Math help please


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  1. #1
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    Default Math help please

    Finishing up my CNC conversion. X and Y all set but need help with Z. Here is what I have.

    1. Stepper motor 5000 steps per revolution.
    2. .200 pitch ball screw so 25000 steps = 1”
    3 20 tooth timing gear @ 1.500 wide on motor
    4 20 tooth timing gear @ 1.200 wide on screw

    I followed Mach 4 formula I thought and did

    1.5 / 1.22 * 5000 / .200 = steps however I’m doing something wrong because it’s off a little and gains the more I go. Can you help me out and show me how you came up with it? The formula I see is for gears with different tooth config. My timing gears have the same amount of teeth but have different circumference. I’m measuring the pully across with a set of calipers.

    thanks

    Rick

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    Member ger21's Avatar
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    Default Re: Math help please

    20 teeth to 20 teeth is 1:1, so you should have 25,000 steps per inch.

    Gerry

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    Default Re: Math help please

    I am a complete moron, thank you!



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    Community Moderator wendtmk's Avatar
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    Default Re: Math help please

    How can you have the same amount of teeth but a different circumference on the timing gears? Are you sure both gears are matched with the belt you are using? That's not making sense. The teeth should be the same width with the identical separation between the teeth. For that to be so, the circumference can not be different.



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    Default Re: Math help please

    Here are a few more things to check that can cause errors in the overall steps per inch.

    1) Stepper motors are often 200 steps per revolution combined with microstepping that takes a variable number of steps per full step. I have seen microstepping values of 2X (half stepping), 4X, 10X and possibly 16X. It depends on the controller and how it is set up.

    2) Metric ballscrews could have a pitch of 2 threads per cm or 5.08 threads per inch. You would have to adjust the steps per inch slightly.

    3) Something seems off if you have a 1.5" gear and a 1.2" gear with 20 teeth each. They would either slip, or maybe one of them has a different tooth count.

    Steve



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Math help please

Math help please