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  1. #1
    Hello All,

    I recently bought a CNC Router, mainly for the solidity of the frame since the electronics there is a bit too complex for me.

    Currently, it has
    Machine spec:
    - x axis: linear slide rail with (I think) SBR25 bearing, Ball screw and SEM ltd motors (MT22R2-24 perm magnetic DC servomotor), belt driven
    - y axis: linear slide rail with (I think) SBR25 bearing, Ball screw and SEM ltd motors (MT22R2-24 perm magnetic DC servomotor), belt driven
    - z axis: pneumatic actuated (no controller connected to it at the moment, the pipes are open) not sure how is called the rail system, it's like trapezoidal

    I will need to change the movement system on the Z axis since I want to use a stepper motor rather than a pison.

    The table is in Bakelite and has a suction system and the pump is there (220V).
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by agors; 09-10-2020 at 01:55 PM.

  2. #2
    It looks like a nice machine.A few questions; why switch the servos for steppers?Servos are normally regarded as a better option as they operate on a "closed loop " basis and the factory would have specified something of adequate power.Are you quite certain that there isn't a servo on the Z axis?It isn't unusual for a machine to have a pneumatic cylinder on the Z axis to take the vertical load of the moving assembly.What seems a bit more mysterious is what moves the X and Y axes or were the servos removed for transport?

    The vacuum system works on most machines by moving a lot of air and using the pressure difference between the top and bottom surfaces to hold the workpiece in place.Some people use a neoprene gasket to seal round the periphery of production runs but your machine may work as is or it might need a spoilboard on top.Something like a piece of MDF or LDF will be porous enough to hold the workpiece in place and it gets better if the edges are sealed with a couple of coats of sealer.I find it a good idea to use brass screws to fasten a spoilboard in place as they wont hurt the tool when the inevitable happens and you cut a bit too deeply.

    In essence,why don't you get the machine connected and see what it can do?Its a lot easier than buying a stepper kit that might be of lesser quality than the hardware you already have and which will need adaptors for mounting the steppers to drive the axes and you won't have to go through the calibration process with a control package that you will have to learn from scratch.It would also be a big bonus if the machine came with any manuals,the learning process would be hugely eased.

    Is there any means of connecting the control box to a computer or network?At some stage you will need to program the machine and its much easier to generate a program on a modern computer and load the Gcode to the controller than it is to sit there pushing buttons for one line at a time,The challenge may be that a machine of the age of yours might not have a huge memory and you may well find yourself wanting to do things that require more memory than the controller has.If this happens you may have to find ways of drip feeding the code.

  3. #3
    Thank for the reply.

    You highlighted why I don't want to use this electronics/motors:
    - I want a system flexible and simple to use (I want to do complex geometry, aluminium is my target, with a 4th axis on a rotary table)
    - I looked into the manual, too old; the way of inserting the code will let me spend lots of time. I wrote G-code at the university and I know i want to have something more modern.
    - regarding the motors, current servomotors are 8NM; I'm planning to put closed loop motors (NEMA34 - 12NM).

    Modifying the machine is not a problem for me, I have a workshop; So plate and new pulley won't be a problem.

    Regarding the Z axis, I can confirm there is only an hydraulic piston. This machine is what they called 2.5D (not 3D router) :D

    About the vacuum surface, it's bakelite and I have LOTS of neoprene gasket. What I don't know is the system layout:
    at the moment, I have the Pump connected to a on/off valve that has a 2 way connection to the plane. Is it ok or do I need a relief valve?
    seems that in the on/off valve there is a possible relief valve but I'm not sure, and I haven't connected yet the pump to the power since I don't wanna brake it.

    here is the system layout:

    Click image for larger version. 

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    is this ok or is missing something?

    I'm not sure if the relief valve is there, can you recommend a way to test it?

