What are the tolerances to expect? - Page 2 - Router Forums
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post #11 of 16 (permalink) Old 10-27-2019, 09:21 PM Thread Starter
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I will definitely check out the Shapeoko. But 99% of what I make is round, so no 4th axis is a problem. I could maybe add one anyway.

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post #12 of 16 (permalink) Old 10-28-2019, 02:22 PM
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post #13 of 16 (permalink) Old 10-28-2019, 04:23 PM
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Quote:
Originally Posted by Nate Banton View Post
I will definitely check out the Shapeoko. But 99% of what I make is round, so no 4th axis is a problem. I could maybe add one anyway.
Not unless you replace the entire GRBL control system, GRBL is remarkable that it can run on a little arduino, but there is just not enough compute power there to handle 4 axis at once. Those who have added rotary either switch Y axis to control rotary or completely have another controller and switch out. Better off starting with something powerful enough to handle a 4th axis, as it is not stiff enough to hold the kinds of tolerances you desire anyway.

Same applies to software. The commonly used VCarve Pro or Aspire has somewhat limited rotary capabilities, what they call "wrapped rotary". The limitation is that the Z-axis cannot move off the centerline of the rotary axis, if you need an off axis hole, it cannot be done with this concept. You cannot have the Z-axis travel below the centerline of the rotary axis either (a capability required for a cabriole or ball and claw leg, for instance). There is other software out there like DeskProto and Rhino that I believe have more capable rotary toolpathing strategies. I believe that Fusion 360 may also allow this type of toolpaths, but do not have a rotary, and have not tried.
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post #14 of 16 (permalink) Old 11-01-2019, 09:44 AM Thread Starter
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Thanks, Richard, that's very helpful to know. And I haven't even begun to explore software options. Looks like I better start!
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post #15 of 16 (permalink) Old 11-05-2019, 12:15 AM
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Nate,

Some pics of one of my projects, wing ribs for an RC sailplane... These are relatively small parts, less than 6"x1/2" for the largest. The smallest steps you see in the part, are around .020". The primary notch in the middle, where they are lined up on the ruler in one pic, has a tolerance of +/- .003 as cut, compared to the CAD drawing they came from. This is in balsa, using a .031" endmill.

Machine is a Probotix Comet, and I use Fusion360 for CAD/CAM. I know Probotix has an option for 4th axis, not sure on the tolerance differences when using that vs the standard 3 axis.

Brian
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post #16 of 16 (permalink) Old 11-11-2019, 07:43 AM Thread Starter
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Brian,

I'm very impressed and encouraged by your work. Thanks, and I'll check out your machine as well.

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