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Thread: Homann Designs TM20LV (BF20,G0704) conversion

  1. #49
    Gold Member Bubba's Avatar
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    Peter,
    On my RF31, my Y servo is located below the center line of the Y screw and uses an adjustable motor mount to maintain tension on the belt. It C-C distance is variable from about 9.4" (~238MM) to about 10" (254mm) I also use an XL belt and except for the time that I ran into a hard stop (before limit switches) at full rapid and the "fuse" was the belt, I have had no problems. In my case, the pulley ratio is 1.4:1 (18:26 teeth) if that makes any difference and I used no idler to gain more pulley wrap.

    Art
    Country Bubba (Older Than Dirt)


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    Registered phomann's Avatar
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    Hi Art,

    Thanks I really appreciate the reply. The idler is there to clear the belt from the Y-Axis way more than anything else.

    The mounts for the stepper will be adjustable to tension the belt. The pulleys in the drawing are 28 tooth. I'll end up with a similar ratio to you as I want the option to try servos. I don't think the machine needs servos but I want to design a BoB for the G320X drives, and this machine will do as a testbed.

    Cheers,

    Peter

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    Peter,

    You'll want more than 2:1 ratio for servos - they are usually reduced 3 or 4 to 1, both to increase torque, and to bring top speed down to a reasonable level.

    Regards,
    Ray L.



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    Hi Ray,

    Yes, that is my concern. I may be able to squeeze 3:1 with a 10:30 pulley set, but there is barely enough room for the 30 tooth pulley.

    The 10 tooth pulley would work with the servo 0.25" shaft and I may have to move the idler to get enough wrap on the pulley.

    The way I've designed the stepper and belt plate, it is very easy to remove it and replace it with another.

    In the end I'll probably go with the 570 oz.in stepper with a 20:20 pulley drive. I also want to try a 387 oz.in motor with a 16:24 pulley setup for a 1.5:1 ratio. That way I'll be able to use a G540.

    Cheers,

    Peter.

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    Homann Designs - http://www.homanndesigns.com


  5. #53
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    Default Ballscrew Drawings

    Attached are images for the ballscrew dimensions. I plan to send these to Chai from linearmotionbearings2008.

    Before I send them off, can anyone see any errors or deficiencies with the drawings?

    Cheers,

    Peter

    Attached Thumbnails Attached Thumbnails Homann Designs TM20LV (BF20,G0704) conversion-x-axisballscrew-jpg   Homann Designs TM20LV (BF20,G0704) conversion-y-axisballscrew-jpg   Homann Designs TM20LV (BF20,G0704) conversion-z-axisballscrew-jpg  
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    Peter,

    Coupla things.... Your dimensions should all reference a single datum, like one end of the shaft. Giving incremental dimensions as you have requires the machinist to do arithmetic, which invites errors. Also, your tolerances are odd - a dimension with two different negative tolerances? That's just weird. Should be either a range, or a value with + and - tolerances, one of which can be zero if you like.

    Regards,
    Ray L.



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    Hi Ray,

    Good points. The tolerances I copied from the FK12 and FF12 data sheets. They are both negative as it needs to be under size for the bearing fit.

    I thought that providing the nominal size of 12mm then the range of under size tolerance would add context.

    But then, I'm no draftsman.

    Thanks for the input.

    Cheers,

    Peter

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    Quote Originally Posted by phomann View Post
    Hi Ray,

    Good points. The tolerances I copied from the FK12 and FF12 data sheets. They are both negative as it needs to be under size for the bearing fit.

    I thought that providing the nominal size of 12mm then the range of under size tolerance would add context.

    But then, I'm no draftsman.

    Thanks for the input.

    Cheers,

    Peter
    Peter,

    More likely to just confuse them, since the base dimension is not really metric to begin with. I would specify the maximum dimension, with a max tolerance of +0.00. That makes the intent very clear.

    Regards,
    Ray L.



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    Hi Ray,

    OK, will do.

    Cheers,

    Peter

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    There is an ISO standard for tolerancing different kinds of fits. In some cases it is proper GD&T to have double positive or double negative tolerances. This is most likely a sliding fit into the bearing (H7g6 fit).

    Draftsmen and machinists know this. Its not at all uncommon.

    In addition to using a datum as stated above, machinists appreciate it when all reading is horizontal.

    Here is a ISO 268-2 tolerancing chart for different kinds of fits: Limit and fit | ISO hole chart | Tolerance



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    Hi,

    I placed the order for the ballscrews yesterday with Chai from Linearbearingsmotion2008. I asked if he could supply extra balls. Chai said he would but in 100 extra ball for free.

    I guess I'll see them next week some time.

    The submitted drawings are attached for reference.

    Cheers,

    Peter

    Attached Thumbnails Attached Thumbnails Homann Designs TM20LV (BF20,G0704) conversion-x-axis-ballscrewv2-jpg   Homann Designs TM20LV (BF20,G0704) conversion-y-axis-ballscrewv2-jpg   Homann Designs TM20LV (BF20,G0704) conversion-z-axis-ballscrewv2-jpg  
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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    Peter, what's the damage for the 3 screws? Interested as I may convert my TM20LV (long term)



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