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  1. #1
    Join Date
    Aug 2009
    Posts
    56

    GRBL CNC lathe?

    Hello everyone

    Anyone done this with good success? I have already lathe sort of ready for this, Emco compact 5 and this is half way refitted with usable electronics. There is only 2 axes, but is it going to be still overcomplicated solution. Currently I can think only negative things about this solution.
    -No spindle sync --> no threading
    -No canned cycles, this can be avoided
    -No tool change or tool library, this one is bad.

    Most of these problems can overcome with good control program, but I can´t think any.

    Second plan is linux cnc on parellel, but no idea will it do any better, have to investigate on this one.

  2. #2
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    I am using GRBL on my desktop lathe for more than a year. No problems, have a stepper on the spindle for threading, broaching, knurling, grinding etc.
    I also will convert my mill to CNC using GRBL.
    I use TB6600 drivers for my steppers so when needed, i can change the controller to connect to Mach or any thing else.
    By the way, GRBL supports G41.1 dynamic tool offset on all axis and G49!
    My program CNCL (microsoft store) does support toolchange and a tool library in the next release at the end of this month.
    I found this tool, maybe you can use it https://github.com/zeevy/grblcontrol...-Documentation

  3. #3
    Join Date
    Aug 2009
    Posts
    56

    Re: GRBL CNC lathe?

    Thanks for info, so not yet discard GRBL. Problem is spindle motor, currently huge DC motor with pwm drive and rotation sync. Have to investigate more on this, tool change is important because lathe has 6 tool turret, makes no cense to not use it.

  4. #4
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    If you have a resolver (rotary encoder) on your spindle, you could go for a closed loop controller. They are not cheap but you can drive them like a stepper without losing torque!
    Google on "closed loop dc motor control"

  5. #5
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    Quote Originally Posted by hfjbuis View Post
    I am using GRBL on my desktop lathe for more than a year. No problems, have a stepper on the spindle for threading, broaching, knurling, grinding etc.
    I also will convert my mill to CNC using GRBL.
    I use TB6600 drivers for my steppers so when needed, i can change the controller to connect to Mach or any thing else.
    By the way, GRBL supports G41.1 dynamic tool offset on all axis and G49!
    My program CNCL (microsoft store) does support toolchange and a tool library in the next release at the end of this month.
    I found this tool, maybe you can use it https://github.com/zeevy/grblcontrol...-Documentation
    Today I discovered GRBL supports G41.1 only on Z-axis. Did not see it before because i have implemented the tool offset on X and Z axis in my own software.

  6. #6
    Join Date
    Aug 2009
    Posts
    56

    Re: GRBL CNC lathe?

    Quote Originally Posted by hfjbuis View Post
    My program CNCL (microsoft store) does support toolchange and a tool library in the next release at the end of this month.
    I found this tool, maybe you can use it https://github.com/zeevy/grblcontrol...-Documentation
    Totally missed your program over here and will be looking how it turns out, looks promising already. Link to other program confused me.



    Quote Originally Posted by hfjbuis View Post
    If you have a resolver (rotary encoder) on your spindle, you could go for a closed loop controller. They are not cheap but you can drive them like a stepper without losing torque!
    Google on "closed loop dc motor control"
    Yes I can do all kinds of sorcery, known to happen, but at the end I have to connect this spindle to GRBL and this part does confuse me greatly. Lathe cam gives speed, direction and cutting parameters, sending these codes to GRBL is no good at all. There must be synced movement using stepper port, lets say Y axes. So if there is stepper on spindle motor, how to translate commands to this stepper, I cant figure this out. This can be achieved with gcode, but going back to basic, using generic lathe cam is out question on this point.



    Quote Originally Posted by hfjbuis View Post
    Today I discovered GRBL supports G41.1 only on Z-axis. Did not see it before because i have implemented the tool offset on X and Z axis in my own software.
    But Z-axis is enough, X can be relative to 0. It´s been few year since I ran and teach full size lathe daily.

