Ballnut External Return Tube
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  1. #1
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    Default Ballnut External Return Tube

    Hey gang- I'm having a hell of a time tracking down what I thought was going to be a simple part, so I figured I'd see if anyone here had any advice. I'm needing an external return tube for the Y axis ballnut on an older (early 2000's) Milltronics 9"x48" CNC knee mill. The tube itself is 2 parts (split down the centerline) and appears to be some flavor of high carbon or tool steel. Milltronics gave me a hard no & referred me to a rebuilder they have a relationship with. I got a similar hard no from them & went further down the rabbit hole with dozens of different rebuilders. Lots of them will sell me a new screw/nut assembly, but no one seems to have the part. The screw & nut are in fantastic shape so I'd definitely rather not spend 2-5k on a new assembly. Anyone know where/how I might be able to buy the tube? Anyone have a junk machine that'd sell me one?

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    What size are the balls and how "wide" does the recirculator have to be?
    There's barely any load on the recirculator. Can you find the right size tube and make your own? Don't split it. Harder to load but doable.

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    Is this a VK series machine? (Does the whole head slide up and down AKA "millslide" ) - Or does it have just the quill

    I think those Millslide machines are YCM Supermax machines origianally - You can probably find a nut from one of the tiawan suppliers if supermax is no help (not sure if they are around anymore)

    The Quill machines are Shizouka machines - Usually have a Cent V or earlier control on them.

    Not sure if any of this helps you but a Ebay search might work as well

    Chris

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    Quote Originally Posted by welderboyjk View Post
    What size are the balls and how "wide" does the recirculator have to be?
    There's barely any load on the recirculator. Can you find the right size tube and make your own? Don't split it. Harder to load but doable.
    1/8" balls and the ID of the tube is 5/32". I'm squeamish about making it out of anything soft... the balls are at least file-hard and I think they'd wear through a soft tube pretty quickly. I'm going to try to make something up from drill rod, but not super confident I can bend a 90 in it without kinking

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    Quote Originally Posted by 50BMG DUDE View Post
    Is this a VK series machine? (Does the whole head slide up and down AKA "millslide" ) - Or does it have just the quill

    I think those Millslide machines are YCM Supermax machines origianally - You can probably find a nut from one of the tiawan suppliers if supermax is no help (not sure if they are around anymore)

    The Quill machines are Shizouka machines - Usually have a Cent V or earlier control on them.

    Not sure if any of this helps you but a Ebay search might work as well

    Chris
    That may be helpful, I'll start checking ebay. It's a quill only machine, so I'll add "shizouka" to my searches

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    You should be able to find a part number for the ballnut lasered on it somewhere. Ebay should find you a NOS or used one and swap parts. Number may be etched on the barrel of the nut.

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    If it needs to be hard, make from carbon steel tube and case-harden it after bending. Clean and polish the ID to ensure no "grunge" from the hardening compound is left in the ball path.

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    You might ask on the other cnc machining site, there's a dedicated section for milltronics there and a lot of guys that have gone through their machines pretty thoroughly. Also look up sportybob over there, he does a lot of repairs on them and might be able to help you out.

    Sent from my SM-N960U using Tapatalk

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    Those tubes are generally not hardened, I think the one you are talking about is made from 2 identical halves and held together with the clamp.

    You could probably mill out a couple tracks in 1018 and profile the outside to work. It's not rocket surgery, they just get the balls from one end to the other.

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    That's a lot smaller than what I could get my hands on.
    I wouldn't make them out of butter but there are steering boxes out there that have plastic recirculator on them.
    Like I said. There's no load on then once they are in the recirc. It's just there to get them to the other end.

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    Quote Originally Posted by jmcghee View Post
    1/8" balls and the ID of the tube is 5/32". I'm squeamish about making it out of anything soft... the balls are at least file-hard and I think they'd wear through a soft tube pretty quickly. I'm going to try to make something up from drill rod, but not super confident I can bend a 90 in it without kinking
    I don't think you need to worry about the differences in hardness between the balls and the transfer tube because under normal conditions they never touch. That's what lubrication does for you. Things wear against each other because of -

    1) lack of lubrication
    2) contamination from dirt/chips/coolant etc
    3) excess load
    4) incorrect lubrication type

    -and probably a few more I can't think of right this minute.

    It's hard to know from here what system failure(s) contributed to your transfer tube breakdown, but once the repaired screw is in place, take a moment to make sure the ball screw lube and isolation/protection systems are in place and working properly, or you might find yourself back to square one sooner then you'd like.

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    On the ones I worked on, the tubes weren't hard. The tricky parts would be 1. getting the correct ID and OD material, 2 bending it correctly, correct radius and location, 3 cutting the ends to fit into the screw grooves correctly, that seemed to be important to scoop the balls out of the groove and into the tube smoothly. I'd try it if I was faced with your need, but I'd plan on lots of trial and error time.

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