# “Intentionally underpowered” Atlas lathe motor



## xyz07 (Jan 7, 2021)

Being in the middle of a 9” Atlas lathe “refresh” effort, I have a number of fairly important questions on completely different and largely unrelated subjects. I first tried to bundle them in a single thread, but then thought it would make more sense to start separate threads focusing on specific topics. My apologies for adding all this content, but I’ve been getting great responses that really helped me make important decisions about this lathe.

Anyway, I’m considering buying a new motor with enhanced safety features. (1) I want it to have a built in brake to stop it immediately (without any runout) once the power is cut by an emergency stop button (though this solution would likely mandate a VFD or at least a potentiometer to prevent every motor shutdown from becoming an “emergency” one, which would be hard on the spindle bearings and drive parts, I suppose). (2) I want the motor to be “underpowered” so that it will both be easy to stall for safety reasons, and yet it won’t be too inadequate for actual lathe turning operations (yes, I do know these are sorta mutually exclusive criteria, but you probably know what I’m talking about; otherwise, I do realize that, leaving safety aside, more power is better).

Which made me wonder: what level of motor power would be a reasonable compromise between usability and safety? For example, would a 1/8 hp motor meet my criteria (being easy to stall but still very usable)? Or, is this too little power? As usual, would greatly appreciate any inputs. Thank you very much in advance.


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## pdentrem (Jan 7, 2021)

I would stick with 1/2 or 3/4 hp. If running a VFD, get an inverter rated motor at 3/4 or 1 hp, but limit the top end to avoid damage to the weaker Zamac components. As for E Brake motor, I would suggest not! The chance of running at a speed that the sudden stop, will spin off the chuck is too high.
Pierre


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## Jim F (Jan 7, 2021)

I have a 1/3 hp on my SB9. If you keep the belts at the proper tension, it has a built in safety feature.
It stops quick enough for me when I switch to off on the switch.
You also have the belt tensioner you could dis-engage.
An abrupt stop will not un-spin the chuck, unless it is loose.
You really do not want more than 1/2 hp due to the weak Zamac parts.


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## Ulma Doctor (Jan 7, 2021)

I would concur with Pierre.
The inertia from an instant stop can spin a threaded chuck right off 

i would consider a 1/4 or 1/3 hp motor but not less

i use a coasting deceleration on my lathe vfd’s. 
They all seem to stop quickly without any braking


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## Moderatemixed (Jan 7, 2021)

A sudden stop should tighten the chuck. In theory doing so would only be done in the event of emergency and not on a regular basis. I draw attention to this because repeated sudden stops could act like an impact gun and make getting the chuck off the spindle challenging at best. 

People have used these lathes for years and with common sense they are quite safe. You seem remarkably concerned about the “safety” of it. I’m an Airline pilot, and we regard safety as being of prime importance, but to be 100% safe, you wouldn’t fly. If you want to enjoy the lathe, and be able to use it safely you have to work between two extremes. Too much power and the lathe can be dangerous, like putting a jet engine on a VW Beetle (see the Darwin awards). But under powering it can be equally dangerous as you may start to cut corners or come up with creative ways to make it work. 

If you follow established guidelines, gold standard guidance and use good common sense you will bot enjoy and accomplish with your lathe. Wear short sleeves, hair, cut or tied back. Be well rested, use sharp tools, make sure the machine is tuned, level, square and tight. Keep your mind on the task and install guards when necessary. Aside from that list there will likely be hundreds more. I use this analogy with my kids, but it has followed me since I was a boy. If a baseball is thrown at you, you have 2 options, turn away, loose sight and it will likely hit you..... or, keep your eye on it, get out of it’s way, or catch it.

My point is that you should 1. educate yourself (clearly you are doing so) and 2. Keep in mind that you can not operate safely a machine that you are afraid of. Take from the analogy, keep your eye and focus on the task and operate your lathe safely, but you need not wrap it in bubble wrap, under power it, put “sawstop” mechanisms in place and perhaps by doing so make it more dangerous. Imagine turning a 2 pound flywheel at 1000rpm and stopping that mass dead..... where does the energy go? 

I have operated, rebuilt and been around Atlas lathes for years. My current lathe is a QC10F. I power it with a 2HP DC motor and find it to be both capable and very safe. The manual calls for 1/2 hp AC motors as I recall. Better to under power than over power will likely be the popular theme; I’d suggest powering to the task. If turning delrin, go 1/4 hp, but if you are looking at metal, then stick with 1/2 hp. 

