing 0.65mm pitch PCBs, but I am saying you'll need any and all help you can get for that sort of precision - I never went that far. Good luck!
    Hi and thanks for your reply
    I've put a 120x120mm PC fan blowing across the perf board with the easydriver boards on it.
    I also wired all switches except for one, I had to get more switches ordered due to a brainfart on my part.
    I'll read the pages you linked, thanks!
    I've decided to use ballscrew for both X and Y axis, Z will remain as is with the leadscrew. There's hardly any backlash with the 1mm one and with the added weight of the spindle motor, axle etc I think it's going to be all but eliminated.

    Is it really that hard to mill 0.65mm pitch SMD's?
    With the spindle axle and motor separate, only connected via belt, that should get the runout way down.
    Atleast that is my hope. The axle has 4 ballbearings on it, tight enough fit that I can feel no play at all.
    The ballbearings in turn will mount to the Z-plate with CNC'd alu-clamps, one for each ballbearing. The OD of the ballbearings seem to match a popular OD for carbon fibre "tubes" used in quad-copters. Lucked out there lol.

    When I thought about the shady looking wood parts of the mill, I got to thinking that wood might actually absorb some vibrations? Adding precision if done right?
    Speaking of vibrations, I've seen "gasket" type things that dampen vibrations from the stepper motors. Could that be something worth looking into?

    The probe, should I add an external pull-up resistor as in the limit switch schematic?
    I've downloaded a probing SW I found via a YouTube video, autoleveller or similar I think it's called.
    Writing from my phone, so I don't have more info at hand than I retain in my head...not that much in other words lol

    Once again, thanks for the reply and wishing me good luck

    /Jonas

  4. #4
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    Re: First CNC PCB mill build started, advice etc appreciated

    Quote Originally Posted by mayday_75 View Post
    Is it really that hard to mill 0.65mm pitch SMD's?
    I couldn't really tell you to be honest because I never even tried that small. I did try normal SOP (1.27mm) spacing and I could get it to work, with some room left, when everything was going just right - but it was clear I would be pushing things to the limit if I tried. At 0.65mm pitch, you have to be able to mill 0.3mm or so thin grooves _reliably_, and that's not easy considering the typical tool used is a "V"-tipped engraving stylus* with a 0.2 ... 0.1mm width _at the tip_, which grows as soon as you plunge into the copper - the deeper you go, the wider the groove becomes because of the "V" shape. It's possible levelling would solve this for you - as I noted, I never tried it, choosing to pre-mill the sacrificial HDF bed under the PCB flat first instead. It has to be said, this method definitely doesn't guarantee uniform groove depth unfortunately - you might be not going completely through the copper in one corner and going too deep and wide in another. Perhaps probing can fix all that for you though.

    Quote Originally Posted by mayday_75 View Post
    When I thought about the shady looking wood parts of the mill, I got to thinking that wood might actually absorb some vibrations? Adding precision if done right?
    Speaking of vibrations, I've seen "gasket" type things that dampen vibrations from the stepper motors. Could that be something worth looking into?
    PCB milling isn't really a high load milling operation (and it should be a high RPM one) so there really shouldn't be any vibration to speak of. What there will be however is lots of rapid movements jumping from track to track (or worse - form some part of track to some part of another track, randomly, depending whether your gerber-to-gcode converter optimizes or not) meaning that the rigidity of your frame does get tested (think of a printer starting to swing the whole table it's on while its carriage goes back and forth). If there's enough give in the frame to not get you back _exactly_ in the groove, you'll have misaligned grooves (and that's assuming you runout and backlash are zero - they never really are - and your motors are doing perfect microstepping). Wood frames are also rather vulnerable to humidity-caused subtle warping (so I hear - mine is aluminium), and in an application like this that can't possibly be good... As for the "gasket" things, I'm not sure what exactly those might be; at these hobby sizes, I haven't seen the motors themselves mounted any other way than rigidly screwed to the frame. However, what I have seen used (and my CNC came with them) are flexible shaft couplings (looking like normal couplings with transversal slots in them), which are supposed to dampen the instant torque change of the steppers against the inertia of the axes. I can't really tell you how indispensable or not they are, as I said my CNC came with them...

