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



## Glenn Brooks (Oct 17, 2017)

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


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## Dave Paine (Oct 17, 2017)

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.


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## Technical Ted (Oct 17, 2017)

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


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## 4GSR (Oct 17, 2017)

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!


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## Kernbigo (Oct 17, 2017)

my south bend 9" is running that set up 1.75 hp works great


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## markba633csi (Oct 17, 2017)

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


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## woodchucker (Oct 17, 2017)

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?


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## fradish (Oct 17, 2017)

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...


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## 4GSR (Oct 17, 2017)

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.


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## Blackjackjacques (Oct 17, 2017)

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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## Kernbigo (Oct 17, 2017)

i disagree my dc treadmill motor will not stall but the poly v belt will slip  (1 3/4 hp motor


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## Silverbullet (Oct 17, 2017)

I was thinking of doing that with my enco mill , it's 1HP and under powered in my book. I don't think it would be to much power for the 9" lathe . My worry is do they run hot and need more cooling then a.c. motors. As a kid who's burnt out dc motors it's a factor in my brain.


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## Glenn Brooks (Oct 18, 2017)

Thanks all, for your replies.  The price for motor and controller, plug and play is $200. This particular motor is the only one the guy has, apparently.   I see Grizzly now charges $150 plus tax and shipping on their high end 1/2 hp fully enclosed machine tool motor. So not much difference in my cost.  More for 3/4 hp and 1hp.  

I plan to mount a motor on the standard SB countershaft motor mount assembly and run an automotive serpentine belt between the cone pulleys. Maybe leave it set up on an optimal speed range on the pulley and use variable speed control when necessary. This works fine on my 7" x 36 Dalton lathe - using the same style SB countershaft assembly. 

Also suppose I could scratch around eBay or CL and save 50 bucks for a used motor.  But, getting tired of making do with old used equipment - partixularily electric motors that let the magic smoke out soon after landing in my shop.

Think I will explore this D.C. Motor thing a bit more - confirm max RPM limit, variable speed control, etc.  if a nice, cheap 1/2 or 3/4 horse AC shows up locally in the next few days, then D.C. would be moot.

Glenn


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## Kernbigo (Oct 18, 2017)

you will be sorry for not going with the 1.75 hp dc, i have done 2 lathes with this setup, and no problems. The first was a atlas 10", which i sold , now i own a 9" wide bed south bend. The first 1 i used the treadmill controller and it worked great, this one i'am using a danfoss 2000, really no difference. Be sure to use the fan, they will run hot on the slow speed, and keep the counter shaft setup. I also have my band saw dc powered running off the same controller.


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## Glenn Brooks (Oct 18, 2017)

Kernnigo,  What fan do you speak,of?  Is there a an internal fan, or should I add one?  If so, how big and where is it placed etc? 

I emailed the seller and am likely going to pick it up a few days.  He will put an internal limit switch inside  the controller  to limit the max rpm to 1750.  (The motor is rated at 6000 RPM! I don't want that speed ever to kick in around this lathe). Plus an external control to adjust speed during operation, plus a digital tach. If the digital tach is a workable solution, I think I will put one on my old 1919 Dalton Lathe, and another on my 21" camelback drill press.  The DP needs a motor installed, but has power down feed on the quill.  Iam thinking it will be useful to tweak speeds on this big machine, if the downfeed still proves workable.

The SB guys in 1925 that made this particular lathe would never have imagined how it would  be powered and tweaked whilst turning work a hundred years in the future!

Thanks very much for your comments and encouragement to move ahead with the DC setup.

Glenn


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## Kernbigo (Oct 18, 2017)

yes you need a external fan, running slow rpm it will over heat and kick out thermal overloads


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## woodchucker (Oct 19, 2017)

Glenn Brooks said:


> He will put an internal limit switch inside the controller to limit the max rpm to 1750. (The motor is rated at 6000 RPM!


Sounds a little slow to me. I would think you would want it to be capable of approx 3000rpm so you can slow it, and speed it up without changing it. if you limit to 1750 you cannot take advantage of your higher speeds since you will have to adjust the belt. 
Tonight I used the highest speed cones while in back gear.  I needed to take some big honking cuts but wanted to get it done as quickly as I could. So I went to back gear and fast for torque and speed.

you may not need the 3000, but 1750 is too slow...


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## markba633csi (Oct 19, 2017)

Glenn is this a treadmill setup the guy is selling or something else?  Have you any pictures? 
Mark


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## Kernbigo (Oct 19, 2017)

i believe your 9" south bend spindle is only rated 1000-1200 rpms max, you will burn it up any  higher


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## woodchucker (Oct 19, 2017)

Kernbigo said:


> i believe your 9" south bend spindle is only rated 1000-1200 rpms max, you will burn it up any  higher



But we are not talking the spindle speed, he is still using the motor drive unit with reduction already built in.


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## Glenn Brooks (Oct 19, 2017)

woodchucker said:


> Sounds a little slow to me. I would think you would want it to be capable of approx 3000rpm so you can slow it, and speed it up without changing it. if you limit to 1750 you cannot take advantage of your higher speeds since you will have to adjust the belt.
> Tonight I used the highest speed cones while in back gear.  I needed to take some big honking cuts but wanted to get it done as quickly as I could. So I went to back gear and fast for torque and speed.
> 
> you may not need the 3000, but 1750 is too slow...



Yep,  I plan on still using the cone pulleys and countershaft assembly to drive the spindle.  I am thinking I would just set the belt on the higher speed pulley and adjust the speed downward with the controller.  And not averse to moving the belt around as need be.

Not sure if this is a treadmill set up or not. He says it is all new equipment.  No pics except for the original Craigslist ad.  Haven't seen the motor in person yet - just emailing back and forth...

I asked him to limit the motor RPM's to 1750 as that was/is what AC Motors generally were on these older manual machines. 

(Note this is a 1925 9" x48" lathe)

Now, I have no first hand experience with D.C. Speed control.  So please let me know if I should plan for different operating conditions.  The lathe came without a motor or the old line countershaft assembly! So I am retrofitting the newer SB 9 style tensioning assembly with this DC  motor.  i can ask the guy to change the set up as needed. Not going to pick it up untill Friday.

Thanks!

Glenn


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## woodchucker (Oct 19, 2017)

Glenn Brooks said:


> Now, I have no first hand experience with D.C. Speed control. So please let me know if I should plan for different operating conditions



I don't either Glenn, I was just observing and thinking that you would probably setup a lower gearing and speed the motor up to take advantage of more torque.  That way you get the most torque and better speed range. And can still go up on higher speed to kill torque if you need to.

But all this was just me over analyzing things as usual.


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## Kernbigo (Oct 19, 2017)

99% of the time i run my south bend on the spindle middle pulley


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