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  1. #1
    Hi All

    I bought an Amadeal CJ18A Mini Lathe a few years ago and its been a good little machine for me, now I know this is a Chinese Clone machine and they dont have a great reputation but for what I use it for, making small aluminium and steel parts for Robotics projects it works well enough.

    However one thing I have always struggled with is my own ability and would like to create more complex parts and want to convert the lathe to CNC.

    So my idea is to change the lead screw to a ball screw and use a Nema 23 420 Oz Stepper Motor for this axis.

    However on the compound slide I am not sure what to do as the space is really constrained so not sure I could get a ballscrew to replace the current screw or just attach another Nema23 420 Oz to the existing screw?

    Due to the noise it makes I would like to remove all the different gears and be able to index the spindle, have better speed control and still be able to cut threads so was thinking about either changing the motor to a servo motor or a closed loop stepper motor. Is this even possible?

    Any help or advice would be great.

    Cheers DJ

  2. #2
    Quote Originally Posted by djbsystems View Post
    Due to the noise it makes I would like to remove all the different gears and be able to index the spindle, have better speed control and still be able to cut threads so was thinking about either changing the motor to a servo motor or a closed loop stepper motor. Is this even possible?

    Any help or advice would be great.

    Cheers DJ
    Yes, it's possible, but the control software you use will play a big part in this because you need to read the encoder and feedback to the controller so it can sync the spindle to the axis.
    You actually don't need a servo motor or stepper Motor just to keep the threading ability and your existing motor would work provided the speed can be controlled, but you do need an encoder on the spindle and the controller must be able to read the encoder and control the spindle speed.
    Indexing is slightly more difficult and a servo motor is best for this, but in practice, unless you have a brake on the spindle they don't work very well unless it's a really powerful servo motor.

    LinuxCNC is probably your best option for control software if you are wanting to use encoders and indexing etc. Forget Mach3 it's limited when it comes to encoders and threading etc.

    Best advice, as always is to do lots of research and the Linux forum is a good place to start for lathes, loaded with Geeks but lots of info and people who have done it already.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  3. #3
    I converted a Super7 to CNC 12 years back. I did not fit a ball screw to the Z axis on the basis that the vast majority of turning operations can be done only moving the tool towards the headstock. Initially I used ordinary screw on the cross-slide but quickly found this didn't work so fitted a 5mm pitch x 12mm ballscrew to that, directly driven from the stepper. In order to fit this I had to "reverse" the nut as its diameter was too large, though having a power XF S7 the hole in the cross slide was just big enough for the 12mm ballscrew itself. If you can't fit a 10 or 12 mm screw it is possible to get 8mm ones though they are more expensive. Have a look at https://cncyourmyford.com/ to get some ideas.

    That website shows a ballscrew on the Z axis too, one day I may get round to that but manage without it.

    For the controller I use Mach3. I have a single slot encoder on the spindle and for a lathe like the Myford with a fair amount of power and inertia this is fine for screwcutting. There is a lot of disinformation around about Mach3 and screwcutting, it does actually work pretty well. I attach a photo of the thread cut for an ER16 collet chuck which is a perfect fit in the nut. I cut this using the threading wizard, no adjustments needed, home-made tool, infeed calculated from the Martin Cleeve formula in his book.

    However Mach3 is long in the tooth now and unsupported, Mach4 is better and can I believe support a multi-slot encoder which can accomodate a less powerful spindle drive. I have flirted with Linux CNC but I'd rather cut metal than wrestle with software.

    Just to add that you don't need active spindle speed control to do good threading provided the speed remains sufficiently constant while cutting - in fact I believe that systems with multi-slot spindle encoders adapt the feed rate not the spindle speed. My spindle is not even controlled from Mach3, I turn it on and set its speed via a VFD.

    And also to add that I run Mach3 on a Dell mini PC with Win10, using a UC100 motion controller connected via USB. The one change that I would like to make is to update the stepper drivers as the ones I have are limited in step frequency.

    Click image for larger version. 

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    Last edited by JohnHaine; 29-09-2022 at 08:32 PM.

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