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  1. #1
    Join Date
    Aug 2005
    Posts
    180

    Minimill to 4th Axis....

    After upgrading from my minimill to an Optimum BF30 mill and doing the cnc conversion, I have been debating what to do with the minimill. Sell it? keep it as a mill? Hmmm. I have also been looking around at designs for a 4th axis and it struck me that the head of the minimill might make a pretty good basis for a 4th axis for the BF30.

    So the other night I set too and got the head off the minimill and from first inspection it looks like it will work quite well. The plan is to use a harmonic drive and stepper motor coupled to the minimill spindle for the motive power and attach an adaptor plate to the front of the spindle. In this way I retain the MT3 tapered bore plus I have mount point for lathe chucks and tooling plates if required.

    Attached is the first bit of CAD, more to follow.....

  2. #2
    Join Date
    Aug 2005
    Posts
    180

    Re: Minimill to 4th Axis....

    So things have moved on a bit. I now have a working design that connects a Harmonic drive FB type pancake drive to the spindle of the minimill. Motive power will come from a small NEMA34 stepper motor - the harmonic drive is 160:1 ratio so no need for masses of input torque.

    Attachment 258136
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  3. #3
    Join Date
    Sep 2005
    Posts
    1195

    Re: Minimill to 4th Axis....

    Hello,
    What kind of harmonic drive? Can you show me? Where is the source of cheap harmonic drive?

  4. #4
    Join Date
    Nov 2009
    Posts
    4415

    Re: Minimill to 4th Axis....

    Did you click on the highlighted "Harmonic Drive" in his post? It takes you straight to the ad on Amazon.
    A lazy man does it twice.

  5. #5
    Join Date
    Sep 2005
    Posts
    1195

    Re: Minimill to 4th Axis....

    Hi,
    Yes, I clicked on the highlighted "Harmonic Drive" . I found it not clear explanation. Then I tried to find on alibaba, Many type of "Harmonic Drive", I do not know which one the best suite for 4th axis. Maybe in the future, I plan to make 4th axis, It is low backlash as said in the ads.

  6. #6
    Join Date
    Jul 2007
    Posts
    1602

    Re: Minimill to 4th Axis....

    Quote Originally Posted by Fastest1 View Post
    Did you click on the highlighted "Harmonic Drive" in his post? It takes you straight to the ad on Amazon.
    You can't be sure of any link on this site anymore. Most are just some autolink advertising/redirction crap. Like harmonic drive for instance... I didn't add a link there btw so if one shows up...

    bob

  7. #7

    Re: Minimill to 4th Axis....

    Right, you can disable Skimlinks in your profile under general settings, I see no highlighted text for harmonic drive in any of the posts here.
    Hoss
    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com

  8. #8
    Join Date
    Nov 2009
    Posts
    4415

    Re: Minimill to 4th Axis....

    I see a highlight AND it took me to a harmonic drive for 400 bucks. Weird you didnt link it. In fact I just clicked on every phrase "harmonic drive" in this thread (all have highlighting from my side, will have to check into settings) and they all take me to the same Amazon ad.
    A lazy man does it twice.

  9. #9
    Join Date
    Aug 2005
    Posts
    180

    Re: Minimill to 4th Axis....

    Links added by site not by me. Harmonic drive came off ebay after a bit of waiting. Reference is here for the FB series drives.

    Products | Component Sets | FB Series Pancake Component Sets :: Harmonic Drive LLC.

  10. #10
    Join Date
    Sep 2005
    Posts
    1195

    Re: Minimill to 4th Axis....

    It is clear enough I learned from catalog. Thanks.

  11. #11
    Join Date
    Aug 2005
    Posts
    180

    Re: Minimill to 4th Axis....

    Well after a bit of a break, I've started to make parts for the 4th axis. Tonight, I just about completed the connection between the minimill spindle and the harmonic drive (red part in 3d views above). I still need to cut the slot for the key but that shouldn't take much time - I have a CNC script for cutting slots. I've added a few images of the machined part plus the assembly with one half of the harmonic drive and the minimill spindle.

