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Thread: Calibration question

  1. #46
    I have been shopping for a another CNC for a couple of months now. Trying to compare everything that they advertise as far as components and accuracy. I have spoke to a few companies also. Seems like there is no standard to how different companies measure things. Some have told me that some companies only post the accuracy numbers or repeatability numbers of the best axis. They told me that if the Z axis has +/- .001 but the other axis is not near as accurate then they will advertise it as .001.

  2. #47
    Join Date
    Mar 2003
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    SE PA - Central Bucks County
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    Bobby, the kind of work you expect to do has to be taken into consideration when you are selecting your machine. For many woodworking type activities, the absolute accuracy can be more flexible than for say, machining aluminum parts that have to fit together with super precision. Same goes for "very intricate" inlay type work with materials that are less forgiving than wood is. The nature of these machines is that there will always be a variance in the "accuracy" of gantry and spindle movement and the higher end you go, the "more accurate" things should be, theoretically. My Stinger II does a pretty darn good job with how it's built and designed, but I absolutely would have chosen at least the next step up for "more precision" if I anticipated I needed that.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #48
    Join Date
    Mar 2014
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    Iowa USA
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    Quote Originally Posted by Gary Campbell View Post
    You should be easily able to adjust that out with independent auto squaring if your control has it, most decent ones do
    I see my Mach3 machine does. I would say if you really need milling machine accurately you need to purchase a milling machine. But your working with a medium that both expands and contracts with temperature and humidity.
    Last edited by Bill George; 08-19-2018 at 1:30 PM.
    Retired Guy- Central Iowa. , Ray Fine 20w Galvo Fiber laser , LightObject 40w CO2 Laser and Chiller, MakerGear M2 3D Printer. Qe60+ Vinyl cutter. Automation Tech Chinese 6040 Router running on Mach3 and UC400ETH, Fine Line Automation 4x4 CNC Router

  4. #49
    Join Date
    Oct 2009
    Location
    Marquette, MI USA
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    355
    Bobby...
    When you say:"
    Some have told me that some companies only post the accuracy numbers or repeatability numbers of the best axis."


    What you need to remember is that even if they did publish numbers, they NEVER give numbers under load. That number is what separates the men from the boys, or "machines from the toys". Some use the linear equivalent of their preset step resolution, often for the highest resolution axis. Most every machine out there is capable of sub .001 step resolution. Because they can be set to that. It is the quality of the drives, motors and mechanical components that will determine if the bit will actually get to that position on a repeatable basis. The quality (read as cost) of those components is what determines the price category of the machine.

    What this means in layman's terms: If you put a 1/4" bit in the machine and cut a 4" circle or square will it actually measure that when I am done? Answer is: usually pretty close, give or take .005" to .010" and the more experience the operator has, the closer he will get. The higher priced machines with higher priced components will simply do the job easier and in most cases faster. Lets say that a $10K machine can hold .005 tolerance, which should be more than adequate tolerance for wood, at much higher feedrates and depth of cut than a $2.5K machine can. Its that simple.
    Gary Campbell
    CNC Technology & Training
    The Ultimate Woodworking Machine
    GCnC411(at)gmail.com

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  5. #50
    Quote Originally Posted by Bill George View Post
    David, it would be interesting for Gary and others on here to share the results of the tests your doing and done on their machines
    I ran the shape test on ours just for my own fun and games. I'll run the diagonal next time I toss on a new spoil board which will be soon.

  6. #51
    Join Date
    Jan 2012
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    NW Louisiana
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    482
    Quote Originally Posted by Bill George View Post
    Isn't that within the published specs for the machine?
    I don't know, Bill. Is there a spec for a 52" diagonal or are you looking at the specs per linear foot?

    Quote Originally Posted by Jerome Stanek View Post
    Repeatability is just that it will be out the same every time.
    My quick test for repeatability, Jerome, is that when I cut a complex shape a second time, or even a simple shape, because I didn't set the Z height deep enough to cut all the way through a piece is that the bit doesn't touch the side walls, only the bottom of the cut. So my ears provide the feedback on repeatability. This machine is very good in that respect.

    Quote Originally Posted by Bill George View Post
    I see my Mach3 machine does. I would say if you really need milling machine accurately you need to purchase a milling machine. But you're working with a medium that both expands and contracts with temperature and humidity.
    Yes, it expands and contracts but right when I cut cavities and inlay pieces I want them to fit with the smallest of gaps. How they expand and contract after that is ok with me because they'll likely be in concert on that anyway. But some of the inlay I do is with Abalone or MOP into wood and there is a huge difference in how those react to changes in humidity. Just so they fit when I cut the pieces is where my concern resides.

    David
    David

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