    Quote Originally Posted by mayday_75 View Post
    The probe, should I add an external pull-up resistor as in the limit switch schematic?
    I've downloaded a probing SW I found via a YouTube video, autoleveller or similar I think it's called.
    Yeah, you should - strictly speaking these things shouldn't be needed because there are internal pull-up resistors in the Arduino itself already doing the same job. However, CNCing is an electrically noisy business (which gets downright horrible if your spindle is VFD driven), so in practice you definitely want those resistors there (at the probe too), and possibly even some small capacitors in parallel with the switches / probe for the same purpose, if you keep encountering false "limit" triggers. Again, good luck!

    *There are horribly thin cylindrical mills that don't care about penetration depth for consistent groove width but they're definitely not as widely used by amateurs due to higher cost - and frankly, they look like they're about to break if you just look at them wrong; even the tips of the sharper 0.1mm "V"s tend to break quite easily if you go too fast or spin too slowly (10000 RPM minimum, 20000 or more would be better) - you just notice that the tool suddenly doesn't seem to cut all the way through the copper anymore... There are also some nice "floating" attachments that "ride" the surface of the PCB and guarantee a uniform depth, but those are typically even rarer than the hair-thin cylindrical tools...

  5. #5
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    Re: First CNC PCB mill build started, advice etc appreciated

    Hi,
    Well I've gotten some 2020 profiles in various lengths(4x 400mm and 4x 382mm) and T-nuts, T-bolts, angle brackets of a few different sorts etc ordered.
    I've got quite alot of slow setting epoxy, some chemical metal and of course the cyanoacrylate glue.
    That should take care of atleast some of the frame for the thing lol

    I also got a second ballscrew kit (for the X-axis), leaving only Z-axis using a leadscrew.

    I'm now trying various methods of mounting the ballscrew endbrackets (or what they're called) to the 2020 profile.
    The mounts I got with the second kit are FS/FK10's. The first kit came with BF/BK10's.

    I've wired one board for limit switches using 330R pull-up resistors and another using capacitors instead as I read in some thread somewhere that was better, anyway I'm prepared to try both.

    The only "Wooden" part of the CNC at this point is the "base-plate" I'll mount it all to.

    I've, more or less successfully, tried to make my own mounts for the FF/FK10's as I can pretty much bolt the BF/BK10's to the base that's made of MDF and has holes for them allready.

    I've gotten two boards running nicely with Grbl v0.9j, I've got easydriver stepper drivers at home and also the bigger version, the BigEasy stepper motor drive board ordered.
    I ordered a 10A capable DC motor controller to use between the 18Vdc 3A switch mode power supply and the electric motor that'll run the spindle axle via belt and pulleys.


    All the wiring is soldered, apart from the probe as I got the alligator clamps today and haven't gotten around to it.

    I opted for beefier steel rods for the Y-axis, 12mm instead of 8mm that all the others are. At the same time I got a pair of SC12LUU figuring that if they're long enough I can get away with one per side.

    I'll have enough left over once this is done to build a small cnc-laser or something lol.

    I know I would have gotten off cheaper buying a kit, but for me part of the fun is building it myself, and in the process I learn what the different parts etc actually do.

    Anyway, any tips, hints or ideas as to where to get brackets that mounts the ballscrew ends to the 2020 profile?
    Attached Thumbnails Attached Thumbnails FF10_mount_first_attempt_2.jpg  

  6. #6
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    Re: First CNC PCB mill build started, advice etc appreciated

    Wow, this thread is really in need of an update.
    I've abandoned all wood parts, ordered HY-div168n-3 stepper motor drivers, started a small collection of 2020 & 2080 profiles. Ballscrews on X and Y, still only leadscrew on Z. I've got a 300W spindle with a 36Vdc 10A supply.
    As I'd like to be able to mill aluminium as well, the spindle will need to be upgraded at some point.
    I will use sbr10 rails with sbr10uu blocks for the Z-axis.
    12mm steel rods with the 12luu blocks for the Y-axis.
    3 mgn12 rails with mgn12h carriages for the X-axis, one on top of the upper 2080 profile and two on the front of the two 2080's that make up the horizontal part of the gantry.
    I'm thinking of going mach 3 or linuxcnc instead of arduino for the control.
    Just a short update off the top of my head.
    I'd forgotten I made this thread.