Good luck, please don’t take any offence to the above, as none was intended. I have been where you are and have over time come to realize that sometimes less is more, and that a sharp knife is safer than a dull one. We’re all in this together.

Cheers,

Derek


Sent from my iPad using Tapatalk


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## benmychree (Jan 7, 2021)

Moderatemixed said:


> A sudden stop should tighten the chuck. In theory doing so would only be done in the event of emergency and not on a regular basis. I draw attention to this because repeated sudden stops could act like an impact gun and make getting the chuck off the spindle challenging at best.
> 
> People have used these lathes for years and with common sense they are quite safe. You seem remarkably concerned about the “safety” of it. I’m an Airline pilot, and we regard safety as being of prime importance, but to be 100% safe, you wouldn’t fly. If you want to enjoy the lathe, and be able to use it safely you have to work between two extremes. Too much power and the lathe can be dangerous, like putting a jet engine on a VW Beetle (see the Darwin awards). But under powering it can be equally dangerous as you may start to cut corners or come up with creative ways to make it work.
> 
> ...


Saying that sudden stops tighten a chuck is just plain absolutely incorrect, the inertia of the chuck causes it to want to thread off the spindle with sudden stops, such as plugging the motor into reverse rotation; having done this a time or two over my 58 year working this trade, I know whereof I speak, one time the chuck came all the way off, and the other, I went back to forward rotation and got the chuck back where it belongs before it could thread all the way off.


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## silence dogood (Jan 7, 2021)

Well, I suppose if you're going to power a lathe with 1/8hp or less, you could check out the lathes built in the 1890's.  Barnes, W.C. Young, or a Seneca Falls were peddled powered lathes.  Otherwise, keep to the recommended hp on motors.  I don't know what type of off/on switch that you have on your lathe.  You can purchase magnetic switches that have either a paddle or a large  off button.  Grizzly is one company that sells them. The best safety feature on any machine is to know your machine and practice safe procedures.


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## shadetreedad (Jan 7, 2021)

I've been using a 1/3 hp motor for years on my 10-F Atlas. The only time it has stalled is when I did something wrong. But since that is the hp sweet spot no damage was done, except to my pride. The 9” Atlas lathes are even designed a little less robust than the 10” ones. So, I would highly recommend a 1/3 hp motor for your application. Better to stall than break. Use a 1/4 hp motor and you'll probably be disappointed with performance. A 1/8 hp motor would not be practical at all. And there is really no need for an e-brake motor.
Mike


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## Larry$ (Jan 7, 2021)

John York is correct about chuck spin off from a sudden stop. Adding the mass of the work will increase the force to spin it off. That said  under normal stopping and with a properly tightened chuck it would be extremely unlikely to happen. Your reaction time to get to an emergency stop is likely too long to make a difference in the result. My lathe has a pedal for quick stops/ off & brake. I've only used it when starting a dubious setup by having my toe on it before starting. Even then I'm not so sure my reaction time is sufficiently fast. 3 hp on the cam lock spindle.


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## Moderatemixed (Jan 7, 2021)

benmychree said:


> Saying that sudden stops tighten a chuck is just plain absolutely incorrect, the inertia of the chuck causes it to want to thread off the spindle with sudden stops, such as plugging the motor into reverse rotation; having done this a time or two over my 58 year working this trade, I know whereof I speak, one time the chuck came all the way off, and the other, I went back to forward rotation and got the chuck back where it belongs before it could thread all the way off.



Having thought about that a bit more, and then waking down to the lathe, and you are right..... disregard some of what I had to say, lol. 


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## xyz07 (Jan 7, 2021)

All comments are much appreciated! I think I got an idea now of what sort of new motor I need (well, actually I do have a 3/4 hp non-original motor that came with it, but I would feel more comfortable with a bit less power, also for the reasons outlined above).

Larry$, would you mind sharing what type of brake you are using?


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## markba633csi (Jan 7, 2021)

Having a lathe that stops instantly will not eliminate all safety risks. Operating any machine tool entails some risk. Plenty of ways to get injured if one is not paying attention.  Good reason to never operate a lathe or milling machine when tired or distracted.  Even an unpowered machine can be potentially dangerous from sharp exposed tool bits and cutters and so forth.  Learn your machine well and approach it with a safety first attitude always.  
-Mark


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## Jim F (Jan 7, 2021)

xyz07 said:


> All comments are much appreciated! I think I got an idea now of what sort of new motor I need (well, actually I do have a 3/4 hp non-original motor that came with it, but I would feel more comfortable with a bit less power, also for the reasons outlined above).
> 
> Larry$, would you mind sharing what type of brake you are using?


