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  1. #1

    Join Date
    May 2020
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    37

    Construction of a CN lathe

    Hello everyone,

    After having designed and manufactured a bench-top CNC milling machine (around 450kg), I set out to make an CNC lathe from a conventional machine, a Linz lathe to be honest. And of course from an MK3.
    Can Planet CNC give me some advice on the choice of motors as well as some explanations or diagrams in order to allow the synchronization of the spindle with the other axes?

    I don't have the machine yet, but it will be soon.
    I plan the following functions:
    - Spindle from 0 to 2500 rpm with a 130ST-M15025 type servo motor. This motor must also be able to achieve the C axis if possible, otherwise I would use the original asynchronous motor for turning mode and another motor with a disengageable coupling for the C axis. In this case, I assume that the synchronization with the asynchronous motor should be done with an additional encoder.
    - closed loop stepper motors for the X and Z axes.
    - Possibility of having rotating tools in turret.
    - Put, instead of cranks, impulse wheels in order to keep a manual mode.

    Best Regards

  2. #2
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    1714

    Re: Construction of a CN lathe

    concerning step motors. Think twice. Do you know and industrial brand using steppers for axis control?

  3. #3

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    Re: Construction of a CN lathe

    No, but it's still an amateur machine. In addition, closed loop stepper motors have advantages like:
    - the price.
    - the holding torque with respect to a servo motor.
    - much less step loss compared to simple stepper motors.

    Nothing is decided yet. For now, it's a reflection.

  4. #4
    Community Moderator Jim Dawson's Avatar
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    Re: Construction of a CN lathe

    You might want to look at Delta or DMM servo motors for your spindle. Looking at the specifications for the 130ST-M15025, it seems that their 3.8kW motor is really closer to a 1.5kW motor.

    Here is the specs from the
    130ST-M15025 web page



    Here is the specs from a Delta 1.5kW motor. The price shown includes the drive and all needed cables.
    https://www.automationdirect.com/selectors/sureservo2



    And here is the specs for the DMM 1.3kW motor.
    https://www.dmm-tech.com/Files/ACSMTR-G1-1002A18A.pdf



    When you compare the torque curves, you can see that the Delta and DMM servos out perform the Synvance servo. I have both DMM (X, Z, live tooling, and Turret) and Delta (Spindle) servo motors on my lathe and have been very happy with the performance of both.

    If your controller will sync the spindle to the X and Z axis, then using a separate encoder on the spindle works when using an asynchronous motor. I have a seperate encoder on the spindle of my lathe and I also have a servo spindle motor. Up until about 3 months ago I used the original asynchronous spindle motor until I needed a C axis and repowered the spindle with a servo motor. An asynchronous motor/VFD with a spindle encoder works fine for threading and rigid tapping.

    I looked at adding a servo motor to the original spindle drive to achieve the C axis, but found it was more economical and much less complex to replace the original spindle motor with a servo.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5

    Re: Construction of a CN lathe

    Over the last 3/4 year I converted a SIEG SC4 to CNC with PlanetCNC. While this is clearly a different weight class I might be able to give some hints regarding planet CNC:

    - at the moment its not supported to have the spindle motor as a positional axis. While you can drive a servo with the output for the spindle you can not use it to position the spindle. So no rigid tapping and no positional work.
    - There is no native support to have two encoders controlling two axis in the official software at the moment as far as I'm aware. However I think you can tweak something with an arduino as a input device
    - no fancy on machine programming for typical lathe tasks as one might know from other software, either you write the complete code by hand or use a CAM. (and some typical lathe cycle gcodes are not implemented up to now, have a look at the gcodes pdf to check if you have everything you need)

    beside these "limitations" I'm quiet happy how planet cnc works on my small lathe. As I'm using the original Motor from the SC4 with the original Controller I have no direct RPM control but up to now this is working OK for the work I do. I get the RPM to Planet with a rotary encoder as described in the PlanetCNC Blog.
    If you get a servo drive that can report the position similar to an encoder you can skip the encoder and have the servo driver report directly to planetcnc.
    Once you have the RPM in Planet active G95 to have the feed synced to the revs of the spindle (note: jogging with MPG is not synced, I think only normal feed gcodes are synced, not sure about rapids) and G33 to cut Threads.

  6. #6

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    May 2020
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    37

    Re: Construction of a CN lathe

    Thanks for your advices,

    I suspected that Planet CNC does not take into account the spindle motor with the C axis.
    This is the reason why I will maybe integrate a second motor for this function. It's up to me to find a mechanism to disengage the motor from the C axis when it will not be used.

    I am awaiting the response from Planet CNC on the most relevant solution with the MK3 card and TNG V2.

    For the 130ST-M15025, the rated torque is 15Nm, the maximum torque is 30Nm. I will still take a closer look at this.

  7. #7

    Re: Construction of a CN lathe

    Quote Originally Posted by Steler View Post
    Hello everyone,

    After having designed and manufactured a bench-top CNC milling machine (around 450kg), I set out to make an CNC lathe from a conventional machine, a Linz lathe to be honest. And of course from an MK3.
    Can Planet CNC give me some advice on the choice of motors as well as some explanations or diagrams in order to allow the synchronization of the spindle with the other axes?

