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  1. #16
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by russ57 View Post
    There's an app for that...
    I saw a guy on YouTube checking a turntable speed. Start the app, drop your phone on the turntable and read the speed. (the display rotates contra to the turntable to keep the view fixed..) may be easy enough to attach your phone to the rotating thing you want to measure.
    Of course that begs the question how accurate is the phone but it's likely to be highly accurate.
    There are indeed heaps of Apps some that a better than others..
    For slower speeds there are apps that use the phones inbuilt accelerometer, some of which claim to measure up to 50Hz (3000rpm) so measuring 33rpm is a doddle.
    In practice reliable measurement these accelerometers are only good up to about 25Hz (1500 rpm)
    I use a App called Vibration to measure - vibration - what else. It's accelerometer readout stops at 25Hz.

    It also depends on how clean the vibrations are, as usually you have to pick the main vibration peak out amongst a whole lot of other noise peaks.
    If its a smooth rotation like a turn table then the it's quite easy easy, but if not, the numbers can be all over the place.

    To measure above 25Hz you need an app that uses the inbuilt microphone but between 25 and 50z the responses of most phone mics is ordinary so don't expect that reliable a result.

    The phones don't need to be strapped to rotating shafts etc to detect the vibe.
    Usually enough vibe can be picked up by placing the phone on a surface in direct contact with the vibe source eg motor.
    Adding a small off axis weight to accentuate the vibe can help.

    Here I'm using the Vibration App on an iPad to measure the vibrations of a dust extractor impeller under that 6mm steel plate.
    Ipad.jpg

  2. #17
    Join Date
    May 2018
    Location
    Cairns, Qld.
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    70

    Thumbs up Rpm indication

    Well, I received the previously ordered fleabay hand-held laser strobe rpm indicator a day or two ago (About $25 delivered), so proceeded to check it vs the hall-effect rpm indicator system that initially prompted this query. Short answer; both indications agree within 1 or 2 rpm up to about 2900 rpm which is the highest reading I can find on my workshop machines (Bench Grinder). Lowest was less than 100 rpm on a lathe chuck. So all is fine.

    As suspected, the posted rpm table on my HF-46 mill (for 50hz operation) shows about 6% low at each of six speed selections. Not a really significant issue, but now we know. Correction chart to be filed away somewhere.
    Another gadget for the tool collection.

    Thanks for all the responses.

    Halifax 614

  3. #18
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    6,439

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    Quote Originally Posted by Halifax614 View Post
    Well, I received the previously ordered fleabay hand-held laser strobe rpm indicator a day or two ago (About $25 delivered), so proceeded to check it vs the hall-effect rpm indicator system that initially prompted this query. Short answer; both indications agree within 1 or 2 rpm up to about 2900 rpm which is the highest reading I can find on my workshop machines (Bench Grinder). Lowest was less than 100 rpm on a lathe chuck. So all is fine.

    As suspected, the posted rpm table on my HF-46 mill (for 50hz operation) shows about 6% low at each of six speed selections. Not a really significant issue, but now we know. Correction chart to be filed away somewhere.
    Another gadget for the tool collection.

    Thanks for all the responses.

    Halifax 614
    Hi H614, that 6% low could quite easily be the difference between 50 and 60 Hz mains frequencies !
    Best Regards:
    Baron J.

  4. #19
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by BaronJ View Post
    Hi H614, that 6% low could quite easily be the difference between 50 and 60 Hz mains frequencies !
    I doubt it as that is a 20% difference.

    Most likely the Posted HF46 speeds are for a nominal load where the speeds drop a bit.

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