Chinese Ebay 4th axis Harmonic Drive


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Thread: Chinese Ebay 4th axis Harmonic Drive

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    Question Chinese Ebay 4th axis Harmonic Drive

    Hello!

    I have just received the harmonic drive. I read before and I was aspecting a gapless drive, with no backlash. Now I ma new to harmonic drive but if I try to move the chuck by hand it has a play of like 4mm back and forth. Does it come from the harmonic drive or it something else? How can I get rid of it? I do not find anyone else with a similar problem.

    Here the video showing the problem

    This is the type of harmonic drive. I have the 1:50 reduciton.

    https://www.ebay.de/itm/3-Jaw-K11-10...8AAOSwJTNbvW2H

    Thanks a lot! I need it to make helical gear and like that won't work :-(

    Similar Threads:
    Last edited by rey8801; 09-15-2019 at 06:59 PM. Reason: Posted the wrong video :-)


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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    OMG I must be bored...
    Apart from that thing is a complete toy, does the motor shaft move in conjunction with the chuck. What you are looking for is the difference of movement between the two,, this is your backlash. If no backlash either put some more current into the stepper motor or get a bigger one with better holding torque.



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    I need for making small gear, it doens't have to go through heavy cuts. Based on what also reported in this forum this style of harmonic drive should have almost zero backlash. That why I wanted to try.
    Anyhow the motor is not moving, you have back and forth play only in front. That's why I coaaled backlash.



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    I would actually be amazed if this is a harmonic drive... However, even a worm drive or direct drive shouldn't move like that. Something is wrong.

    I think your options are send it back or pull it apart. Good luck!



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by FastFarmer View Post
    I would actually be amazed if this is a harmonic drive... However, even a worm drive or direct drive shouldn't move like that. Something is wrong.

    I think your options are send it back or pull it apart. Good luck!
    Others with this cheap harmoninc drive didn't mentioned such degree of freedom, they actually stated almost zero backlash. I think I got a fautly one. So lucky. I guess I will try to see if the seller can check other dirves at the factory if they all "feature" this fantastic backlash otherwise I will try to solve it, but not sure how since it's not a simple gear drive.



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    I pull itll it apart. The back lash is really from the harmonic drive. Now I do not know if I got a fautly one or if this type are all like this one





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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Good lord.
    Well, if it is an HD (and it seems to be), then the unit as a whole has a serious defect, and should be returned.

    But then, one asks why.
    One possibility is that the flexspline, which is the heart of the unit, is really seriously worn out. Just how this could happen, I do not know, and if it did happen I would expect the whole thing to collapse.
    Another possibility is that the outer part of the wave generator has been worn out and is far smaller than it should be. Same comments.

    Another possibility is that something is actually missing or is of the wrong size. This seems like a possibility, as the bit on the stepper motor did not look as though it had any bearings. I note that you are able to push the motor drive back in place fairly easily: this should not be possible they way you did it, except with great care and skill. I would prefer to say it looks wrong. And when you wobbled the front end, I could see the flexspine wobbling back and forth.

    Underlying all this is the question of how could the thing backlash like that. It could be that the spline is not fully engaging with the outer teeth, but is instead able to rattle from side to side - like rattling poorly engaged gear teeth in a conventional gearbox. This would be consistent with a missing or wrong-sized part.

    Have a look at the attached picture (from HD catalog). Does the drive bit look like this, with either balls or rods as bearing elements? Some detailed close-up still pics would be more useful now than videos.

    Incidentally, that unit is a 14-50 one according to the label on top: the smallest in the whole range. It has a rather large chuck mounted on it. In my book, the chuck is a bit big for the bearing.

    Cheers
    Roger

    Attached Thumbnails Attached Thumbnails Chinese Ebay 4th axis Harmonic Drive-hdspine1-jpg  


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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by RCaffin View Post
    Good lord.
    Well, if it is an HD (and it seems to be), then the unit as a whole has a serious defect, and should be returned.