  7. #7
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    Quote Originally Posted by james_III View Post
    So if there is stepper on spindle motor, how to translate commands to this stepper
    I connected the spindle stepper to GRBL Y axis and configured this axis resolution as 0.01° / mm step. GRBL just thinks it is a common Y-axis. In my software, C-axis rotations (positions) are converted to Y-axis positions. By doing this, i can do threading, knurling, broaching etc.

    I think it is also possible to change the GRBL firmware to have G41.1 (Tool offset) support on all the axis, but i prefer adjusting my own software, and keep GRBL unchanged, that way it works on all kinds of GRBL compatible boards.

    Quote Originally Posted by james_III View Post
    But Z-axis is enough, X can be relative to 0. It´s been few year since I ran and teach full size lathe daily
    I found it easier to use Tool length offset on X-axis than adjusting the tool holder. Now i do a turning pass (inner or outer), measure the real diameter and the software calculates the X-axis tool offset, fast and easy.

  8. #8
    Join Date
    Aug 2009
    Posts
    56

    Re: GRBL CNC lathe?

    Quote Originally Posted by hfjbuis View Post
    I connected the spindle stepper to GRBL Y axis and configured this axis resolution as 0.01° / mm step. GRBL just thinks it is a common Y-axis. In my software, C-axis rotations (positions) are converted to Y-axis positions. By doing this, i can do threading, knurling, broaching etc.

    I think it is also possible to change the GRBL firmware to have G41.1 (Tool offset) support on all the axis, but i prefer adjusting my own software, and keep GRBL unchanged, that way it works on all kinds of GRBL compatible boards.
    Now I keep wondering where do you get C axis positions? simplest lathe cam don´t support C axis and it is more milling work with milling cutters. I understand how GRBL drives spindle, but where position code comes from? Actually this is exactly as milling code with fourth axes. Is this something that your software translates or something? Excellent idea to keep GRBL unchanged, there are too many slightly modified GRBL´s without any support.

    I´m sort of interested this idea and that´s why I keep asking.

    I found it easier to use Tool length offset on X-axis than adjusting the tool holder. Now i do a turning pass (inner or outer), measure the real diameter and the software calculates the X-axis tool offset, fast and easy.
    This is what I was after, just typed things wrong, no need to adjust tools.

  9. #9
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    Quote Originally Posted by james_III View Post
    Now I keep wondering where do you get C axis positions? simplest lathe cam don´t support C axis and it is more milling work with milling cutters. I understand how GRBL drives spindle, but where position code comes from? Actually this is exactly as milling code with fourth axes. Is this something that your software translates or something?
    Spindle Stepper 200 Steps / 360 °, full step, no gears.
    GRBL Y-axis configuration = 200 / 360 = 0.556 steps / mm = 0.556 steps / °
    To turn the spindle 90 °, Send command to GRBL to turn Y-axis 90 mm. GRBL moves Y-axis 90 mm = 90 * 0.556 = 50 steps. The spindle rotates 50 steps = 50 / 200 x 360 ° = 90 °
    My software translates the rotational C-axis moves to Y-axis moves. GRBL is not aware of this.
    Hope this helps to understand how it is done.

  10. #10
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    Quote Originally Posted by james_III View Post
    Now I keep wondering where do you get C axis positions? simplest lathe cam don´t support C axis and it is more milling work with milling cutters. I understand how GRBL drives spindle, but where position code comes from? Actually this is exactly as milling code with fourth axes. Is this something that your software translates or something?
    I think i misunderstood your question,
    To use my software, you don't need CAD, CAM or GCode programmaing, just the dimensions of the part to turn. To turn a M12 bolt 5 mm length, you select the M12 Metric thread, set start position Z to 0 and end position Z to -5, select CVC (Constant Volume Cut), and set the starting depth of cut. Then press AutoCut and wait until it is done.
    I added a screenshot for clarity
    Attached Thumbnails Attached Thumbnails Knipsel.jpg  

  11. #11
    Join Date
    Aug 2009
    Posts
    56

    Re: GRBL CNC lathe?

