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IndustryArena Forum > MetalWorking Machines > CNC "do-it-yourself" > 4th axis as a "poor man's lathe"
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  1. #1
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    4th axis as a "poor man's lathe"

    A few months ago I bought a rotational axis with a 4 jaws chuck for my CNC. I intend to use this as both a 4th axis on my CNC, or as an independent "poor man's lathe". I know, it will be a very primitive lathe with a lot of limitations, but I intend to try it out anyway to toy with, and to learn. I am sure I will be able to use it for some sort of work, but I will see that later.

    To get the lathe function I had to design a control box. This is based on an Arduino Uno module with a 2x16 lines LCD. It is a very simple design, using only three buttons, one for clockwise rotation start, one for counter clockwise rotation start and of course, one for stop. Stepper acceleration and deceleration is also implemented, with a possibility to select acceleration in 7 steps. The chuck rotation can be adjusted between zero and 380 RPM, which is the maximum with the stepper. This corresponds to 2280 RPM on the stepper, due to the 1/6 reduction pulley the stepper drives the chuck with. So it is a respectable rotation speed for being a stepper. The rotation speed is set using a rotary encoder and that speed is saved in the EEPROM, so after a power off, the last used rotation speed is restored. The rotary encoder push button is connected to the Arduino reset and acts as an emergency stop, in case there is a need for stopping as fast as possible. Of course, this means no deceleration, just an abrupt instant stop.

    I made a short video about testing the control box functions and showing the rotations. I have not used it yet as a lathe, still waiting for some necessary tools before I can do any real tests, but I thought this can be interesting to show as well. Maybe it will give other people some ideas as well.

    https://youtu.be/qfiPTDvZlIs

    For powering and control I also built a separate PSU, which provides 48V 7A DC through four individual 12V power supplies connected in series. Three of these are 9A supplies, the fourth is though only 7A, which is why the maximum is limited to 7A, but considering that the stepper is only 3A, I figure that the PSU will be good enough for the purpose. The PSU box also contains a DM542 stepper driver, which is configured to the maximum current and 2x micro stepping, which results in 400 steps per rev.

    There is also a relay inside the box. This relay decides if the 4th axis is to be driven as A axis by my CNC using UCCNC software, or independently run as a "lathe", controlled from my control box and rotated non-stop until i press the stop button. The relay can be switched from the control box and the default setting (with the relay off) is that the rotational axis is controlled by UCCNC.

    If anyone is interested to use the Arduino code, here is a link which you can use to download it:

    https://drive.google.com/file/d/1CJN...ew?usp=sharing

    It is well commented, so based on the code, the simple box can easily be built by anyone understanding the basics of Arduino.

    I hope you will enjoy watching this video. More on the way...

    By the way, "poor man's lathe" is a joke. I know that once ready, this is going to cost me at least $800, and for that money I can buy a much better real lathe, but this way it is more fun, even if the performance will not be as good as a lathe for 5-600 USD.

  2. #2
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    Re: 4th axis as a "poor man's lathe"

    Interesting project. I’m doing something similar using my wood lathe. I found arduino to be too slow so I’m using Teensy 3.2. The goal is to be able to just turn the machine on and not be bothered by a pc and software. Also cutting threads seems easier using a microcomputer.

    Regarding your machine; Steppers don’t have enough torque to rough cut wood. You could spin something for sanding. You can cut wood if you add an XZ axis and a router.



    Sent from my iPhone using Tapatalk

  3. #3
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    Re: 4th axis as a "poor man's lathe"

    Quote Originally Posted by Dean448 View Post
    Interesting project.
    Thanks.

    Quote Originally Posted by Dean448 View Post
    I’m doing something similar using my wood lathe. I found arduino to be too slow so I’m using Teensy 3.2. The goal is to be able to just turn the machine on and not be bothered by a pc and software. Also cutting threads seems easier using a microcomputer.
    The Arduino is fast enough for one axis, and in fact, also for three, depending on the microstepping settings of the driver. I run only one axis (the spindle) so that's not a problem for the Uno I am using. Of course, I use the FastAccelStepper library, which I had to modify a bit because for for some reason, it has a built in upper pulsing limit of 25kHz. I removed that limit, and now I can happily run at very high speed.

    Quote Originally Posted by Dean448 View Post
    Regarding your machine; Steppers don’t have enough torque to rough cut wood. You could spin something for sanding. You can cut wood if you add an XZ axis and a router.
    I think the problem is not torque but the speed. Wood, plastic and aluminium needs much higher rpm than the 380 rpm I can get from this stepper. I mean, the torque here is actually multiplied by 6 due to the gearing, so I guess that's not the issue and should be more than enough for wood. This stepper can actually used for drilling in a steel rod, which I tested in my initial test.

    https://youtu.be/g8rXwJtne38

    I have a CNC router already, which is also my own design and build.

