1.75 hp D.C. Motor for SB 9??

Glenn Brooks

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A local guy is selling a D.C. Motor and controller, plug and play for repowering lathes. The motor is 1.75 hp.

Are there any downsides to having this much horsepower hooked up to a South Bend 9" lathe?

I like the idea of being able to adjust the RPM's with the motor...

Thanks
Glenn
 
A 1.75 HP motor is certainly far more power than SB ever imagined using in a 9in lathe. It may allow taking too much of a cut and putting too much of a load on something that is not designed for the load causing something to break.

You will love being able to adjust the RPM's. I think if you keep the cuts and loads to more like the capability of the original motor you should be fine.

For my projects the only time I can feel the load on my lathe is when I am cutting coarse threads. I may only be cutting on one side, but a lot of tool contact as the thread depth increases.

You could add some kind of current limitation such as smaller fuse to restrict the max power the motor can develop. It may be interesting to see if or how often a smaller fuse pops.
 
I looked in an old SB catalog I have and it shows that at the time those particular lathes came with a 1/4 HP motor. I'm not sure about your lathe, but with my 1935 15in SB the flat belt will slip before I can stall out my 1-1/2 HP motor (when not in back gear). When I have the back gear engaged it's a different story.

A man can most likely do just about anything they want as long as they use common sense while doing so! ;)

Ted
 
My dad's South Bend lathe came from the factory with a 1/4 HP motor. It finally died 50 something years later. I replaced it with a 1/4 PM DC motor with VS controller. Being a permanent magnet DC motor, it has much less torque than to old factory motor did. Still get it to make some good healthy cuts for a 9" swing lathe. I have a 3/4 HP PM DC motor I want to put in its place, just haven't had time to do so.
A 1.75 HP DC motor is in m mind a big over kill in HP needed. If the price was reasonable, like free, it works for me! Go for it!
 
Glenn: Sure it's overkill but if the price is right- If you wanted to limit the power there is probably a current limit adjust on the controller
depending on what brand/type it is
Mark
 
I think you'll be fine. I have slowed my I believe 1/2 hp taking deep cuts, would like more power just to power through.
Can the VFD dial it back?
 
I would think your flat belt would limit how much trouble you'd get into.
I have a 1/3 hp single phase that I've never stalled. The flat belt (in my case
a serpentine belt) always slipped first. Don't even get me started on when I
had the leather belt... :)
 
My 9" South Bend lathe has been converted to a true Poly-Vee groove system with a belt to match. The motor will stall before the belt slips. Even with the belt saturated in oil.
 
For a given hp, dc motors are usually larger - so you will require more real-estate. However, the concept you are considering is plausible
 
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