    I managed to remove the spindle from the minimill housing - I had to drift the spindle out from the bearings, not a task for the faint hearted. When I re-build the spindle, I will replace the 6206ZZ bearings with 6206RS versions to protect from swarf.
    Attachment 263922
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  12. #12
    Join Date
    Feb 2014
    Posts
    197

    Re: Minimill to 4th Axis....

    The torques specs for that drive have me a little curious. Are they listing the input or the output torque? If its output are you not going to be way over that with the gear reduction?

  13. #13
    Join Date
    Aug 2005
    Posts
    180

    Re: Minimill to 4th Axis....

    Torque specs are output and yes a 1Nm stepper theoretically can deliver 160Nm at the output and probably destroy the drive in the process! I plan to use the axis for light cuts / engraving rather than taking really heavy cuts with big endmills. Its up to me to program the machine within its limits.

  14. #14
    Join Date
    Feb 2014
    Posts
    197

    Re: Minimill to 4th Axis....

    I am not to be trusted with "self limiting". I will be watching you progress.

  15. #15
    Join Date
    Dec 2009
    Posts
    1416

    Re: Minimill to 4th Axis....

    I was thinking the same thing a few years back. The headstock on the X2 is pretty much the same as the 7" lathe so it would make sense. I would unfortunately be saddled with an R8 spindle instead of an MT so not ideal but should be useful for engraving, indexing, and light milling.
    CNC: Making incorrect parts and breaking stuff, faster and with greater precision.

  16. #16
    Join Date
    Aug 2005
    Posts
    180

    Re: Minimill to 4th Axis....

    Well a bit more progress. The part I made the other night now fits nicely on the spindle. I cut the keyway using a purpose made tool mounted in the CNC miller, and then wrote a simple loop to shave off 0.001" per pass.

    I then made a start on the housing which involved cutting a 100mm dia steel bar - a job for the new bandsaw!. I got it at Xmas during a Machine Mart vat free day, after changing the blade to a bi-metal M42 blade from Tuff Saws - Tuff Saws, Quality Bandsaw Blades the saw cuts an absolute treat - I advise anyone getting one of these saws to change the blade to a quality part prior to performing complex "tune-ups". I did extend the vice and added a screw jack at the far end, I also junked the "stand" and built a wooden wheeled trolley out of an old kitchen work surface.

    I mounted the steel bar in the lathe and started to rough machine the outer body. As this proceeded it struck me that a NEMA23 motor rather than the size 34 motor would result in a much neater design solution and would allow me to create all the flanges / mountings from the 100mm dia steel stock.

    Back to TurboCAD...and here are the results, much better than the first attempt.


    Attachment 265440 Attachment 265442 Click image for larger version. 

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    Attachment 265446 Attachment 265448

  17. #17
    Join Date
    Jan 2015
    Posts
    2

    Re: Minimill to 4th Axis....

    Quote Originally Posted by asuratman View Post
    Hi, Yes, I clicked on the highlighted "Harmonic Drive" . I found it not clear explanation. Then I tried to find on alibaba, Many type of "Harmonic Drive", I do not know which one the best suite for 4th axis. Maybe in the future, I plan to make 4th axis, It is low backlash as said in the ads.
    you can order things from alibaba? Isnt' that site just a listing? its not like ebay with buyer protection and a very removed payment process like paypal to protect customers or anything like that. You deal direct with the manufacturer right?

  18. #18
    Join Date
    Jan 2008
    Posts
    1523

    Re: Minimill to 4th Axis....

    Aliexpress is the business to customer site. Alibaba is business to business really, aimed at large quantities.
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  19. #19
    Join Date
    Jan 2015
    Posts
    2

    Re: Minimill to 4th Axis....

    I have never ordered frm them. So how does it work with aliexpress? Is it like Ebay with all the buyers protection and all that stuff? Sometimes I see good deals just random web searches and showing alibaba sites. But since its direct to the business that inquest stops right there. But if they make transactions safer for buyers like ebay, could have more options.

  20. #20
    Join Date
    Aug 2005
    Posts
    180
    Anywhooooo...
    I've been machining the outer housing from the 4" bar stock and made a start on the jig plate for machining the reverse side of the outer housing and motor plate.

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