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PCB Making plotter/drill only 100x150mm. Any ideas?

Discussion in 'CNC Mills/Routers' started by Johan Smit, Sep 29, 2015.

  1. Johan Smit

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    Hi,
    I am in need of a cnc machine to do pen plotting/scraping, cnc drilling, and maybe light milling with a Dremel.
    The PCB's I need to make will only be 100 x 150 mm max.
    Any ideas please?
    I can use a 3d printer, but the z axis movement need be small, so it would be a waste to get a complete 3d printer. Accuracy is important, especially if scraping is used, because multiple passes will be done.
    Please point me to a reasonably priced solution.
    Thank you
    Johan Smit
     
  2. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Hello Johan,

    Are you going to build it yourself? What is a reasonably priced solution, what's the budget? Frequency of use? Precision requirements?

    -Ronald
     
  3. David the swarfer

    David the swarfer OpenBuilds Team
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    I think you need a C-Beam machine, it has the rigidity and the accuracy for doing PCB work.
    remember that the copper layer is very thin and you on;y want to cut through it and not the rest of the board (-:
    accuracy is prime for very shallow cuts like this, since any warp in the substrate will result in shorts between traces.
    http://openbuilds.com/threads/c-beam™-machine-plate-maker.2349
     
  4. David the swarfer

    David the swarfer OpenBuilds Team
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    hmmm, in Africa I see, welcome to the club! I am in Grahamstown.

    and don't worry about having stuff shipped here, Mark does a brilliant job of packing in the strongest cardboard I have ever come across!
     
    #4 David the swarfer, Sep 29, 2015
    Last edited: Sep 29, 2015
  5. Johan Smit

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    Thank you David and Ronald.
    Milling pcb's is only an option for large tracks and components, I am now told.
    I think I would rather stay away from that.
    I had used a pen plotter for years, and it works well for tracks 12 mil and over.
    I still have a Roland A3 plotter. Unfortunately it uses HPGL, and Eagle, the pcb drawing software I currently use really sucks at hpgl.
    It covers all the drill holes, so you have no way to centre the drill, making the plotter useless.
    Also, I want to go to smaller tracks, down to perhaps 6 mils. (I can dream.) From all I read, there are two ways to do that as DIY.
    First is scratching. The board is covered with engineers blue. Then a cnc machine use a carbide stylus to scratch the blue away. This can make real thin tracks and thin spacing. It is very light work. The board is then etched in the usual way.
    The next method is to cover the board with black paint and then use a laser in a cnc machine to cut the paint away where required. This can also make very fine boards, but at least 1 watt laser with very good focusing is required. This can be cause some smoke and smell. I think I will prefer the scratch method. The method really depends on an accurate cnc machine, as the scratch is very thin, and multiple passes is required to have a wider clearance.
    I have electronic and C programming experience, but the only cnc work I have done was on a tractor that automatically moved forward the required distance, then drilled six holes simultaneously for tree planting.
    I don't mind building the machine myself, if I can get the parts bundled. I will also buy a machine, if the price is not too exorbitant.
    The C-beam machine appears to be an overkill for such light work.
    The alternative appears to be a Prusa i3 3d printer. I am wary of the stability and accuracy. The price is very attractive.
    I simply don't know, and am relying on members' experience and knowledge.
    I am in George on the south coast of South Africa, and specialized stuff is simply not available locally.
    David, can you give me contact information for Mark please?
    Thank you.
    Johan Smit
    smitjs@vodamail.co.za
     
  6. David the swarfer

    David the swarfer OpenBuilds Team
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    I used to use a program called EasyTrax that ran under DOS. It did plotting very well and I had forgotten that. I have been trying to use Eagle but havn't really got into it. I can dig out a copy of Easytrax if you want to try it, if it won't run under Windows it will run in a virtual machine.
    that is an interesting technique. you would need to have a fair bit of resolution and repeatability for that.
    6 mils is 0.1524mm, so I think you'd need 0.05/step resolution or less. 0.05 would put three passes in your 6mill track. how wide is the stylus? if it is less than 0.05 then you'd need a step size less than the stylus size.

