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Thread: pulley question?

  1. #1
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    pulley question?

    in another thread i saw where jim delany had told the person the speed at which his bandsaw would run properly due to pulley size configuration.. wel this is for jim or anyone that understand the ratios i have 2.5" pulley on a 1725 rpm motor running a 6.5" pulley on a 12" Bsaw.. am i in the right speed range or should i change a pulley for better use? it seems to be cuttin ok

    thanks for the help from where ever it comes.
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  2. #2
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    "Forget the flat stuff slap something on the spinny thing and lets go, we're burning daylight" Bart Leetch
    "If it ain't round you may be a knuckle dragger""Turners drag their nuckles too, they just do it at a higher RPM"Bart

  3. #3
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    hey bart think i need to do something else???? i know that its gong fast than 1725.. i have a 1725 pushing a 2.5 pulley that is connected to a 6.5 pulley that is driving a 12" wheel some how the wheel size needs to enter in a some point if i was using just a 2 to 2 on a shaft it would be running at 4 times the moter speed right as i see it then its running at arond 630rpm??? thats not even close to what i though was normal speed.. so what do i need to get to get i running upto speed?
    Last edited by larry merlau; 04-05-2009 at 03:13 PM.
    If in Doubt, Build it Stout!
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  4. #4
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    Here's the formula:

    Drive pulley diameter / driven pulley diameter * input RPM = OUTPUT RPM

    So for yours it should be:

    2.5 / 6.5 * 1725 = 664

    12 / 6.5 * 664 = 1225

    Edit...sorry had 6 in vs. 6.5...also the shaft for the 12" is moving the same speed as the 6.5", so it should be swapped in the formula above.
    Last edited by Darren Wright; 04-05-2009 at 03:35 PM.
    Darren

    To a small child, the perfect granddad is unafraid of big dogs and fierce storms but absolutely terrified of the word “boo.” – Robert Brault

  5. #5
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    Larry, I think this is how it works. I'm using * for multiplication and / for division.

    driven pulley speed = motor speed * (motor pulley circumference / driven pulley circumference)

    Note that circumference is linear with respect to either diameter or radius, so either of these measurements may be substituted for circumference as long as you're using the same measure for both pulleys.

    To go from rpm to fpm on a bandsaw we remember that the bandsaw wheel rpm is equal to the driven pulley rpm since it is a one piece construction.

    bandsaw fpm = driven pulley speed (rpm) * bandsaw wheel circumference

    In this calculation circumference must be used, as the circumference is the translation between rotational speed to linear speed by definition.

    A quick reminder:

    circumference = pi * 2 * radius = pi * diameter

    So, for your saw:

    driven pulley speed = 1725 rpm * 2.5 / 6.5 = 663 rpm

    circumference = 3.14 * 1 = 3.14 (12" is 1 foot even in MI, right? )

    bandsaw fpm = 663 * 3.14 = 2084 which seems slow (I used many more decimal places for pi and the driven motor speed, so if you come up with 2082 or 2083 fpm just accept this as rounding error) for hardwoods. If Larry mistyped and meant he had a 14" bandsaw his fpm would be 2430. If Larry has had too many beers already and meant he had a 17" saw the fpm would be 2951, about right for hardwoods.

    I hope this helps and that I didn't screw up my physics or math.
    Last edited by Mark Kosmowski; 04-05-2009 at 03:28 PM.

  6. #6
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    well darren the driven pulley is 6.5 and reguardless of the differnece there it isnt going very fast???? i am pretty sure that its set up the way it was intended yearas ago its a 40's model of a atlas and cuts ok but i thouhgt jim delany said the rpm or blade speed should be around 3ooo rpm???? if thats the case i am going way to slow.. what are most pulley configs on a 14 " saw?

    motor pulley size and wheel pully size?
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

  7. #7
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    Well Larry I'm running a 2" & a 5" on my old Craftsman 12" Band-saw with a1/2 hp 1725 motor & I see the chart only goes down to 2 1/2" But this saw seems to work just fine for every thing I do with it.
    "Forget the flat stuff slap something on the spinny thing and lets go, we're burning daylight" Bart Leetch
    "If it ain't round you may be a knuckle dragger""Turners drag their nuckles too, they just do it at a higher RPM"Bart

  8. #8
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    The blade speed should be around 3K fpm, not rpm.

  9. #9
    Larry,
    Here's a calculator over at OWWM:

    http://www.owwm.com/math/sfpm.aspx

    It will allow you to play with the pulley sizes etc.
    I had to do something similar with my old TomLee bandsaw when I restored it.

    Good luck!

    Wes

  10. #10
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    no beers today actuall been a week plus,, saving room for the good stuff coming up so it is a 12" mark.. and it is old. older than me even thanks for the help so mark do me a favor,, play with the link wes gave us and figure out what pulleys i need to get tyhe right spped on this thing,, 12" wheels i got to make saw dust so i can take a trip soon
    If in Doubt, Build it Stout!
    One hand washes the other!
    Don't put off today till tomorrow!

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