VFD Speed modulator to counteract chatter in a lathe
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  1. #1
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    Talking VFD Speed modulator to counteract chatter in a lathe

    I have an import lathe that is not that rigid. Therefore I often have issues with chatter.
    I have come across several time on a solution that might medicate some of this chatter problem.
    Since chatter is actually a resonance condition and it takes some time to develop. I mean, the chatter does not start right away, it may take a second or two to develop into the disturbing form.

    If the spindle speed is varied constantly, this does not allow enough time for the chatter to develop. I have done this manually, since I have a VFD, and it looks like it could do something for the problem.

    For this reason I have designed a device that involves a microcontroller (Atmel Atmega32) and some PWM filtering. I am at the moment on making a housing for that thing and then go into practical testing with the lathe.


    forumshot.jpg


    I have made a video series of this thing in YouTube at Finno Ugric Machining

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    Higher end VFDs will do this for you automatically by the way.

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    Higher end, yes, but the ones I can afford lack this kind of service. Either I have to keep on doing that manually or then make a thing that can do the knob twisting for me.

    And then there is one more thing in play here. My profession is not a machinist. I am a darn IT-Consultant who does not do machining for living - it is a hobby for me. Therefore I am willing to make the feature myself.

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    Quote Originally Posted by FinnoUgric View Post
    Higher end, yes, but the ones I can afford lack this kind of service. Either I have to keep on doing that manually or then make a thing that can do the knob twisting for me.

    And then there is one more thing in play here. My profession is not a machinist. I am a darn IT-Consultant who does not do machining for living - it is a hobby for me. Therefore I am willing to make the feature myself.
    Servo controllers do this too. It's called a "Load Observer" functionality, but typically needs an encoder feedback (inherent in most servo drives).

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    Because I an old guy I would have taken an analog approach. A function generator chip a handful of components and done. No programming. A couple of pots to adjust amplitude and frequency and maybe a switch to set waveform type.

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    Not exactly what you're doing, but I set up near-constant-surface-speed by using a long-travel slider potentiometer coupled to the lathe cross-slide to control the VFD frequency, wiper goes tot he analogue input (0-10v), the ends of the slider pot go to the wipers of max/min setting pots (with resistors to bias them to 0 to half, half to full) - it helps a lot getting a decent surface finish on facing cuts and adjusts to part diameter on successive cuts. Doesn't give infinite speed at the centre though!

    Could you couple an AC waveform of a volt or so peak-peak into the analogue input through a capacitor? Similar to Bill's suggestion?

    Dave H. (the other one)


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