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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Converting a Jet JMD-18 to CNC.
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  1. #1
    Join Date
    Oct 2012
    Posts
    0

    Smile Converting a Jet JMD-18 to CNC.

    I'm a newbie so I hope that everyone will be gentle.

    I want to convert my Jet JMD-18 to CNC for cutting mostly aluminum and nylon/UHMW parts. I do plan to make an occasional part from steel as well.

    I have the ability to do all of the design and machining of the necessary parts. I've been working on the design in 3D and thus far it is coming together well.

    The OEM screw are trapazoidal 23.5 mm for the X and Y? I was thinking of changing those to 2005 series ball screws. Any opinons about using a smaller ball screw? Since the ball screw is more efficient then I would think that would be ok.

    The Z-axis (quill only) I was planning to drive 3:1 since it does not have a lead screw. The Z-axis is 3.5 inch/rev.

    My questions:

    1) Why am I seeing that many are using 2:1 drive ratios for the X and Y axis? My calculations show that I can get well over 100 in/min with a direclt drive (stepper or servo driven) @ near 1000 rpm. Maybe I cant drive the motor that fast??

    2) I am trying not to spend a ton on the lead screws. I've pretty much convinced myself to use ball screws but I have no ideas whether I really need C5 or is the Chinese C7 stuff good enough for my application.

    I'm hoping to get several opinions of how to proceed.

  2. #2
    Join Date
    Jan 2005
    Posts
    1943
    For servos you generally use a reduction drive. This allows using a servo with a lower constant torque rating (smaller and cheaper) while still maintaining the same torque to the screw via the reduction drive. A servo has a pretty flat speed/torque curve, so this doesn't hurt high speed performance.

    With a stepper, the motor's torque is high at 0 RPM and drops off from there. At higher rpm, the torque drops off to the point where the motor can't keep up and steps are lost. So, hooking up a stepper is a trade off between resolution and top speed. For this reason, people generally step up a stepper as direct drive. With a typical 0.200 inch lead screw that means 0.001" per step which is satisfactory with microstepping activated.

    As for your Z-axis, I believe your machine has a fine downfeed mechanism. I have a smaller round column mill drill and used that to hook up the Z-axis. I then reversed the quill spring so that it pushes the quill down rather than trying to retract it. That setup works very well and is easy to implement. I used a 2:1 (big pulley on the stepper) to get 0.001" per full step on the stepper motor.

    You can see in the link below that the Z axis simply required a falt plate to mount the motor and a coule pulley and a belt.

    http://www.cnczone.com/forums/bencht...ill_drill.html

    Hope this helps.

  3. #3
    Join Date
    Jan 2005
    Posts
    1943
    Oh yeah. The pictures in my thread of the Z show the small pulley on the motor which gave 0.00025" per step which while OK, reduced the speed I could achieve for rapids in the Z axis. I eventually flipped them around to where the big pulley was on the motor. Just didn't want to confuse.

  4. #4
    Join Date
    Mar 2011
    Posts
    525
    Quote Originally Posted by Subaru_7224 View Post
    I'm a newbie so I hope that everyone will be gentle.

    I want to convert my Jet JMD-18 to CNC for cutting mostly aluminum and nylon/UHMW parts. I do plan to make an occasional part from steel as well.

    I have the ability to do all of the design and machining of the necessary parts. I've been working on the design in 3D and thus far it is coming together well.

    The OEM screw are trapazoidal 23.5 mm for the X and Y? I was thinking of changing those to 2005 series ball screws. Any opinons about using a smaller ball screw? Since the ball screw is more efficient then I would think that would be ok.

    The Z-axis (quill only) I was planning to drive 3:1 since it does not have a lead screw. The Z-axis is 3.5 inch/rev.

    My questions:

    1) Why am I seeing that many are using 2:1 drive ratios for the X and Y axis? My calculations show that I can get well over 100 in/min with a direclt drive (stepper or servo driven) @ near 1000 rpm. Maybe I cant drive the motor that fast??

    2) I am trying not to spend a ton on the lead screws. I've pretty much convinced myself to use ball screws but I have no ideas whether I really need C5 or is the Chinese C7 stuff good enough for my application.

    I'm hoping to get several opinions of how to proceed.

    I did a build thread on a JMD 18 if you search my name. If you are near Maryland I would like to sell it.
    Kelly
    www.finescale360.com

  5. #5
    Join Date
    Oct 2012
    Posts
    0

    Design photos....

    I'm working on the design.
    Attached Thumbnails Attached Thumbnails Jet JMD-18_iso view.jpg   Jet JMD-18_top view.jpg   Jet JMD-18_right view.jpg   Jet JMD-18_bottom view.jpg  


  6. #6
    Join Date
    Oct 2012
    Posts
    0

    Jet JMD-18 mill/drill conversion to CNC

    I've been working on my Jet mill quite a bit lately.. It's really coming together...
    Attached Thumbnails Attached Thumbnails carriage oiling.jpg   carriage oiling_01.jpg   claerance table for ball nut.jpg   increase y_axis travel.jpg  


  7. #7
    Join Date
    Oct 2012
    Posts
    0

    Y-axis assembly.

    I spent today putting together the Y-axis...
    Attached Thumbnails Attached Thumbnails Y_axis screw installed_01.jpg   Y_axis screw installed.jpg  

  8. #8
    Join Date
    Oct 2012
    Posts
    0
    Let me know what you guys think..... I'm hoping to order the controls next week.

  9. #9
    Join Date
    Mar 2011
    Posts
    525
    Looks great, what manual mill are you using in the pics?
    Kelly
    www.finescale360.com

  10. #10
    Join Date
    Oct 2010
    Posts
    0
    Here is some motivation for you.

    JMD-18 CNC Converted & PlasmaRoute Blaze HD 4x4
    Ran by very custom dust covered cpu's

  11. #11
    Join Date
    Oct 2012
    Posts
    0

    I'm getting close to cutting chips..

    The X and Y axis as mechanically complete. The controls package from CNC4PC will here soon..

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