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  1. #21
    Quote Originally Posted by magicniner View Post
    I chose it for the decent through capacity which you don't get with harmonic drive versions, - Nick
    Picked up this harmonic drive some time ago for a 4th axis project, not yet got round tuit. 50 -1 with 25mm through and pre-loaded cross roller bearing on the output ring

    Click image for larger version. 

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  2. #22
    I just found these things existed but I already feel a deep need to own one, was this an e-bay find?

  3. #23
    Quote Originally Posted by johnsattuk View Post
    Picked up this harmonic drive some time ago for a 4th axis project, not yet got round tuit. 50 -1 with 25mm through and pre-loaded cross roller bearing on the output ring

    Click image for larger version. 

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    Yeah,
    Harmonics with through capacity exist but are not fitted to the Chinese eBay 4th axis models under discussion here, nice thing to have in the parts drawer, please post some photos when you've completed a project with that,
    Regards,
    Nick.
    You think that's too expensive? You're not a Model Engineer are you? :D

  4. #24
    Quote Originally Posted by Robin Hewitt View Post
    I just found these things existed but I already feel a deep need to own one, was this an e-bay find?
    Yes, came across it after I had bought a 5phase stepper with 50-1 harmonic drive ( 25000 steps /rev ) which I was going to belt drive a head 2-1 so that I could incorporate a through hole. I also have some very low backlash 5 phase 10-1 (5000 steps/rev ) epicyclic drives that I thought I might use with perhaps ~4-1 belt drive.

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  5. #25
    I have now bought a 50:1 harmonic to play with, eBay item number: 291926642351
    I thought maybe connect it to a shaft using my favorite Myford change wheels. Not easy to cut the middle out 100% concentric so I would have to spring two together, that seems to do the trick if you want low backlash with Myford wheels. I think I could enjoy this. Somewhere in my junk boxes I have a new pair of 40mm self-aligning, flange bearings, featuring grub screws on the extended inner race. They could easily become a part of this.

  6. #26
    They come in various sizes, 11 is quite a small one, do you know shaft sizes

  7. #27
    I use lots of harmonic drives for my motion control rigs. I buy them second hand from ebay, but I have also bought a couple of modern brand new ones from the Harmonic Drive rep in the UK. They are very expensive new. HQ is in Germany but usually made in Japan, they own the monopoly, so the cheapo Chinese contraptions may not live up to expectations re. "zero" backlash, quality of bearings and so on. A brand new size 25 HD will usually cost a couple of thousand. I paid 1500 for each size 11 for a camera rig. They are beautifully made.

    The one above from Johnattuk is a proper one with very good angular bearings. These usually come from small robotic machines that are decommissioned, a lot from S Korea, and a bit old, but perfectly usable. Some work perfectly, some have seen better days and will work, although they may be a bit bumpy at certain speeds, which you wouldn't probably notice on cnc rigs, but you do notice in motion control where perfect smoothness throughout the range is paramount.

    The one you bought, Robin is too small, being size 11, with small bearings. You need at least a size 25, with size 14 being a bit marginal. Typical price for a good decent second hand size 25 with hollow shaft is around 450.

    Here is a render of one of mine showing both ends

    Edward

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    And this will give you a perspective on sizes. Size 11, size 14 and size 25

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    Last edited by Edward; 20-08-2017 at 09:29 PM.

  8. #28
    Quote Originally Posted by Robin Hewitt View Post
    I thought maybe connect it to a shaft using my favorite Myford change wheels..
    Surely you'll be using Anti-Backlash gears from HPC Gears as it would be a strange choice to add backlash in the primary drive (regardless of how small an error this would introduce) of a system designed specifically to avoid backlash?
    Last edited by magicniner; 20-08-2017 at 10:23 PM.
    You think that's too expensive? You're not a Model Engineer are you? :D

  9. #29
    Quote Originally Posted by Edward View Post
    And this will give you a perspective on sizes. Size 11, size 14 and size 25
    Lightweight ;), here's a size 50:

    Click image for larger version. 

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    I had two of these sitting in my shed for 5-6 years - like Robin I found out about them and immediately decided I must have two. Then I got very sidetracked, so I sold one recently and held on to the other. I think I'm more interested now in coaxing a high torque motor into a direct drive axis, as the cost of encoders is decreasing. Seems more elegant.

    One interesting point with harmonic drives is that although they don't exhibit backlash (if well made), they still do have some hysteresis. Still, beats buying a chuck driven from a stepper motor via a rubber band.
    Last edited by Jonathan; 20-08-2017 at 10:26 PM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  10. #30
    Quote Originally Posted by Jonathan View Post
    Still, beats buying a chuck driven from a stepper motor via a rubber band.
    It could, but I've been making parts with my "rubber band" for a couple of years, how's it going with your "Doorstop" ?
    You think that's too expensive? You're not a Model Engineer are you? :D

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