3ph Motor Install, Need Recommendations

[chevydyl]

I have an Atlas 12" underneath drive, and pretty much since I have owned it I cant use the top 2 speeds, it vibrates pretty bad from a sprung pulley. I have however made a pulley for just one of those speeds, number 3. I have a 1.5hp 3ph motor that I want to install and use my vfd to control speed, partially. Still want to use pulleys for the torque advantage. The new motor is a Baldor inverter rated 1755rpm motor, i was wondering what size pulleys i should use, or how i should do the drive, i was thinking of deleting the step motor pulleys, what size would i replace those with? i also thought of driving the countershaft with the motor, and having 2 or 3 steps at that point, basically for a low and high range. let me know what you guys think, thanks.

 

[kd4gij]

That motor is quit over size for an atlas. They came with either a 1/3 or 1/2 hp motor.

 

[Ulma Doctor]

it is a larger motor, but shouldn't be too big an issue unless you crash the lathe repeatedly-
it will get expensive to put humpy dumpty together again!
you are free to do as you'd like, but if i could..
i'd see if i could somehow keep the stock motor drive pulley, or approximate them on a homemade pulley-
you'd be better off.
that way you can utilize the lathe with intended speeds, then use the frequency control to fine tune the speed you'd like to operate at.
you could gain a lot of mechanical advantage in backgear, with pinpoint rpm control- a very useful thing.

i may suggest limiting your vfd's output, as to not over speed the lathe.

good luck.

 

[chevydyl]

to be truthful, the lathe also has had a broken motor pulley, so I bought a single v pulley to put on the stock motor, for high range of speeds. One issue that I have is the 3ph motor is a bit longer than the stock one, which to mount it I would have to cut into the cabinet, that would be to retain the original drive configuration, not sure if I could make a deep dish pulley to move it close to the cabinet wall so I could move the motor over without having to cut into the cabinet.
on another note, whats the max rpm you would run the lathe at? im thinking 2750 for short durations of around 5mins would be ok

it currently has a 3/4hp motor

 

[Nitmare67]

Thats a really big motor. Youre going to find a hard time finding an appropriate frame size 3 phase motor in that hp... basically you wont find one. thats probably a 143 or 145 frame size and you need something much smaller. I would strongly suggest running a 3/4 or 1hp motor and setting the drive up for vector control as compared to volts over hz. You will have peak torque at 20hz just like you do at 60hz. Then just set the lathe up on a middle of the mill belt drive speed and overspeed the motor if you need high rpm and still use the back gear for threading. Basicaly you would end up being capable of prob 25% more top spindle speed and still be able to run 25% of the charted speed and still have full torque for any range selected.

I would suggest something like an AB Powerflex 40 VFD.

 

[chevydyl]

Lol you guys, I don't need to hear how much too big the motor is, I don't care, I'm putting that motor on my lathe, end of story. All I wanted to know was what I should do with the pulleys as far as having the listed speeds, currently I mostly thread in direct drive on low speed of high range.... I know what my lathe can handle, just because I'm putting a bigger motor on it don't mean I'm gonna take bigger cuts, cause it simply can't handle anymore than what I do now.
Number 1, I will NOT have adjustable motor pulley steps. Single V or serp.
Number 2, I will install that 1.5hp motor, and use a mitsubishi 3hp vfd
Ps, I already run the motor belt loose, and I've stalled the spindle on heavy cuts where I've had to tighten it up to get through the job then put it back, all part of knowing the limits, but knowing there is a little more there if I need it.

 

[chevydyl]

Oh yeah, I also have a 1.5hp DC high torque treadmill motor I could use, it has about a 5000rpm range, problem with that motor is it has a screwed on pulley, that's a serpentine type belt drive, that's my other option, I could use that instead of the 3ph motor. I think that one would need some underdrive pulleys to use so I would stay in the range of lathe speeds, with some extra speed for polishing or whatever

 

[Ulma Doctor]

to be truthful, the lathe also has had a broken motor pulley, so I bought a single v pulley to put on the stock motor, for high range of speeds. One issue that I have is the 3ph motor is a bit longer than the stock one, which to mount it I would have to cut into the cabinet, that would be to retain the original drive configuration, not sure if I could make a deep dish pulley to move it close to the cabinet wall so I could move the motor over without having to cut into the cabinet.
on another note, whats the max rpm you would run the lathe at? im thinking 2750 for short durations of around 5mins would be ok

it currently has a 3/4hp motor

if you have a broken pulley and do not have room for a suitable sized multi pulley, i'd suggest picking the larger motor drive pulley or something that closely approximates it's size.
you don't really want the motor going much past 1800 rpms with a stock sized pulley- the lathe was not constructed for high speed operations
going slower is fine for short periods of time

 

[chevydyl]

With the current pulley configuration the lathe goes 2025 right, I don't remember exactly, but all my high speed range is intact except the sprung countershaft pulley which limits me to the two lower ranges, the top two ranges create massive vibration where the tool post shakes like a money maker

I wouldn't be spinning the 3ph motor all that fast anyway, as it is now I don't use freq control on my mill, I just use the vari speed

 

[wa5cab]

1-1/2 HP 3-ph motor is 'way too large for a 12" Atlas, even the Commercial. The max recommended is 3/4 HP. If you use a surplus (Chinese made) tread mill motor, it would probably be OK, as the mainland Chinese usually grossly overrate their motors.