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  1. #16
    Join Date
    Sep 2009
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    Sydney
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    148

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    Whatís a good jack shaft axle diameter? I was thinking 16-18mm. My plan was to tension the belts with the weight of the motor. Plus I want the pulleys to use the shaft and rotate on it.

    I want minimal deflection but donít want to over engineer it either.

  2. #17
    elanjacobs is offline Apprentice gear maker and machine doctor
    Join Date
    Aug 2008
    Location
    Melbourne
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    29
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    278

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    Just checked and I can index 127 teeth no problem, you'll have to confirm the tooth pitch and angle but we do have an 18DP 14 1/2 degree hob

  3. #18
    BobL is offline Member: Blue and white apron brigade
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    Feb 2006
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    Perth
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    5,356

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    Quote Originally Posted by Michael G View Post
    Another one of those thoughts that occur when you are trying to get to sleep...

    Cutting speed for MS is around 30m/min. Cutting speed for Al is around 90m/min. A wood cutting saw (circular or band) can be used for cutting Al which suggests that a cutting speed for wood is also around that speed. The exact number is in the TBD column but does not matter. The point is that that is only around a 3:1 ratio. Even if that were pushed to 4:1 or 5:1, that is still a long way from 48:1.
    Wood cutting bandsaws typically have two speeds 500 and 1000 m/min. Optimum speeds for cutting wood are 1500 m/min but this is pretty scary and also heats the band up so that in some cases like long cuts band cooling is required (on the Bandsaw mill I sometimes use we use water).

    The 4 pole 3HP WW bandsaw in my shed with non-vector drive VFD can run up to 1500 m/min (75 Hz) and theoretically down to zero. I don't worry about slow speeds because the motor has an independent 2x motor speed fan on it. I don't use the 1500 m/min often but for ripping short (~500mm long) logs it saves time and does not overheat too much in this length of cut.

    At 50Hz my BS runs 1000 m/min, so at 17Hz it's still able to generate ~1HP and 340 m/min which is still way too fast for steel but works fine for Al - I have not been able to stall the band at this speed in small pieces but it will gall if pushed. In fact I can cut the Al on 1000 m/min and often do that, but for thick pieces some form of lube (wax) is required to prevent galling. Interestingly on my WW circular (1200 m/min) with the composite (negative raked) blade I rarely use lube.

    If 30 m/min is the max needed for steel and 1000 m/m is needed for timber this suggests a 33:1 range overall might suffice

    If a vector drive VFD is used then at 17Hz I would expect at least half the motor power to be available but if the motor power is doubled then original power could be had at the same speed. Then if the top speed is engineered to occur at say 100 Hz that would provide a ratio of ~6:1 in working speed.

    Then, based on the 33:1 range required, the 6:1 obtained via the VFD suggest about a 5:1 pulley is all that is needed on the BS itself.
    This is of course cutting it fine, and it would be nice to operate say from say 10 m/min to say 1200 m/min (120:1)

    If 6:1 can be obtained by the VFD this leaves 20:1 to be obtained mechanically, so perhaps a 4:1 and a 5:1 pairs of pulleys would do that?.

    Using a non vector drive VFD with a double HP motor will give original power from 25Hz up, to say 100 Hz or a 4:1
    To get 120:1 then requires 30:1 mechanically which starts to get tricky but not impossible.

    Alternatively if one is happy enough to work overall with a 33:1, then with 4:1 from a non-vector drive VFD, means only ~8:1 is needed mechanically.

    Lots of options.

  4. #19
    BobL is offline Member: Blue and white apron brigade
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    Perth
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    FWIW I just remembered the Steelfast upright metal cutting BS in the mens shed starts out like the Woodfast, but it has a 5 pulley pairs that generate up to a 20:1? reduction.

    Its usually left on the middle (10:1?) pulley pair (sorry don't know what this means in m/min) and it's used to cut curves in thin steel metal and Al sections.

    For HD cuts a power hacksaw is used.

  5. #20
    Join Date
    Nov 2010
    Location
    Gippsland Victoria
    Posts
    729

    Wink

    63 teeth the current minimum.

    Depending upon what other spur gears you have and what ratios are in your gearbox you might be able to lower that a bit further

    Have seen people discussing 21 , 31, 32, 33, 34, as being helpful for cutting metric on old myford lathes - again this would depend upon your current spur gears and gearbox ratios.

    A forum member called VernonV wrote a terrific calculator called Lathegears for calculating all possible gear trains given your leadscrew TPI, gearbox ratios and required output thread, well worth a look and a download.

    Bill

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