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  1. #1

    Adding a rotating 4th axis

    I could search forums for a day or so but I’m hoping some experienced people can direct me please.
    I have a reasonably large 3 axis CNC Router table and would like to cut 3D shapes in timber (MDF) or dense foam.
    If I could angle the router to variable but fixed angles and have a 4th axis that rotates the spindle motor then I could hopefully cut a workpiece from all sides. Is this common practice ?
    I’m effectively locking the 4th axis and only using a rotating 5th axis. I want to avoid the expense of a 4th & 5th axis head and buy or DIY make only the 5th rotating axis.
    Can my Mach 3 be programmed to cut a shape like for instance a toy car body like this ?
    My water cooled spindle motor is (from memory) 80mm diameter.
    Will I find a head that can do this or parts to make such a DIY head please ?

  2. #2
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    Re: Adding a rotating 4th axis

    Mach can control the 4th axis and I’m pretty sure the 5th. Not sure if it can move everything simultaneously. The bigger challenge is to find a CAM package that can handle the 5th. And without hitting anything, at a reasonable cost.


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  3. #3
    Quote Originally Posted by Dean448 View Post
    Mach can control the 4th axis and I’m pretty sure the 5th. Not sure if it can move everything simultaneously. The bigger challenge is to find a CAM package that can handle the 5th. And without hitting anything, at a reasonable cost.
    Thanks Dean,
    What I would like is the 4th axis to be fixed at say 45 degrees and only be adjustable by Re-clamping so I don’t need to buy an expensive 4 & 5 axis driver. Am I correct in understanding that the 5th axis swivels in the horizontal plane ? If so it can rout, for instance a pear shape with a ball end tool.
    So to rout that pear shape would I use CAD designed for a 5 axis router somehow ?
    Is this solution to avoid spindle motor clash with a workpiece commonly used ? If not then whats another economical solution please.
    cheers, Andy.

  4. #4
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    Re: Adding a rotating 4th axis

    So most home cnc machines can have something called an A axis or 4th axis.
    An A axis to the CAM is the same as an X or Y axis but only as long as the circumference of the cylinder you are machining.
    You put the A axis parallel to the X axis and make the machine think the A axis is a short Y axis. The real Y axis is basically not used at that point.
    These are the terms defined on hobby machines. Sorry I’m not familiar with a fifth axis but anything that locks in place isn’t really an axis, in my opinion.


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  5. #5
    Gold Member
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    Apr 2004
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    Re: Adding a rotating 4th axis

    I think what you really want to do is reposition the workpiece, not the spindle. This is called "indexed" machining, and it is possible to do without a rotary table, although that makes it a lot easier to do. The simplest way to make a full-round object like a pear is to cut one side down to the half-way point in Z, then flip the whole thing over and machine the other side so it all lines up. Inevitably, though, you'll start seeing mismatches, coarser cuts, and a ridge where the two halves match up. To combat that, you can go with 90 degree rotations, which can give smoother results if you've programmed it correctly and everything works okay. There are ways to build a fixture that can facilitate this and locks in the required positions. But you still have to figure out how to support your pear or whatever while you're doing all this. After struggling with it for a while, perhaps the motorized 4th axis and the software that produces continuous 4-axis code won't seem so expensive after all.
    Andrew Werby
    Website

  6. #6

    Join Date
    Jun 2021
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    Re: Adding a rotating 4th axis

    Since you're working with a table, rotating the work might not be possible. Especially if it's large. If the work is radially symmetric (lathable), or radially millable (like a face), you can build a rotating disc table. A human head can be made using 3-axes: angle (rotating table), radius and height.

    Really the better option for true 5-axis 3D milling is a robotic arm. Cheap software is a problem.

    The best poor mans solution to 3D routing is to slice in software, and then route each layer. When done stack and laminate the layers and finish by manual smoothing.

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