    but, don't panic, an 8mm leadscrew with 8mm lead will give you 0.0025mm/step with 1/16 microstepping. quite easily doable.
    I wanted to build a laser into my OX but though I can find laser modules, or harvest one from a DVD player, I cannot find safety goggles at a reasonable price. The cheapest I saw were about R5000! so, scrap lasers!
    smoke and smell are easily solved with a vacuum cleaner/vent fan just outside your window, with the pipe sucking the smoke up near the laser.
    hehe, that is one I have not seen!
    I believe you are mistaken here. to get the accuracy and repeatability required, you need stiffness in the machine. The C-beam is perfect on those counts, especially compared to a belt drive printer type structure, or even the OX or Routy.
    If you click 'part store' at the top of this screen you can see the C-beam bundle.
    also keep in mind that the moment you have a C-beam (or other cnc router) you will immediately find other uses for it, like face plates, mounting panels, switch mounts etc, and that is if you stick to electronics related stuff, there are many more uses for it.
    the Prusa is great as a 3D printer, but when it comes to any kind of contact cutting you will need a lot more rigidity.
    in fact I am tempted by a Prusa kit myself, but only for 3D printing.
    There are local mail order places though, from which you can get all sorts of stuff like motors and drivers etc, so those do not have to be shipped from the USA.
    http://netram.co.za
    http://hobbytronics.co.za
    http://www.diyelectronics.co.za/store/
    I have ordered from both the first two, and just about to get a leadscrew from diyelectronics.
    As with any mail order place, if it says 'out of stock' DO NOT order it <-:
    He is the man that runs this place @kram2422 (-: (and putting his name there like that will make him look at this thread)
    had a nice holiday in George some years back. I don't suppose there is any ChooChoo activity anymore?
     
  7. Johan Smit

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    Thank you David,
    I still have a dos program called Tango, thank you. The problem is that you end up having to make footprints for every component, as the older programs do not have the footprints of all the newer parts. This multiplies the time to draw up boards tremendously. With a newer program like Eagle footprints are no problem. Eagle is widely used, and footprints and advice is available on the net.
    The carbide stylus has a sharp point, it makes a real thin scratch. It will be fruitless to ask at the engineering shops which sell these things to ask the point size. These things are normally used by hand. One can grind it blunter, I suppose, but then you would need more effort to make the scratch.
    It does appear I have to use Facebook. I have been avoiding that seeing how some people waste their time using Facebook.
    I looked at the C machine. It is certainly impressive. One can then do cnc drilling, pick and place, and such like. The only disadvantage is the total price, which will be over R10 000, almost double that of a Prusa i3. I see the controller is also out of stock.
    I am unsure if the Prusa will handle the weight of a Dremel to do cnc drilling, though. If this is possible, the problem with the drill holes may just disappear.
    Now I am still undecided, even more so. It would be nice to have a C machine, certainly. Lasers are certainly scrapped.
    The Outeniqua choo-choo is out of action for some years already. A flood took away a bridge, and with the collapse of the rail system, Knysna is still without rail service.
    Thank you again
    Best Regards
    Johan smit
     
  8. David the swarfer

    David the swarfer OpenBuilds Team
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    then the standard C-beam will do it fine at 0.0025mm per step. (8mm lead, 200 step per rev motor at 16 microsteps at 24 volts)
    I don't understand? you just click your name at the top right of this screen, select 'conversations' then 'start a conversation', and add kram2422 to the conversation. bingo, a private conversation with the inventor himself.
    you can pick and choose what you buy. as I pointed out, there are local sources for motors and controllers, so do not ship those in, you only need the rails and other hardware like wheels, leadscrews etc.
    An Arduino (R260) and 3 motor boards (R80 each) from diyelectronics, make a shield (i use vero board!) load GRBL and you are done for the controller.

    Your alternative is something like this
    http://www.cnc-step.co.za/high-z-sseries
    that tiny s-400 on the left is R80000
    it will not handle the weight!
    cya
     
  9. David the swarfer

    David the swarfer OpenBuilds Team
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  10. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    If DIY is not a problem, you might consider doing something in a C-Beam format except built around V-Slot linear actuators built with Nema 17 end plates and motors. For finer resolution, you could also use 0.9 degree NEMA motors. I'm not sure if this would offer significant savings over the standard C-Beam setup but it definitely would be more customizeable and could easily be built around shorter lengths so it would be more workable in a desktop environment.

    Rough concept shown below. Economy is based on starting with 1m lengths of C-Beam, (2x) 20x60 V-slot, and TR8*8 threaded rod and cutting them all 400-400-200 to trim the size of the machine. Further economy could be achieved by replacing the cast corner brackets with 2 and 6 hole L brackets.

    C-Beam PCB Mill.jpg
     

    Attached Files:

  11. Johan Smit

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    Thank you all.
    Totally out of reach!
    I am really glad of the replies.
    Sorry, my mistake, I thought this was a facebook address.
    That alone saved me a lot.
    Thank you, more savings.
    Rick, thank you for your reply. I really like your idea.
    Why should the frame not be welded of 50mm square tubing? That should be really rigid, and save more money.
    I need to go do work away from home, should be back by Sunday.
    I am itching to start building this cnc machine.
    Thank you for the help so far.
    Best Regards
    Johan Smit
     
  12. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    I'm all for anything that saves money but as welding is beyond my skill set and equipment availability, it never crosses my mind. As far as rigidity goes, with the low speed, low drag, low inertia system you are creating, building in substantial rigidity should not really be necessary. But if welding is cheaper and readily available there is no reason not to go with it.
     
