# Spindle speeds/rpm of the Atlas 12" lathe



## chevydyl (Jul 19, 2013)

So the PO of my lathe purchased a new motor and installed it and wire it for 120v. Looking through the book it says the lathe is supposed to run on a 1725rpm motor but when my motor is wired to 120 it will only turn 1480rpm when i get back from work i will be rewiring the motor to run on 240 so I can obtain the proper speeds. Can anyone tell me what speeds i have been using while th motor was spinning at 1480. I just wonder how much it was off. I had always set it up to run faster than what the book recommended because it just seemed slow and now I know why lol thanks to anyone who can answer that


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## Kroll (Jul 19, 2013)

Changing voltage won't change the rpm's,but if you should change the motor pulley to a smaller diameter that will increase the rpm's.But since your only alittle off I would only drop down maybe one size----kroll


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## chevydyl (Jul 19, 2013)

Haha kroll your wrong lol. As stated on the motor  120v 1480rpm  240v 1725rpm


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## cdhknives (Jul 19, 2013)

The RPM change will be exactly proportional through the drive train (assuming no increase in belt slip from increased RPM.)

1480/1725==0.858

So take the published spindle speeds for 1725 RPM motor and multiply them by 0.858


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## chevydyl (Jul 19, 2013)

thanks cdh that's exactly what I wanted to know


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## Kroll (Jul 19, 2013)

I stand corrected,guess that applys to specific motors none which I own.But I plan to put this information in my memory banks just in case I need a motor like yours.If you get a chance and feel like it please post some pics of your motor.----kroll


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## chevydyl (Jul 19, 2013)

will do man, yeah it seemed odd to me but that's what it says on the sticker


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## shovel80 (Jul 20, 2013)

Kroll said:


> Changing voltage won't change the rpm's,but if you should change the motor pulley to a smaller diameter that will increase the rpm's.But since your only alittle off I would only drop down maybe one size----kroll



Actually, if you decrease the Motor pulley size, it will decrease the final rpm's Not increase.

Terry)


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## chevydyl (Jul 21, 2013)

and lol, if you decrease the jackshaft pulley smaller that will increase spindle speed but make the motor work much harder to produce that same RPM, as well as shorten the service life of the motor if worked hard.....just think of a 21 speed bike.... top gear is a small sprocket on the wheel with a large gear on the pedals but you cant pedal up hill with those gears lol you'll be worn out haha


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## wa5cab (Jul 21, 2013)

There is a speed chart for the 10" and 12" machines in the Downloads.  It is, of course, based on a nominal 1725 RPM motor.

However, I can't think offhand how one could build a single phase AC motor to run at 1480 RPM on a 60 cps supply.  If you go to a 6-pole motor, it will run at around 1150 RPM.  1480 is in the ballpark (although a little on the high side) of what a 1725 RPM/60 cps motor would run at on 50 CPS.

Robert D.


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## pdentrem (Jul 21, 2013)

Not the same motor but made me wonder what OP has. 

http://www.mgmelectricalsurplus.com/Details/Motors/AC Induction - Squirrel Cage/213.php

Need to see the motor tag!
Pierre


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## wa5cab (Jul 21, 2013)

Interesting.  Note that this is a 25 cps motor.

Robert D.


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## chevydyl (Jul 22, 2013)

im at work right now, but when I get home Wednesday I will snap a picture, I looked at a motor here at work and it also has different rpm ratings but looking at that one I know it has to do with the hertz, at 50 cycles it does this rpm, but at 60 cycles it does that rpm, so that also is probably the case with my motor, but I coulda sworn it was voltage but I prolly just read that label wrong it was just a glance at the label and was like hmm, maybe that's why I always run the lathe 1-2 speeds higher than recommended by the book, sometimes even 3 speeds faster just seems to cut better and with a nice finish...


BTW the 1480 was just a guess, I know its in the 1400s so I just through the 80 on there cause that's what I thought it was.....like I said im at work and while home I glanced at the label while I was doing the hole layout for mounting the lathe on the concrete pad I poured for it to rest on


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## george wilson (Jul 22, 2013)

I don't quite understand the last post. Was the motor also be supposed to run on European current? Theirs is 50 cycles. If you take a European motor and use USA current of 60 cycles on it,it will run fine,but will run 20% faster.


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## wa5cab (Jul 22, 2013)

We'll just have to wait until Wednesday to find out what he actually has.

Robert D.


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## bigman1 (Aug 3, 2013)

Hi my sphere 5" lathe(atlas clone) has 16 speeds 30 rpm to 2000 and will screw cut down to 4 tpi the spindle speeds and coarse pitch ability are far superior to a lot of the asian lathes where you have to buy a much larger machine to get the same ability.Thanks.Ronnie.


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## wa5cab (Aug 4, 2013)

Ronnie,

Yes, I assume that's what in US practice is called a 10".  The 12" models are the same.  But the spindle speed charts all assume a nominal 1725 RPM motor.  Which is the question to be answered.

Robert D.


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## Codered741 (Aug 4, 2013)

How did you measure the speed of the motor? The difference between 1400-1500 rpm and 1700-1800 is somewhat to difficult to judge by eye. An inexpensive photo tachometer will tell you for sure. 

Motor tags will sometimes list things in a strange way. I suspect that this tag is really telling you the rpm for 50 hz. Often listed like this. 

120/240vac 
50/60 hz
1480/1750hz

As someone said above, assuming 60 hz, it is not possible to construct a squirrel cage induction motor to run at 1480 rpm.  Induction motors need an even number of coils, usually 2, 4, or 6, sometimes more. This is where you find motors in the 3600 rpm range, with 2 coils, 1800 rpm with 4, and 1200 with 6. 

The formula for this is 
RPM= 120*frequency/# of poles.  

So for a four pole motor, at 60 hz, you get an RPM of 1800. Of course, a motor will not run at 1800 rpm, due to slip, which is what generates torque. 

Still curious to see a photo of the nameplate on this motor to be sure. 

-Cody


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