    I don't have the machine yet, but it will be soon.
    I plan the following functions:
    - Spindle from 0 to 2500 rpm with a 130ST-M15025 type servo motor. This motor must also be able to achieve the C axis if possible, otherwise I would use the original asynchronous motor for turning mode and another motor with a disengageable coupling for the C axis. In this case, I assume that the synchronization with the asynchronous motor should be done with an additional encoder.
    - closed loop stepper motors for the X and Z axes.
    - Possibility of having rotating tools in turret.
    - Put, instead of cranks, impulse wheels in order to keep a manual mode.

    Best Regards
    130ST-M15025 type servo motor is use for XYZ axes feeding axes, for spindle there are AC servo spindle motor and driver, which can achieve orientation.
    http://cncmakers.com/cnc/controllers/CNC_Controller_System/CNC_Retrofit_Package.html

  8. #8
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    918

    Re: Construction of a CN lathe

    I'm using ToAuto servos on my machines:
    https://www.fasttobuy.com/Supply-toauto-servo_c440

    For closed loop steppers I use these:
    https://www.omc-stepperonline.com/cl...p-stepper-kit/

    So far I have good experience with them.

    ToAuto servos have some a nice features. You can use their "encoder" output to monitor real speed. Make sure you use high speed optocoupler to connect this signal to controller.
    When used as spindle there is no need for output board because they can be controlled with frequency (steps).

    There are plans to implement positional control but I doubt there is a lot of interest. There is a walkaround. You can connect servo to both connectors via switch or OR gate. I've tested this and it worked great.

  9. #9

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    May 2020
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    37

    Re: Construction of a CN lathe

    For cncmakers001: I already use this type of servo motor (110st-m06030) for the spindle of my milling machine, so far it is fine. We can use them in Speed ??or Position control mode. The engines that you present are certainly more torque, heavier (but not very important in my case) and they must be expensive.
    In my case, the ZJY182-2.2CF model (27 kg weight and 2000-10000 trmin) with the GS2075Y driver would be more than enough. A reduction in speed by 3 or 4 (my spindle limit being 3000rpm max) would increase the torque even more. Would you have the price of this set (with shipping costs)?

    For Planet CNC: Very interesting these 2 links with advantageous prices.
    For the ToAuto servo, I did not know it could be driven directly with the frequency in spindle mode, I drive the link in -10V + 10V by a converter + a pole reversal relay.

    These first exchanges put me in doubt. I will perhaps carry out the evolution in 2 axes only to quickly have an operational lathe, then I would reflect on the interest and the complexity of passing it in 3 axes with rotating tools.

    If I am using ToAuto type servos, the 'Encoder' output is used for spindle synchronization. Do you have an example or a tutorial on this?
    I assume that the threads can be programmed in G33 as well as in G76?

    In case I use the original assynchronous motor (4.4KW), I would have to get a drive and add an encoder to get the synchronization, right? which will cost me as much as buying a full servo motor but with twice the torque.

  10. #10

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    May 2020
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    37

    Re: Construction of a CN lathe

    Hello everyone,

    Eventually I followed cncmakers001's advice in choosing a spindle servo motor. On the other hand, I did not buy it from them, the price being a little excessive for my budget. The motor I chose is a SZGHTECH of 2.2kW for 14Nm (rotation of 8000 rpm maximum).

    For the motorization part of the X and Z axes, I am tempted to test integrated servomotors of STEPPERONLINE iSV57T-180 of 0.6Nm. After calculation according to the equipment that will make up the lathe, the vast majority of my machining operations should require a maximum torque of 0.65Nm. If I reduce the speed of this servo motor by 3, I would have about 1.8Nm, which should be enough. In addition, this motor keeps its torque over the entire speed range unlike many others.



    Anyone among you already implemented these servomotors?
    PlanetCnc, what do you think?

    Best regards
    Attached Thumbnails Attached Thumbnails iSV57T-180.jpg  

  11. #11
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    Re: Construction of a CN lathe

    I think that 8000 RPM is little high.for lathe.

  12. #12

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    May 2020
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    37

    Re: Construction of a CN lathe

    Hello,

    No, in my various calculations, I need about 35Nm at the spindle for machining Ø100 with 1mm depth of cut with a material having an Rm of 1013N / mm².
    If I reduced the speed of rotation by 3, I would have around 42Nm at the spindle by rotating it at 500rpm, so 1500rpm for the motor. The maximum spindle speed will be 2670tr / min and approximately 14Nm for a speed of 8000tr / min of the motor.
    So on the spindle side, everything should work.