  7. #7
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    Re: First CNC PCB mill build started, advice etc appreciated

    Quote Originally Posted by mayday_75 View Post
    Wow, this thread is really in need of an update.
    I've abandoned all wood parts, ordered HY-div168n-3 stepper motor drivers, started a small collection of 2020 & 2080 profiles. Ballscrews on X and Y, still only leadscrew on Z. I've got a 300W spindle with a 36Vdc 10A supply.
    As I'd like to be able to mill aluminium as well, the spindle will need to be upgraded at some point.
    I will use sbr10 rails with sbr10uu blocks for the Z-axis.
    12mm steel rods with the 12luu blocks for the Y-axis.
    3 mgn12 rails with mgn12h carriages for the X-axis, one on top of the upper 2080 profile and two on the front of the two 2080's that make up the horizontal part of the gantry.
    I'm thinking of going mach 3 or linuxcnc instead of arduino for the control.
    Just a short update off the top of my head.
    I'd forgotten I made this thread.
    I have to say I am a bit confused. The thread title says "First CNC PCB mill build started, advice etc appreciated" but I am not sure which advice you are looking for or what the status is.

    I have built a CNC but I went for 4590 for most parts, 1.5kW 3ph 24krpm spindle, VFD and so on. Personally I think 2020 and 2080 is too weak, even if you only plan milling PCB. In my opinion the design you had in mind is too weak for aluminium, for PCB it might work. The spindle you have is far too weak (speaking out of experience) and is questionable even for PCB, but for PCB, if you run with slow feed rate, it will be OK, though I don't think you will get good enough accuracy.

    Right now I am in the process of designing/building a 3D printer and even that is designed out of stronger, more rigid material, since I will use 3030 and 3060 for the frame, 15x120 for the Z holder and under the table (part of the frame), 2 x 12mm ball screws for the Z, 2x MGN12 for Z, and 2x MGN12 for Y, 2x MGN9 for the X, so I actually think my 3D printer will be very much suitable for PCB milling as well, with the exception that if I had plans for using it as a mill I'd change the MGN9 to MGN12, but other than that, nothing needs to be changed to convert it to a very good PCB mill.

    BTW, your blog is empty... does not show anything at all. Perhaps it is supposed to be like that, perhaps you need to change some settings, I don't know.

  8. #8
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    Re: First CNC PCB mill build started, advice etc appreciated

    Quote Originally Posted by A_Camera View Post
    I have to say I am a bit confused. The thread title says "First CNC PCB mill build started, advice etc appreciated" but I am not sure which advice you are looking for or what the status is.

    I have built a CNC but I went for 4590 for most parts, 1.5kW 3ph 24krpm spindle, VFD and so on. Personally I think 2020 and 2080 is too weak, even if you only plan milling PCB. In my opinion the design you had in mind is too weak for aluminium, for PCB it might work. The spindle you have is far too weak (speaking out of experience) and is questionable even for PCB, but for PCB, if you run with slow feed rate, it will be OK, though I don't think you will get good enough accuracy.

    Right now I am in the process of designing/building a 3D printer and even that is designed out of stronger, more rigid material, since I will use 3030 and 3060 for the frame, 15x120 for the Z holder and under the table (part of the frame), 2 x 12mm ball screws for the Z, 2x MGN12 for Z, and 2x MGN12 for Y, 2x MGN9 for the X, so I actually think my 3D printer will be very much suitable for PCB milling as well, with the exception that if I had plans for using it as a mill I'd change the MGN9 to MGN12, but other than that, nothing needs to be changed to convert it to a very good PCB mill.

    BTW, your blog is empty... does not show anything at all. Perhaps it is supposed to be like that, perhaps you need to change some settings, I don't know.
    Hi,
    Well tbh I'm confused as well.
    I know the spindle was a poor choice. I could always re-use the power supply for that to power stepper motors. It's 36Vdc but I have a few LT1083CP voltage regulators and they are 7A capable with adequate heatsinking.
    I just made some holes with my power drill in the drill press stand. Even reinforced with steel epoxy it's pretty much useless as I think my drill has about the same runout as an oscillating sander.
    The blogger, should work as I have quite a few viewers.
    Mayday DIY audio | DIY is about the process as much as the results, keep it fun!

    I appreciate all advice and criticism, as long as I learn something from it.

    In this area I'm less than green. Diy audio, pc building, circuit design and PCB layout...those areas I know more about. Bodybuilding and diets, there I am a "guru" and I have coached a few competitors.
    Sorry about the ot.
    I have to cut this post short as my baby girl needs my attention.

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