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  1. #1
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    CNC Tube Bender

    Hi All,

    I'm starting a new project, I want to build my own CNC Tube bender.
    The idea is to build the machine fully controlled by servomotor and everything controlled with Arduino.
    I would like to be able to bend steel tube with an OD up to 2.5" with wall thickness of 3-4mm.

    For the first version I will use the dies of my manual bender.

    For the bending part I will need a servomotor with pretty high torque and it will be direct drive.

    This is where I need help,
    I have no clue about what would be the required torque?
    and what brand/models exist on the market and what is good or not?

    I found some brands like Yaskawa on google that seems to have a pretty high torque but once again, I have no clue if it's enough or not and what alternative could also work?
    I also have no idea about the price range of a such servomotor so any indications would be appreciable.

    Thank you very much.

  2. #2

    Re: CNC Tube Bender

    Let's start with your manual bender. What type is it? Linear or rotary? Mechanical or hydraulic? Then how much pull or push is required on the handle to bend the largest tube? You can calculate the required torque from this information. Maybe a picture or a link to a picture would be helpful.
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    It's a CNC rotary bender (mandrel) that I want to do, I start with the bending part and later I will do the axis positioner, and of course the whole actioned by servomotor to achieve accuracy and repeatablity.
    the manual bender is a chinese copy of the Baileigh RDB 100.

    But be aware that the dies of my bender is just a temporary solution, it's more to do some servomotor test, I will later make my own dies later, I know a shop that have the equipment to do it.

    I found some article that was mentioning a required torque of 350-400Nm but once again I have no clue.

  4. #4

    Re: CNC Tube Bender

    Just to put this in perspective, first concider that 400 Nm is about the torque output of a mid-sized auto engine, and that number seems pretty reasonable for a direct drive tube bender. That would be a huge servo motor.

    But not very practical in this application. First you don't need to turn the tube bender at 2500 RPM, more like maybe 2 RPM. A much smaller servo motor and a massive gear reduction would be practical. Maybe a gear reduction of about 1000:1. The gearbox is going to be more expensive than the servo motor. The motor torque is multiplied by the gear ratio. I would be looking for a planetary gearbox in the 500 to 1000 : 1 range, then choose a servo motor to match.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Re: CNC Tube Bender

    As nice as direct-drive servos are; I'd give some thought to using a hydraulic drive; an encoder; and a solenoid valve. I'm suspecting that it may turn out to be lower cost...

  6. #6
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    Re: CNC Tube Bender

    Interesting project, an acquaintance used to pay occasional visits to a company that bent car exhausts.The machine had the facility to feed the tube along to the next bend location and then rotate it before adding the desired bend so that the finished article just needed an end flange added.Do you intend to build a machine with this sort of capability?

  7. #7
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    Quote Originally Posted by Jim Dawson View Post
    Just to put this in perspective, first concider that 400 Nm is about the torque output of a mid-sized auto engine, and that number seems pretty reasonable for a direct drive tube bender. That would be a huge servo motor.

    But not very practical in this application. First you don't need to turn the tube bender at 2500 RPM, more like maybe 2 RPM. A much smaller servo motor and a massive gear reduction would be practical. Maybe a gear reduction of about 1000:1. The gearbox is going to be more expensive than the servo motor. The motor torque is multiplied by the gear ratio. I would be looking for a planetary gearbox in the 500 to 1000 : 1 range, then choose a servo motor to match.
    I don't think it require a gear box as the speed of a servo can be controlled, and you are right it's going to be more around 2-3rpm.
    I want it to remain quite compact and using a gear box is not going to be compact.
    If you look at the CNC Tube Bending machine on the market, many seems to be direct drive with a big servo with a size of around 15cm X 15cm X 30 cm.

  8. #8
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    Quote Originally Posted by routalot View Post
    Interesting project, an acquaintance used to pay occasional visits to a company that bent car exhausts.The machine had the facility to feed the tube along to the next bend location and then rotate it before adding the desired bend so that the finished article just needed an end flange added.Do you intend to build a machine with this sort of capability?
    Yes it's correct I'm looking to build a real CNC as I explained in first post, so after the bend part solved, I will build an axis positioner that will push and rotate the tube to the next bend position.

    I have build a bike frame with the manual bender and it has been very annoying to do the mirror part so I looked at CNC Tube bending and obviously the cost of those machine is huge so I thought why not building one as it doesn't seems to be unreachable

  9. #9

    Re: CNC Tube Bender

    Quote Originally Posted by garthos View Post
    I don't think it require a gear box as the speed of a servo can be controlled, and you are right it's going to be more around 2-3rpm.
    I want it to remain quite compact and using a gear box is not going to be compact.
    If you look at the CNC Tube Bending machine on the market, many seems to be direct drive with a big servo with a size of around 15cm X 15cm X 30 cm.
    To get a servo motor with that much torque for direct drive you are going to need one in the 75KW range. There are some lower power, low speed, very high torque servo motors available, but it would be less expensive just to buy a CNC tube bender.

    I looked at a number of electric servo tube benders on the net, and all of them had a gear box on the bending mandrel drive. I agree that the servos are about 30 cm long, but about 15 cm of that length is gearbox.
    Jim Dawson
    Sandy, Oregon, USA

  10. #10
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    Re: CNC Tube Bender

    The commercial tube benders I have retrofitted have used hydraulics and servo valves for the bending process.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  11. #11
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    I was looking a CNC like that:
    https://www.youtube.com/watch?v=Ux1GB1gpXDw

    I'm not 100% sure but this kind of CNC seems to use Servomotor, and I'm not sure it's really relevant to speak of kilowatt, the important point is the torque.

    from what I see there is 3 possibilities for the bend:

    - a electric induction motor (like an industrial 2 hp motor from Mitsubishi for example), a gearbox, and then control the rotation angle with a sensor
    - a hydraulic actuator , with also an angle sensor
    - a servomotor

    I looked many model of CNC bender and the one that uses hydraulic actuator always have visible hydraulic pipe.
    the smaller bender (Not CNC) but electric, seems to use the first option but many CNC seems to be using servomotor for the bend as well.

    So before to eliminate the Servomotor option, I would like to see some reference of servomotor that have a sufficient torque (eg: 400Nm) and see how much space it take and how much it costs.

    The reason I would prefer using a servomotor is also for high accuracy.

    By the way, it doesnt matter if the servo have an integrated gearbox, as long as it comes with the servomotor and it's accurate that's fine, any reference of such servo to share?

  12. #12
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    In addition, I found this article that tend to confirm my thought:
    https://www.thefabricator.com/tubepi...ectric-machine

    the bend can be ensure by a servomotor, the question is more then what reference is suitable, any of you have experience with the Yaskawa or any other brands that have very high torque?
    My domain is IT and electronics, no issue for me to do the programming part but I have no clue how to calculate the required torque, any suitable servomotor reference will allow me to make some progress

    if I look the machine proposed here, they claim that there is no hydraulics component and that it consumes less than 5kW:
    https://www.blmgroup.com/en/tube-bending
    so the 75KW servomotor mentioned earlier seems to be way oversized.

    I also found this Servo with geared mounted on it that seems suitable:
    https://precision.nabtesco.com/en/products/detail/AF-N
    Is anyone know those servos?
    Last edited by garthos; 11-14-2019 at 05:12 PM. Reason: Adding details

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