I have been lurking on this site for a few months trying to get some understanding of what‘s involved in machining. Machining is a hobby that I am taking up in my retirement with absolutely no experience and am now awaiting the delivery of a new to me Harrison M300 lathe with a 3hp three phase motor. It is a gear head with an ample range of speeds for anything I am likely to try. Having said all that I need to know what will be the best way to convert the single phase 240v in my shop to three phase for the lathe when it gets here. Or should I swap the motor out for a single phase? What’s the simplest and cheapest way to get it up and running? Don’t think I’ll need any other options like variable speed. Some advise from some of you guys with experience would be much appreciated.
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VFD, rotary phase converter or motor swap to single phase?
- Thread starter BEI
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- Jan 20, 2018
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Simplest and cheapest is static phase converter. I bought one as a stop-gap until I got my rotary converter. Still using it 4 years later.
There is a reduction of power of about 1/3 when using an SPC.
VFDs can be had relatively cheaply but are not as simple.
There is a reduction of power of about 1/3 when using an SPC.
VFDs can be had relatively cheaply but are not as simple.
- Joined
- Feb 25, 2021
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Any of the three will work.
Buying a rotary phase converter is the simplest but probably not cheapest. It does cover other possible (future) machines.
VFDs are relatively cheap but take some work to install as all the on/off/forward/reverse control needs to be done by the VFD, so rewiring the controls is necessary. A motor swap is usually the least desirable approach. Single phase motors do not have uniform torque as they turn, this can impact surface finish .
Buying a rotary phase converter is the simplest but probably not cheapest. It does cover other possible (future) machines.
VFDs are relatively cheap but take some work to install as all the on/off/forward/reverse control needs to be done by the VFD, so rewiring the controls is necessary. A motor swap is usually the least desirable approach. Single phase motors do not have uniform torque as they turn, this can impact surface finish .
Can a VFD not be used to simply convert the single phase to three phase to power the unit without having to get into other wiring issues in the lathe? I really don‘t want to complicate the setup of the lathe.
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- Feb 25, 2021
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In short, no.
VFDs are meant to control a motor, completely, entirely, and with no other mechanism interfering with how they interact with the motor. You tell the vfd what you want (via electrical inputs), it makes the motor do that. Trying to get around that is not completely impossible but isn’t practical and can easily result in a dead vfd.
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- Oct 11, 2016
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- 3,870
@BEI @rabler is quite right. You have a 3 phase machine. All of the electrics in the lathe are expecting well behaved 3 phase power. unless you want to rewire the machine. It can take considerable effort to do so.
You can NOT just use a VFD to 'create' 3 phase power for you. It depends on motor feedback to start (and stop) the motor. You can also not wire it between the lathe controls and the motor. It will not work correctly unless it is permanently attached to the motor it controls.
@MrWhoopee and @rabler have the right of it. Go static or rotary, and your machine will work as it is intended to. Go with a VFD and you are in for a world of work. One of my friends converted a 1PH machine to 3PH with a VFD, and took about 80m hours to rewire it. He is a competent electrical tech.
I have rotary converter, VFD, single phase and a static converter in my shop. I would choose a 5HP rotary for your lathe. Every time. It will also 'future proof' your shop in case you get a 2 or 3HP 3phase mill or surface grinder.
My rotary converter is 15HP, but I have bigger machines. I run one machine off of a VFD and have installed 5 others for other people. I have a milling machine in another shop that is on a static, but it has reduced the torque noticeably. Two of my machines are single phase. (Yes I have too many machines)
A very good static converter will preserve over 70% of the torque, but a lathe needs all the starting torque you can get, hence the rotary.
You can NOT just use a VFD to 'create' 3 phase power for you. It depends on motor feedback to start (and stop) the motor. You can also not wire it between the lathe controls and the motor. It will not work correctly unless it is permanently attached to the motor it controls.
@MrWhoopee and @rabler have the right of it. Go static or rotary, and your machine will work as it is intended to. Go with a VFD and you are in for a world of work. One of my friends converted a 1PH machine to 3PH with a VFD, and took about 80m hours to rewire it. He is a competent electrical tech.
I have rotary converter, VFD, single phase and a static converter in my shop. I would choose a 5HP rotary for your lathe. Every time. It will also 'future proof' your shop in case you get a 2 or 3HP 3phase mill or surface grinder.
My rotary converter is 15HP, but I have bigger machines. I run one machine off of a VFD and have installed 5 others for other people. I have a milling machine in another shop that is on a static, but it has reduced the torque noticeably. Two of my machines are single phase. (Yes I have too many machines)
A very good static converter will preserve over 70% of the torque, but a lathe needs all the starting torque you can get, hence the rotary.
- Joined
- Mar 22, 2020
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- 175
Buy a rotary phase. American rotary is a great option. You’ll be able to use it to power other machines in the future.
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If you just want to run a 3 phase motor a vfd is the way to go. I have one on my surface grinder and it works great. I have a Hartinge lathe that has a two speed 3 phase motor and I chose to use a rotary phase converter to run it. I didn't want to rewire the entire lathe. It all depends on what you have and what you want to do.
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- Apr 22, 2016
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As @Nutfarmer said, A VFD is the way to go. Rewiring is as easy as cutting the plug off the machine and sticking the wires in the VFD. Put the lathe switch in RUN/FORWARD, put a bag over it or tape it so you never touch it again. Spend a little time learning to set the VFD controls (once and done forever). Lots of help on this site for that last step.
Cheap, easy and satisfying!
I have 4 of them so far. Just yesterday, I was threading a 1 1/2" - 16 shaft that was sticking out of the chuck only 5/8". Using the speed control of the VFD, I was able to speed up to get to the number on the thread dial and then slow down to watch closely the tool advancing to the chuck. Stopped less than 1/8" from crash. I don't think you can do that with an RPC or SPC.
My seasoned opinion respectfully submitted.
Aaron
Cheap, easy and satisfying!
I have 4 of them so far. Just yesterday, I was threading a 1 1/2" - 16 shaft that was sticking out of the chuck only 5/8". Using the speed control of the VFD, I was able to speed up to get to the number on the thread dial and then slow down to watch closely the tool advancing to the chuck. Stopped less than 1/8" from crash. I don't think you can do that with an RPC or SPC.
My seasoned opinion respectfully submitted.
Aaron