  13. Johan Smit

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    Hello all,
    I tried to get the parts for the design from David with C-beam, minimum size.
    The price quoted was R42k, totally out of reach.
    Because I had not built anything like this before, I tried to get a parts list requirement from Hobbytronics.
    They do sell most parts, as far as I can gather, not the wheels and cart for c-beam, but linear shafts, ball screws, and such like.
    The reply short and sweet was "we do not sell kits".
    I only need a small machine, no more than 200 x 200 mm travel. Nema 17 motors should do.
    Now it is simply not on for me to order parts from them with no idea of what fits what.
    Motor couplings, for instance, which sizes both sides.
    Linear shafts, what size? Shaft support - which size is required for which shaft?
    Ball screws and nut - which size?
    Housing brackets, etc etc?
    How is the ball screw shaft prevented from linear motion?
    The frame can be welded together, no need to use C-beam for a frame.
    Of course, I need this small machine, badly.
    There are nice small drill motors available, much lighter than a Dremel. That should help.
    I think I will stay with pen plotting and scratching, but cnc pcb drilling with the machine will be a big help.
    Help please!
    Thank you
    Johan Smit
     
  14. Jonny Norris

    Jonny Norris Veteran
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    I am under the impression pcb drilling etc required C3 accuracy screws with fully closed loop servos and at c3 accuracy your then talking high precision carriages on precision rail, but on a very small scale, it's not going to be cheap but it could be cheaper making one than buying a pcb mill.
     
  15. Johan Smit

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    Thank you Johnny.
    If the drilling is a problem, I can do it manually using the machine as a drill press only, or even using a separate drill press.
    The absolute requirement is for pen potting and scratching. Both take very little energy, but accuracy is required.
    Yet others have done this even with 3D printers. I would like to build a dedicated small desktop machine.
    Price is a factor.
     
  16. Jonny Norris

    Jonny Norris Veteran
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    Suppose it's all down to resolution, if they are capable of close then maybe adding gearing of something like 20:1 would be advisable just to improve the chances.
     
  17. David the swarfer

    David the swarfer OpenBuilds Team
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    I was doing some calculating yesterday.
    an 8mm diameter, 8mm pitch lead screw can give you some impressive resolution.
    here is a quick table
    Code:
    motorstepsperrev microsteps pitchinmm mm/step steps/mm thouperstep
    200 1 8 1 0.04 25 1.5748031496
    200 2 8 1 0.02 50 0.7874015748
    200 4 8 1 0.01 100 0.3937007874
    200 8 8 1 0.005 200 0.1968503937
    200 16 8 1 0.0025 400 0.0984251969
    200 32 8 1 0.00125 800 0.0492125984
    
    so 4 microsteps puts you at 0.01mm per step, less than half a thousandth of an inch.
    8 microsteps gets you half that, and so on.
    so resolution is not a problem.
    repeatability is a bit harder though (-: reducing backlash and increasing stiffness are the goals.

    for the scratching, I think all you need is a resolution that is about 1/4 of the scratch width. this allows the mechanism to move to almost any desired scratch overlap width.
    keeping repeatability down to a similar figure should produce good results.

    there is no product in South Africa that is comparable to Vslot rail in terms of price and accuracy.
    with proper construction and some messing around, you can probably build a suitable machine out of drawer slides and plywood! however, don't be fooled by th stuff available for 3D printers, like 8mm round rails and linear bearings that fit it. That rod will not be stiff enough unless you use several in parallel, which puts the cost up, and the alignment problems can get out of hand quickly.

    my advice? get some motors (nema23) and control electronics and build something, anything, that moves and cuts, out of whatever you feel you can afford. this will teach you more than we can ever type, and will guide you in where to go next.
    here are some ideas.....
    DIY Aluminum 3-AXIS CNC Router
    The Anni Router 0.3 - All
    Router CNC Nylon
    nice welded one...
    DIY CNC Router
    Homemade 2'x4' Wood CNC Router
    this one uses linear rails, very nice
    Building your own CNC router/milling machine
    Mini CNC router, complete plans and instructions
    DIY Mini Mill Router Machine by Slide Axis CNC and Aluminium Alloy Profile - All
    drawer slides (I have a pile of them...)
    Build A Cheap Handcrafted CNC Mill

    have fun (-:
     
  18. Jonny Norris

    Jonny Norris Veteran
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    Typically the larger the pitch the larger the holding torque required to achieve the resolution so the bigger the motor, for 10mm pitch and over nema 34's would be the first choice, but for resolution the lower the better. will be rather sloppy at 8mm with nema23 unless you use a good quality zero backlash planatary gearbox.

