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Thread: Servo CNC conversion of Vertex BS0 dividing head

  1. #13
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    Quote Originally Posted by handlewanker View Post
    Hi, that sounds like a very complicated process for a simple job.
    If you already have a spindle encoder and a rotary axis then the hobbing setup is just a few lines of code in the HAL file. (literally a few).
    The second point is, how much does a bought in commercially made HSS hob cost compared to a set of gear cutters, at 9 in a set, ranging from 10 teeth to a rack, and buying just the separate cutters as needed.
    I get the hobs second-hand from eBay. But to buy them new they cost about the same as a set of involute cutters.
    Gear Hobs - Arc Euro Trade



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    Default Re: Servo CNC conversion of Vertex BS0 dividing head

    Andy, I know this is a old thread but hopefully you still get notifications. I have the identical BS-0 head that I plan on cnc'ing. What size servo did you use? I have been wondering what size servo motor would be suitable for cutting while rotating. Also, now that you have had it a while, how did the backlash end up? Any other comments now that you have had it a while would be appreciated.

    George



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    Default Re: Servo CNC conversion of Vertex BS0 dividing head

    Hi, one thing that has apparently escaped the thread watchers......if you cut gears it is most important to have the gear teeth running true to it's bore........one reason why cutting gears with a manual mill and dedicated single gear cutters is done with the blank mounted on a mandrel in a dividing head that is dialed to run true otherwise the gear will run unevenly as it rotates.

    The video previously screened shows a blank being cut without a hole to subsequently mount it onto a spindle.....whatever.........boring a gear after teeth cutting and to have it run concentrically with the pitch circle is going to be very difficult.

    While you may cut teeth of some description on a gear blank with this set-up, the outcome is not practical........it's purely cutting a gear by CNC for CNC's sake.

    BTW.....when cutting gears you need a gear tooth vernier to ascertain when the tooth thickness at the pitch circle is correct, otherwise the gears just fit where they touch........with that you may as well buy accurately cut gears from the experts who do gear cutting as a business.

    To ensure the gear comes out right the tooth thickness at the pitch circle has to be measured and the setting re-set for the cutter depth/tooth width............doing this with CNC is not CNC per se.
    Ian.



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    Default Re: Servo CNC conversion of Vertex BS0 dividing head

    Quote Originally Posted by Sparky_NY View Post
    What size servo did you use? I have been wondering what size servo motor would be suitable for cutting while rotating.
    I used a NEMA23 sized servo, 24V and rated at something like 0.8Nm. I used it because I had it. It works OK for indexing, gear hobbing and engraving, but I think that it would stall with moderately heavy rotary cutting. If you expect to do a lot if that then I think you would eant something bigger.
    Also, now that you have had it a while, how did the backlash end up?
    Backlash is higher than I would ideally prefer. The limitation is how low I can get it in the tightest spot compared to the backlash in the loosest spot, because the work wheel isn't perfect. Your backlash in CNC-operation should end up the same as in manual. Get it as good as you can, then see if that it good enough.

    If you can find a decently big harmonic drive on eBay then that would probably be a better starting point, though I don't think that there is any way you could ever fit one to a BS0. You would have to think in terms of building from scratch.
    Here is one I designed earlier (but never made).



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    Default Re: Servo CNC conversion of Vertex BS0 dividing head

    Thanks much for the info Andy. Big harmonic drives would not be easy to come by or inexpensive unfortunately, even on ebay. Another route I am considering is a nema34 servo with a planetary reducer directly attached and then a robust timing belt drive to the spindle shaft. I would think that both the timing belt and the planetary drive would yield very low backlash.

    George



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