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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
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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
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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.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  4. #49
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    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 Replacement & Upgrade Controllers
    Custom 9012 Centroid ATC

  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
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    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
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  7. #52
    How did your inlay go David? Have you run it yet?

  8. #53
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    Yes, Mark, and delivered it today - thanks for asking!

    The inlay pieces fit precisely with no sanding, filing, Dremel, or hand work of any kind. There is no perceivable glue line and that's perfect, I think.

    Finished in Nitrocellulose lacquer and about 12" x 18" -
    039 - SFC Stripe plaque.jpg

    040 - SFC Stripe plaque.jpg

    And for size comparison here it is in front of the guitar I just built (yes, that's another shameless plug for my guitar - LOL! )-
    041 - SFC Stripe plaque.jpg

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  9. #54
    Congratulations. So rewarding to work through a problem and come out the other side with a great solution. Good for you man.

  10. #55
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    David you do excellent work, thank you for posting.
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  11. #56
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    Quote Originally Posted by Mark Bolton View Post
    Congratulations. So rewarding to work through a problem and come out the other side with a great solution. Good for you man.
    Thanks, Mark!

    Quote Originally Posted by Bill George View Post
    David you do excellent work, thank you for posting.
    Thanks, Bill!

    Here's an update - Yesterday I loosened and/or removed the 24 fasteners required to square the gantry at least 5 times before I got it dead perfect. You can see in the spoilboard how many rectangles I cut so I could measure the diagonals. I cut multiple rectangles of 23x46, 22x44, and 20x40 and kept sneaking up on 'perfect' until I finally got it to where no matter what size rectangle or square I cut the diagonals are identical. At least, they're as identical as I can see with 3.0 reading glasses and getting right down on the tape to compare each measurement.

    At one point the diagonals different by 3/16" on the 23x46 rectangle. And I don't have to be concerned with temp and humidity because the shop is climate controlled 24/7 but that aside, neither temp or humidity will have enough effect on MDF in the span of a few minutes to cause a change. I'm comfortable enough with my measurements and methodology at this point to say this is as close in calibration as I can get this CNC machine.

    You can see here how many times I cut for these tests (patience is one of my strong points - LOL!) -
    002 - Calibration rectangles.jpg

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

  12. #57
    Or you could use a square with an indicator and not have to waste a piece of material or be reliant upon how close your eye is.

    IMG_1442.jpg
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  13. #58
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    Brian...
    Kudos on the shameless marketing plug!

    Is that square anodized aluminum? (I buy everything I can that is anodized)
    Gary Campbell
    CNC Replacement & Upgrade Controllers
    Custom 9012 Centroid ATC

  14. #59
    Yes, hard anodized, and they are square to under .002" over the 24" length, most check under .001", but we say .002". I don't want to plug it, I'll get my hands slapped here, but regardless of what square you use, it would save a load of effort to square up the gantry of the machine with one. Lay it on the table and square one axis using an indicator and then check the opposite axis and you will know exactly what your machine is doing.
    Brian Lamb
    Lamb Tool Works, Custom tools for woodworkers
    Equipment: Felder KF700 and AD741, Milltronics CNC Mill, Universal Laser X-600

  15. #60
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    Quote Originally Posted by Brian Lamb View Post
    Or you could use a square with an indicator and not have to waste a piece of material or be reliant upon how close your eye is.

    IMG_1442.jpg
    Yes, Brian, but I would still have to use my eye to see how close I'm coming to the end of the triangle, even with an indicator. And I'm fairly certain a 23" x 46" hard anodized triangle as nice as those is fairly pricey. I already have the 60° V-bit, the spoilboard, and the patience to do this multiple times to get it right.

    Now, if you want to donate one of those awesome triangles to 'the cause', I'll give it a good test against my now very accurate machine and write a review...

    David
    David
    CurlyWoodShop on Etsy, David Falkner on YouTube, difalkner on Instagram

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