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Cheap 3-Axis Mills

Discussion in 'General Electronics Discussion' started by Rixen, Sep 21, 2017.

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  1. Rixen

    Rixen

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    Feb 16, 2016
    edit: Post moved from this thread: https://www.electronicspoint.com/threads/3d-printer-thread.283584/

    Shamelessly bumping this.

    I know it's not a 3D printer but.. Has anyone tried those 200$ 3-axis mills from eBay?

    I actually already made a box for exposing PCB's, but then I stumbled on an instructables guide of a guy making a mill, it looks pretty easy to convert a layout to g-code. Could be a viable alternative to all those nasty chemicals, especially considering it would just be in my apartment. :)
     
    Last edited by a moderator: Sep 22, 2017
  2. Ian

    Ian Administrator

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    I've moved this post to a new thread, as it'll hopefully generate a bit more attention and keep both threads on topic :).

    I've also been considering getting one of these 3-axis CNC machines, as the price has dropped substantially over the past few years. Hopefully someone on the forum already has one and can advise on how well they work :).
     
    Rixen likes this.
  3. Minder

    Minder

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    Apr 24, 2015
    Is it really worth it when the likes of Seeed et-al offer qty 10 double sided PCB's 100mm x 100mm for $5.00?
    From your Gerber file.
    M.
     
  4. Rixen

    Rixen

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    Feb 16, 2016
    The problem I have with that, is that we still have to wait an eternity for it.

    Often when im fiddling around with something, I just want to whack some layout together and go make/etch it. Right now I gotta drive to my work to do that, being able to do it at home, easily, whenever I want, appeals to me :)

    Ofcourse a more "final" PCB would be ordered..
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Exactly.

    The cost for me to produce a single PCB on a laser cutter way exceeds the cost of getting a real one from China, but I can go from concept to prototype in a day.

    I'm pretty sure these milling machine would be faster because I just use the laser to get a resist pattern on the board.
     
  6. Doug3004

    Doug3004

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    Sep 5, 2014
    The typical t-slot-extrusion mills are often called "3040 routers", because the table size is usually 30 x 40 cm.

    I don't have one but people who do say that the cheapest ones aren't really precise enough for anything more than artistic use, since they only use one acme screw for each axis and the (cheap) slides wobble. They might work well enough for copper-clad routing, but they're not accurate enough to make machined metal parts.

    If you have access to a drill press then you can buy better parts than that, but it's not hard to spend over $1K just for the metal parts for a little machine.

    I have a benchtop mill and benchtop lathe that are both manual. For various reasons I don't think they're worth converting to CNC.

    I've seen a few of the typical "router bits" that are sold for CNC routers--I've ordered some out of curiosity and I've gotten some for free when ordering other stuff--and they're all made very poorly. They are real carbide, but the grinding is usually done very badly. The cutting edges don't meet properly and they are totally unusable for milling metal. Sometimes the cutting edges are left totally unground in spots.... A lot of the problems people have with crappy CNC router results could be helped by better bits, but the china bits cost $1 and good bits cost ~$10.

    One thing I've always wondered is why you can't use a CNC mill also for 3D printing. Nobody online seems to be doing it. A 3D printer isn't stiff enough to work as a mill, but a mill should be able to do 3D printing with just a change of spindle attachment.
    ,,,
    The main reason I've heard people claim is that "a CNC can't move fast enough for a 3D printer", but then,,, I've also heard of people printing big & complicated stuff that takes 12-18-24+ hours to print. How fast can the thing really be moving if it's taking that long? And extrusion printing with thermoplastic has an inherent speed limit in how fast the plastic can heat up and cool anyway. I have a hard time believing that such a dual-use machine would be impossible to build inexpensively.
     
    hevans1944 and bushtech like this.
  7. kellys_eye

    kellys_eye

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    Yup, I agree - total b0ll0x. A CNC can easily move at 10's or 100's mm per second and I've never seen a 3D printer move at anywhere near those speeds anyway!

    I did watch a Youtube video of a milled PCB that did 0.4mm pitch IC's (it was an adapter board - to standard 0.1" pads) which was certainly impressive but also looked to be $1,000's worth of kit to achieve.

    I'm sure the quality will improve and prices will fall as time goes by but isn't that always the case..... when is the right time to buy?

    If you have any decent mechanical construction skills I don't doubt that making a PCB router wouldn't be within anyone capabilities but we can all wish for the workshop facilities that such a task would require!
     
  8. Rixen

    Rixen

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    Feb 16, 2016
    This is a valid concern I think, is the axis movement really that sloppy or what's going on ? And what materials are those people trying to machine? I mean, the raw PCB i buy has a Cu layer thickness of 35µm.

    I must say, im not overly concerned about these small mills ability to machine actual metal parts, I have pretty much unlimited access to CNC lathes, mills, professional 3D printers, whatever tool I could ever need.. So i'd never use them for that anyway, my only interest in them is to mill euro card sized PCB's in my appartment :)

    At uni we have a tiny mill called Taig(?) I think it's one of the more expensive ones, could try mill a PCB on that maybe..

    Uhhm.. My own 3D printer made of the finest chinesium.. The stock printspeed in Cura was 20mm/s, but it's quite happy printing at 60-70 mm/s.

    But there's a ton of factors to also consider when looking at total print time, print speed, layer height, fill density, shell thickness, brims/rafts and im sure alot of other things.. :)
     
  9. Doug3004

    Doug3004

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    Apparently it's the type of linear rails they use. The cheapest ones just have a lot of lateral play. Plus the table has the mounting points at opposite ends set rather close, and the screw they use is just one centered acme screw with a relatively-light-tensioned anti-backlash nut, driven by a fairly small stepper motor directly.

    It's not difficult to obtain better parts, but if you replace all the bad parts then it's not going to cost $200 anymore... To do one the way I'd want would cost nearly $1500 just for the metal parts alone, not including the spindle motor. And I'm not talking about building a high-power, ultra-fast servo-motor machine.

    I also don't like the way that CAD/CAM software tends to be fragmented into three stages. You have a CAD program, a CAM program and a third program to feed the g-code to the machine interface. Problems can arise in later stages that aren't apparent in the CAD stage, and so you don't know anything is wrong until you ruin a $5 piece of metal, or a $10 mill bit. This seems to be a holdover when small CNC machines were used with a PC running DOS with only 64K of RAM and they all used dumb interfaces connected to the printer port.

    With 3D printers they bypassed that and used smart interfaces (arduinos and such, with their own on-board processors) and they unified the software as well. You can design and print parts without leaving one program, and using Windows isn't a problem (RTLinux not required). Plus the software can have special features that are related to extrusion printing. With many 3D printer programs you can still import common 3D CAD files and you can still mess with the g-code if you want to, but you don't usually need to. This makes 3D printer software easier to use overall.

    I had assumed that (if I ever got around to building any CNC mill) I would first try writing my own CAD/CAM software--partly out of curiosity and partly out of a desire to avoid the silly things about 'normal' low-end CAD/CAM software. Things like needing plugins to make common parts like cams or screw threads, or to operate a more-than-3-axis machine.
     
  10. Minder

    Minder

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    Apr 24, 2015
    Generally one of the reasons they are 'Fragmented' is a Post Processor is usually required as all CNC machines are not created equal, depending on manuf. the post processor usually provides the serial or other transmission as well as formatting the CAM program for the particular machine it will be used on.
    Many systems are designed to develop the part off line, this way it does not tie the machine up.
    BTW, I have two mills running under dos based control, it also has a graphical display for dry run etc.
    If a motion card is used for the CNC control, little is required in the way of HMI etc.
    M.
     
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