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how much side load can a stepper motor take?

Discussion in 'CNC IN THE HOME SHOP' started by bpimm, Apr 20, 2017.

  1. bpimm

    bpimm United States Active User Active Member

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    I rescued a CNC plasma table a couple years ago and haven't had time to get it up and running until now. This was a diy someone else had put together and the price was right so it followed me home. It has some issues with RFI noise (not a single shielded wire on it and the plasma cutter is 1" from the CNC control box...) and it suffers from some shall we say less than optimal design ideas, I'll just leave it at that.

    The Zaxis assembly was crude at best and didn't hold the hand torch strait so it cut at an angle and the touch off mechanism took so much force to move it that it flexed the head every time it touched off. I built a new Z axis for it and am in the process of reassembly and rewiring (with all shielded wire) and noticed that the Y axis carriage on the gantry that carries the Zaxis was oscillating in the Xaxis direction as it moved through it's travel, my suspicion is that the motor shaft is bent slightly, I pulled the motor off and discovered that the only thing carrying the load of the head is the motor bearings. it is built from 2" square tube and uses a kit for the carriers that uses 6 bearings on each carrier, these work fine on the gantry because the gantry holds them in place in 1 axis but on the Y axis it can rotate on the square tube because there is nothing holding it but the motor. the direction of rotation is toward the head meaning that all the weight from the head is pulling against the motor bearing.

    So I guess my question is are these nema 23 stepper motors designed to carry machine load on the shaft bearings or are they designed to only have the drive torque on their bearings. I can't seem to find any info on the motors which suggests that they are of Chinese decent, they have a number on them, 60H366DF1B, it leads to a couple hits on a google search to suppliers not anything about a manufacturer and no specs on the bearings at all.

    I'm working on a solution to get the load off of the motor but haven't really come up with something good yet, I'll take some pics in a bit and get them on here.
     
    Last edited: Apr 20, 2017
  2. Ulma Doctor

    Ulma Doctor Infinitely Curious Active Member

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    the radial bearings in a NEMA 23 can take modest radial loads,
    they however can't take an axial load, there are no thrust bearings
     
    bpimm likes this.
  3. bpimm

    bpimm United States Active User Active Member

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    Here are some pics.
    [​IMG]
    I added the second bearings on top and that stopped the rotation CW in this pic.
    [​IMG]
    this is the side the zaxis mounts to.

    [​IMG]
    this is how it should be.
    [​IMG]
    This shows the amount of CCW rotation it has without the motor installed so with 10 Lbs. of head mounted out on the left side of the pic it is going to putting some radial load on the motor shaft.

    In my thinking the motor shouldn't carry any load from the machine only it's torque load.

    Options I'm thinking of;

    Replacing the motor with a new one and running with it to see how it goes.

    Move the gear rack down to the middle of the 2x2 gantry so I can get a bearing on top of it to stop the movement to the left, in this pic, and make a shaft extension for the motor to reach. I already added a bearing to the right side under the rack and it helped but was to close to the center of rotation to be very effective which is why I think it needs to be at the top.

    All thoughts and opinions are welcomed
    Thanks
     
  4. bpimm

    bpimm United States Active User Active Member

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    Attached Files:

  5. bpimm

    bpimm United States Active User Active Member

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    What motor specs are important to match in a replacement motor? It's being driven by a G251 Gecko so it's a 3.5A driver.
     
  6. JimDawson

    JimDawson Global Moderator Staff Member Director

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    That would be the ideal condition, but I think the motor would take the radial load with no problem. I guess you could put bearings on either side of the motor that would contact the edge of the tube. Would require a new motor mount.
     
  7. JimDawson

    JimDawson Global Moderator Staff Member Director

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    Match the inductance and the torque.
     
  8. bpimm

    bpimm United States Active User Active Member

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    How close do I need to be on the Inductance? I haven't found any 3mH motors, I have found 1 at 3.6mH but it's a 270 oz/in instead of 300 and 1 at 5.4mH at the same 270 0z/in.

    The 5.4 mH is on amazon and is Prime eligible so it would be here in 2 days, the other one could be 2 weeks out.
     
    Last edited: Apr 20, 2017
  9. JimDawson

    JimDawson Global Moderator Staff Member Director

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    As I remember, the higher the mH the higher the voltage that is required for the motor to have max performance. I can't remember the formula. I'm guessing either of those motors would work, but you may not be able to accelerate as fast. If the price is cheap, then give it a try and see if it performs to your needs.
     
  10. bpimm

    bpimm United States Active User Active Member

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    That's kinda what I remember as well, I ordered the one off of Amazon so it'll be here Sunday and I can test it.
     

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