Single Phase or 3-Phase?

M

MWCurl

Registered
Registered
Joined
Dec 31, 2018
Messages
18
Hi Guys

I am in the process of purchasing a new lathe. I have the option of 1-phase or 3-phase power. My shop is wired with single phase. I am aware of the benefits of a VFD ..... but that adds about $500 to the cost of the lathe. And, based on the anticipated use of the lathe, I do not place much value on having a variable speed motor.

I saw a review where the person stated that threads cut with a 1-phase motor would not be as smooth as threads cut with a 3-phase motor. The rational is that 3-phase power produces a smoother current than 1-phase power. This difference in the current will translate into a difference in how smooth the thread is cut. I understand the theory, but question how much difference it makes as a practical matter.

Does anyone have experience using the two different sources of power for cutting threads? Is there a distinguishable difference?

Any comments on the topic are welcome.

Mike
 
There would likely be no discernable difference in thread cutting smoothness with the different motors; there are so many other factors involved, such as motor balance, gear irregularities, material being cut, tool geometry and sharpness, cutting fluids, and the relative ridgidity of the machine and setup, not to mention the skill level of the operator.
 
Polyphase has attributes that single phase lacks, if possible use a polyphase system.
If not practical do not.
It is a simple as that.
 
One good point about 3 phase is instant reversibility. I have this on my 19" lathe, which has a direct belted drive, and I use it to slow the machine down and also for some threading work, such as metric and coarse leads up to shoulders.
 
Also you can cut threads with geometric style die heads(instant class 3 threads) or 3/4 of the way single point threading and finish with an appropriate die . Those 2 methods will produce very nice threads.
Having said that I still believe in 3 phase and VFD's for a lathe.
 
Always use 3 Phase if its available..... You lose horsepower running a 3 Phase motor on Single Phase and most VFDs....
 
MWCurl said:
.
.
I saw a review where the person stated that threads cut with a 1-phase motor would not be as smooth as threads cut with a 3-phase motor. The rational is that 3-phase power produces a smoother current than 1-phase power. This difference in the current will translate into a difference in how smooth the thread is cut. I understand the theory, but question how much difference it makes as a practical matter.
.
.
Click to expand...
Hi Mike,

I think the person that stated that is either overthinking the issue or pulling someone's leg. If it made a discernible difference in how smooth the thread is cut, it would also make a discernible difference in how smooth it makes finish cuts. IMHO, it's a non-issue.

Tom
 
higgite said:
Hi Mike,

I think the person that stated that is either overthinking the issue or pulling someone's leg. If it made a discernible difference in how smooth the thread is cut, it would also make a discernible difference in how smooth it makes finish cuts. IMHO, it's a non-issue.

Tom
Click to expand...
No one would ever pull any ones leg on the internet, go on pull the other one (-:
 
There is nothing wrong with using single phase. For a small lathe, it will work fine. Anything over ~3 hp will be a bit harder to find in single phase, and above 5HP it starts to make for a more expensive motor. 3 phase works better (simpler motors) and so most commercial equipment is going to be 3 phase. It is really up to you and what you plan to do with your work shop activities - if you are looking at one or two machines and plan to get pretty small machines, or stick with machines that you know will be single phase - then go with single phase. If you get into anything a bit bigger (still not a "big " machine), or used commercial machines - the single phase options get pretty sparse.

If you end up with a "few" machines - then a whole shop solution really works well (the most popular being an RPC). Of course a VFD can provide the phase conversion and variable speed - but it is a bit of work to convert the electrics over so that the control is on the VFD (typically have to gut the existing controls). The VFD option is motor specific. Each of the motors on your machine needs to have the power requirements met.

I have not used a VFD powered lathe, and I can't say it has ever held me back. I have a VFD on one drill press and a variable drive on one mill - they are nice features, but IMO it is not a game changer. For a lathe, there are a number of features I would place ahead of a VFD. Perhaps others could comment on the contribution of a VFD on a lathe.

I went 3 phase off the bat on my first lathe (with an RPC) - turned out to be an excellent choice, it opened up options for more machines that were then easy to power (reduced the competition at the auctions).
 
Cooter Brown said:
Always use 3 Phase if its available..... You lose horsepower running a 3 Phase motor on Single Phase and most VFDs....
Click to expand...

This is not correct. You lose horsepower with a static phase converter, not a VFD and not with a rotary phase converter.
 
You must log in or register to reply here.
Back
Top