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  1. #1
    Join Date
    Mar 2017
    Location
    Brisbane
    Posts
    245

    Default Allowable y axis overhang for extending the travel?

    I've seen a few people have the mill table of bench top machines move out on the y-axis beyond being flush with the saddle.

    My question is how much is ok? I am trying to size a y axis ballscrew and I need to allow for this, as well as a kind of riser for my servo so it is positioned further back to let the y-axis come out.

    An example: https://youtu.be/k2F6100RKOE?t=432
    You can see his y-axis coming out further than usual here at about 7:10

    I have read that tables with larger saddles are more accurate, and this would explain why surface grinders have enormous tables/saddles with relatively little x movement. Less overhang is better. Still, how do you calculate what's acceptable?
    I posted this in cnczone too, I am just hoping here it might attract the eyes of someone who knows as I need to order ballscrews soon. Thanks.

  2. #2
    Join Date
    Aug 2011
    Location
    Melbourne
    Posts
    4,779

    Default

    As you would expect, the more a table overhangs the saddle, the more it will droop. One thing you can do is put a dial indicator from the head of the mill and touching the table. As the table extends from the saddle you will be able to measure this droop and pick a figure that may be allowable to you. I think it's just a matter of trancating the table travel to an acceptable figure.

    Adjusting the gibbs so that are snug (but ot tight) will also reduce this droop.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #3
    Join Date
    Aug 2011
    Location
    Melbourne
    Posts
    4,779

    Default

    PS. Also using your mill with the table extended will create more wear on your saddle.

    Simon

    Sent from my SM-G900I using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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