    This second explanation is better suited, so there is build in canned cycles basically, it will work. If there is no need for CAD/CAM, but how about free shape? Let´s say I need to make V groove pulley with bearing hole inside, is this possible?
    -Facing and turning V groove outside
    -drilling and turning inside
    -cutting off
    -and it is nice to have chamfers or radius on every corner

    -One thing more, I need to make 25 of them, so how this is going to be repeated?



    If somebody is interested on this, we are talking about https://www.microsoft.com/en-us/stor...l/9p42tb5t697h CNCL program found on microsoft store.

  12. #12
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    Basically there are several tasks, facing, turning, chamfer, threading, parting, taper, filet and radius. As long as the shape you want to turn, can be split into these basic tasks, it is doable. A task can be recorded for playback. You can even record a series of playbacks in to one large combined task. There is a tool library for manual tool change and manual tool change is also supported during playback.
    If the tools are mounted on the cross slide (side by side), then the tool change could be fully automated during playback, if I skip the popup for the manual tool change during playback. This would require a minor change in software that can be done in the current release.

  13. #13
    Join Date
    Jul 2016
    Posts
    41

    Re: GRBL CNC lathe?

    Quote Originally Posted by hfjbuis View Post
    Basically there are several tasks, facing, turning, chamfer, threading, parting, taper, filet and radius. As long as the shape you want to turn, can be split into these basic tasks, it is doable. A task can be recorded for playback. You can even record a series of playbacks in to one large combined task. There is a tool library for manual tool change and manual tool change is also supported during playback.
    If the tools are mounted on the cross slide (side by side), then the tool change could be fully automated during playback, if I skip the popup for the manual tool change during playback. This would require a minor change in software that can be done in the current release.

    How much is the subscription for your program?


    Not sure what you meant in one of your posts above by "broaching". What comes to mind is shaping on the lathe. Did you mean CNC controlled shaping on a lathe ? (such as making a keyway parallel to the Z axis, for example) ? In years bygone that task was achieved on a shaper (I have one) but on a lathe it can be done by hand by in-feeding the tool in X and feeding by hand along the Z axis - returning to start point (all by hand) and repeat (usually around 0.002 cut each time). I've never actually done it on a lathe but I have read of others doing it quite sycessfully - having a South Bend 7" shaper I don't need to do it and it is painfully slow by hand on a lathe. But a CNC shaping operation on a lathe brings up some very interesting possibilities: Here's one....how about cutting a sun planetary gear (internal teeth - can't do that on a mill or conventional lathe ! HaHaHa!) assuming you can accurately index the spindle and your "shaper" cutter in ground to the correct involute profile.

  14. #14
    Join Date
    Mar 2015
    Posts
    409

    Re: GRBL CNC lathe?

    How much is the subscription for your program?
    The app costs €3. Besides the app you need an annual subscription €2

    Not sure what you meant in one of your posts above by "broaching". What comes to mind is shaping on the lathe. Did you mean CNC controlled shaping on a lathe ?
    Yes that is what I mean. It is intended for making a keyway or internal gear.

    assuming you can accurately index the spindle and your "shaper" cutter in ground to the correct involute profile.
    My spindle has a retractable stepper running at 16 micro steps and a 20:45 gear ratio resulting in 0.05° step resolution. My (CNC) rotary table dial has 0.12° tics. Keep in mind that step resolution isn't the same as accuracy.
    CNCL has a task to turn a gear cutter (button method). The cutter produced by the button method isn't a true involute cutter, but if you cut a 13 tooth gear using a 12 - 13 tooth involute #1 gear cutter, the tooth cut also isn't a true involute. Because it only takes a few minutes to make a gear cutter on the lathe, I make a dedicated gear cutter for each gear to cut. This compensates more than adequate for not being a true involute profile.

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