1/4 hp really enough on 9" ?
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  1. #1
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    Default 1/4 hp really enough on 9" ?

    I have a brand new Leland 1/4 hp from probably mid 30's I'd completely forgotten about until last night . Funny how, as I age, yesterdays memories are foggier than 30 years ago. Got it someplace for $5 new in the box with big plans to make a grinder. It sure looks the part for my 1935ish lathe. Even has a chrome flip top oiler. I see 9' lathes shipped with 1/4hp. Is it enough hp for actual use? Mine has a countershaft assembly. Seems pretty low hp by "todays" standards.

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    What speed is the motor? Older motors tend to be larger frames, with more spinning mass, so they are a little smoother. You are also limited by the narrow belt, so you can't put tons of power into the machine without slippage. That said, I'd probably consider 1/2 horse the minimum.

    allan

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    1/4 HP is absolutely adequate for running a 9" South Bend. My 1936 Workshop 9 ran with a 1/4 HP motor for the 50 years it lived at my dad's house. After I inherited the lathe I changed it over to a 1/3 HP motor with VFD just for the convenience of the variable speed. I would have used a 1/4 HP 3 phase motor if I'd had one.

    I made a lot of stuff on that late with the 1/4 HP motor and never thought it was under-powered and never over heated the motor. The motor still powers my horizontal metal-cutting band saw so it was obviously not harmed by its late running duties. My dad was an electric motor sales engineer so I'm sure the lathe would have had a bigger motor if he had thought it was necessary.

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    Probably could go 3/4 hp with a flat belt, bottom line is if you can stall the motor (or overload it) before the belt slips the machine is capable of transferring more hp.

    My 9 is v-belts which are far better than old leather belts at transferring torque, and i can stall an inverter-duty 1hp motor before the belt will slip.

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    it takes roughly 1 hp to make 0.8 cubic inches of chip of 1018 steel per minute. to get 1hp at spindle its common to need a 1.5hp motor cause of belt and gearing power loses.
    1/4hp would be be for light small diameter turning. literally if you got the patience to take 10 to 1000 times longer sure you can use a low hp setup

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    I think you'll find that those small South Bend lathes, particularly the 9" Workshop, were designed for use with relatively small drive motors because they were intended for modest workloads and speeds. Remember that all those cutting forces are reacted in the spindle bearings, particularly the front one. Spooling off huge strings of metal means large cutting forces and neither the spindle bearings nor the bed and carriage are stout enough for that sort of operating. If the goal is removing 1/4" inch diameter or more per pass, then a more robust lathe would be the choice.

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    Yes. No. Depends.

    My original BP M head is circa 1940 with 1/2 HP 3-phase motor maybe 60 years old.
    Runs great.

    My 12" lathe had a very good industrial 1.5 kW AC motor on it.
    But..
    A 2.5 kW AC brushless servo is == 10 kW of modern turning center torque and power (HAAS ST10).
    The new servos is vastly, vastly, superior to the old motor.

    All lathes can run 3-10x the power/torque of typical oem motors.
    Just the way it is.
    Machine tools are max loaded to 2% of their "strength".
    Fact.

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    A nice feature of the South Bend hobby is that it's your lathe and you can run it the way you want. Rolling smoke if that's what you like or nice and easy if that's what you prefer.


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