# VFD and 3 phase motor to power my Atlas lathe



## shaskell (Dec 11, 2012)

Hi. Anyone out there using a VFD and 3 phase motor to power their lathe? I have an Atlas 10 inch lathe (10F54) and would like to replace the single speed 1/2 HP AC motor and 16 speeds and constant belt changes with a variable frequency drive and 3-phase motor to try to eliminate some of the belt changes and have opportunity for variable speed. 

What HP motor would be recommended? I was thinking 3/4 or 1 HP which I can get in a 56 frame size which would fit in place of the current AC single speed motor. I don't know if I should go 3600 RPM motor or 1800 RPM motor, they also are available in 1200 and 900 RPMs.

I do like to run carbide tooling occasionally which requires higher RPM's. I machine anything from mild steel and alumnimum from usually 1/4" diameter up to the capacity of the lathe (max 10 inch diameter).

I would like to stick with 120V input power to the VFD as I have 120V available in the vincinity of the lathe and not necessarily have to run a new 220V line to that corner of the shop. But I am not against running a new 220V line if that is better.

I also have 3-phase power available via a rotary phase converter that I own. 

If anyone out there has made this conversion, what HP motor are you using, what make/model of VFD do you have, what spindle speeds can you get with your setup?

Thanks for any advice.


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## Ray C (Dec 11, 2012)

I thought about doing this a couple years ago but decided it wasn't worth the effort.  Some things to consider...

You will still need to change gears/pulleys manually.  You will not find one particular pulley setting that runs the gammut of speeds -even with a VFD setup.  -Think about how your car feels when you try to get rolling in 2nd or 3rd gear.  It's ugly because the torque curve is all messed up.  With the VFD, you'll only be able to tweak speeds just a bit for any given gear/pulley setting.

Unless you have an expensive 3 Phase motor that specifically permits it, you should not over-rev a motor if you want it to last a while.  Also, you should always try to keep the speed somewhere between 70 to 100% of it's rated value.  At speeds lower, it might not have enough air cooling from its internal fan (assuming it's TEFC type).  Newer 3 phase motors will post the allowable settings for VFD.

... just some food for thought.


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## pdentrem (Dec 11, 2012)

It is a bit of overkill but no reason that you can not do so. Be sure to use a motor that is rated for VFD and you will be ok. 

A good motor can be driven to 90 hz or even 120 hz but I would hesitate to do so unless it is rated for that.  See here and look around as well.
http://motors.automationdirect.com/Information/compare.html

Once you get that chuck spinning over 2000 rpm things start to go to the bad side real fast. If you were using collets then that is different.

At work the VFDs are set for a minimum of 30 hz and max of 60 hz as we are still using a 4 spd gear box. There are rolling mills not lathes. We also use DC drives on some of our machines.

On the Atlas 10F24 that I used to own, I almost never changed the pulley position of the belts, the middle two pulleys and backgears were the favoured positions, and no VFD. Just a 3/4 HP motor when the 1/2 packed it in. I used the higher RPM range very infrequently as the work did not require it.

I do suggest that the carbide stuff will be over rated for the lathe. It is just a bit too light in most peoples opinion. I did have carbide stuff too but usually used HSS except for hard stuff.
Pierre


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## shaskell (Dec 11, 2012)

pdentrem said:


> It is a bit of overkill but no reason that you can not do so. Be sure to use a motor that is rated for VFD and you will be ok.
> 
> A good motor can be driven to 90 hz or even 120 hz but I would hesitate to do so unless it is rated for that.  See here and look around as well.
> http://motors.automationdirect.com/Information/compare.html
> ...



Thanks for your opinion. I might just leave well enough alone. Where I really should install a VFD is on my 1942 Bridgeport M head Round Ram mill. I is a 6 speed step pulley setup with the slowest speed 410RPM and it sure would be nice to slow it down further for some cuts and some larger drills. Also can't get the proper RPM with say a 3/4" diameter TiN coated end mill. I believe its probably the original motor ( old General Electric 1/2 HP, 3 phase, 220V, 1400RPM) so I don't know how long it would last with a VFD, but what the heck, if motor failed, I could probably upgrade to 3/4 or 1HP.


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## shaskell (Dec 11, 2012)

Ray C said:


> I thought about doing this a couple years ago but decided it wasn't worth the effort.  Some things to consider...
> 
> You will still need to change gears/pulleys manually.  You will not find one particular pulley setting that runs the gammut of speeds -even with a VFD setup.  -Think about how your car feels when you try to get rolling in 2nd or 3rd gear.  It's ugly because the torque curve is all messed up.  With the VFD, you'll only be able to tweak speeds just a bit for any given gear/pulley setting.
> 
> ...



Thanks for your opinion, I might leave well enough alone. Where I really should invest in a VFD is with my 1942 M-Head Bridgeport mill. It is currently a 1/2HP 1440 RPM 3 phase 6-step v-belt drive setup with the slowest speed 410 RPM. Top speed is 6450 so that's not a problem, I rarily go that fast. But 410 is just too fast for some cutters and some larger drills. The next speed is 645RPM and then 1065RPM. So can't really run a 3/4" or 1 inch diameter TiN coated end mill the proper speed. Not sure if this old General Electric motor would last long with a VFD but it might be worth a try.


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## pdentrem (Dec 11, 2012)

It is a good question to ask, as VFD are getting more and more popular. I will be doing the same in the new year on the new old lathe that I picked up to replace the Atlas.

I really wish that BP had made their mills for regular sized people. The controls on the top of the head are just in reach for me, 5'6", and that is with the riser removed!
Pierre


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## Hawkeye (Dec 11, 2012)

I'm running my lathe with an FM50 VFD feeding a 1 1/2 HP motor. I don't remember changing belts once I got the current setup going, but I can if I want to turn faster than 700 RPM. With the belt on the slowest range, I can go from 78 to 700 RPM neat and from 14 to 130 with back gears.

This VFD is 240 volts only, but other members have used VFDs running off 120 volt single phase.


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## Kennyd (Dec 11, 2012)

I have VFD's on my lathe, mill, and belt grinder-its the only way to fly IMHO.


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## Ray C (Dec 11, 2012)

I think you can get away with that since you have a 1.5HP motor.  If it was lower HP, you wouldn't get enough power out of it at the lower speeds.  I do believe that AC motors can only produce peak HP at their rated top speed; whereas, DC is the opposite.

EDIT:  Do you have a newer motor to be able to run at those lower speeds?  I remember when VFDs were first getting popular that older motors were dying in droves from overheating.  When I got my first one, the warning was prominent.



Hawkeye said:


> I'm running my lathe with an FM50 VFD feeding a 1 1/2 HP motor. I don't remember changing belts once I got the current setup going, but I can if I want to turn faster than 700 RPM. With the belt on the slowest range, I can go from 78 to 700 RPM neat and from 14 to 130 with back gears.
> 
> This VFD is 240 volts only, but other members have used VFDs running off 120 volt single phase.


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## Ray C (Dec 11, 2012)

Totally agree.  -Thought I found machine-shop-heaven when I got my 1st VFD.  Have 3 in the shop now.  The only time they cause problems is when the machine has other electronics onboard requiring a constant 60 (or 50 as the case may be) HZ.

I've got one on the way that can input 120 or 240.  The others I have are 120 only but, they're only powering 1/2 and 1HP motors so, it's not a problem.  If I get inspired, I'll test both voltages and see if there's any difference.  I'm guessing not.




Kennyd said:


> I have VFD's on my lathe, mill, and belt grinder-its the only way to fly IMHO.


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