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Thread: Small milling machine conversion to CNC

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    thehomeengineer's Avatar
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    Small milling machine conversion to CNC

    Hi All
    I have just manage to pick up a lovely little mill at a steal. I was thinking of selling it on to purchase a surface grinder. Then I thought about converting it to CNC. I have never tackled such a big electronic project as this.

    I was wondering how easy it is to do and if a kit of bits is the best way forward and what is a good and easy software package to use.
    I am very much mechanical and have tackled small projects but have little electrical/electronic knowledge but am willing to learn. I have a good PC and the mill its the bit that fits in the middle to link it all together I need .

    Just need a good starting point.

    Any advice welcome and appreciated and I thank you in advance for viewing.
    The Home Engineer

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    Seedtick (04-14-2018)

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    Conceptually, it's a controller, (which can be a cheap as some $20 Arduino-based RAMPS system), a beefy power supply, and three hefty steppers.

    Here's a Make Magazine article on doing it with one of those cheapo chinesium benchtop ones.https://makezine.com/projects/cnc-mi...-kit-hardware/

    CNC Zone is probably another good place to start: https://www.cnczone.com/forums/

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    thehomeengineer (04-14-2018)

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    The electronics is easy enough. For a parallel port setup you need a Break Out Board and you connect step and direction signals to stepper motor drives, then you connect your stepper motors to your drives. That's about it unless you want to wire up limit switches too. Though there are other ways to go with the electronics. There is a lot of other stuff to learn about CNC too though. Like what makes a good stepper motor. And how to dial in your current limit.

    This is the motion control software that I use
    LinuxCNC

    They have a forum and an IRC channel for support. They will get you up and running.

    Here is a picture of my CNC machine control cabinet

    http://i.imgur.com/2frKz9O.jpg

    It is pretty basic. I built in in a gutted out old PC case. You can buy break out boards. They're pretty cheap today. I just made my own because I like electronics. I made my own drives too but I upgraded to better drive IC drives. They were only $8.50 a piece. I can't even make them that cheap. Now I have 3 matching drives.

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    CNCzone seems pretty single minded to me. They're all about Crap3 and Gecko drives. There are other ways to do CNC.

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    https://cnc4pc.com/ Is where i got allot of my conversion parts. Breakout Board, power source, servos, encoders, cables and line drivers. They sell dedicated Mach3 and 4 computers as well as control boxes if your not ready to try building your own.

    I have not had any issues with Mach3. You can DL a trial version to play with before you buy. It has some Wizards for cutting common things like gears and hole patterns.

    I will check out the LinuxCNC too. There are many ways to do CNC like pfredX1 says. I am always looking for better ways of doing.

    Do some research and find out what fits for you. I live in a small oil town that has a few machine shops i can goto to ask stupid questions. There is also a small local network of fellow hobby CNC guys who helped avoid some of the pitfalls.

    My system keeps evolving as i add better components and more functions to it. Like a Touch Probe. Next is a 4th axis. It's probably just as satisfying building and trouble shooting the system as it is watching chips fly. When your first drive moves under computer control... Well you will see.

    I tried the Gecko controllers, which i found to be hard to tune. I have since gone to a PID controller that is self tuned. Alot more money, but less headaches.

    The latest in hobby CNC is the AC Servos. These were reserved for the industrial CNCs untill fairly recently. https://cnc4pc.com/dmm-dyn4-servo-ki...-34-frame.html

    The reason i went with servos instead of steppers, is steppers can lose steps and have no feedback loop that detects the error. Servo's have encoders that track rotation and can apply more power when they detect higher loads.

    I also added magnetic linear encoders as a calibration aid. They have a 2 micron resolution. These are not tied into the system directly, just used as an instant visual reference when setting offsets and calibrating drives.

    Another thing to consider is your CAD and CAM software. This lets you create, import and edit files. I use Solid Works and Mesh Cam. Solid Works is likely the most expensive part of the whole system. I use it for other things so i can kinda justify the rather substantial cost. They recently added a CAM function to Solid Works. Though i find it clumsy.

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    thehomeengineer (04-14-2018)

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    Did you know that LinuxCNC and Mach3 are both forks of the same public domain NIST EMC code base? So I think it is silly to pay for something that I can get for free. Plus for some strange reason being a genuine Real Time Operating System LinuxCNC outperforms Mach on Windows anyways. Though some do say Mach is easier to configure. LinuxCNC has a GUI configuration wizard today. So I think it is easy to do.

    Stepper Configuration Wizard

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    Thank you for the advice and information This is what I needed a good starting point so I thank you all for taking the time to share with me. If I run into problems (which I am sure I will) I will post for further help and advice from you all
    Thank you again
    The Home Engineer

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    I was not aware of the History of these two systems. I'm going to look into it and maybe try loading it up on an old tough book i have. Thanks.


    Andy

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    Hi All

    More help needed please.
    I think I am going to us the Mach3 package: Reasons, I have a windows PC, I also use AutoCAD and there seems to be more information on the Mach 3 system.

    This is where I need some advice:
    Motors: Nema23 seems to be very popular and come with different torques 438 oz in being the highest I can find which I think is 3.1Nm

    The donor mill has the following travel and table size:
    Table size 500mm long x 110mm wide. With longitudinal (x)l travel of 250 mm and in traverse (y) of 140 mm and 200 mm vertical (z)

    First question are these motors OK for converting a small milling machine so CNC so it can cut steel?

    Second question what size motors do you guys run on your CNC mills?

    Third and last question (for the moment) I would also like to run a fourth axis so is it best to buy a three-axis kit and add the fourth axis. Alternatively, just buy a four-axis kit.

    The third question may seem at first a silly question to ask, but I have seen fourth axis indexing/dividing heads complete with tailstock, 3-jaw chuck and motor drive cheaper than I can buy just a 3-jaw chuck.

    I look forward to your views on all the above and thank you in advance

    The Home Engineer
    Last edited by thehomeengineer; 04-19-2018 at 10:08 AM.

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    The nema 23s might be enough if you are using the acme threads to drive. Ball screws have a much faster pitch. I went with the reduction so i can add ball screws later if i feel the need.

    I run the nema 34 80v dc servos with low backlash 5:1 gear reduction on the x & y. For the z i went with a slightly larger 1100 oz-in 80v dc servo with a 10:1 reduction due to the large gearhead and 220v motor it has to lift.

    The servos will spin up to 3000 rpm so even with this reduction the inches per min are good. As for the different gear ratios, the two on the table are matched. Servo tuning makes the larger servo run faster to match the inches per min called for by Mach.

    Most breakout boards have room for up to six axis. So adding another drive is simply plugging it in and wiring it up. I went with a 4th axis setup as you mentioned "fourth axis indexing/dividing heads complete with tailstock, 3-jaw chuck and motor drive." It is a nema23 drive on that.


    Andy

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