    On the servo motor side, I have no more doubts. STEPPERONLINE servomotors have 0.6Nm of torque. I also realize a speed reduction of 3 to obtain about 1.8Nm. I'm going to use 5-pitch ball screws, which will be equivalent to 2035N to move the saddle. Knowing that the latter has a drag of 100N and that my machining can reach 745N, I need 0.74Nm of torque with the screw, 1.8 should also be sufficient.
    I am looking for 25 screws at a pitch of 4 to better secure my system, that is to say 2545N in capacity and 0.6N at the screw for the most constrained machining.

    PlanetCnc or someone else, have you ever used STEPPERONLINE iSV57T-180?
    A test was carried out here:
    https://clough42.com/2021/06/19/is-t...screw-part-26/

    I would like to have your opinions before buying them.

    Best regards

  13. #13

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    May 2020
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    37

    Re: Construction of a CN lathe

    Hello everyone,

    Another week of waiting before going to get the tour. I finally bought 1.27Nm (400W) servo motors for the axes.

    I have a new question for Planet Cnc. For the spindle synchronization, I can use the motor encoder in order to have the feedback.
    On the other hand, in the old versions of TNG V2, the encoder had to have a ratio of 1: 1 with the real speed of the spindle. In the new versions, a notion of Index PPR X / Y appears.

    Do we have to understand this in order to have another ratio?
    If I have a ratio of 2.5, should I indicate 5/2?

    Best regards

  14. #14

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    Re: Construction of a CN lathe

    Sorry to bother you,

    I just read the latest version of the TNG docs, and everything is described.
    Next time, I will get carried away less quickly.

  15. #15

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    May 2020
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    37

    Re: Construction of a CN lathe

    Hello everyone,

    While waiting for the hardware, I start to rely on TNG V2 and set up the software for the lathe.

    Here are some questions:
    - I noticed that the roughing and grooving cycles are not taken into account, but appear in progress because they can be observed on some TNG options. An idea on their implementation?
    - The 3D representation includes rather huge axis displays for small parts. Do we have a possibility to configure their size?
    - The representation of the 3D grid is done only on the XY plane. Working on the ZX plane, can the grid be brought back to this plane?
    - Being on the ZX plan, I declared the machine on the G18 plan. TNG refuses the use of G41 / G42 compensation in this regard. Will this be taken into account in a later version?
    - In the same order, the tool radius is not taken into account in the tools table, so it is difficult to manage the radius compensation. In addition, the tool table does not define the dial (orientation, because I do not know how to translate it into English) associated with the tool. Will this information be taken into account in future versions?

    Here are for the first questions :-).

    Another on material: I would like to set up a probe to gauge the tools (in X-, X +, Z- and Z +). The only ones I can find are overpriced. Are any of you using it? What are your models and where do you buy them?
    Otherwise, I might adapt a milling tool gauge probe to probe each of the axes according to its assembly.

    Best regards

  16. #16

    Re: Construction of a CN lathe

    Regarding the Probeing: When starting out with my lathe probing I evaluated different options for the tool length measurement. But in the end I decided to go with a fully manual approach. The biggest reason was that I found no easy way to place the probe somewhere within the movement area without either being in the way all the time. Or by having the required reputability if its a movable probe.
    As I'm using a quick change tool post (Multifix) Its not a big issue as I don't need to measure each tool after every toolchange.
    I wrote a small dialog script to quickly set the x and z offset for the current tool.
    For X I simply make a test cut, move the tool on Z out of the way without moving X after taking the cut. Then measure the diameter of the workpiece, enter it into the dialog and the offset is set correctly.
    For Z I have one "master" tool that has the Z offset to 0, I make a cut at the end of some old stock where I set Z to 0. I switch to the new tool, bring it over to the cut surface till a small 0,5mm feeler tape gets pinched between the surface and the tool. The Z offset script then askes for the thickness of the feeler tape and sets the Z offset correclty.

    Both scripts can be found on my github if you want to take a look: https://github.com/Klaus-Michael/Pla...-Lathe/UserCmd

    With this Methode I get a quiet acceptable repeatability within the limitations of my machine (alignment of the x & z axis is limiting at the moment). I've got it to a point where thermal expansion seems to be my biggest issue for repeatability.
    I typically have only one tool for the last finishing cut, that's the most critical for me. The Roughing tools normally stay within tolerance good enough that it does not matter for my work. For the finishing tool I typically repeated the X calibration when starting on a new day and I typically do only a few number of parts, not large series.

    I figured that this is not much more work compared to a automatic probe and far cheaper ;-)

  17. #17

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    Re: Construction of a CN lathe

    Thank you ScorpionTDL for your experience and the provision of your scripts.

    I could also imagine making this type of probe. By making sure, as you say, to have very good positioning repeatability.
    Or integrate a camera for this measurement thanks to a sight. I'm not sure if this case will be accurate enough for finishing tools.

    For now, this is only reflection. I will look for the lathe the day after tomorrow, the spindle and axis motors should leave next week, delivery certainly first or second week 2022.

    The goal of my (machine) realizations is also to push my limits and my knowledge.

    I also hope that PlanetCnc will answer my first questions.
    It may be professional deformation, but it seems normal to me to work in radius correction and not systematically in fictitious point, especially for the finishes.

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