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IndustryArena Forum > MetalWorking Machines > Uncategorised MetalWorking Machines > Starting knee-mill retrofit. Your input appreciated.
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  1. #1
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    Question Starting knee-mill retrofit. Your input appreciated.

    I've just taken delivery of a full sized knee-mill (a Sharp bridgeport clone with 3hp/4500 max RPM vari-speed head). It was converted to 2-axis CNC over a decade ago, but the controls are dead. So, I've got a mill with X/Y ballscrews, an appropriately sized power supply, and servos with mechanicals on the X & Y axis -- a great place to start a retrofit. The current servos are 70V Nema 42 size, so I'm going to go the Mach 3/ Gecko G320 route. I've already got a VFD to run it on the single phase in my garage/shop (GS2 from Automation Direct).

    Some questions for the list (any & all input greatly appreciated - I've never done this before):
    1) Z-axis: I'd like to CNC-enable either the quill or the knee. Currently, I'm leaning toward the knee due to greater travel and less cost/complexity.
    - Anyone out there got drawings/.dxf's for knee mechanicals they'd be willing to share?
    - Anyone know a source (other than eBay - I'm watching it) for NEMA 42 servos appropriate for the knee?

    2) Motion controller: I'm willing to fork out the $400 for a G-Rex, since I'm tempted by the smooth, fast motion it promises, plus I won't need to invest in a breakout-board (which removes the p-port requirement on the computer). However, I hear an awful lot of problems/complications with that unit.
    - Is the GRex worth the hassle?
    - Is the ncPod with a ModIO unit likely to be a better bet? (I do want to use a pendant of some sort and understand that the ncPod won't support one, hence the need for ModIO. ModIO also makes up for the IO shortcomings of the ncPod in a big way).

    3) Home/limit switches: Looks like these got pulled from my machine. I have to say, this is the area I know the least about, so any help here is appreciated.
    - Does one run home *and* limit switches for each axis (meaning 6 switches)?
    - How exactly (or even generally) are they positioned/set up?
    - Can anyone recommend a source/part number for such switches?
    - Are home/limit switches easily/well supported by the G-Rex?

    4) Computer: I'd like to put the computer in the current enclosure that's bolted to the mill. A cheap Dell or other standard size computer won't fit. Rather, I probably need something like a mini-ITX.
    - Any recommendations for a motherboard/barebones setup? Preferred vendor? I know there have been problems with certain chipsets, is there anything I should explicitly avoid?

    - The other approach would be to use a touchscreen panel PC. I'd like to keep the computer/screen budget under $1000. Do panel PCs exist that meet the spec (~1Ghz processor /512 MB RAM) for that price? I haven't found anything on eBay.

    5) Monitor: If I can't locate a panel PC, I'd still like to use a touchscreen monitor. I've found a good deal on a 15" one ($300), should I splurge the extra $185 for a 17"?

    6) Tooling: The machine didn't even come with a single collet. I need a vice, collets, end-mills, etc, etc
    - Any recommendations for good/cheap tooling besides Grizzly & Enco?
    - I've been looking at the Tormach Tooling System (TTS). Looks like a good way to ensure consistent Z-offsets. Anyone got one that cares to comment on their value?

    Thanks in advance for your input. I've been wanting to do this for years, and am excited about finally starting.

  2. #2
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    >>Some questions for the list (any & all input greatly appreciated - I've never done this before):
    1) Z-axis: I'd like to CNC-enable either the quill or the knee. Currently, I'm leaning toward the knee due to greater travel and less cost/complexity.<<<



    The knee is never intended for real active use, it is not fast enough, and are you going to put a ballscrew on it? Find some brackets for the quill



    >>3) Home/limit switches: Looks like these got pulled from my machine. I have to say, this is the area I know the least about, so any help here is appreciated.
    - Does one run home *and* limit switches for each axis (meaning 6 switches)?
    - How exactly (or even generally) are they positioned/set up?
    - Can anyone recommend a source/part number for such switches?
    - Are home/limit switches easily/well supported by the G-Rex? <<<



    You only need 2 switches each for the x and y, 3 for the z[assuming quill, would be 2 if the knee]

    You mount the switch such that an actuator hits it for overtravel [emo string] in either direction. the other switch is a trip dog only for homing. Hopefully you controller will have software limits for day to day use


    >>5) Monitor: If I can't locate a panel PC, I'd still like to use a touchscreen monitor. I've found a good deal on a 15" one ($300), should I splurge the extra $185 for a 17"? <<

    You watching videos on it?

  3. #3
    Community Moderator Al_The_Man's Avatar
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    Dec 2003
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    Here is a Knee mill I retrofitted in this link http://cnczone.com/forums/showthread...hlight=EXCELLO
    I also think you are asking for trouble in CNC'ing the knee, by the time you take into account the weight of the knee and XY tables, coupled with work-piece weight, the inertia involved in doing things like peck drilling are enormous.
    I have the quills as Z axis but I do have a motorized knee just for positioning.
    The only real advantage to touch screen is it cuts down on PB's etc on the Operator panel.
    If you go that route, look on ebay for the kiosk style panel mount.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

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