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  1. #1
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    Wanted: Vibration damper.

    Hi everybody.

    This is my very first post in this furum.

    I am converting a universal drilling mashine to a CNC mashine. I have very high vibrations in my steppers Nema34 size. There is dampers for some nema steppers. see link below

    https://www.ebay.co.uk/itm/NEW-Nema-...Cclp%3A2334524

    I have tried to search in several places for such damper for my steppers with no hits. So I have to ask here if anyone know if there is dampers of that kind for Nema 34 and where to find them.

    Thank You for Your effort from John Eriksson in sweden

  2. #2
    Community Moderator Jim Dawson's Avatar
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    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Re: Wanted: Vibration damper.

    What gear or belt reduction do you have on the drive to the motors?
    How many steps per motor revolution are your drives set for?

    I would say you are operating the motora in their resonant zone so a reduction is probably help.
    Microstepping will also help.
    Rod Webster
    www.vehiclemods.net.au

  4. #4
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    Re: Wanted: Vibration damper.

    Hi.

    First of all thank You for Your repals.

    The links that You provided was interesting.

    I am using Mach3 latest version. the reduction is 48/70 (outer diam of timing belt wheels) HTD5M profile. The clock in Mach3 is running at 60 KHz. My steppers is 8,5 NM and 1,8 degree step, I have tried several microstepping values, now I am using 6400 steps/revolution (32 mikrosteps). The noise is ocuring about 160units/minut according to Mach3. The leadsrew has a pitch of 5 mm/revolution (no ballscrew)

    One solution that I have is to completly aviod feedrate about 160 units/minut. But then I would like to have an exlusion of that feedrate in mach# or in the CAM software, but I do not know if that is possible.

    Thank You once moore for Your answers. from John Eriksson in Sweden.

  5. #5
    Community Moderator ger21's Avatar
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    Re: Wanted: Vibration damper.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  6. #6
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    Re: Wanted: Vibration damper.

    Em ..
    You could make your own dampers, cast a disc as large as will fit with silicone from a caulk tube 4€ and powdered cast iron 40€ / 5 kg.
    The bigger the radius the more the damping, by radius power of 4 iirc.
    Anyway, the radius has a huge effect on the inertial damping.

    But if you face this problem, it might be better to just swap the drivers for new ones.
    New stepper drivers essentially don´t have jitter or vibration problems.
    And they are not too expensive, around 100€ in general for nema 34 / 60-80 v.

    If your steppers of 8 Nm have high inductance, they may simply be not well suited for the use.

    Your 160 units/min, is this speed of 160 mm /min (surely not) or something else ?
    Or inches, 160 inches / min as being more reasonable.

    Nema 34 steppers should run around 300-600 rpm, 8 Nm, with low voltage around 80V-- or less (not 220V mains as some new stepper drives can do).
    Around 600 rpm one would expect about 30-40% of max torque, so about 4.8 Nm x 48/72 belt drive == x 0.66 == 3.2 Nm.

    But the max acceleration at that speed will be about 1/2 - 1/3 of the max you can get from standstill, and that is one of the reasons bigger steppers of low voltage generally run about 600 (900) rpm max.
    The inertial effects of the table or gantry mean that you need a lot of momentary push to change direction, or stop in a rapid.

    In practice, the typical max torque usable is about 1/3 - 1/4 of the rated torque at rest, and this tends to be about 600 rpm max speed for Nema 34 and 900 rpm for nema 23 motors.

    Looking at torque curves for similar sized / inductance motors shows a torque around 40% for around 600 rpm for nema 34, low voltage.
    Running at 220V might gain you 50% more speed.

    But if You need to swap the drivers, then you might also swap the motors.
    And at 8 Nm / Nema 34, the driver motor combo is around 200€ +/- 50€.

    And you can get ac servos for about the same money, +40€.
    And the ac servos will be 5x more accurate, 10x faster in use (acceleration), and 5x faster in top speed (not material).
    Ac servos of 220V run less than 300€ with motor, driver and cables.
    And they are vastly, vastly, better.

    E.g.
    A stepper accelerates about 1 sec, 1000 ms, to top speed of say 900 rpm.
    (In use. You can do it much faster no-load, but not with a real machine connected).

    An ac servo accelerates to 3000 rpm in about 20 ms, around 50 ms - 100 ms with a real machine.
    About 10x - 20x better.
    And the servo will position to about 1-3/5000 steps, vs a stepper at 1/400 steps - about 10x better.

    I am not a servo zelot.

  7. #7
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    Re: Wanted: Vibration damper.

    Hi .

    I am afraid that I made a small misstake when writing that my reduction was 48/70 it should have been 70/48. My steppers is Leadshine 860A, power supply is S350-60 that is 60V DC 5,85A. I use 55V DC to power up the driver. one power supply to each driver. Steppers is Wantai motor WT86StH118-6004A that has 0,55 Ohm resistance 5,5mH inductance rotir inrtia 2,9Kg. Am using the metric system so feedrate shuld be 160mm/minute. But that could not be true, but it is what Mach3 displys. I do not know the stepper rpm when they are most annoying.

    I have thinking at make my own damper by making an outer part that hjas inside tooth and an inner part thar has outside tooth with a diference of inner-outside diameter of about 0,5 mm the inner part is running on a bearing, the outside part is boled to the timing belt pulley on the stepper. Than the gap between inner and outside part is filled with oil or some other fluid. The inner part is free to rotate in both left and right direction. And the fluid is then driving the inner part jusst as in automatic gearbox. the bthre is a lid that is bolted to the outside part to prevent fluid disappearing from the damper.

    The fastening bracket is made of 15 mm and 8mm aluminium. All nuts and screws is well tighten. I put a dial indicater to he xdrive unit and then made a test run when the unit is at the most noisy rpm. The indicater was "ratteling" about 0,03-0,04 mm. I do not know if that is a "big" value or if it is acceptable.

    This is my first attempt to convert or bulid a cnc mashine so servo drive is not an option for me just now


    Attachment 458116
    X drive unit
    Click image for larger version. 

Name:	Y_drive_stepper.jpg 
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Size:	60.6 KB 
ID:	458118
    Y-drive unit

    Best regards from John Eriksson in Sweden.

  8. #8
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    Re: Wanted: Vibration damper.

    I think the real issue is as I said you are operating in the resonant zone becasue you do not have sufficient gear reduction. You are currently running at 1.45:1 which is not enough. I would swap out your pulleys so you have between 3:1 and 5:1. (I myself without doing any calcs would go to 5:1)
    Rod Webster
    www.vehiclemods.net.au

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