  4. #4
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    Re: 4th axis as a "poor man's lathe"

    Still not a fan of arduino for stepper control. Check this out

    https://www.pjrc.com/teensystep-fast...ntrol-library/


    Sent from my iPhone using Tapatalk

  5. #5
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    Re: 4th axis as a "poor man's lathe"

    Quote Originally Posted by Dean448 View Post
    Still not a fan of arduino for stepper control. Check this out

    https://www.pjrc.com/teensystep-fast...ntrol-library/


    Sent from my iPhone using Tapatalk
    That's OK. Anyway, I am a fan of anything that works and for a single stepper or servo Arduino definitely works. I am not saying that there is nothing better and of course I would not chose it for my CNC, but for a single motor it is good enough. At least for now.

  6. #6
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    Re: 4th axis as a "poor man's lathe"

    If anyone ever removed the motor holder from a fourth axis then please share how you did it.

    https://youtu.be/v9tR_K8eTek

    I can not for my life understand why it is been done this way and how they installed the whole thing. Is the spindle just pressed into the housing or is it glued also?

  7. #7
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    Re: 4th axis as a "poor man's lathe"

    i can't help, just here to wish you good luck with your projects
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

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    Re: 4th axis as a "poor man's lathe"

    Quote Originally Posted by deadlykitten View Post
    i can't help, just here to wish you good luck with your projects
    Thanks.

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    Re: 4th axis as a "poor man's lathe"

    I made a severe update, basically changed everything. This was planned from the start, but it was a major update. Everything is changed, except the control box, but even there the Arduino code had to be updated for enabling the use of servo. Made a video regarding the current status.

    https://youtu.be/ILFjNXn3Z0k

    I have also made two machine hand wheels which will be used for initial testing. I am not sure I will install steppers later on, probably I will, but in the meantime, these wheels will enable using the lathe while the steppers are installed. Of course, without a proper cross slide, the use will be limited, but still, for testing it will work.

    https://youtu.be/-YxlNM-9n5Y

    The hand wheel is 3D printed, it took a total of about 7.5 hours to print the three parts necessary for each, but that's because my extruder has a 0.4 mm nozzle and I printed with 0.2 mm layer height and 65% density. The material in my case is PLA, and I think for me that will be good enough. I chose to print in three parts, not just two, because I want the coupler part to be exchangeable and the wheel usable for other purposes also. Anyway, if you are interested in printing it, in the video there are instructions on where to download the stl files from.

  10. #10
    A lot of that noise is servo tuning, if you are able to on your controller, it would be worth going through the manufacturer recommended servo tuning procedure.

    The servo may also be highly salient, that is electromagnetic lingo for it has really distinct non-sinusoidal poles and a sharp waveform, trapezoidal likely. That typically is also exacerbating motor cogging and the noise can be a combination of cogging frequency, drive frequency due to drive waveform to motor waveform mismatch, and oscillation in the PID loops.


    You can only (maybe) control the PID loop tuning, so it's a good place to start. That will be with the controller manufacturer. If it's an integrated controller, then the servo manufacturer would be the place to start.

  11. #11
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    Re: 4th axis as a "poor man's lathe"

    Actually, most of the noise comes from the belt and that weird motor holder I had to make for this quick test installation.

    Btw, I did go through all the parameters and tuned the motor, but not aimed at silencing it, but to get the highest power and holding torque out of it.

  12. #12
    Quote Originally Posted by A_Camera View Post
    Actually, most of the noise comes from the belt and that weird motor holder I had to make for this quick test installation.

    Btw, I did go through all the parameters and tuned the motor, but not aimed at silencing it, but to get the highest power and holding torque out of it.
    Fair enough, I've honestly never worked with timing belts like this before, so good to know about the noise.

  13. #13
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    Re: 4th axis as a "poor man's lathe"

    Quote Originally Posted by StrawberryBoi View Post
    Fair enough, I've honestly never worked with timing belts like this before, so good to know about the noise.
    It is the rubber hitting and releasing the grooves and rubbing against the sides of the pulleys, plus the motor holder which I think is not rigid enough, so there is some resonance. In this video I am also running the motor at maximum speed, and here it is very silent.

    https://youtu.be/NKZBIqMDUL8

    I believe with tuning it can be made more silent also, but after playing quite some time with the parameters, I think that silence has a price on performance also.

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