  4. #4
    If you only intend to machine aluminium,you should have bought a mill.I fear that you may be introducing difficulties by installing 12NM steppers as the machine was built to hold the workpiece in place with 8NM applied to the drive and you won't be able to increase atmospheric pressure by 50% as easily as you can bolt a new motor in place.You also need sufficient surface area to allow the workpiece to remain in place and a piece of wood occupying most of the table would be enough a small aluminium component or a machine vice wouldn't have the area.While you could bolt a machine vice in place,it would lose a proportion of your Z axis.

    I have only used two machines with vacuum systems and only one of those had a pressure relief valve.It only operated if we turned off all the valves to the zones of the table.The other ,smaller machine had no valves to table zones and no pressure relief valve-we just turned the pump on or off with a push button switch.

  5. #5
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 6 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,745. Received thanks 331 times, giving thanks to others 8 times.
    You need to do a bit reading up about servo and stepper motors.

    Those servo motors you've removed, are 1.2Nm continuous stall, and will deliver that torque all the way to it's maximum speed of 5000RPM. They also have a higher instantaneous/peak torque, which gives you a boost for fast acceleration.

    Stepper motors on the other hand, only produce the rated torque at zero speed. As you increase speed, torque drops of very quickly.
    I couldn't find a speed/torque diagram for those HSS steppers, but Leadshine have one published for their similar motor -
    Click image for larger version. 

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    Running with a 70VDC supply, torque has dropped to around 1Nm at only 2400rpm, so you have under half the performance of the servo motors you've removed at continuous torque, and probably under 20% once you factor in the instantaneous torque available with the servo, which is where servos excel over steppers.

    Those servos you've removed are around the 600-750W power, however you'll struggle to get modern AC servo motors that spin to 5000 (one major benefit of DC motors, is you can spin them very fast with primitive technology!).
    Last edited by m_c; 11-10-2019 at 09:54 AM.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #6
    good to know for the relief valve, I'll try to have a go to see how my vacuum system works.

    As you pointed, I'm not sure I'm going to keep the vacuum table.
    But before deciding if maintain it or not, I want to test the axis; so for the moment, I'll leave the vacuum bed there
    Last edited by agors; 09-10-2020 at 01:56 PM.

  7. #7
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 6 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,745. Received thanks 331 times, giving thanks to others 8 times.
    Forgot to mention, I'd guess the vacuum pump will be some kind of simple design with high leakage, so it's unlikely any kind of valve is needed. You just need to plumb the pump to the bed, although depending on the bed design, it may be better to put it through a manifold to control zones (if the bed is machined with zones?), and also some kind of filter to stop anything being sucked through the pump.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  8. #8
    Thank you M_c.

    - Vacuum bed: it has 3-4 connectors on the back, but I'm not sure if are zones. I'll check.

    - Motors: Thank you a lot for the info.
    Last edited by agors; 09-10-2020 at 01:57 PM.

  9. #9
    I'm thinking at what you said and I did a couple of calculation,

    So I'm thinking at alternatives,
    Last edited by agors; 09-10-2020 at 01:57 PM.

  10. #10
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 6 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 9-10 years. Has a total post count of 2,745. Received thanks 331 times, giving thanks to others 8 times.
    If the servos have only be running of 70VDC, then they won't have been running at the full speed anyway (for electric motors, voltage = speed, current = torque).

    Those leadshine drives do look like they'd be capable. CNC Drive also do suitable drives (http://cncdrive.com/DG4S_08020.html for 80VDC/20A version).
    The key to using those will be making sure the encoders are suitable. You need quadrature encoders, not resolvers which your machine might just be old enough to have.
    For modern servo drives, the tacho output from the motor is generally not needed.

    Z axis you can do however you want. It's not likely to have a lot of travel, or need to move that fast, so a suitably geared Nema 23/4 motor is likely to be a good option. You will however still need a driver for it.

    You'll also need a breakout board of some form, but I would advise against using a parallel port, as it won't be fast enough to get the maximum benefit from the servos.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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