Trying to make a foot brake for your lathe would be more trouble than it is worth.


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## markba633csi (Jan 7, 2021)

If the idea of a motor running full speed makes you nervous, you might want to consider a variable speed motor system.  A welcome improvement to any fixed-speed lathe, IMO
If you're like me, once you have it, you won't want to go back 
-M


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## Larry$ (Jan 7, 2021)

I really don't think the amount of power will make any difference on the safety. When something goes wrong it happens so fast that you can't really do much about it. Until you get used to running it just use the gearing for lower speeds. Being able to vary the speed between what you can get using the gearing might be helpful. The one thing about it that seems best is being able to dial up the speed as the cutting diameter decreases. 

The braking system on my lathe is factory, not something I did. A pedal bar runs along the the bottom of the machine. When stepped on it cuts power to the motor pickup coil and engages a mechanical brake. It stops the spindle almost instantly. (Not something you should do with a threaded chuck) But there is still the issue of the response time of the operator. You can see the brake being used by some of the YouTube creators just to not have to wait for the machine to spin down. Some bigger lathes use a combined clutch and brake lever that allows the motor to keep running but stop the spindle. Adam Booth has one. 

A lot of new lathes come with a shield that covers the chuck. You could fabricate one. Getting hit by the chuck jaws seems like something that could easily happen. They often have a switch that prevents running the lathe with the guard up.  Bigger lathes don't seem to come with them but the small hobby lathes often do. Work safe, wear those safety glasses.


xyz07 said:


> Larry$, would you mind sharing what type of brake you are using?


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## projectnut (Jan 8, 2021)

I would also be of the thought that under powering the lathe is not the best of ideas.  My 1916 Seneca Falls Star lathe has a 1 hp motor.  You can always control speed and torque with a VFD, or even leave the belt a bit loose if you're afraid of crashing it.

If yours is like most South Bends the flat belt can be tensioned or loosened relatively easily.  I have on several occasions loosened the belt on my machine when trying to get into tricky places.  There's still enough tension to make light cuts, but it's loose enough that the spindle will stall should you do something you shouldn't.

As mentioned you should be comfortable using the machine before you try it.  Having respect for it is quite a bit different than being afraid of it.  You might want to find a friend who's familiar with machine tools to give you some initial instruction and guidance.  If that isn't practical you can always watch some of the hundreds of instructional videos on YouTube.  

There are several out there by Lyle Peterson aka tubalcain.  He's an excellent instructor and spent many years as a high school Industrial arts teacher.  In my opinion he's one of the best on YouTube.  He takes time to explain each operation, and the reason for doing it.  Keep in mind he was training potential professionals for over 30 years.  Here's a link to a video of what he offers.   This particular video is just an index of the over 700 videos he has made.   Many of the actual videos are on the maintenance and operation of a South Bend 9" lathe.

INDEX OF TIPS MACHINE SHOP TIPS & COURSES tubalcain - YouTube


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## xyz07 (Jan 9, 2021)

Once again, I would like to thank everyone for great advice. I will likely go with a 1/3 hp motor, especially since I already have a 3/4 one. I do understand the arguments about life being a risky proposition in general, and the best thing to do being to learn how to use the lathe safely, but I am also a great believer in doing my best to stack the chances in my favor ). After all, we all make mistakes (whether pros or amateurs); this is part of being human. Therefore, I firmly believe it makes sense to take measures reducing the potential "cost" of these mistakes down to an absolute (feasible) minimum. Of course, in this particular case these measures should result in a reasonable compromise, where the usability of your machine doesn't suffer too much, and that was the rationale for creating this thread.


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## rwm (Jan 9, 2021)

Am I the only one who tries to measure the part while my lathe is still slowing down?! 
That's the one reason I think a foot brake could be helpful.
Robert


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## Bi11Hudson (Jan 9, 2021)

I have a Craftsman 12x36, a 101.27440. It  was originally rated for a 1/2 HP motor. I have a 1/3 HP motor that will slip belts but has never stalled. To my thinking, a 1/8 HP motor wouldn't be good for much of anything heavier than a middlin' size fan. 1/4 HP is about as small as I would go on a machine. But that's just my thinking. . . 

.


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## Larry$ (Jan 9, 2021)

XYZ, you can always change motors later. Maybe on that type of lathe that's all you need. I have no experience with them. 
Be safe, have fun.


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