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Biggest motor you'd put on a 9A?

shaggy

Hot Rolled
Joined
Sep 29, 2010
Location
Oakland CA
I'm just getting around to putting a 3/4 hp 230V motor on my 9A. I've used it for years with just a 1/3 hp motor that started out as a temporary fix, but worked well enough, so was just left on.

When I got my (1962) 9A it had a 3/4 hp motor on it that was broken, so that is what I'm putting back on. My opinion is that a 1 hp would probably be pushing the design limits of the lathe and the drive system. (BTW, my 9A sports a Goodyear Gatorback serpentine flat belt, which I found rarely slipped, at least with the smaller motor).

I'm curious what kind of HP you guys have seen or tried on an SB9.
 
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I run out of belt traction with the 1/2 hp so don't see the benefit of going larger.. Mine's an undermount drive with vee belts.
 
fatigue limit for the cast iron bull gear is on the order of 40 foot pounds of torque, which is why those lathes shipped with a 1/3rd hp motor, which is all they can deliver, and its about how much torque is needed to drill a 1" hole in mild steel. so that in the event of a crash or stall, the bull gear should not break as the motor stalls.


my 9" with wick oilers and 6 cst oil (a bit thinner than the recommended 10cst oil), i was able to put a 56 pound bar in the spindle, which had a center of gravity 2 feet away from the chuck. this corresponds to about 150-170 pounds of downwards force at the chuck, and about 100 pounds upwards at the left side of the spindle. about 40-60 rpm was needed to maintain a low friction oil film.


so if you want to put a 1hp motor on it, and tighten the belt till it doesn't slip, that should be fine provided you verify a low friction oil film at the slowest speed you intend to use, and you loosen the belt for high rpm. (i'm presuming the bearing will overheat, you would need to measure the belt tension and how much it affects bearing temperature.
 
Thanks for replies. I'm pretty sure a 1 horse motor would be overdoing it. My 9A originally had a 3/4 hp on it that looked stock, and intuitively, that's the most power I'd want to subject it to.

BTW, I'm obsessive about keeping oil levels topped up on the headstock journals (Velocire #10), and treat the gears with great respect as well.

I might end up leaving it, as I really have no complaints. It's amazing what an efficient machine it is, and how much work you can do with just 1/3 hp.

Thanks again for the feedback, guys :)
 
I was going to use a 3-phase 1-horse run off my 5 hp RPC, but then saw a nice 230V single phase 3/4 hp and got that instead. I don't wanna have to run a 5 hp RPC just to power an SB9 :)
 
Thanks for replies. I'm pretty sure a 1 horse motor would be overdoing it. My 9A originally had a 3/4 hp on it that looked stock, and intuitively, that's the most power I'd want to subject it to.

BTW, I'm obsessive about keeping oil levels topped up on the headstock journals (Velocire #10), and treat the gears with great respect as well.

I might end up leaving it, as I really have no complaints. It's amazing what an efficient machine it is, and how much work you can do with just 1/3 hp.

Thanks again for the feedback, guys :)

A half HP would be better.

1959-60 the factory was shipping 3/4 HP on the "toolroom" ten as well. It had NO trouble "chirping" the belts!

IF... going for a VFD'ed rig? THEN you could go 1 HP or even 2 HP because of the drop-off at the extremes of the RPM range.

VFD could and SHOULD be set to limit MAX power, so a wide power band at the quivalent of "around" 3/4 HP could be sweet.

Not a lot of risk unless .... a person got greedy and did NOT apply sane limits.

That said, so long as an SB has its "normal" set of mechanical ratios to chose from? There isn't much to be gained from a VFD beyond 1-P to 3-P conversion.

The lathe already has all the RPM flexibility to do the basics well-enough, and "basic" is what it is. Beating on it doesn't gain much, regardless.
 
I was going to use a 3-phase 1-horse run off my 5 hp RPC, but then saw a nice 230V single phase 3/4 hp and got that instead. I don't wanna have to run a 5 hp RPC just to power an SB9 :)

Got THAT shot right!

There's more than enough monkey-motion in the drivetrain to absorb the slightly rougher input power, and 1-P doesn't much even display rougher running until under significant load.
 
Got THAT shot right!

There's more than enough monkey-motion in the drivetrain to absorb the slightly rougher input power, and 1-P doesn't much even display rougher running until under significant load.

I doubt I'd notice the difference, what with motor vibration and assorted wobbles being such a part of the usual SB9 experience.

I spose I could finally get around to pouring that concrete slab, War Dept. style. Or just get another, heavier lathe, which is naturally the best option, 'cause, you know, 'more old iron' :D
 
I doubt I'd notice the difference, what with motor vibration and assorted wobbles being such a part of the usual SB9 experience.

I spose I could finally get around to pouring that concrete slab, War Dept. style. Or just get another, heavier lathe, which is naturally the best option, 'cause, you know, 'more old iron' :D

Not really.

IF.. you had the option for the "heavy bed" nine, it is rightous enough. Partly because it isn't all that long, and it can't handle really heavy work over top of the cross. Not heavy. Easily moved. Good enough for a lot of "hobby" work.

More than a few of us have industrial lathes largely becase they were cheaper to buy! Under $1,200 for my older 10EE.

And it was in working order. PO had been posting on PM as he sorted all but one of its problems - and even that one was more nuisance than show-stopper. Bent dog-clutch operating fork. Another PM member had a decent one from a part-out.
 
Mine is V-belt drive so it's probably not accurate to compare to a flat-belt.
But I can stall the 1hp, 220v (inverter) motor without slipping the belts. It was previously powered by 1/2 a pony and it just wasn't up to what the lathe was capable of taking. I don't know if 1/2 is enough to chirp the flat belts, if not I don't believe 3/4 would be overkill.

Better in my mind to have as much power as the belts can transfer.
 








 
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