# What Size Motor?



## 98rangerll (Apr 15, 2015)

i picked up a 109 craftsman and I debating between a 1/2 and 1/3 horse motor not sure what I should try to find anyone know what they came with new?


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## RJSakowski (Apr 16, 2015)

I am running a 3/4 hp 3450 rpm motor on my Craftsman/Atlas 6".  It was some time ago but I believe that the original was 1/2 hp.  I think that I also went with a smaller drive pulley to compensate for the higher rpm.  I looked at the user manual but they do not specify a motor size.  
If it were me, I would go with the larger motor.  I don't believe there would be any harm in doing so.


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## wa5cab (Apr 16, 2015)

AA made several lathes that Sears sold and there is no way of knowing which one you are asking about.  But the first period (1942 +/-) during which Sears sold AA built lathes, they recommended a 1/4 or 1/3 HP 1750 RPM motor, which had to be purchased separately.  After WW-II, they recommended a 1/4 HP minimum, and for an additional $13.50, sold the lathe with a 1/4 HP sleeve bearing motor.  Note that the same motor today would have an advertised full load speed of 1725 RPM.  And I would get one with ball, not sleeve, bearings.

The Atlas 618 has a spindle about twice the diameter of any of the AA lathes.  But still, putting a 3/4 HP motor on it is a waste of money and asking for trouble.  It isn't strong enough to stall a 3.4 HP motor without most likely breaking something.  In your case, regardless of which AA model you have, the same is true of a 1/2 HP motor.  So to answer your question, I would put a 1/4 HP motor on it, and if you stall it, you probably won't bend the spindle.  And don't use a 3450 RPM motor.  The motor pulley diameter required to safely run it on either brand of lathes is too small for the belt size.


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## RJSakowski (Apr 16, 2015)

wa5cab said:


> AA made several lathes that Sears sold and there is no way of knowing which one you are asking about.  But the first period (1942 +/-) during which Sears sold AA built lathes, they recommended a 1/4 or 1/3 HP 1750 RPM motor, which had to be purchased separately.  After WW-II, they recommended a 1/4 HP minimum, and for an additional $13.50, sold the lathe with a 1/4 HP sleeve bearing motor.  Note that the same motor today would have an advertised full load speed of 1725 RPM.  And I would get one with ball, not sleeve, bearings.
> 
> The Atlas 618 has a spindle about twice the diameter of any of the AA lathes.  But still, putting a 3/4 HP motor on it is a waste of money and asking for trouble.  It isn't strong enough to stall a 3.4 HP motor without most likely breaking something.  In your case, regardless of which AA model you have, the same is true of a 1/2 HP motor.  So to answer your question, I would put a 1/4 HP motor on it, and if you stall it, you probably won't bend the spindle.  And don't use a 3450 RPM motor.  The motor pulley diameter required to safely run it on either brand of lathes is too small for the belt size.


I used a 3/4 hp on my 6" atlas because I happened to have one.  As I recall, there was a 1/2 hp on the lathe when I bought it used in 1970.  Looking at the manual , the rating on the lathe is 3050 rpm in the high range on the primary pulleys.  It appears that the stock primary pulleys may have been changed by the previous owner as it now has single sheave pulleys.  With the current pulley arrangement, the lathe maxes out at about 1100 rpm.  
I control torque by adjusting the tension on the secondary drive belt.  If I stall the spindle, the belt slips.  I have run that little lathe for 34 years, sometimes asking more than I should of it, and it is still going. My biggest wear problem is the spindle cone pulley.  There is wear in the drive pin socket and the drive pin slams into it whenever I start up.  I have gotten into the habit of rotating the chuck backward to take up the play.


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## The Liberal Arts Garage (Apr 16, 2015)

Please ! Get a good heavy quarter- horse motor , no larger . Just turned five good 
ones to my local tool store - five bucks each in credits......BLJHB  PS. 1750 rpm.


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## master53yoda (Apr 25, 2015)

I used a treadmill motor on mine and really liked the variable speed,  the 109 has a 1/2 x 20 spindle and it can be bent if the motor has enough torque and you stall it.  The DC motor gets lower torqued as you slow it down but when you slow down a shaft using pulley sizes it increases the delivered torque.    with small spindles it can be deadly.
Art b


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