    good work on the calculations tho, at a guess i would have believed they werent quite as good as that but most likely because of the issue above. your calculations are with a completely accurate screw, im not familiar with lead screw accuracys only balls screws but they will have be machined within a certain accuracy. so the actual accuracy will be the less accurate of the two, the motor or the screw.

    but I think a 2, 3 or 5 pitch would be what this guy needs, for sure.

    like dave said low backlash and good rigity is key to good resolution, im thinking as the cutting area you require is rather small your best bet would be a fixed gantry moving bed design, with welded steel frame.

    this type has lower weight moving parts and in respect rigitity is slightly less compromised by inertia.
     
    #18 Jonny Norris, Oct 25, 2015
    Last edited: Oct 25, 2015
  19. Jonny Norris

    Jonny Norris Veteran
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    if a cnc solution proves to be too expensive. ever heard of a 3d pentogram? this could be used with care to trace tracks from a drawing or wood template with scores the tracing rod could sit in and follow and it could part drill holes.
     
  20. Jonny Norris

    Jonny Norris Veteran
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    The part about lead screw pitch and motor size on second thought it is definitely a factor for ballscrews, And it Does exist in Leadscrews also but I'm not sure to what extent so it may be worth looking into.

    Just occurred to me that there is a difference between screws. Sorry for any confusion.
     
  21. Johan Smit

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    Thank you for all the replies.
    Thank you, that is very good to know.
    Thank you Johnny, very good tip, I was not aware of a pantograph. I'm having one made as a stopgap until the cnc machine is ready.
    I do not have any woodworking tools. Metal is more my choice.
    Then I struck a luck. I knew this workshop had built an x-y thing on a tractor to extract seedlings from a seedling tray. I heard it was not working, so my query resulted in some parts coming to me. Looks like this chap was a bit embarrassed about those parts lying there. I am oh so thankful.
    Round rods 16mm, enough for my whole project. Nice shiny, looks perfectly straight.
    Linear bearings, awful, sloppy, useless. Did they really expect linear bearings (with grease nipples even) to stay tight in such dirty conditions?
    Motors, SureStep 115 oz-inch 1.8degree/step 2 ohm 2 amp. Shaft 5mm. They look awful weak to me, but I have no experience. I would not know what the equivalent in Nema is.
    They used toothed belts, with a toothed pulley on the motors. I did not get that, but I was never thinking to use that scheme.
    Presumably the stepper motors are usable for my project.
    Now the questions are: Use the rods with some wheels running on them or forget them and go for v-slot extrusions?
    Are bearing with an outside contour to run on the round rods even available?
    Couplings, 5mm to 8mm shaft available?
    Thank you David, wise words, I think. That is what I plan to do.
    I have looked at all the web sites mentioned, and at this stage have at least an idea of cnc working, and with all the help I get here I have no doubt that the machine will be a success.
    Thanks again
    Johan Smit
     
  22. Jonny Norris

    Jonny Norris Veteran
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    Cool, glad to be of help. 2nm is okay. I have 3nm moving 125kg each with no problem.
     
  23. David the swarfer

    David the swarfer OpenBuilds Team
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    Hi Johan
    Those steppers will be fine when driving leadscrews since the leadscrews increase the force. The OX normally has a Nema17 on the Z which happily raises a trim router. However, don't make the machine too heavy, there are limits.

    Those rods, lovely. Now you just need linear bearings for them, like these
    LM16UU Linear Bearing [HWPBRNGLM16UU] - R39.90 : DIYElectronics, Electronic Parts, 3D Printers and Professional Advice!
    'more is better' up to a point, and widely spaced to minimize any lash.
    make it adjustable rather than accurate, ie rather than try to drill exactly accurate holes that will locate the bearings exactly where needed, make the mountings adjustable so you can adjust for accuracy. takes much less time and effort (-:

    some other things you may need
    Hobbytronics. Machine / CNC Parts

    leadscrew : only place I have found them in SA so far, and maybe a bit short, except for ballscrews which are fiendishly expensive
    8mm Lead Screw [9LEADSCREW] - R285.00 : DIYElectronics, Electronic Parts, 3D Printers and Professional Advice!
    note that the nut is not an antibacklash type. this will not be a problem on a Z axis since the weight will take up the slack on all but the heaviest of cuts, but on X,Y you will need to make a plan. Molding some plastic around the thread itself is a good way and I'll be trying this out, sometime.

    Run those motors on at least 24 volts, steppers just love high voltage due to the inductance.

    have fun!
     
  24. David the swarfer

    David the swarfer OpenBuilds Team
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    also keep in mind that the bigger the motor, the lower the top rpm you can expect from it.
     

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