Yet another DIY CNC From Car Parts

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  1. #1
    Member BeNimble's Avatar
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    Default Yet another DIY CNC From Car Parts

    Yep, another newbie here going to build a CNC machine.

    What I'm wondering about is using two ways of moving something in one axis. So have the router Z move 4 inches, but then be able move the table 12 inches,
    so local movement is along a 4 inch travel, but if I need more, move the table (slow), but then I can build taller stuff, but fast and firm for mostly flat work.

    Can the software handle that type of setup? I can see issues in transition between the two methods.

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    Community Moderator ger21's Avatar
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    Default Re: Yet another DIY CNC From Car Parts

    Can the software handle that type of setup?
    Depends on the software.

    I've seen one machine do something similar, and it used a mechanical linkage to lock the movement between the two, so that moving the spindle would move the table.

    Gerry

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    Member BeNimble's Avatar
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    Default Re: Yet another DIY CNC From Car Parts

    I'd be using whatever is the open source cam software, isn't that mach3 or mach5, have not looked into that yet.
    I would not want them mechanically connected, the table would only move when the spindle is maxed, or really center the spindle movement after moving the table,
    which requires some optimizing planning in the software. If it can't do it, maybe I could add it if open source, or just forget that idea and move on..

    To my next question/idea:
    Can one eliminate/reduce backlash by having two steppers, both always "push", but one pushes left, the other pushes right so always tight against the screw mechanism.



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    Community Moderator ger21's Avatar
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    Default Re: Yet another DIY CNC From Car Parts

    Mach3 is not open source.
    LinuxCNC is the only open source control, and I'm not familiar with it enough to answer your question. But, I doubt it.

    But you definitely can't use two steppers to remove backlash like that.

    Gerry

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    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Yet another DIY CNC From Car Parts

    Having a secondary Z axis has been done on many machines.

    Sometimes called a W axis I think

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    Default Re: Yet another DIY CNC From Car Parts

    Hi BeN - I think you may as well just have a moving table for Z. The redundant "z" is going to be difficult to control with low cost software and you will increase your machine compliance with two bearing systems. Better off having a fixed spindle which will be very stiff and have the table move up and down to your hearts content.. KISS... Peter



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    Default Re: Yet another DIY CNC From Car Parts

    Quote Originally Posted by pippin88 View Post
    Having a secondary Z axis has been done on many machines.

    Sometimes called a W axis I think
    Like powering both knee+quill ? That's what I'm picturing but the original question is a bit murky. And where (what) are the car parts ?

    As for 2 steppers, a more conventional anti-backlash approach is 2 nuts.

    Anyone who says "It only goes together one way" has no imagination.


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    Default Re: Yet another DIY CNC From Car Parts

    Quote Originally Posted by cyclestart View Post
    Like powering both knee+quill ? That's what I'm picturing but the original question is a bit murky. And where (what) are the car parts ?

    As for 2 steppers, a more conventional anti-backlash approach is 2 nuts.






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    Default Re: Yet another DIY CNC From Car Parts

    Hi BeN - How do you imagine using windscreen wipers and unitised bearings in the machine? Peter



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    Default Re: Yet another DIY CNC From Car Parts

    Those are electric window motors. Any ideas on how they can be used? I have a lot of them, free and powerful.

    Here is my next idea, the material sits on the table at the bottom, I'm thinking put the spindle under the table so the chips fall down using gravity.



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    Default Re: Yet another DIY CNC From Car Parts

    Hi BeN - If you use that sort of motor for an axis you will need to use a position feedback device to be able to control it. That will cost more then using a stepper or a servo. You'll need to include a drawing or photo of what your thinking. Machines that require lots of chip clearing usually go the horizontal spindle approach. Conventional machines are configured for good reasons, we have been making machines for over 200 years and several standard configs have evolved over that time. I suggest you look at machines in general and pick one that does what you want it to do then start from there. Peter



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    Default Re: Yet another DIY CNC From Car Parts

    Which design from 200 years ago has a robot arm doing the machining?





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    Default Re: Yet another DIY CNC From Car Parts

    Hi BeN - If you want to bring industrial robots into the equation then they are simply a copy of the human arm which has been around for quite a while. Milling machines replaced "machinists" which were people with files. So the anthropomorphic configuration predates machines. If you want to build a 6 axis IRb then look at Freecad it has a 6 axis robot cam module. Peter



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    Default Re: Yet another DIY CNC From Car Parts

    ok



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