    But then, one asks why.
    One possibility is that the flexspline, which is the heart of the unit, is really seriously worn out. Just how this could happen, I do not know, and if it did happen I would expect the whole thing to collapse.
    Another possibility is that the outer part of the wave generator has been worn out and is far smaller than it should be. Same comments.

    The teeth on the flex spline are really small, I also thought they look worn out but then it's a new drive so I thought it must be normal to allow the teeth to disengaged when rotating.


    Another possibility is that something is actually missing or is of the wrong size. This seems like a possibility, as the bit on the stepper motor did not look as though it had any bearings. I note that you are able to push the motor drive back in place fairly easily: this should not be possible they way you did it, except with great care and skill. I would prefer to say it looks wrong. And when you wobbled the front end, I could see the flexspine wobbling back and forth.

    That what I think as well, to me there is too much gap between the flexspline and the circular spline, so the flex spile has to deform too much before properly engaged the circular spline.

    Underlying all this is the question of how could the thing backlash like that. It could be that the spline is not fully engaging with the outer teeth, but is instead able to rattle from side to side - like rattling poorly engaged gear teeth in a conventional gearbox. This would be consistent with a missing or wrong-sized part.

    Exactly, that what I think as well


    Have a look at the attached picture (from HD catalog). Does the drive bit look like this, with either balls or rods as bearing elements? Some detailed close-up still pics would be more useful now than videos.
    Incidentally, that unit is a 14-50 one according to the label on top: the smallest in the whole range. It has a rather large chuck mounted on it. In my book, the chuck is a bit big for the bearing.

    Yes attached to the stepper there is the wave generator, the part where I was putting back in place the C-clip. This part also looks like a bit too small. I would aspect way more compressor from it to the flex spline.

    Cheers
    Roger


    In bolted the reply to your thoughts. I think the only solution is returned. Still have to understand if I got a faulty unit or they are all like that.

    Thanks for the help!



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by rey8801 View Post
    I need for making small gear, it doens't have to go through heavy cuts.
    To my knowledge you do not need backlash management for cutting gears; one-way continuous rotations. As long as it index accurately you'll be making great parts with this tool. Small parts, but still great.
    You were looking for a dividing head btw. Rotaries meant for machining gears needs lock/unlock capabilities


    edit: ignore my first sentence. I've just watched the first min of your vid. You will not be able to cut gears with this. That's not called backlash anymore, it's called free-play. yikes. Case for Return & Refund/Replace, your unit is unusable unfortunately. Worst scenario disassembly and complete rebuilt required. Sorry friend

    Last edited by Mecanix; 09-17-2019 at 03:26 AM.


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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by Mecanix View Post
    To my knowledge you do not need backlash management for cutting gears; one-way continuous rotations. As long as it index accurately you'll be making great parts with this tool. Small parts, but still great.
    You were looking for a dividing head btw. Rotaries meant for machining gears needs lock/unlock capabilities
    Continuous cutting can be a solution in some case but forgot to mentioned, with gears I mean duoble helical gears and not simple spur gears. So I need the 4th axis to be able to move with a decent precision. THe holding torque of an harmonic drive is really good. Even in this one is locked in place. The problem that in this drive you have the backash first and then it locks, whihc makes it unusable for what I want to do.



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by rey8801 View Post
    Continuous cutting can be a solution in some case but forgot to mentioned, with gears I mean duoble helical gears and not simple spur gears. So I need the 4th axis to be able to move with a decent precision. THe holding torque of an harmonic drive is really good. Even in this one is locked in place. The problem that in this drive you have the backash first and then it locks, whihc makes it unusable for what I want to do.
    Return the unit. Get a replacement.



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    Default Re: Chinese Ebay 4th axis Harmonic Drive

    Quote Originally Posted by Mecanix View Post
    edit: ignore my first sentence. I've just watched the first min of your vid. You will not be able to cut gears with this. That's not called backlash anymore, it's called free-play. yikes. Case for Return & Refund/Replace, your unit is unusable unfortunately. Worst scenario disassembly and complete rebuilt required. Sorry friend
    Hahaha. You make me laugh...



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